Current Conditions at Sanborn Field 

 

Wednesday: Mostly sunny. High: 93
 

Wednesday Night: Cloudy. Slight chance for light rain. Low: 59

 

Thursday: Becoming partly cloudy. High: 70

 

 

Thursday Night: Mostly cloudy. Low: 54

 

Friday: Cloudy. Chance for afternoon showers. High: 60

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Discussion:

From summer to fall! Thanks to the passage of a cold front, temperatures are expected to plummet Wednesday afternoon bringing fall-like conditions and some  isolated showers. Things dry out, but remain cool, Thursday before another wave of moisture moves into the region Friday.

Russell

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Forecasters: Russell, Shaw, Travis

Date Issued: 09/21/2022 9:00 AM CDT

Technical Discussion:

 

The long-awaited break from the unusual, almost July-like heat will finally arrive in the form of a cold front. Model guidance has fallen into much better agreement regarding the timing of the surface cold frontal passage, but still diverge in regards to moisture availability. Still, have gone with a blend of the GFS and NAM. Unfortunately, some data issues have resulted in a break in the feed of new model data. Latest models available are from Tuesday at 18z. 

The story today remains the active weather associated with a weak, ridge-running shortwave. A strong, 150-kt jet streak centered over the Upper Mississippi River Valley will provide upper-level forcing for ascent in the form of divergence on its southern flank. The NAM and GFS have some disagreement in how far south this divergence reaches. In a reversal from Monday morning's forecast, the GFS now has the disturbance remaining further to the north. Upper-level WV imagery shows the upper high parked over northern TX, so the more northern solution of the GFS seems more likely. The 500-hPa vorticity field shows a small difference in timing of the propagation of the strongest circulation into Missouri. 

At the end of the day, the timing in forcing will not be the limiting factor, but in fact, is moisture availability. Neither the GFS nor the NAM are impressive with moisture in the mid or low levels. Both models' respective soundings favor a near-surface, dry layer with 10-20 degree dewpoint depressions between the surface to 850 hPa. Mid-level WAA is virtually non-existent over Missouri with much of that forcing confined to central KS. The low-levels are equally unimpressive. With all this in mind, thinking that this will be a largely dry frontal passage. Can't rule out scattered light showers/drizzle, but precipitation will STRUGGLE to reach the surface with the aforementioned dry layer.

Attention turns to Friday as a shortwave trough currently over the Pacific Northwest moves east across the CONUS. By Friday, the upper-level low will be centered over the upper Midwest helping to deamplify the ridge that has dominated the Lower Plains States. Mid- to low-level moisture as well as WAA is much more impressive for Friday. Model soundings show another low-level dry layer albeit much moister. Confidence in afternoon showers for Friday is increasing. Future forecasters should pay attention to how this evolves with (hopefully) more updated model data.

Travis