Current Conditions at Sanborn Field
Tuesday Night: Partly cloudy. Low: 54
Wednesday: Mostly cloudy. Isolated showers in the morning. High: 75
Wednesday Night: Mostly cloudy. Low: 46
Thursday: Mostly cloudy. High: 62
Thursday Night: Clearing sky. Low: 44
Discussion:
Who asked for so much cloud cover this week? Tonight we are going to see partly cloudy conditions. A small chance of rain on Wednesday is possible out ahead of a cold front pushing through the area Wednesday night accumulating up to .10” of rain with mostly cloudy conditions lingering. A jacket will be necessary as the night will get colder behind the frontal passage. Cloud cover and colder conditions will persist on Thursday afternoon but will begin to clear that night.
-Watts
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Forecasters: Watts, VanUnnik, Bongard
Date Issued: 10/19/21 5:00 PM CST
Technical discussion:
This forecast was put together using the 12z GFS run. GFS was chosen over NAM due to the two having very similar values for isobars, and placement of the Low Pressure System. A mid-latitude cyclone is going to be our main focus for this forecast period.
At 250-mb, there is an active meridional flow across the CONUS. During the day on Tuesday, there is a ridge over Missouri, giving us fair weather. At 12z Wednesday, a trough to our west begins to move in, pushing the ridge out to our east. Around 00z Thursday, the trough moves directly over Missouri, bringing divergence along with it from around 00Z to 06Z, with the Low Pressure System directly to our north. By 21Z Thursday, winds have shifted from southwesterly to northwesterly. Missouri remains under the influence of a longwave trough for the rest of the forecast period.
At 500-mb, Missouri has west-southwest winds as the trough moves in on Tuesday. As the trough deepens, an area of vorticity associated with the Low Pressure System will advect into the region at 21Z Wednesday, though it will stay mostly to the north. From 15Z Thursday to 00Z Friday, some vorticity advects back into the region associated with the wraparound flow of the low pressure system.
At 700-mb Tuesday night, a small area of moisture over Missouri will lead to a greater RH value around 06z Wednesday. At 12Z Wednesday, moisture increases, along with convergence. This clears around 21Z Wednesday. At 09Z Thursday, a frontal passage will cause a wind shift from west-southwest, to northwest, as the trough axis passes over mid-Missouri. Thursday into Thursday night, due to the cold front, winds remain northwesterly, and the region remains dry and stable.
At 850-mb, abundant moisture and an LLJ are seen over Kansas at 00Z Wednesday. As Missouri has a southwesterly flow, at 18Z Wednesday, moisture increases and moves into Missouri, as the Low Pressure System to the north strengthens into a mature mid-latitude cyclone, creating a comma cloud. This moisture remains through 00Z Thursday, until mid-Missouri enters the dry slot pushing in just behind the cold front around 00Z Thursday. With the cold front passage occuring between 00Z and 06Z, the comma cloud wraps back around at 09Z, bringing with it more moisture. Moisture begins to move out around 09Z Friday, and future forecasters should watch the moisture that will trail along from the southwest.
-VanUnnik
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