Current Conditions at Sanborn Field

 

Tuesday: Partly cloudy. High: 88

 

 

Tuesday Night: Cloudy. Rain starting late. Scattered thunderstorms possible. Low: 64

 

 

Wednesday: Cloudy in the morning. Becoming partly cloudy throughout the day. High: 82
 

 

Wednesday Night: Clear skies. Low: 61

 

Thursday: Clear skies. High: 86

 

 

 

 

 

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Discussion:

Cloud cover will increase throughout the day Tuesday due to the passage of a weak cold front, bringing the potential for rain and scattered thunderstorms late Tuesday night. Temperatures will remain warm for mid-September, with highs in the upper 80s Tuesday. The rain showers will move out of the area by early Wednesday morning, and skies will continue to clear throughout the day. Calm conditions and clear skies persist over Wednesday night and into Thursday, with warmer high temperatures and seasonable lows.

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 Forecasters: Duff, Orr

Date Issued: 09/14/21 10:30 AM CST

Technical discussion:

    The 06Z GFS model run was used in this forecast due to its accurate initial conditions and an overall better performance than the NAM model. GEFS and SREF plumes were used to help create temperature forecasts, and GFS soundings were consulted to assess rain potential and cloud cover.

     At the 250-mb level, plots of heights, winds, and divergence depict zonal flow dominating the Missouri region until around 15Z Tuesday when divergence and an upper-level trough make their way into the area. A shortwave trough passes over Mid-Missouri which, in combination with a weak jet streak, brings abundant divergence through the region. These factors move out of our forecasting area by 00Z Thursday, and Missouri will see a return to zonal flow and calm conditions. 

    At 500-mb, circulations move into the region at the same time as the upper level divergence at 250-mb. These circulations are smaller and weaker than the regions of divergence, but the two could still work together to spur up some minor, scattered thunderstorms. 

    Plots of winds and relative humidity at 700-mb show that there will be enough moisture in the region to further support the potential for rain and thunderstorms. Moisture resulting from both a LLJ and from Tropical Storm Nicholas pushes into the area around 21Z Tuesday, and remains until early Thursday at 03Z. 

    At 850-mb, plots of heights, winds, and temperatures begins showing better indications of the passage of a cold front between 18Z and 21Z Tuesday. The potential for rain follows this cold front, which brings an increase in UVM. This, working with the other factors at the upper levels, increases the potential for scattered thunderstorms. By early Thursday, winds at this level are southerly, favoring warmer temperatures, even after the passage of a front. 

     At the surface level, the passage of a cold front is even more apparent in the shift in winds and the MSLP pattern. Again, the front passes through the region between 18Z and 21Z Tuesday, and by late Wednesday, a weak high pressure system appears over northeastern Missouri. Winds return to a southerly direction by early Thursday, but any moisture transport is cut off by the location of Tropical Storm Nicholas at this time. 

    GFS soundings indicate that rain begins around and after the passage of the cold front, beginning at 18Z Tuesday. Negative Omega values in the lower levels along with MUCAPE values of up to 1600 J/kg provide the potential for scattered thunderstorms, but anything severe is unlikely. Soundings also show the atmosphere continuing to become less saturated until clear skies make a return Wednesday afternoon.