SWOP Weekly Weather Discussion

HEADLINE

After a storm system brings a rain/snow mix this weekend, a bitterly cold airmass will settle into central Illinois through next week.  

DISCUSSION

A deep upper low centered west of Hudson Bay will continue to be the dominant weather feature across the Midwest for the next several days.  As a short-wave trough evident on the latest water vapor imagery off the coast of California tracks across the U.S. beneath the prevailing low, it will provide southerly flow and a temporary warm-up for Friday, February 14th into Saturday, February 15th.  High temperatures will reach the lower 30s on Friday, then will climb into the upper 30s and lower 40s by Saturday.  As the wave approaches and warm air flows northward over the cold snow-covered ground, mixed precipitation will develop across central Illinois late Friday afternoon into Friday night.  While the atmosphere will initially be cold enough to support light snow, conditions will warm sufficiently to allow the precipitation to transition to rain along and south of a Rushville to Paris line late Friday night into Saturday.  Further north, a mixture of snow and patchy freezing drizzle Friday night will change to rain on Saturday.  Minor snow and ice accumulations are likely...especially along and north of the I-74 corridor.  As the wave departs and winds switch to northwesterly, cold air advection will allow the rain to transition back to snow across all of central and southeast Illinois Saturday night.  After that, the Hudson Bay upper low will dig southward...sending a bitterly cold airmass into the Midwest.  High temperatures will likely drop into the teens from Monday, February 17th through Thursday, February 20th while overnight lows dip to near zero.      

The Arctic Oscillation (AO) is presently strongly negative while the North Atlantic Oscillation (NAO) is neutral...supportive of a cold weather pattern for at least the next week.  The latest GEFS forecast shows excellent agreement among its members that the AO will steadily increase and return to positive territory by the end of the month.  This combined with a clear warming signal seen in Week 3 CFS output gives confidence that a major warming trend will occur during the last week of February into the first week of March. 

The latest 6-10 day outlooks (Feb 18-22) from the Climate Prediction Center (CPC) suggest BELOW normal temperatures and NEAR normal precipitation across central Illinois.

Issued: 2/13/25