Wednesday, September 22, 2021

 

 Current Conditions at Sanborn Field

 

Wednesday Night:
Clear. Low: 46
 
 


Thursday:
Sunny. High: 75
 
 


Thursday Night
:
Clear. Low: 52
 
 


Friday: 
Partly Cloudy. High: 83




Friday Night:
Mostly Cloudy. Low: 54

 
 
 
Thanks to IconArchive.com for the icons! 
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Discussion:  

With the frontal passage earlier this week, cooler temperatures befitting of the Fall Equinox have moved into the area. Clear skies and northerly winds will continue to keep our temperatures low through Thursday. Friday will start to warm up with a change in our winds to the west. Beginning Friday afternoon our skies will start to become cloudy as a low pressure system over Wisconsin brings moisture into our region. The end of the forecasting period will see a return of summer-like weather as we gear up for the weekend.

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 Forecasters: McMullen, Noblitt, Cochran

Date Issued: 09/22/21 5:00 PM CST

Technical discussion: 

The 12Z GFS20 was used for today's forecast because it has been handling the LPS over Illinois with more accuracy than the NAM. GFS soundings were used to aid in forecasting sky conditions and SREF and GEFS plumes were referenced for temperatures.

Looking at the 250-mb heights, winds, and divergence plot, the LPS over Illinois can be seen moving east as we start our forecasting period. This system closes off starting Wednesday at 15Z and continues to develop as it moves over the Great Lakes region. During this time, a ridge overtakes the central United States including Missouri, this keeps our winds from the NW. Friday sees westerly winds as the ridge leaves and zonal flow remains until Saturday at 03Z when a new trough extends from eastern Ontario down to north Missouri.

500 mb plots of heights and vorticity show vast amounts of circulation associated with the LPS in the Midwest. This vorticity is sitting just east of Columbia on Wednesday, so we will no longer see the effects in the form of cloud cover from this system. When the 03Z Saturday trough arrives, it bring with it high values of rotation with a vort max in southern Wisconsin. We receive the remnants of this rotation, giving way to clouds Friday afternoon and evening.

From evaluating relative humidity, heights, and vertical velocity on the 700-mb level, we see the moisture leaving with the week's earlier frontal passage. Mid-Missouri stays dry at this level until the trough nears at the end of the forecasting period. This paired with the GFS soundings supports clear skies until Friday when clouds begin to form and continue forming into Friday night. Since the majority of the moisture stays north with the trough, rain is not expected to fall in Columbia. 

850 mb heights, winds, and temperatures show the northern winds from the cold front continuing to dominate the area keeping our days cool and nights cold. This persists until 09Z Friday when we see a wind shift to the west. 1000-500 mb thickness shown on a plot with MSLP shows some WAA at this same time making Friday much warmer and closer to the summer temperatures with which we're accustomed.

The next forecasting period should pay attention to the building moisture in our area associated with the LPS north of us on Friday night.


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