The setup for significant winter weather in the Southern Plains over the next two days is meteorologically pretty simple. A deep, frigid air mass at the surface has been driven south by high pressure centered in southwestern Canada. It lies underneath southwesterly flow on the east side of an expansive upper trough, which is providing both ample moisture and strong forcing for ascent (especially along embedded shortwaves).
Model guidance has converged on the idea of a transition from freezing rain to sleet to snow, moving southeastward with time as the warm nose around 700-800 mb cools. The heaviest precipitation appears likely to fall within a narrow band oriented roughly from southwest to northeast. The forecast challenges are
1. Nailing down precipitation types in space and time, and
2. Placing the band of heaviest precipitation
Precipitation types will depend almost completely on subtle variations in temperature in the lowest 3 km or so of the atmosphere. Even one day out, this is pretty tough to assess without relying on model forecast soundings. For Norman, consensus between the NAM and GFS seems to be some freezing drizzle and light sleet possible in the earliest stages of the event Thursday afternoon, changing to snow as the column wet-bulbs Thursday night. Moderate to heavy snow appears likely into Friday morning, ending midday. It appears the amount of sleet in central Oklahoma might be trending downward, with classic heavy snowfall soundings making more appearances there in both models late Thursday night/early Friday morning. Freezing rain looks to be a major, major issue for parts of southeastern Oklahoma into Arkansas, where the warm layer will be much more pronounced even after reaching saturation.
As far as the band of highest QPF, models have been wobbling back and forth across an area from I-44 to a Fort Smith-Dallas line. A lot will depend on the exact placement of the front (from the surface up to 700-800 mb) For what it's worth, the surface front ran a bit ahead of the forecast overnight. With that in mind and the major models coming into better agreement, Norman looks to catch at least the northwestern edge of some pretty hefty precip totals.
Norman forecast: A fine glaze of freezing drizzle on elevated surfaces during the day Thursday, with an inch or less of sleet accumulation through evening. Precip will rapidly turn to snow Thursday evening. Periods of heavy snow overnight into Friday morning; 2-5" total snowfall.
