Back to showing more than 27 inches for our region. I'm looking at the shorter-term models to see what they say.
Thursday, January 21, 2016
The sanity on the GFS lasted one run...
Back to showing more than 27 inches for our region. I'm looking at the shorter-term models to see what they say.
Not much changed overnight...
The models (especially the GFS) stopped talking about 35-40 inches but other than that and a slight (but possibly concerning) creep of the rain/snow line northward towards the south and east suburbs, everything is pretty much on track for tomorrow.
1-2 feet of snow - around the immediate DC metro, I'd guess at least 15 up to 2 feet.
I'm swamped with stuff this morning but I'll be trying to get a look at the afternoon models and post some graphics.
If you haven't picked up bread already well (Found this on twitter. Too awesome.)
1-2 feet of snow - around the immediate DC metro, I'd guess at least 15 up to 2 feet.
I'm swamped with stuff this morning but I'll be trying to get a look at the afternoon models and post some graphics.
If you haven't picked up bread already well (Found this on twitter. Too awesome.)
Wednesday, January 20, 2016
Haven't seen one of these...well, ever.
Blizzard Watch
URGENT - WINTER WEATHER MESSAGE NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1013 AM EST WED JAN 20 2016 DCZ001-MDZ004>006-011-013-014-016>018-503>508-VAZ052>057-505-506- 202315- /O.NEW.KLWX.BZ.A.0001.160122T1700Z-160124T1100Z/ DISTRICT OF COLUMBIA-FREDERICK MD-CARROLL-NORTHERN BALTIMORE- SOUTHERN BALTIMORE-PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS- CALVERT-NORTHWEST MONTGOMERY-CENTRAL AND SOUTHEAST MONTGOMERY- NORTHWEST HOWARD-CENTRAL AND SOUTHEAST HOWARD-NORTHWEST HARFORD- SOUTHEAST HARFORD-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX- ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA- KING GEORGE-WESTERN LOUDOUN-EASTERN LOUDOUN- 1013 AM EST WED JAN 20 2016 ...BLIZZARD WATCH IN EFFECT FROM FRIDAY AFTERNOON THROUGH LATE SATURDAY NIGHT... THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS ISSUED A BLIZZARD WATCH...WHICH IS IN EFFECT FROM FRIDAY AFTERNOON THROUGH LATE SATURDAY NIGHT. * HAZARD TYPES...HEAVY SNOW AND WIND. A WINTRY MIX IS POSSIBLE FRIDAY NIGHT INTO SATURDAY MORNING EAST OF INTERSTATE 95...BEFORE CHANGING BACK TO ALL SNOW ON SATURDAY. * ACCUMULATIONS...POTENTIAL FOR A FOOT OR MORE OF SNOW. * TIMING...FRIDAY AFTERNOON THROUGH SATURDAY NIGHT. CONDITIONS ARE EXPECTED TO DETERIORATE FRIDAY AFTERNOON WITH THE HEAVIEST SNOW...STRONGEST WINDS...AND POTENTIAL LIFE THREATENING CONDITIONS EXPECTED FRIDAY NIGHT THROUGH SATURDAY NIGHT. * IMPACTS...HEAVY SNOW AND BLOWING SNOW WILL CAUSE DANGEROUS CONDITIONS AND WILL BE A THREAT TO LIFE AND PROPERTY. TRAVEL IS EXPECTED TO BE SEVERELY LIMITED IF NOT IMPOSSIBLE DURING THE HEIGHT OF THE STORM FRIDAY NIGHT AND SATURDAY. VISIBILITY WILL BE REDUCED TO NEAR ZERO AT TIMES IN WHITEOUT CONDITIONS. * WINDS...NORTHEAST 10 TO 15 MPH FRIDAY. NORTHEAST WINDS WILL INCREASE TO 20 TO 30 MPH WITH GUSTS TO 40 MPH FRIDAY NIGHT...THEN SHIFT NORTH SATURDAY THROUGH SATURDAY NIGHT. * TEMPERATURES...MID TO UPPER 20S MOST LOCATIONS. UPPER 20S TO LOWER 30S ACROSS SOUTHERN MARYLAND. PRECAUTIONARY/PREPAREDNESS ACTIONS... USE THIS ADVANCE NOTICE TO PLAN AHEAD! ADJUST TRAVEL PLANS...AND PLANNED ACTIVITIES. STOCK UP ON NECESSITIES. MAKE PLANS FOR ELDERLY FAMILY AND THOSE MOST AT RISK. PREPARE FOR THE POSSIBILITY OF POWER OUTAGES DURING SNOWY AND COLD CONDITIONS. USE THIS TIME TO MINIMIZE IMPACT ON YOU...YOUR FAMILY...AND YOUR COMMUNITY.
The bread. Go get it.
The model runs last night were good, if you like snow.
Nothing has changed about the reasoning behind the forecast and the differences in the models were mostly regarding precipitation onset, duration and any mixing issues to the south and east of the city.
Every model I reviewed last night predicts at least a foot. 15-20 inches seem a good bet at this point, a few models have totals near 2.5 feet.
It's going to snow.
So what could go wrong at this point?
I'm not sure, actually. Yesterday there was a southward trend to the modeled storm track but that stopped in last night's runs and now that the energy being sampled is actually in North America (as opposed to over the ocean), the models become more and more accurate.
The GFS is by far the most bullish on the snow situation. It stalls the low just off the coast for almost 12 hours and just pours down snow in our area. If this verifies - and it's not out of the question - we're talking 2-3 feet, not 1-2 feet.
Here's the "clown map" (it's what it's informally called) so you can see:
Still in the bullseye. A closer look shows that the GFS models around 3 feet of snow for the area. This pattern of "stall off the coast for 12 hours" has been consistent in the GFS but is not shown in the other models for quite the same duration. As a result, this is considered a bit of an "outlier" solution...it shouldn't be discounted but it maybe should be taken as a "worst-best-case scenario".
The CMC isn't a model I usually trust and until the last few runs it had one of the most northeast tracks of the models. And yet:
That's well over 2 feet for our area and much of the northwestern part of Virginia and almost all of Maryland.
Here's a map of precipitation potential for the storm. This is in liquid precipitation so remember that to get an approximate amount of snow from liquid measure you multiply by 10.
This model suggests 3-4 inches of liquid for the storm - again, the bullseye is in line with the other models and is right over us. If this verifies, well...you can do the math :)
There has been some talk of analogs to this storm and the one I've heard most is the Blizzard of '96. Every storm is different as are the ingredients that make up the conditions around the storms. Yet, it's worth showing the snowfall map from that storm:
There are some parallels to that situation and this could be a storm of similar (or greater) proportions.
Finally, this is the Euro from early this morning. The Euro had consistently been the most southern track which moved the highest snow totals to Central Virginia. Even in this run, we are hit hard:
The models are called "guidance" for a reason. Meteorologists are supposed to use them - and their skill - to make a prediction. When all of the models mostly agree it's a reason to sit up and take notice. When all of them - without exception - show double-digit snowfall potential for an area, it's time to get the bread.
Why are you still reading? Go get bread!
Tuesday, January 19, 2016
This morning's models are singing the same tune...
...maybe even more loudly than they were.
Still excellent agreement in the models overnight and everything seems to be on track for a major snowstorm in the DC area beginning Friday and possibly not ending until late on Saturday. The rain/snow issues seem to be working themselves out a bit - the concern here is a slight southward trend to the storm track which certainly keeps us all snow throughout the event but also starts to move the bullseye further and further to the south.
As of right now - some 72 hours before the start of the storm - we're right in the bullseye. If the GFS model from this morning verified, we'd be digging out for quite some time.
Here's the snowmap from this morning's GFS for reference:
It doesn't get to be more of a bullseye than that: 2+ feet of snow for the DC metro. If you like snow a lot, you'd love the models to have you in the bullseye the night before not 72 hours before so we'll see how this evolves.
Just wanted to note that the game is still on and with each hour that passes and each model run that confirms and intensifies the prediction, it's almost time to go get bread.
Stay tuned.
Still excellent agreement in the models overnight and everything seems to be on track for a major snowstorm in the DC area beginning Friday and possibly not ending until late on Saturday. The rain/snow issues seem to be working themselves out a bit - the concern here is a slight southward trend to the storm track which certainly keeps us all snow throughout the event but also starts to move the bullseye further and further to the south.
As of right now - some 72 hours before the start of the storm - we're right in the bullseye. If the GFS model from this morning verified, we'd be digging out for quite some time.
Here's the snowmap from this morning's GFS for reference:
It doesn't get to be more of a bullseye than that: 2+ feet of snow for the DC metro. If you like snow a lot, you'd love the models to have you in the bullseye the night before not 72 hours before so we'll see how this evolves.
Just wanted to note that the game is still on and with each hour that passes and each model run that confirms and intensifies the prediction, it's almost time to go get bread.
Stay tuned.
Monday, January 18, 2016
It's Been So Long, I Forgot My Password...
But now that I'm in to my own blog, let's talk.
All the signs and signals are there for a major winter storm threat from Thursday of this week into the weekend. We have unusual model agreement (this far out) but the usual questions are still there.
Years of DC weather should have inoculated you against too much excitement when we're still more than 72 hours from the start of any precipitation but since it really doesn't work that way for me either, let's see what we've got.
First and foremost, we've got El Niño. Yes we do. On Christmas Day, I turned on the air conditioner and the same ocean anomaly that was responsible for that is also responsible for sending storms across the US with more moisture and energy than "normal". We just haven't been able to get the cold air (when it has been there) timed right. This looks to be less of a problem (gut feeling tells me "no problem") this time.
We've got a high pressure system moving into the New England states which will keep the cold air going.
And, we've got a storm:
That model output is from 7 PM on Friday by which point, according to the GFS, it has been snowing for the better part of 7 hours in the DC area. The storm is still transitioning to the coast and taking its sweet time about it giving us a potential prolonged period of heavy snow.
By 7 AM Saturday, the GFS has us at the tail end of the storm's peak. Heavy snow would have fallen all night - although the storm's proximity to the coast brings mixing with sleet into question.
The Euro (which I usually trust more than the GFS this time of year) will be running a bit later but just for fun, let's look at GFS predicted snow totals from the storm:
That's right, kids. Those areas of brown/orange near DC and north suggest a potential for storm totals measured in feet around here.
This is typical of El Niño. When the storms do arrive, they pack a moisture and energy punch.
The other models I have seen are slight variations on this same theme. The most pessimistic of them (that also happens to be one of the ones that usually suck the most) still has 12-14+ inch totals around the DC-Baltimore area.
Let's buckle in. There's still WAY too much time for things to change to go clear the stores of bread. The thing that concerns me most is storm track (as usual) and in this setup, the potential is there for what we call "supression". The whole thing could be shunted southward leaving us out of the heaviest snow.
But. We can say the potential exists for a major storm starting Friday morning and stretching into Saturday and that the models, at this point, are hinting at a crippling storm for this area.
We'll see what the Euro says.
All the signs and signals are there for a major winter storm threat from Thursday of this week into the weekend. We have unusual model agreement (this far out) but the usual questions are still there.
Years of DC weather should have inoculated you against too much excitement when we're still more than 72 hours from the start of any precipitation but since it really doesn't work that way for me either, let's see what we've got.
First and foremost, we've got El Niño. Yes we do. On Christmas Day, I turned on the air conditioner and the same ocean anomaly that was responsible for that is also responsible for sending storms across the US with more moisture and energy than "normal". We just haven't been able to get the cold air (when it has been there) timed right. This looks to be less of a problem (gut feeling tells me "no problem") this time.
We've got a high pressure system moving into the New England states which will keep the cold air going.
And, we've got a storm:
That model output is from 7 PM on Friday by which point, according to the GFS, it has been snowing for the better part of 7 hours in the DC area. The storm is still transitioning to the coast and taking its sweet time about it giving us a potential prolonged period of heavy snow.
By 7 AM Saturday, the GFS has us at the tail end of the storm's peak. Heavy snow would have fallen all night - although the storm's proximity to the coast brings mixing with sleet into question.
The Euro (which I usually trust more than the GFS this time of year) will be running a bit later but just for fun, let's look at GFS predicted snow totals from the storm:
That's right, kids. Those areas of brown/orange near DC and north suggest a potential for storm totals measured in feet around here.
This is typical of El Niño. When the storms do arrive, they pack a moisture and energy punch.
The other models I have seen are slight variations on this same theme. The most pessimistic of them (that also happens to be one of the ones that usually suck the most) still has 12-14+ inch totals around the DC-Baltimore area.
Let's buckle in. There's still WAY too much time for things to change to go clear the stores of bread. The thing that concerns me most is storm track (as usual) and in this setup, the potential is there for what we call "supression". The whole thing could be shunted southward leaving us out of the heaviest snow.
But. We can say the potential exists for a major storm starting Friday morning and stretching into Saturday and that the models, at this point, are hinting at a crippling storm for this area.
We'll see what the Euro says.
Tuesday, February 11, 2014
UPDATE: NAM, GFS are in - Still No Consensus
Here we are, less than 24 hours before the onset of this storm and this is what I have to work with from the NAM and GFS so far:
NAM: heavy, early burst of snow most of which falls in the 12 hours between around 8 PM Wednesday and 8 AM Thursday (and especially in the early morning hours of Thursday). A lot of precipitation is simulated (which is a known NAM bias). The wettest, coldest of the models simulates at least 10 inches of snow for most of the region DC and westward with few snow to sleet/rain changeover problems except for southern Maryland.
GFS: longer, significantly drier snow event which extends from 8-9 PM Wednesday into Thursday night. Half (or less) of the precipitation simulated by the NAM and it's a bit warm as well which causes precipitation-type issues. Widespread 4-6 inch snowfall from DC westward.
Here's a comparison of the forecast storm position for the same time from the GFS (top) and NAM (bottom):
NAM: heavy, early burst of snow most of which falls in the 12 hours between around 8 PM Wednesday and 8 AM Thursday (and especially in the early morning hours of Thursday). A lot of precipitation is simulated (which is a known NAM bias). The wettest, coldest of the models simulates at least 10 inches of snow for most of the region DC and westward with few snow to sleet/rain changeover problems except for southern Maryland.
GFS: longer, significantly drier snow event which extends from 8-9 PM Wednesday into Thursday night. Half (or less) of the precipitation simulated by the NAM and it's a bit warm as well which causes precipitation-type issues. Widespread 4-6 inch snowfall from DC westward.
Here's a comparison of the forecast storm position for the same time from the GFS (top) and NAM (bottom):
You can see that the NAM is much faster with a low off Cape Hatteras at this hour while the GFS still has the low off the coast of the SC/NC border.
I'm still fairly worried about mixing on Thursday and I would base my forecast on that except that the NAM (and some other models as well) keep coming up with these solutions where the bulk of the precipitation falls before the temperatures become an issue.
Right now I feel that 4 inches is something we can count on. From that point, I'm less certain. My gut tells me 6-10 is where this will end up but without better guidance consensus, I'm relying on forecasting skills which haven't been professionally practiced in many years. For what it's worth, the official forecast from the National Weather Service is as follows:
Afternoon NAM run is a big hit...
Widespread 10+ inch amounts throughout the area according to the NAM.
I'm taking a closer look.
I'm taking a closer look.
Significant Snow Likely - But How Significant?
Things are still not as clear as I'd like them to be.
The Euro is still the westernmost track and the Canadian model (CMC) has come into line with that Their tracks are quite close to the coast which create precipitation type issues in the forecast even west of DC and cuts down on the overall amounts.
The NAM, on the other hand, is a much colder solution and keeps us in the heavy precipitation but now it seems like the outlier. The GFS is somewhere in between.
Here's the ECMWF deterministic output:
ECMWF Deterministic FORECAST FOR: DCA LAT= 38.85 LON= -77.03 ELE= 16
TUE 12Z 11-FEB -7.6 -12.6 1030 60 9 0.00 546 523
TUE 18Z 11-FEB -2.0 -12.8 1030 43 9 0.00 547 524
WED 00Z 12-FEB -4.6 -11.8 1031 58 13 0.00 547 523
WED 06Z 12-FEB -6.3 -11.3 1033 51 4 0.00 549 523
WED 12Z 12-FEB -7.4 -9.5 1034 53 3 0.00 553 527
WED 18Z 12-FEB -1.8 -7.7 1032 39 3 0.00 555 530
THU 00Z 13-FEB -2.9 -6.7 1028 57 44 0.00 556 534
THU 06Z 13-FEB -3.2 -3.9 1021 88 98 0.18 554 537
THU 12Z 13-FEB -0.5 0.0 1010 93 99 0.55 552 544
THU 18Z 13-FEB 0.9 2.8 998 91 76 0.21 546 547
FRI 00Z 14-FEB 1.2 -1.2 992 89 53 0.15 533 540
FRI 06Z 14-FEB 1.8 -2.7 996 87 90 0.25 532 536
The same two highlighted times are still problematic - maybe even a bit more than they were last night. The surface temperatures rise above freezing in the afternoon Thursday (0.9) and the thicknesses go well above the 540 benchmark (544, 547) meaning that mixing issues will almost certainly be present for areas east of I-95, DC included.
Looking at the GFS, I don't see as many issues. This frame from the GFS shows heavy snow in our area Thursday afternoon:
The NAM shows a similar story but the precipitation is heavier. However, this is a common bias with the NAM model so we can't take it too literally.
I'll be looking carefully at the upper level low as it moves into position over the next 12 hours. If the storm "wraps up" too quickly it will make for a more potent storm but a more westward track. The further west the track, the more mixing issues we have. You really get a sense here of the precision necessary to produce big snows in the DC area. The model data supports this. There are SREF members forecasting everything from 2 inches to 20 inches for the DC area. Clearly, that's not useful basis for a forecast.
I think we're in for some snow. I think 4 or more inches is a good bet areawide with the first 3-5 accumulating overnight Wednesday into Thursday morning. After that, it gets tricky. Where will the storm track? How close to the coast? Does banding set up in our region? Does the amount of lift in the atmosphere counter warming temperatures?
I think all of those questions are left to be answered still and will make the difference between a good storm, a big storm and a major storm.
The Euro is still the westernmost track and the Canadian model (CMC) has come into line with that Their tracks are quite close to the coast which create precipitation type issues in the forecast even west of DC and cuts down on the overall amounts.
The NAM, on the other hand, is a much colder solution and keeps us in the heavy precipitation but now it seems like the outlier. The GFS is somewhere in between.
Here's the ECMWF deterministic output:
ECMWF Deterministic FORECAST FOR: DCA LAT= 38.85 LON= -77.03 ELE= 16
TUE 12Z 11-FEB -7.6 -12.6 1030 60 9 0.00 546 523
TUE 18Z 11-FEB -2.0 -12.8 1030 43 9 0.00 547 524
WED 00Z 12-FEB -4.6 -11.8 1031 58 13 0.00 547 523
WED 06Z 12-FEB -6.3 -11.3 1033 51 4 0.00 549 523
WED 12Z 12-FEB -7.4 -9.5 1034 53 3 0.00 553 527
WED 18Z 12-FEB -1.8 -7.7 1032 39 3 0.00 555 530
THU 00Z 13-FEB -2.9 -6.7 1028 57 44 0.00 556 534
THU 06Z 13-FEB -3.2 -3.9 1021 88 98 0.18 554 537
THU 12Z 13-FEB -0.5 0.0 1010 93 99 0.55 552 544
THU 18Z 13-FEB 0.9 2.8 998 91 76 0.21 546 547
FRI 00Z 14-FEB 1.2 -1.2 992 89 53 0.15 533 540
FRI 06Z 14-FEB 1.8 -2.7 996 87 90 0.25 532 536
The same two highlighted times are still problematic - maybe even a bit more than they were last night. The surface temperatures rise above freezing in the afternoon Thursday (0.9) and the thicknesses go well above the 540 benchmark (544, 547) meaning that mixing issues will almost certainly be present for areas east of I-95, DC included.
Looking at the GFS, I don't see as many issues. This frame from the GFS shows heavy snow in our area Thursday afternoon:
The NAM shows a similar story but the precipitation is heavier. However, this is a common bias with the NAM model so we can't take it too literally.
I'll be looking carefully at the upper level low as it moves into position over the next 12 hours. If the storm "wraps up" too quickly it will make for a more potent storm but a more westward track. The further west the track, the more mixing issues we have. You really get a sense here of the precision necessary to produce big snows in the DC area. The model data supports this. There are SREF members forecasting everything from 2 inches to 20 inches for the DC area. Clearly, that's not useful basis for a forecast.
I think we're in for some snow. I think 4 or more inches is a good bet areawide with the first 3-5 accumulating overnight Wednesday into Thursday morning. After that, it gets tricky. Where will the storm track? How close to the coast? Does banding set up in our region? Does the amount of lift in the atmosphere counter warming temperatures?
I think all of those questions are left to be answered still and will make the difference between a good storm, a big storm and a major storm.
UPDATE: Euro Puts Bullseye on DC
The early morning run of the ECMWF (Euro) model does nothing to dissuade snow forecasts and, in fact, paints a bullseye over DC.
Still some disagreement in the models - particularly the GFS and the Euro is still a bit too close to the coast for comfort (precip mixing issues).
I'll write more later this morning.
Still some disagreement in the models - particularly the GFS and the Euro is still a bit too close to the coast for comfort (precip mixing issues).
I'll write more later this morning.
Monday, February 10, 2014
Let the Games Begin
First - a Winter Storm Watch has been put in place for our region for Wednesday night through Thursday. By strict National Weather Service definition, a "Winter Storm" is one that has the potential to produce 5 or more inches of snow.
So what do we have here?
I'll start with what we don't have: guidance model consensus. The solutions range as follows:
GFS: a smaller shot of snow - less impact
ECMWF (Euro): big hit, "warmer" solution - possible snow/sleet/rain mixing issues on Thursday
CMC, UKMET, NAM: some variation of "keep the dog inside lest it disappear beneath the snowfall"
I'd really like to have better model consensus about 60 hours out from the storm but that's why this is such a difficult area for which to make a forecast.
Right now, my instinct tells me that we're going to get snow - quite a bit of it - but that where you are might make a big difference as to how much you see. I'm reasonably confident at this point that the western suburbs will see a lot but I worry about DC and points east. If the Euro verifies as-is, it could be too warm to snow on Thursday.
If the GFS verifies as is, we're all out of the huge snow ballgame.
Here's a bit of the GFS run from this afternoon. (Note: the afternoon run of the GFS is considered less trustworthy because it is not initialized from upper air data - it uses physics to make a forecast based on the now-6-hours-old upper air data from the morning)
This would be Thursday afternoon. The low is positioned off the coast of Norfolk and is throwing back precipitation into our region. This is a "colder" solution which gives us no precipitation-type problems but gives us overall precipitation amount problems.
The storm is gone in the next frame working its way offshore and up the coast. The GFS predicts the following as snowfall totals:
As you can see, this guidance suggests our region misses the jackpot zone and we find ourselves in a VERY tight precipitation gradient with almost nothing to the northwest and heavier precipitation to the southeast.
At this point, however, the GFS is an outlier. It has, by far, the most eastward track for the surface low and the least impact to our region.
On the other hand (hide the dogs!), this is what the NAM model guidance suggests for the same storm period:
which is a monster hit for the DC area and really no precipitation gradient problems to worry about.
The ECMWF (Euro) forecast for our area is a little more problematic. Here's the raw model output for National Airport:
ECMWF Deterministic FORECAST FOR: DCA LAT= 38.85 LON= -77.03 ELE= 16
MON 12Z 10-FEB -4.0 -10.1 1023 65 64 0.00 543 526
MON 18Z 10-FEB -0.9 -11.3 1024 49 7 0.00 543 525
TUE 00Z 11-FEB -5.4 -11.5 1025 59 4 0.00 544 524
TUE 06Z 11-FEB -5.4 -12.5 1028 52 7 0.00 543 522
TUE 12Z 11-FEB -7.1 -13.4 1030 49 9 0.00 546 523
TUE 18Z 11-FEB -2.2 -12.6 1030 39 9 0.00 547 523
WED 00Z 12-FEB -5.0 -11.5 1031 51 9 0.00 548 524
WED 06Z 12-FEB -7.0 -10.8 1033 55 3 0.00 550 524
WED 12Z 12-FEB -7.9 -8.1 1034 57 3 0.00 553 527
WED 18Z 12-FEB -1.9 -6.6 1032 40 9 0.00 555 530
THU 00Z 13-FEB -2.9 -6.3 1027 62 85 0.00 555 534
THU 06Z 13-FEB -2.4 -2.3 1018 92 98 0.30 552 538
THU 12Z 13-FEB 0.6 -0.6 1005 93 98 0.66 549 545
THU 18Z 13-FEB 1.1 -3.8 995 92 42 0.45 537 541
FRI 00Z 14-FEB 1.6 -4.1 996 89 89 0.30 533 537
FRI 06Z 14-FEB -0.2 -2.3 1002 73 20 0.04 536 534
FRI 12Z 14-FEB -6.2 -1.2 1007 79 54 0.00 540 535
I have bolded the two problem times. During the heaviest precipitation, two not-so-good things happen. One, the 2M temperature goes positive (0.6 and 1.1). That means surface temperatures are expected to be above freezing. We've seen a couple of times recently where that made a big difference in snow acummulation.
The second thing is that the 1000-500 mb thickness rises above 540 (545, 541) which is the "benchmark" for snow vs sleet or rain. The Euro is indicating that a little over an inch of liquid precipitation (normally around 10 inches of snow) is going to fall with marginal - at best - temperatures aloft and at the surface.
This type of thing can bust a forecast like a piñata.
The evening model runs will be very interesting to watch. I'll let you know what things look like as we get closer.
For now, prepare for a significant winter storm from Wednesday night into Thursday night with snow and wind. Amounts, timing and track to be determined as we get closer to the event.
So what do we have here?
I'll start with what we don't have: guidance model consensus. The solutions range as follows:
GFS: a smaller shot of snow - less impact
ECMWF (Euro): big hit, "warmer" solution - possible snow/sleet/rain mixing issues on Thursday
CMC, UKMET, NAM: some variation of "keep the dog inside lest it disappear beneath the snowfall"
I'd really like to have better model consensus about 60 hours out from the storm but that's why this is such a difficult area for which to make a forecast.
Right now, my instinct tells me that we're going to get snow - quite a bit of it - but that where you are might make a big difference as to how much you see. I'm reasonably confident at this point that the western suburbs will see a lot but I worry about DC and points east. If the Euro verifies as-is, it could be too warm to snow on Thursday.
If the GFS verifies as is, we're all out of the huge snow ballgame.
Here's a bit of the GFS run from this afternoon. (Note: the afternoon run of the GFS is considered less trustworthy because it is not initialized from upper air data - it uses physics to make a forecast based on the now-6-hours-old upper air data from the morning)
This would be Thursday afternoon. The low is positioned off the coast of Norfolk and is throwing back precipitation into our region. This is a "colder" solution which gives us no precipitation-type problems but gives us overall precipitation amount problems.
The storm is gone in the next frame working its way offshore and up the coast. The GFS predicts the following as snowfall totals:
As you can see, this guidance suggests our region misses the jackpot zone and we find ourselves in a VERY tight precipitation gradient with almost nothing to the northwest and heavier precipitation to the southeast.
At this point, however, the GFS is an outlier. It has, by far, the most eastward track for the surface low and the least impact to our region.
On the other hand (hide the dogs!), this is what the NAM model guidance suggests for the same storm period:
which is a monster hit for the DC area and really no precipitation gradient problems to worry about.
The ECMWF (Euro) forecast for our area is a little more problematic. Here's the raw model output for National Airport:
ECMWF Deterministic FORECAST FOR: DCA LAT= 38.85 LON= -77.03 ELE= 16
MON 12Z 10-FEB -4.0 -10.1 1023 65 64 0.00 543 526
MON 18Z 10-FEB -0.9 -11.3 1024 49 7 0.00 543 525
TUE 00Z 11-FEB -5.4 -11.5 1025 59 4 0.00 544 524
TUE 06Z 11-FEB -5.4 -12.5 1028 52 7 0.00 543 522
TUE 12Z 11-FEB -7.1 -13.4 1030 49 9 0.00 546 523
TUE 18Z 11-FEB -2.2 -12.6 1030 39 9 0.00 547 523
WED 00Z 12-FEB -5.0 -11.5 1031 51 9 0.00 548 524
WED 06Z 12-FEB -7.0 -10.8 1033 55 3 0.00 550 524
WED 12Z 12-FEB -7.9 -8.1 1034 57 3 0.00 553 527
WED 18Z 12-FEB -1.9 -6.6 1032 40 9 0.00 555 530
THU 00Z 13-FEB -2.9 -6.3 1027 62 85 0.00 555 534
THU 06Z 13-FEB -2.4 -2.3 1018 92 98 0.30 552 538
THU 12Z 13-FEB 0.6 -0.6 1005 93 98 0.66 549 545
THU 18Z 13-FEB 1.1 -3.8 995 92 42 0.45 537 541
FRI 00Z 14-FEB 1.6 -4.1 996 89 89 0.30 533 537
FRI 06Z 14-FEB -0.2 -2.3 1002 73 20 0.04 536 534
FRI 12Z 14-FEB -6.2 -1.2 1007 79 54 0.00 540 535
I have bolded the two problem times. During the heaviest precipitation, two not-so-good things happen. One, the 2M temperature goes positive (0.6 and 1.1). That means surface temperatures are expected to be above freezing. We've seen a couple of times recently where that made a big difference in snow acummulation.
The second thing is that the 1000-500 mb thickness rises above 540 (545, 541) which is the "benchmark" for snow vs sleet or rain. The Euro is indicating that a little over an inch of liquid precipitation (normally around 10 inches of snow) is going to fall with marginal - at best - temperatures aloft and at the surface.
This type of thing can bust a forecast like a piñata.
The evening model runs will be very interesting to watch. I'll let you know what things look like as we get closer.
For now, prepare for a significant winter storm from Wednesday night into Thursday night with snow and wind. Amounts, timing and track to be determined as we get closer to the event.
Keeping an Eye on Wednesday/Thursday
This past weekend was a perfect example of what happens when two separate storms fail to phase. The result is two rounds of snow showers and that's it.
This Wednesday-Thursday is starting to look much more interesting in the last few model runs. There are still some crucial differences - particularly with storm track. The GFS is currently the outlier showing a storm that phases too late and ends up out to sea, barely brushing the area.
The Euro and other models show a storm moving up the coast - maybe too close (which would draw warmer air from the Atlantic and give us precipitation type issues). But trends in the models seem to be pointing towards a colder solution and more snow.
This could be the big one of the winter but it's still too early to tell. Once I've had more time to look at the guidance, I'll post my thoughts but, for now, keep an eye on this time period.
This Wednesday-Thursday is starting to look much more interesting in the last few model runs. There are still some crucial differences - particularly with storm track. The GFS is currently the outlier showing a storm that phases too late and ends up out to sea, barely brushing the area.
The Euro and other models show a storm moving up the coast - maybe too close (which would draw warmer air from the Atlantic and give us precipitation type issues). But trends in the models seem to be pointing towards a colder solution and more snow.
This could be the big one of the winter but it's still too early to tell. Once I've had more time to look at the guidance, I'll post my thoughts but, for now, keep an eye on this time period.
Tuesday, February 4, 2014
Storm Potential for This Weekend
I'm keeping an eye on models and data suggesting the potential for a significant winter storm in our area Saturday into Sunday. Details are a bit sketchy and the models don't agree so for now, the signal is there for a big storm and some models are trending colder - suggestive of all snow - while others keep us in mixed precipitation.
Storm track is everything and I suspect the models won't have a good grasp until after this ice storm gets through here tonight and tomorrow.
I'll post more once the situation clears a bit.
Storm track is everything and I suspect the models won't have a good grasp until after this ice storm gets through here tonight and tomorrow.
I'll post more once the situation clears a bit.
Monday, January 20, 2014
Significant Winter Storm Expected Tomorrow
All the ingredients are coming together for a significant snowfall in the DC area tomorrow.
For most of the day, I've been trying to figure out how this forecast could end up completely wrong. We do live in the DC area, after all, and if there was ever a place where snowfall forecasts go to die, it's here.
But I can't think of one.
The cold air will be in place, the upper-level energy is where it should be right now and the front is heading this way which will knock a good 25-30 degrees off our high temperatures today by the time the snow starts.
I suppose the only thing that could go wrong is if the storm gets its act together later than forecast by the models which would mean a less intense storm as it passes by. At the moment, this seems unlikely.
The GFS model shows the storm as it leaves the coast tomorrow and rapidly intensifies over the Atlantic. The trough of low pressure is expected to switch from a positive to a negative tilt which almost always means a more intense and slower-moving storm.
As the storm starts to influence our region, it will encounter the sharply-colder air and that should improve the accumulation numbers relative to the amount of precipitation produced by the storm. The rule-of-thumb ratio is 10 inches of snow per 1 inch of liquid precipitation. I think we do better than that tomorrow.
This will produce fluffy snow that will blow around in the strong gusty winds and that will be easier to shovel. It will, however, be complete crap for making snowballs or snowmen.
The snow could be quite heavy in the morning - especially if banding sets up (as it should). Forecasting the precise location of the banding is next to impossible so that's the usual reason for the range of forecast numbers. In this case, the National Weather Service is predicting 4-6" widespread throughout the DC area.
Another metric to consider is vertical velocity - a measure of the movement of the air. In the case of storms, higher vertical velocities imply more intense storms and heavier precipitation.
You can see from the graphic above that vertical velocities should be fairly high during the storm, suggestive of moderate to heavy precipitation.
Some snow amount considerations:
The NAM, which is a pretty good short-range model, shows the general thinking of most mets in the DC area - albeit with slightly higher values. The map above shows 0.5-0.6 total liquid precipitation which, converted to snowfall, produces numbers in the 6-8 inch range.
The GFS forecasts a similar range, maybe even a bit higher than the NAM - more in the 7-10 inch range for the DC area.
I feel that the NWS mets are being a bit conservative. It seems to me that there's potential for more than 6 inches of snow with this storm. Not crippling by any means but certainly more than we've seen around here in a while.
The evening models will be coming soon and I'll check those out as well. The only impacts to this forecast that I can see are the time of storm intensification which is something the models usually handle pretty well. My confidence in this forecast is, therefore, rather high - always considering, of course, that it's a snow forecast and it's for the DC area.
For most of the day, I've been trying to figure out how this forecast could end up completely wrong. We do live in the DC area, after all, and if there was ever a place where snowfall forecasts go to die, it's here.
But I can't think of one.
The cold air will be in place, the upper-level energy is where it should be right now and the front is heading this way which will knock a good 25-30 degrees off our high temperatures today by the time the snow starts.
I suppose the only thing that could go wrong is if the storm gets its act together later than forecast by the models which would mean a less intense storm as it passes by. At the moment, this seems unlikely.
The GFS model shows the storm as it leaves the coast tomorrow and rapidly intensifies over the Atlantic. The trough of low pressure is expected to switch from a positive to a negative tilt which almost always means a more intense and slower-moving storm.
As the storm starts to influence our region, it will encounter the sharply-colder air and that should improve the accumulation numbers relative to the amount of precipitation produced by the storm. The rule-of-thumb ratio is 10 inches of snow per 1 inch of liquid precipitation. I think we do better than that tomorrow.
This will produce fluffy snow that will blow around in the strong gusty winds and that will be easier to shovel. It will, however, be complete crap for making snowballs or snowmen.
The snow could be quite heavy in the morning - especially if banding sets up (as it should). Forecasting the precise location of the banding is next to impossible so that's the usual reason for the range of forecast numbers. In this case, the National Weather Service is predicting 4-6" widespread throughout the DC area.
Another metric to consider is vertical velocity - a measure of the movement of the air. In the case of storms, higher vertical velocities imply more intense storms and heavier precipitation.
You can see from the graphic above that vertical velocities should be fairly high during the storm, suggestive of moderate to heavy precipitation.
Some snow amount considerations:
The NAM, which is a pretty good short-range model, shows the general thinking of most mets in the DC area - albeit with slightly higher values. The map above shows 0.5-0.6 total liquid precipitation which, converted to snowfall, produces numbers in the 6-8 inch range.
The GFS forecasts a similar range, maybe even a bit higher than the NAM - more in the 7-10 inch range for the DC area.
I feel that the NWS mets are being a bit conservative. It seems to me that there's potential for more than 6 inches of snow with this storm. Not crippling by any means but certainly more than we've seen around here in a while.
The evening models will be coming soon and I'll check those out as well. The only impacts to this forecast that I can see are the time of storm intensification which is something the models usually handle pretty well. My confidence in this forecast is, therefore, rather high - always considering, of course, that it's a snow forecast and it's for the DC area.
Increased Snow Chances / Amounts for Tomorrow
Well. That was sudden.
As a frontal boundary approaches our area, it has been clear for a few days that the 21st would be cold, windy and that there was a chance that snow would overspread the area due to a small wave of low pressure riding along the front.
Our big snow producers typically come from the Gulf of Mexico and ride up the coast. It takes quite a potent little low to produce a lot of precipitation if it has terrestrial origins.
For the last couple of days, it looked like this would be a minor event. An "inch-or-less" type of event. Then came yesterday evening's model run.
The models run at 18z (1 PM locally) but since the upper air data from the day isn't available yet, they basically run from "inertia" or, more accurately, a "boatload of physics calculations" using the morning data. Thus, they are used to get a general idea of the forecast. They are rarely used for accuracy.
In any case... the 12Z GFS which is based on upper air data had started to suggest the idea of a stronger and just as importantly, slower moving system. The 18Z NAM then spit this clown map out and the meteorologists of the mid-Atlantic woke up from their nap and said, "hm!":
This shows a narrow area of significant snowfall in our area and especially points south and east. Some of those totals are quite high but it's less about accuracy in the 18Z run and more about the overall suggestion: a stronger, slower moving storm.
Overall, the storm has the look of a "clipper" system that then moves along the coast and intensifies rapidly.
Overnight, the trend in the models continues to be stronger - except for the Euro. Last night's 00Z Euro run showed this:
which still shows snow but in lighter amounts.
One this is certain: it will be cold. Precipitation type doesn't enter the equation like usual. I expect high temperatures in the 20's which will result in high snow rations - perhaps as high as 15:1. The map above shows 10:1 ratios so even taking 1.5 times the above snow produces a forecast for more snow than we've seen around here in 2-3 years.
This morning's data continues to come in and it all points to an increasingly significant storm for our area. The RGEM, for example, calls for 7-10 inches:
The morning GFS is also in that range:
There is a Winter Storm Watch for our area and with the models trending stronger, this looks like it's trending towards a major event for our region. For now, I'd say expect at least 4 inches of snow but the chances of more (maybe in the 8-10 inch range) are not out of the question.
There's unusually little variance with this storm as far as forecasting it goes. I don't see any indications that it could end up producing nothing at all - but with the way winter forecasts go around here, I'm going to keep watching.
I'll update again later.
As a frontal boundary approaches our area, it has been clear for a few days that the 21st would be cold, windy and that there was a chance that snow would overspread the area due to a small wave of low pressure riding along the front.
Our big snow producers typically come from the Gulf of Mexico and ride up the coast. It takes quite a potent little low to produce a lot of precipitation if it has terrestrial origins.
For the last couple of days, it looked like this would be a minor event. An "inch-or-less" type of event. Then came yesterday evening's model run.
The models run at 18z (1 PM locally) but since the upper air data from the day isn't available yet, they basically run from "inertia" or, more accurately, a "boatload of physics calculations" using the morning data. Thus, they are used to get a general idea of the forecast. They are rarely used for accuracy.
In any case... the 12Z GFS which is based on upper air data had started to suggest the idea of a stronger and just as importantly, slower moving system. The 18Z NAM then spit this clown map out and the meteorologists of the mid-Atlantic woke up from their nap and said, "hm!":
This shows a narrow area of significant snowfall in our area and especially points south and east. Some of those totals are quite high but it's less about accuracy in the 18Z run and more about the overall suggestion: a stronger, slower moving storm.
Overall, the storm has the look of a "clipper" system that then moves along the coast and intensifies rapidly.
Overnight, the trend in the models continues to be stronger - except for the Euro. Last night's 00Z Euro run showed this:
which still shows snow but in lighter amounts.
One this is certain: it will be cold. Precipitation type doesn't enter the equation like usual. I expect high temperatures in the 20's which will result in high snow rations - perhaps as high as 15:1. The map above shows 10:1 ratios so even taking 1.5 times the above snow produces a forecast for more snow than we've seen around here in 2-3 years.
This morning's data continues to come in and it all points to an increasingly significant storm for our area. The RGEM, for example, calls for 7-10 inches:
The morning GFS is also in that range:
There's unusually little variance with this storm as far as forecasting it goes. I don't see any indications that it could end up producing nothing at all - but with the way winter forecasts go around here, I'm going to keep watching.
I'll update again later.
Tuesday, December 10, 2013
Forecast on Track, Winter Storm Warnings Are Up
The models have come into better agreement for this quick but potent storm that should be starting in a few hours. I'd expect snow to begin around daybreak and really pick up in intensity between about 7 AM and 10 AM. 3-5" is forecast by the National Weather Service and that seems reasonable to me.
Banding is going to set up as I mentioned in a previous post and that could create locally higher snowfall amounts. Thundersnow is not out of the question!
There is still a chance that most of the precipitation gets pushed south of our area which would result in less snow overall but that doesn't seem likely at this point.
Banding is going to set up as I mentioned in a previous post and that could create locally higher snowfall amounts. Thundersnow is not out of the question!
There is still a chance that most of the precipitation gets pushed south of our area which would result in less snow overall but that doesn't seem likely at this point.
Monday, December 9, 2013
Round 2
For a few days now, both the GFS and the NAM (which is a good short-term model) have been suggesting a reinforcing shot of cold air would come through our region overnight and into the day tomorrow along with enhanced upper level dynamics. This combination was indicative of a second burst of snow that would begin early tomorrow morning and continue into the afternoon.
It now looks more likely that this will happen.
The only thing that gives pause is the Euro model which has insisted for a while now that any precipitation will be pushed south of our region.
The primary difficulty in this forecast is less what type of precipitation will fall (as it was in the last storm) but how much. A lot of the snow totals could largely depend on small localized banding events. If one of those bands forms overhead, it could mean the difference between 1-3 inches and 3-6 inches of snow.
One thing we have going for us is the push of cold air aloft which should mean enhanced liquid-to-snow ratios.
Here's the GFS snow total map for this storm:
you can see the bullseye in the Baltimore area but we in the DC metro are still doing pretty well - in the 3-6 inch range, generally. When I look at the projected temperatures at the 850 mb level:
I see a lot of -4 and -5 degree readings overhead which suggest to me a liquid-to-snow ratio a little higher than the standard 10:1. Maybe as much as 15:1. This means that whatever falls will accumulate and quickly.
The DC metro is under a Winter Storm Watch for tomorrow morning for 3-5+ inches of snow. I think this is reasonable based on the GFS and NAM model forecast. I'm going to wait to see the Euro before I get too excited but, in summary, prepare for more snow starting early tomorrow morning and accumulating quickly.
It now looks more likely that this will happen.
The only thing that gives pause is the Euro model which has insisted for a while now that any precipitation will be pushed south of our region.
The primary difficulty in this forecast is less what type of precipitation will fall (as it was in the last storm) but how much. A lot of the snow totals could largely depend on small localized banding events. If one of those bands forms overhead, it could mean the difference between 1-3 inches and 3-6 inches of snow.
One thing we have going for us is the push of cold air aloft which should mean enhanced liquid-to-snow ratios.
Here's the GFS snow total map for this storm:
you can see the bullseye in the Baltimore area but we in the DC metro are still doing pretty well - in the 3-6 inch range, generally. When I look at the projected temperatures at the 850 mb level:
I see a lot of -4 and -5 degree readings overhead which suggest to me a liquid-to-snow ratio a little higher than the standard 10:1. Maybe as much as 15:1. This means that whatever falls will accumulate and quickly.
The DC metro is under a Winter Storm Watch for tomorrow morning for 3-5+ inches of snow. I think this is reasonable based on the GFS and NAM model forecast. I'm going to wait to see the Euro before I get too excited but, in summary, prepare for more snow starting early tomorrow morning and accumulating quickly.
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