Current Conditions at Sanborn Field
Friday Night: Cloudy with a slight chance of rain. Low: 52
Saturday: Clear skies. High: 77
Saturday Night: Clear. Low: 57
Sunday: Mostly sunny and hot. High: 90
Sunday Night: Clear skies. Low: 60
Discussion:
Autumn temperatures are on their way out and another dose of summer is on its way in. A cold front will be moving through Friday night, keeping temperatures seasonal into Saturday. A lack of moisture suggests that rain is unlikely for Friday night, but an isolated shower cannot be ruled out. High pressure moves in behind the front with clear skies and mild temperatures for Saturday. Saturday night, winds shift from the southwest bringing back summer-like temperatures for Sunday into Monday.
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Forecasters: Ethridge, Millsap, Travis
Date Issued: 09/24/21 5:00 PM CST
Technical discussion:
After an all too brief shot at fall, summer rears its ugly head once again. The main concern for this forecast period is strong WAA that will bring daytime highs back to the upper 80s and lower 90s. Both the GFS and NAM had good consensus resolving the large-scale upper-level pattern, but when compared to GOES upper-level WV imagery, both models had poor handling of the placement, and orientation of the shortwave over south-central Canada. Regardless, the GFS had better handling on daytime highs for Friday. As such, went with GFS guidance.
As the upper-level shortwave trough that brought storms Monday night, and several days of fall-like temperatures moves further to the northeast, a longwave trough will remain parked over the NE CONUS as another shortwave digs in from Canada to reinforce it. GFS 250-hPa winds and divergence show increased divergence with the wave as well as a present albeit weak jet streak moves in on the back side of the shortwave trough. Much is the same story at 500 hPa with plenty of large-scale circulation associated with this system. All this being said, the GFS keeps the bulk of the disturbance to the northeast.
Lacking substantially is sufficient moisture to support widespread precipitation. GFS 700-hPa RH shows saturated air extending southwest along the surface frontal boundary, but decreases substantially over Missouri. A lack of rain is supported by GFS soundings with mid- to upper-level saturation, but a 20-30 degree dewpoint depression near the surface. The near surface dry layer never gets the chance to moisten before the surface cold front passes and pushes remaining moisture out of the area. Current radar imagery from KEAX shows showers over the NW part of the state. The HRRR favors that these showers will be able to survive the dry layer in mid-Missouri as such left in the slight possibility for isolated showers.
GFS MSLP and wind indicate frontal passage will occur between 7pm and 10pm. A current look at METARs across the region places the frontal boundary just off to the northwest over Kansas City and NW Missouri. Seeing as how the GFS had poor handling of the upper-level aspects of this system, would not be suprised to see frontal passage on the earlier side closer to 7pm.
As the system exits, upper-level flow is kept relatively zonal by a cutoff low over the SW CONUS seen in the height field 500 hPa. This will allow skies to clear and temperatures to be on the increase as surface high pressure will park itself to the east, putting Missouri in southerly flow beginning Saturday night. Daytime highs on Sunday will climb back to summer-like in the upper 80s and will remain hot into early next week.
- Travis
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