Model trends

If you want a snow storm-- Yesterday started as a great day and ended on the downslope. 

The trend yesterday was to slow down the system, keep the cold air in place and kept us on any models to an all snow event. Some of the mid day model runs had stripes of 9 to 15 inches across much of our regions. 

A late afternoon model run pulled the low more south and then ALL the late evening model runs went south and most kept the snow out of our region. However, the ensemble runs kept snowfall region. As a refresher, ensemble forecasting is taking a specific model (GFS, ECMWF, GEM- American, European and Canadian) and running a set amount of times with changes in run to weed out a bias of a model. 

IS IT GOING TO SNOW?

Great question and I'll do my best to answer. 

In general, this type event trends north as we get closer. So that's one in the in our favor. We have some subtropical jet interaction and those are famous for last day north adjustments even just in where the heaviest precipitation lines up. 

A concern is that the drastic trend on ALL the models could indicate something. 2 of those issues are:

1. The energy aloft is split, and as a result the storm is sheared out and weak, not throwing back moisture into the cold section. Just like bundling your TV and internet services, bundled energy is good for bigger storms. 

2. COLD air. The track has been adjusted in part because the cold air coming down is harder to forecast and the models adjusted in part because of the cold air in place AND the cold air coming in. 

AND YOUR ANSWER IS?

Yesterday I went 2-4 east regions. (Meaning east of the Blue Ridge) and west 4-8. This was based on the idea that we'd have a mix at certain points. Remember that forecasting is FLUID and information changes. Not much data shows the storm cutting to our west-- so the mix idea has dropped greatly. 

I'm going to blend the ensembles and operational models and hold to an idea that a 2-4 inch snowfall is the most likely outcome at this time. Usually, I'd love a low that is 150 miles too far SE at this time based on the ever present north trend, but with the drastic change yesterday (AKA disturbance in the force) I'm not positive we have a really good grasp on this yet. 

Model runs today between 9 and 1:30-- I'll toss a few ideas from those on FB and Twitter. But, as of now-- the best guess is 2-4 inches region wide, maybe more SE regions.