Current Conditions at Sanborn Field

 

Tuesday Night: Cloudy. Rain potential increasing throughout the evening. Scattered thunderstorms possible. Low: 63

 

 

Wednesday: Partly cloudy. High: 83

 

Wednesday Night: Clear skies. Low: 61
 

 

Thursday: Clear in the morning. Scattered clouds in the afternoon. High: 86

 

Friday: Clear in the morning. Scattered clouds in the afternoon. High: 87

 

 

 

 

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Discussion:

A weak cold front will pass through the Mid-Missouri region Tuesday night, bringing with it cloudy skies and scattered rain showers, as well as the potential for scattered thunderstorms. Cloud cover will carry over into Wednesday morning, but skies will begin to clear as the day progresses. Wednesday night will see seasonably low temperatures, but above average temperatures return by Thursday. Friday will look very similar to Thursday, but has the potential for increasing cloud cover in the afternoon.

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 Forecasters: VanUnnik, Watts, Orr

Date Issued: 09/14/21 05:30 pM CST

Technical discussion:

    The 12Z run of the GFS was chosen to create this forecast based on its accurate initial conditions. SREF and GEFS plumes were used to help forecast temperatures, and GFS soundings were consulted for rain timing, severe potential, and cloud cover. 

    At the 250-mb level, plots of heights, winds, and divergence show that the zonal pattern over Missouri soon gives way to the effects of an upper level trough. By 03Z Wednesday, abundant divergence, associated with right entrance region of a jet streak over northern Missouri, begins to move into the forecast region. This divergence remains in the area until around 18Z Wednesday. After this time, conditions at this level remain fairly calm.

    500-mb plots of heights and vorticity support circulations passing through the area Tuesday night and into Wednesday morning. This is the same time frame as the passage of divergence at 250-mb. Also similar to the timing at the 250-mb level, the vorticity moves out of Mid-Missouri by 18Z Wednesday. Calm conditions return until late Friday evening when Missouri may fall under the effects of a low pressure system in northeastern Texas. Future forecasters should watch the development of this system and see if its effects on Missouri change. 

     Plots of heights and relative humidity at 700-mb provide support for rainfall Tuesday evening and into Wednesday morning. RH values above 80% enter the region at a similar time as the divergence and vorticity at upper levels. These three factors working in conjunction create support for rainfall and the potential for thunderstorms Tuesday night. The abundant RH leaves the region by late Wednesday due to the LLJ being cut off by the winds from Tropical Storm Nicholas. Higher RH values briefly make a return both Thursday and Friday evening, providing enough moisture for cloudy skies, but not for rainfall. 

    At 850-mb, plots of heights, winds, and temperatures depict the temperature pattern for the forecast period. Southwesterly winds advect warmer air into Mid-Missouri Tuesday afternoon and evening, but these winds shift to northwesterly due to the passage of a weak cold front Tuesday evening. A weak high pressure system moves through northern Missouri Wednesday afternoon, shifting the winds back to a southerly direction and causing warmer high temperatures to return Thursday and Friday. 

    At the surface level, MSLP, thickness, and winds clearly depict the passage of the cold front Tuesday evening. The front moves out of the forecasting region by 06Z Wednesday and the high pressure system over northern Missouri moves in soon after. Winds at this level also then shift to a southerly direction, further supporting the warming of temperatures later in the week. 

    GFS soundings were assessed to determine the severe potential of the rain showers passing through Tuesday night. MUCAPE peaks at around 1100 J/kg at 00Z Wednesday. This time step also sees the strongest negative Omega values. These factors provide the strongest support for scattered thunderstorms moving through the region. Given these factors, storms able to achieve severe criteria are not expected.