Wednesday, September 29, 2021

Current Conditions at Sanborn Field

 
 

Wednesday:
Cloud cover increasing throughout the day. High: 85
 
 


Wednesday Night:
Overcast. Possibility for light rain. Low: 68
 
 


Thursday:
Cloudy. Rain in the morning and early afternoon. High: 79




Thursday Night:
Cloudy. Light isolated showers possible. Low: 65
 
 
 

Friday:
Cloudy. High: 78

 
 
 
 
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Discussion:  

Cloud cover will increase throughout the day today and continue into tonight and for the rest of the forecast period. Winds have shifted to the south providing some moisture needed for cloud development. Our first chance of rain is tonight, although the best chance for rain throughout the forecast period is Thursday. Rainfall totals through Friday afternoon are expected to be between 0.5 inch and 0.75 inch. 

-Macko & Kobielusz

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Forecasters: Macko, Kobielusz, Bongard

Date Issued: 09/29/21 10:00 AM CST

Technical discussion: 

 For this forecast period the 06Z GFS model run was favored over its NAM counterpart due to several factors. First, GFS matched better with initial conditions observed at the surface at the start of the forecast period. Secondly, and more importantly, GFS modeled 500 mb height contours matched more favorably with upper level water vapor satellite imagery associated with the developing mid-lat cyclones to the west of the region over the Rockies. This is significant as mid-Missouri will reside in the warm sector of this MLC for the duration of the forecast period. GFS model soundings were used in accordance with modeled precipitation accumulations to determine timing and amounts of rainfall. Plumes were used as quality checks for both models.

 

250-mb upper level models reveal an extremely amplified meridional flow pattern across the CONUS in a trough-ridge-trough pattern at the start of the period. The ridge over the central CONUS will begin to give way to the oncoming trough out west this evening promoting the deep southerly flow that extends from the surface up through 300 mb on GFS model soundings. This extreme pattern will persist through Friday afternoon. 

 

500 mb vorticity maps show an increase in energy over eastern Kansas beginning this afternoon and persisting through Thursday. This vorticity is associated with positive vorticity advection in the upstream flow of the invading trough that will make its way off the Front Range of the Rockies tonight and enter the Midwest by tomorrow. This vorticity will be the catalyst needed for precipitation development over the region beginning as early as this evening.

 

The low levels are rich with moisture and southerly flow throughout the forecast period at both 700- and 850-mb. PWAT values depicted in GFS model soundings will soar from 1 inch today to 1.75 to 2 inches by 18Z Thursday. Soundings also show a moist profile with some CAPE available for convection though CIN may keep convective development to a minimum. The sounding is very reminiscent of a warm sector sounding. Friday's profile will dry out slightly shutting down rain chances briefly at the end of the period though the column will begin to saturate again by 00Z Saturday as the next cold front approaches. Future forecasters will have to tangle with timing of this frontal passage and associated precipitation.

-Bongard

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