Current Conditions at Sanborn Field
Thursday: Becoming partly sunny. High: 70
Friday: Periods of scattered showers throughout the day. High: 58
Friday Night: Decreasing cloudiness, late. Low: 41
Saturday: Mostly sunny. High: 66
Discussion:
This week's cooler, rainy, pattern will continue into at least the first half of our weekend. The departure of rain early Thursday morning will slowly lead to partly sunny skies as clouds slowly move out by the mid-afternoon. A partly sunny evening will ensue, though by the later overnight hours clouds are expected to build back in and bring showers along with them. The showers, part of a front that will shift winds from the south to the north, will not only bring scattered showers throughout the day but also lower temperatures considerably, capping our highs in the upper 50s. Some of the chillier weather Missouri has seen this fall, conditions will be perfect breaking out hoodies and jackets. As clouds and rain depart once again Friday night, moisture will decrease substantially and bring us into the lower 40s for a cold night in the region. Saturday will be a marked change from the wetness seen over the week, and sunshine poking through the clouds will help warm us up a little bit more into the middle 60s.
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Forecasters: Duff, Mcdonald, Aldrich
Date Issued: 10/14/21 10:00 AM CST
Technical discussion:
For this forecast the 06z model run of the GFS was chosen. The GFS performed well when modeled temperatures were compared to observed temperatures. Both the GFS and the NAM modeled vorticity at 500-mb fairly well, but the GFS did a better job at modeling higher values for Mid-Missouri which is expected because of our position on the southeast side of the approaching trough.
At the 250-mb level plots of heights, winds, and divergence, show an upper level trough to the west with a low centered over the Northern Plains. By 12z Friday the trough moves east and higher values of divergence intensify. The jet streak over the Middle Mississippi River Valley, begins to strengthen as it rounds the base of the trough. As the trough moves out of the region by 00z Saturday, any upper level divergence is gone and the jet streak weakens.
At 500mb, heights and vorticity show increasing vorticity starting 00z Friday through 12z Saturday. The bands of vorticity increase due to a trough moving southeast across Mid- Missouri on Friday. By 15z Saturday vorticity values lower as the trough moves away from the forecast area and a ridge builds into southwestern United States.
At 700-mb, heights, vertical velocity, and relative humidity, show a river of moisture originating in Southeast Texas and the Gulf of Mexico moving to northeast. The moisture moves out of the region for most of the day on Thursday, but relative humidity begins to increase again by 12z Friday. As the trough approaches the central United States, relative humidity will increase throughout the day on Friday indicating cloud cover and the potential for precipitation. Along with the moisture, vertical velocity also increases throughout the early morning hours of Friday, with higher values continuing until 03z Saturday. At this time, vertical velocity starts to decrease because the trough moves east out of the Mid-Mississippi River Valley. Less moisture and activity at the 700-mb level is expected on Saturday indicating a clearer sky and drier weather.
At 850-mb, heights, winds, and temperature show southwesterly flow until 12z Friday. At this time the winds will shift to the NW which is associated to the passage of a front and the incoming upper level trough. The northernly winds and potential precipitation will keep temperatures cooler on Friday and into Saturday.
Future forecasters should pay attention to the exiting trough.
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