Tuesday, September 21, 2021

Current Conditions at Sanborn Field

 

Tuesday Night:
  Cloudy. Low: 50
 
 

Wednesday:
Mostly sunny. High: 72
 
 

Wednesday Night:
Clear. Low: 46
 
 

Thursday
:
Clear skies. High: 73
 
 

Thursday Night: 
Clear. Low: 52
 
 
 
 
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Discussion:   The clouds and cool temperatures from Monday night's cold front remain throughout the day Tuesday and into the night. From there, we will see less clouds, but cool temperatures remain, giving us a taste of fall weather. Calm and clear conditions continue over the rest of the forecast period. On Thursday night, winds shift from northerly to southerly, causing our nighttime temperatures to be a bit warmer than the previous nights'.

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 Forecasters:VanUnnik, Watts, Orr

Date Issued: 09/21/21 5:00 PM CST

Technical discussion: 

 This forecast was made using the 12Z run of the GFS. The GFS was chosen due to its more accurate initial conditions when compared to the NAM. SREF and GEFS plumes were used to assess temperatures, and GFS soundings were consulted for sky conditions. 

    At the 250-mb level, plots of heights, winds, and divergence depict a large upper level trough passing over Missouri 06Z Wednesday. Abundant amounts of divergence are associated with this trough, but they only help encourage cloud cover. By Thursday, calmer upper level conditions return as a result of an upper level ridge, and by late Thursday zonal flow returns. 

    500-mb plots of heights and vorticity also depict the passage of a large trough and the abundant amounts of vorticity it brings with it. Missouri is out of its influence by 09Z Thursday and sees little to no circulations for the rest of the forecast period. 

    Plots of heights and relative humidity at 700-mb show why there is no storm development, even though there are high amounts of vorticity and divergence passing through the forecast area Wednesday night. There may be some scattered clouds Wednesday morning due to small amounts of leftover moisture in the atmosphere, but by noon Wednesday all RH values over 70% are out of the region. GFS soundings also favor the lack of moisture after Tuesday night, and by 00Z Thursday, any cloud cover is out of the question. 

    At 850-mb, heights, winds, and temperatures give the cause for the "fall like" temperatures seen over the next few days. Winds remain in a northerly direction after the passage of Monday's cold front. These winds not only cause our cooler temperatures, but their direction is also preventing any moisture from entering the region from the Gulf. This encourages our clear skies seen from Wednesday and onward. A ridging pattern begins entering the region 00Z Thursday, shifting winds to a more westerly direction and encouraging a warmer low temperature Thursday night.

    The surface level plots of MSLP, thickness, and winds tell a similar story to the above levels. Winds remain in a northerly direction until around 12Z Thursday, when they begin to shift because of the incoming ridge. A high pressure system associated with this ridge also encourages clear skies and warmer temperatures, making for a calm day Thursday.

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