Cold! Then Another Chance of Wintry Precipitation Friday

Cold is easier to forecast than snow, so let's start there.

It's cold.  It's going to be cold - until Sunday, at least.  The worst of the cold weather will be today through Friday.  Highs in the 20's, lows in the teens and a noticeable wind which will make it feel even colder.  Bundle up!

Now - let's have a look at Friday...

Most of the forecast models show a fast-moving low pressure system moving out of the southeast on Thursday night and making it here on Friday morning.  That's about all they agree on however.

A few (GFS, Euro) show the storm tracking just to our south before reforming off the coast and moving out to sea.  This would give us a relatively quick shot of precipitation but would keep it all snow. 

Others (UKMET, NOGAPS) show the storm tracking just over us or just to our north.  This would create an "overrunning" situation where warm air on the southeast side of the low slides over the cold air at the surface.  Depending on the depth of the cold air, this can create the "mixed bag" of precipitation which starts and snow then changes to sleet or possibly freezing rain.  I'd consider this the least likely scenario at this point.

The big questions as usual are:

• Storm track.  Half the models are still forecasting a northward track.
• Phasing.  There is a scenario where energy from the Pacific phases with the southern stream jet which then moves across our area.  This scenario, by far, would produce more precipitation.

An extra component to this situation is the cold air mass over our area.  This cold will produce higher-than-normal snow ratios which means we can squeeze a bit more snow out of the same amount of precipitation.

Here is the GFS model showing precipitation overspreading the area on Friday:

You can see that the freezing line (blue) is quite a bit south of here which indicates a mostly snow event.

The storm remains a quick-mover and doesn't really get going until it's well off the coast.  An event like this could produce 2-4 inches but what we want is a phase.  In this scenario, the southern energy is sheared away which produces a weaker low.

The energy that will be producing this precipitation isn't even on the West Coast yet so there's plenty of time for things to change.

This is more of a "heads-up" that some snow is likely on Friday and it looks like there will be multiple parameters to consider before a solid forecast can be made.  We'll see if there is any consensus from the models and what the energy looks like when it finally arrives.

Stay tuned.