UpdateFebruary 20th, 2013 at 10:22 pm by Chad Evans under Chad's WLFI Weather Blog
I like the GFS model for this system Thursday evening-night to Friday morning.
I feel the NAM model is overdoing the snow & total precipitation in general. Its Skew-T looks too “pro-snow” & it seems to have a bit of an issue figuring out deeper moisture & dew points well southwest of us.
For one, dry air will entrench ahead of the precipitation AND in the mid-level dry slot that will come in Friday morning (though LOW-LEVELS will be saturated & will support drizzle/patchy misty rain). This cuts snow totals. Also, I think quite a bit of sleet may mix in the snow & may even change to all sleet for a while.
Now, 3-5″ in eastern Illinois & 4-8″ around Chicago look good, but here I like 1-3″ of snow & sleet with 1/10″ of glaze ice. It still appears the higher-end of the spectrum of snow/sleet totals will tend to be in our northern & northwestern counties of the viewing area. It will turn breezy to windy later tomorrow-tomorrow night with winds subsiding Friday morning. Winds may gust to 30 mph at times, though no power outages are expected.
Despite the dry air ahead of the precipitation, I still would prefer to keep the “southwest counties far game for precipitation after 5 p.m.” & “entire area from Covington & Veedersburg to Rochester & from Atlanta & Tipton to Morocco in the precipitation by midnight”. So, in that post-5 p.m. period to midnight precipitation will overspread the area from southwest to northeast.
Reason is that I like the forcing parameters for precipitation, regardless of the dry air. However, putting this system against all analog data back to 1970, I do have in the back of my mind potential of delaying the precipitation some if the initial forcing isn’t as strong as I am currently thinking. In about half the cases with this data set, there were some issues with precipitation saturating the low levels & getting it to the ground in a timely manner. This was not as much of an issue in scenarios where the forcing is what I think it will be.
All this said, the forecast remains unchanged.