South south south.

As you probably know by now given the forecast trends, the storm track has continued to shift south bringing less and less snow and less cold air to our region.

What looked like a bullseye 3 days ago has become another disappointment in this unusual winter.

I expect to see some snow later this afternoon and evening but certainly no important accumulations.

Guess we would have been better off asking the first model what was going to happen rather than depending on the GFS.

With the further-south track also comes less cold air so any precipitation will likely start as rain and change to snow.

The Return

Both of me, and possibly of SNOW!

I've been conspicuously absent from this blog since, well, August when Irene came along and flooded everything.  Actually, it was Lee that flooded everything but Irene didn't help.

In any case, there hasn't been much to blog about this winter - certainly no one wants to read a blog about the 1/2 inch of snow that's likely to fall on any given day.

But this weekend looks like the first (last?) real chance at a real snowstorm.  If it happens, and the models hold, it looks like we might be in the bullseye for this one which makes it fun, too.  At least it gives me something to write about.

Let's start where we always do:  the models.

Sorry.

The GFS at 57 hours (10 PM Saturday night) shows a pretty good storm organizing in the southeast US.  Note the blue line indicating the freezing point for this particular part of the atmosphere.  We want to be north of that line and at this hour, we're right on it.  That's a good thing.

Also a good thing?  That high pressure area in the Great Lakes that will be moving east and bringing cold air to our area which should make for fewer precipitation issues (snow vs. rain vs. sleet).

By 66 hours, the storm is really getting wound up.  It's phasing (or phased) with northern stream energy from the jet stream and is beginning the turn up the coast.  Notice that we're in the freezing zone by this point.  It's too early to tell how the precipitation will start, but if these model forecasts hold, the major portion of it should be snow.

At 75 hours, early afternoon on Sunday, the main event should be in full swing around here.  This shows moderate to heavy precipitation in our area and that we're well to the north of the freezing line.  The potential for significant accumulating snow exists.  But the storm track means everything and we're still more than 3 days from this model time.

At 78 hours, late afternoon Sunday, we're still in the thick of it.  The storm looks to slide off the coast, right along the freezing line so this likely means not much for our Northeast neighbors but a possible bullseye for us.

By Sunday night the storm is moving away, precipitation ends from west to east and our storm is done. 

Of course, the question is "how much?"

For now, I think the concentration should be on whether the models hold for another day.  If these runs don't change much and the other models fall into line, this looks like the real deal.  The ECMWF has been flip-flopping between a more southerly track and a more northerly track.  The southern solution means less precipitation for us so this all bears watching.

For now - the probability exists, I'd say better than 50%, for a significant snowstorm with 3+ inch accumulations starting late Saturday night and ending Sunday night. The possibility for more exists of course but this is the highest probability range for now.

Just for fun:  the GFS "clown" map:

which shows us just outside of the 4-6 inch range or so.  These aren't all that accurate this far out except to show the path and pattern of the snowfall.

Stay tuned. 

Here Comes Irene

I've decided to post a rare non-winter blog entry because of the impending hurricane here on the East Coast.  As usual, the post will be more concerned with effects in the DC area since that's where I live.

Irene is currently a Category 2 hurricane.  She has weakened a bit in the last day or so and has maximum sustained winds of 100 MPH placing it just inside Category 2 status (which begins at 96 MPH).  The intensity will likely not change significantly before landfall in extreme eastern North Carolina - probably in the vicinity of Cape Lookout tomorrow morning.

Two things to remember:

• This storm is large.  So is the extent of the rain and wind fields.  For this reason, its projected path offshore is still close enough to the coast to cause problems for us.
• However, the cut-off between significant rain and just a few showers is usually pretty sharp with hurricanes passing to our east.  If the storm follows the current forecast track, I'd guess that we'll get significant rain in the DC area - especially south and east of the city.

If this type of forecast sounds familiar it's because a hurricane's impact pattern is similar to the large snowstorms we get in the winter.  Track means a lot - although exactly where the center travels matters less...especially with a storm this large.  That's why the National Hurricane Center cautions people to concentrate less on the line that marks center track and just heed the warnings they issue.

Speaking of which...

We're under a Tropical Storm Warning here in the DC area - mostly for areas near water but including the following counties:

DISTRICT OF COLUMBIA...NORTHERN BALTIMORE...HARFORD...
MONTGOMERY...HOWARD...SOUTHERN BALTIMORE...PRINCE GEORGES...ANNE
ARUNDEL...CHARLES...CALVERT...PRINCE WILLIAM/MANASSAS/MANASSAS
PARK...FAIRFAX...ARLINGTON/FALLS CHURCH/ALEXANDRIA...STAFFORD...

SPOTSYLVANIA AND KING GEORGE.

And in St. Mary's county, the Tropical Storm Warning is now a Hurricane Warning.

So what should we expect?

The storm is likely to move fairly far off the coast so I expect the worst conditions on the Eastern Shore. 

Probably 6 inches of rain and winds gusting to 80+ there at times tomorrow.

Here, things start going downhill late tonight.  The first bands from Irene could arrive tomorrow morning

and the winds will be increasing all day.  Expect winds in the 20-30 MPH range by tomorrow afternoon,

increasing to 30-40 with higher gusts tomorrow night.  The worst should be tomorrow evening and 

overnight as the storm passes by to our east. 

Again, the cutoff for precipitation is expected to be fairly sharp.  I'd guess areas around I-95 could pick

up 1-3 inches of rain, more to the east, less to the west.  Places out in the Blue Ridge might just have a 

cloudy day.

This is a storm to take seriously but in DC, I also don't see the need to go out and buy all the bottled water

you can find.  Flooding is possible, power outages are probable and 50 MPH winds with saturated ground 

can make trees a problem.

The next official advisory from the National Hurricane Center comes out at 5 PM.

For now, here's an excellent graphic with the forecast storm track:

Boston Globe Irene Tracker

Quick Burst of Snow Tonight Into Tomorrow Morning

It's been a while since anything interesting (aside from some unusually warm weather) has happened around here but tonight we have a fairly unusual situation developing that could cause a quick burst of snow and some minor accumulations around the area.

First up is a cold front which will be moving across our area this afternoon.  Precipitation associated with the front will begin as some light rain which will increase a bit in intensity as the afternoon becomes the evening.  The cold air will take a little while to catch up but eventually it will move across the area from north to south bringing a changeover in the precipitation that's falling from rain to sleet and eventually over to all snow.

At the same time, a low pressure area will move out of the midwest and cross the region bringing the bulk of our precipitation - especially towards midnight and into the early morning hours Tuesday.

This should be a brief storm but it could be a bigger deal than it even looks now.  That "banding" effect we've talked about before could lead to locally heavy precipitation amounts and the model trends have been colder and wetter the last few runs.

Waiting for the afternoon models but I think 2 inches is a good possibility in the immediate DC area, more as you go north and west.  There is the potential for more - maybe 4 inches or more - but before we go there, I'd like to see what the afternoon models have to say.  But, just to put it out there, here's the GFS 24-hour total precipitation forecast:

You can see we're squarely in the .5-.75 liquid precipitation range.  Given that we may lose a bit to rainfall and some sleet, this argues for 4 inches or so.

One thing the precipitation will be fighting is the relatively warm ground temperatures that have developed after the past 5 days or so.  On the other hand, the precipitation could be quite heavy later tonight.

Stay tuned...

Snow Totals Currently From 2-6 Inches Around the Area - Snow Will Continue

Here in Arlington, I measure 2 inches of wet snow that is packing itself as it falls.  If the atmosphere were colder, we would probably have 3-4 inches at this point.

Snow will continue into the night ending from southwest to northeast around 10-11 PM.

A few of those small-scale bands have formed and are producing snowfall rates of 1-2 inches per hour.  I expect snow totals will vary greatly from place to place depending on those bands.

In the radar below, you can see the upper-level energy moving to the east where it will phase with the surface low offshore.  As it starts this process there's a "twisting" motion to the precipitation which will keep things going for a while - even though you can see the back edge of the snow around Charlottesville.

Enjoy!

More Data Coming In - Just Keeps Getting Better

The new data looks supportive of more snow - but a lot will depend on those small-scale conditions we've talked about before.  Get under one of the bands and you could see some hefty accumulations.

Right now 6-8 inches seems likely, 10 is within reach here in the immediate metro.

Interestingly, the bullseye is setting up where the models had it this morning - right over DC and up to the northeast.  We may end up with more snow in the immediate DC metro than in points to the west in Loudoun County.

Rain starting here in Arlington - a little windier.  Reports of lightning and thunder in Woodbridge - mostly rain for now...

Major Band of Activity Headed Into DC Area

A line of strong radar returns is moving through the Fredericksburg area and heading north towards us.  Reports with this line have included heavy rain changing to sleet and then to snow fairly rapidly.

This is an unusual situation where you'll probably be able to watch as the thermal profiles in the atmosphere change and support frozen precipitation.

To add to the fun, there are numerous lightning strikes associated with the line.

Shouldn't be long now before the activity starts around here.