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Discussion:Thursday will bring rain starting in the morning and continuing into the late evening hours. A cold front passing that evening causes increased winds and a cool down for Friday and the weekend.
Forecasters: Chirpich and Cook
Date Issued: 03/15/2023 5:00 PM CDT
The 12Z run of the NAM was used for this forecast as its forecast high temperature for Wednesday afternoon more closely resembled the observed high temperature at Sanborn Field. The problem of the day is the precipitation and cold front associated with a low-pressure system which will move through the area tomorrow. As Wednesday ends, the ridge which has been over the area and brought warmer, fair weather will move off to the east as a trough builds in behind it. The southerly winds are accompanied by solenoids suggesting WAA as a supporting factor in Wednesday's warmer than average temperatures continuing into tonight. However, the low-pressure system will start a much different trend to end the week.
The low-pressure system associated with the trough originates near Colorado and will move into Missouri early Thursday morning. Moisture at 700MB is seen beginning at 09Z on Thursday, helping to form cloud cover. At 850MB, dewpoints will begin to increase late Wednesday night. At the same level, a significant LLJ appears on Thursday at 12Z, further supporting the transportation of moisture into the region. Thickness lines also form a into a tight gradient behind the low-pressure system, signalling the location of the incoming cold front.
Precipitation is expected ahead of the FROPA, with rain beginning around noon on Thursday. This initial burst of precipitation will be fairly light rain, as soundings show a dry layer in the mid-levels, inhibiting full saturation of the column. The heavier rain will be Thursday evening into early Friday morning, as the column fully saturates and the cold front moves through. The FROPA is expected Thursday evening, which will drop temperatures quickly while simultaneously setting up the region to experience a few flurries. Soundings demonstrate a cooling of the saturated column to allow for a switch from rain to snow around 06Z on Friday. The 5400m rain/snow line moves through the region the same time, supporting the switch to frozen precipitation. The atmosphere completely dries out around 09Z on Friday, leaving only a few hours of snow to finish off the system. Therefore, no snow accumulation is expected. The measurable accumulation of rain expected ranges from 1/4" to 1/2" for the entire system.
As the atmosphere dries out, cloud cover recedes Friday morning and leaves the area with sunshine. Solenoids return to the region on Friday as well, but this time bring CAA and much cooler temperatures in the low 40s for the weekend.
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