The End in Sight for the Lowlands as the Warm Front Approaches

The final act in our snow drama is about to unfold.

A surface warm front is now pushing on to Washington's southwest shore and the upward motion associated with it is producing a band of precipitation moving northward (see radar at 9 AM below).

With cold air holding on temporarily at the surface, snow is falling from Tacoma southward.

The snow should reach Seattle by 11 AM and move northward during the subsequent hours.

Puget Sound land should experience a few hours...and a few inches of snow... before warming aloft results in a transition to rain at elevations below roughly 500 ft by around dinner time.

This is a very difficult forecast.   In fact, one of my colleagues at the National Weather Service (Jay Albrecht, an excellent and experienced forecaster) called it the hardest forecast he has had to do in 32 years.  Snow forecasting is hard.  One with an active transition from snow to rain is very hard.

And we are dealing with the achilles heel of many of our forecast models:  they tend to mix out low-level cold air too quickly.  So as good as the models are now, forecasters like myself need to make some manual correction for this situation.

Keeping this model issue in mind, here is the predicted 24h snowfall ending 4 AM Tuesday. One is struck by the huge amounts in the mountains, particularly in the central and southern Cascades.  Substantial amounts over NW Washington (4-8 inches) since the cold air should hold in there longest.  And around a half inch to a few inches for central Puget Sound.

But considering the model tendency to mix the cold air too soon, I think the above totals are too conservative.  1-2 inches around Seattle would be reasonable.  Less near the water (where it is warmer).  But there is a lot of uncertainty in this forecast.

This afternoon we will transition to mixed rain/snow and then rain this evening.  Temperatures tomorrow will zoom up to near 40F.  And the great melt out will begin. 

This has been an extraordinary month, with Seattle experiencing the greatest February monthly snowfall on record (14.1 inches).  You can tell your grandchildren about it.

And our temperatures have been unusually cold the last week, with many days not even climbing to our normal minimum.

And as good as our few day forecasts have become, our extended forecasts have been...how do I say this tactfully.... rather poor.  This is something I am working on---but that should be in a future blog.

from Cliff Mass Weather and Climate Blog https://cliffmass.blogspot.com/2019/02/the-end-in-sight-for-lowlands-as-warm.html