Current Conditions at Sanborn Field
Thursday Night: Overcast clouds with moist conditions. Low: 53
Friday: Afternoon showers reducing cloud cover. High: 66
Friday Night: Becoming partly cloudy. Low: 56
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Discussion:
Conditions start out seasonably cool today in the aftermath of the passing cold front, with moist conditions presenting the possibility of 0.05in of rain on Friday. The sky will be overcast through most of the forecast period with occasional breaks on Friday and Saturday around noon. Winds will switch from the north to the south going into the weekend, bringing warmer conditions back on Saturday.
Sausen
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Forecasters: Sallot, Baker
Date Issued: 09/21/2022 5:30 PM CDT
Mid Missouri is waking up to a much cooler air mass this morning as the cold front that moved through yesterday afternoon. The lagging precipitation and residual moisture behind the front subdued by the time it made it through Missouri, resulting in no rain amounts for Sanborn Field. The GFS and NAM model runs were both used for this forecast period; however, we leaned towards GFS as it had a better handling of the timing of the frontal passage as well as the shift of the trough.
The bottom of the jet stream is currently situated over northern through central Missouri. With the upper atmosphere being dominated by the 70 knot winds. It does look to shift north throughout the day today, but returns by 06Z Friday. As the jet stream moves over Friday morning, a jet streak is centered over southern Nebraska, placing Missouri in the right entrance region. Combined with low divergence values around 18Z Friday, there is power in the upper atmosphere as the upper level trough shifts to the east. By Saturday 12Z, the central CONUS seems to take on a more zonal flow.
With the 250mb level staying quiet throughout the day today, the 500mb vorticity map shows a line of circulation stretching out from the low pressure system situated over the pacific northwest. These values move through in a uniform line through the STL area this evening. Behind the band, there is a pocket of high levels of circulation around 12Z Friday. This is in support of the upper level jet stream as well. It does look to dance around the Missouri area through Saturday, but as the jet stream tracks norther, and winds take on a more northerly component, there does not seem like much to support precipitation.
The 700mb relative humidity map is where it is all happening. Right now, there is interconnections between the moisture associated with the pacific NW LPS and the LPS tracking north of the United States/ Canadian border. This line of moisture stretching across the southern CONUS is situated across central Missouri. Throughout the day today, the northerwesterly wind will push the moisture south over the Ohio Valley. It does look to stay in southern Missouri before winds switch to out of the south and bring the moisture back up over Missouri. As the trough progresses east throughout the day tomorrow, the heaviest of moisture returns to Missouri as we take on a more zonal flow. This moisture finally heads off with the LPS as of Saturday 15Z. This would cue the clouds to finally track out of mid Missouri.
A surface and sounding analysis was analyzed to determine the precipitation amounts through out forecast period. A sounding was very helpful, the 12Z GFS sounding shows a fairly saturated upper levels, similar to what we were seeing on the 700mb relative humidity map. However, all layers up to 500mb looks to dry out fairly fast through 18Z today. The clouds looks to stick around, evident with a saturated profile 500mb and up, a PWAT of 0.45’ further supports the idea of rain holding out until tomorrow morning. The GFS 12Z sounding for Friday shows 880mb through 600mb higher omega values. Along with the increase in updrafts, PWATs rise to 1.28’. This would support a saturated profile again, through the surface, indicating rain through Friday evening before drying out.
Baker
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