Tuesday, October 26, 2021

 

Current Conditions at Sanborn Field




Tuesday Night:
Developing clouds. Low: 51
 

 

 


Wednesday: 
Overcast. Increasing rain. High: 59
 




Wednesday Night:
Overcast. Moderate showers. Low: 47
 



Thursday:
Cloudy. Decreasing rain. High: 50

 


Thursday Night
:
Cloudy. Light rain. Low: 47


 
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Discussion:  You won't want to forget your umbrella this week! Rain will begin Wednesday and will be heaviest overnight. These showers will begin to taper off on Thursday, and by Thursday night, just light rain remains. Overall, these showers will accumulate to around 1.25" of rainfall. Temperatures will feel more like fall, staying in the high 40s and 50s.

- VanUnnik

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Forecasters: VanUnnik, Watts, Bongard

Date Issued: 10/26/21 5:00PM CST

Technical discussion:  

For this forecast period, the 12Z run of the NAM40 model was used over GFS20. This was the choice despite both models running a couple of degrees warmer and placing the low pressure systems across the CONUS in correct positions. The difference lies in the plumes where the model disagreement with NAM was only slight compared to a much larger discrepancy with GFS. The largest challenge with this forecast was tracking the movement of the low pressure system and how it impacts precipitation totals for the region.

At 250-mb we have meridional flow aloft across the CONUS in a trough-ridge-trough pattern. Overnight the ridge starts to become a trough with divergence aloft over the mid-South going into tonight. While energy will start to increase from a positive trough tilt Wednesday night divergence will exist over us, while areas to the west will reside in the trough axis. Thursday evening we will transition to northerly winds going into the night with a closed upper-level low.

At 500-mb vorticity is coming from the western Kansas border tonight and will reach the Midwest tomorrow evening. A low-pressure system will be coming from Oklahoma City as the ridge over the region will become a trough at midnight Wednesday. A low will be passing to the south Thursday morning going into Thursday night changing southerly winds to northerly winds over mid-Missouri.

The 700-mb level will start to dry tonight with a downstream trough beginning to advect moisture into the region tomorrow morning getting divergence to transition into convergence by tomorrow night at 03Z. As the low pressure system passes to the south of mid-Missouri easterly winds in the low level will back to a northerly flow by Thursday night.

Following the low level jet, we will have warm air advection at 850 mb tonight. Due to that advection, tomorrow afternoon is going to increase moisture along with cloud cover. Again, as the low pressure system passes to the south cold air advection  will take over tomorrow behind the system. Despite this passage the moist profile continues to stick around through Thursday night.

- Watts

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