Monday, September 27, 2021

 

Current Conditions at Sanborn Field

 

Monday:
Clear skies. High: 91
 
 

Monday Night:
Clear. Low: 66
 
 

Tuesday:
Clear. High: 90
 
 

Tuesday Night:
Becoming partly cloudy overnight. Low: 66
 
 

Wednesday:
Becoming cloudy. High: 86
 
 
 
 
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Discussion:   

Summer-like temperatures will stick around for the first part of the week. High temperatures Monday will approach a Columbia record of 93 for September 27. High pressure will keep our skies clear with winds out of the southwest, bringing in warmer air. Temperatures overnight will stay above average in the mid 60s. Clouds finally move in Tuesday night into early Wednesday morning out ahead of a low pressure system. Isolated showers can not be ruled out Wednesday evening, but the bulk of the rain should hold off until overnight Wednesday into Thursday.

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Forecasters: Cade, Baker, Travis

Date Issued: 09/27/21 10:00 AM CST

Technical discussion: 

A return of summer is in full swing here in mid-Missouri with daytime highs Monday and Tuesday approaching record highs. The main concern for this period is the approach an upper-level low that will bring an abrupt end to hot and sunny conditions. Both the GFS and NAM had excellent consensus in the upper-level setup when compared with GOES upper-level WV imagery. As such, went primarily with GFS guidance, but consulted the NAM for narrowing down timing of precipitation. 

Models' handling of the upper-level setup lines up well with each other and with what GOES WV imagery shows. One would hope so, since there is not much up there at the time of forecasting. Model 250-hPa height and wind and 500-hPa height and absolute vorticity depict zonal flow across much of the CONUS with a pesky cut-off low over the Four Corners region. Deamplified flow has kept and will keep low-level high pressure in place over the SE allowing southwesterly flow at the surface to facilitate WAA. This will change by the end of the forecast period. GFS 500-hPa height and vorticity shows an amplifying longwave trough digging far south from the Pacific NW Tuesday into Wednesday. This will finally overtake the cut-off low and carry it to the NE where it will become the Midwest's problem.

GFS 700-hPa RH and UVM depict a heavy increase in mid-level saturation ahead of the system Wednesday morning into early afternoon. A lack of a LLJ seen at 850 hPa over Missouri would suggest precip will hold off until the overnight hours when the nocturnal LLJ develops. 

Of note at the surface is a prominent boundary that will sit over northern MO Tuesday into Wednesday. Winds to the south will remain westerly, turning southwesterly further south in the state. Winds to the north change rapidly (<50 miles) by 180 to be out of the east. The boundary, believed to be a weak stationary front, will linger in Northern Missouri until the approach of the next system Wednesday night. Though unlikely with little horizontal forcing, if this boundary were to sag further south than models are anticipating, daytime highs could be knocked down by ~5 degrees. 

As far as precipitation goes, the bulk of the rain looks to hold off until the overnight hours Wednesday into Thursday thus making it future shifts' "problem of the day," but as GFS soundings begin to saturate from the top on down, the slight chance of isolated showers beginning in the afternoon cannot be ruled out right now.

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