Current Conditions at Sanborn Field
Thursday: Partly Cloudy. High: 60
Thursday Night: Mostly Cloudy. Low: 44
Friday: Partly Cloudy. High: 66
Friday Night: Mostly Cloudy. Low: 48
Saturday: Increasing cloudiness with showers likely in the afternoon. High: 67
Discussion:
Cooler temperatures and fall-like weather are the story for the end of the work week. After the passage of a cold front yesterday temperatures will remain cool for Thursday, staying in the upper 50s and lower 60s. Winds will be out of the northwest until Friday afternoon, when a shift from a northerly to southernly direction will allow temperatures to reach the upper 60s. Clouds will begin to increase on Saturday ahead of the chance for rain late Saturday afternoon. Enjoy the seasonal conditions as we head into the second half of the semester and keep the umbrella handy as you are going out on Saturday.
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Forecasters: McDonald, Duff, Aldrich
Date Issued: 10/21/21 11:00 AM CST
Technical discussion:
The 06z run of the GFS 20 was used for today’s forecast, as it initialized current temperatures and vorticity values more accurately than it’s NAM counterpart.
A jet streak situated over northeastern MO was present at 250 mb, with an accompanying low pressure system centered to the north over Iowa. Both the jet streak and low move off to the east quickly, exiting the area by 12z Thursday. Winds will be of a more zonal nature, flowing easterly from Thursday onward, indicating a continuous pattern that will keep conditions on Friday and Saturday similar.
Vorticity values decrease throughout Thursday at 500 mb, PVA associated with the exiting low pressure system in Iowa continues to wrap down into MO, but will exit completely by Friday 12z. Vorticity will then remain low until Sunday morning, with further PVA occurring northeast of the state. Partial cloud cover is indicated to continue, but without significant chances of precipitation until the increase in vorticity until Sunday for Missouri.
700 mb relative humidity will remain low through Saturday at 15z. Values will increase into Sunday as humidity flows in from the northwest, wrapping around a strengthening LPS that has now translated to Ontario from Iowa. This will bring greater chances of rain back into the forecast area on Sunday, as the humidity builds up vertically into this level of the atmosphere.
Temperatures at 850 mb will stay continuous through Friday and Saturday, as MIssouri straddles between the center of colder air from the LPS situated over Ontario and warm air seeping upwards from Mexico. Humidity values will remain strong at this level for the next 72 hours, indicating formation of lower stratus clouds while 700 mb humidity remains barren.
GFS soundings indicate humidity values will remain high at 850, further increasing with each day until the threshold required for rain is reached on Sunday at 12z.
Future forecasters should pay attention to increasing vorticity values and larger jet streaks beginning to form on Sunday 15z. Flowing in west from the rockies.
- McDonald
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