© 2019 Terry Swails

THOUGHTS ON SUNDAY SNOW...

March 21, 2020

A late season weather system with the potential of producing some wet snow is approaching the area from the southwest. Some important differences remain regarding the intensity, location, and amounts of snow. Saturday's new model runs can be broken down into 2 different camps. You have the major deterministic models (the EURO and GFS) and then the hi-resolution models designed for short range forecasts with higher details. Theoretically the hi-res models should be better but in this case I prefer what the EURO and GFS are offering.

 

The reason I prefer the EURO and GFS over the hi-res solutions is that the system is lacking a well defined surface low and upper air support is weak. Essentially this is what's known as an over-running event with the snow caused by nothing more than return flow, (warm moist air over-running the cold air at the surface). Without good forcing for any extended period of time I think precipitation totals will be less than what the hi-res models are showing by at least 1/10 to 2/10's of an inch. That get's it more in line with the EURO and GFS.

 

With lighter qpf, warm ground, and marginal surface temperatures the snow may have a tough time accumulating, especially on hard surfaces, and especially during daylight hours. Readings will cool during the evening around sunset and that is when most of the accumulations will occur. Even then, those are likely to be more in grassy and elevated surfaces as opposed to roads. I don't see this being much of an issue for travel.

 

As far as timing is concerned. it seems that the snow (perhaps mixed with rain for a time south of I-80) begins around noon near I-80 and reaches HWY 20 around 3:00pm. There may not be much at all around HWY 20 which seems to be the cut-off line for the northern extent to the snow shield on the EURO and GFS. The hi-res models are further north.

 

Currently it looks like the best chances for 1 to perhaps 2" of slushy snow would be HWY 30 south. There seems to be a preference for any 2" amounts closer to I-80 and points south.

 

My model of choice at this point is the EURO and this is what it shows for snow totals.

You can see it is similar to both the GFS and GEM below.

 

The GFS

The GEM

Here are the hi-resolution models which just look overdone to me on the amount of total precipitation and thus snowfall. There is a chance they could end up being correct but I think the chances are small. 

 

The 3K NAM

The 12K NAM

We'll get a couple more model runs to see where things are trending between now and the beginning of any snow early Sunday afternoon. In summation, I think amounts should generally be 1 (to perhaps 2") mainly near and south of HWY 20, and more likely HWY 30. The majority of the accumulations should be on grassy and elevated surfaces. More to come. Roll weather and master that social distancing thing...TS

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