Current Conditions at Sanborn Field
Friday: Increasing clouds into the afternoon. High: 68-72
Saturday: Overcasts with rain showers persisting all day. High: 62 - 66
Sunday: Rain showers, possibility isolated thunderstorms in the morning. High: 60-64
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Discussion:
As we move into the weekend and clouds start to build in the sky Friday afternoon with some small showers during the night. Around this time our winds shift from the north to the southwest, so expect slightly warmer temperatures than Thursday. Saturday experiences moderate rainfall throughout the day. Sunday brings chances of thunderstorms in the morning with showers lasting all day, giving us a gloomy start to finals week.
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Forecasters: Lamb, Cochran, Nixon
Date Issued: 05/06/21 05:00 PM CST
Technical discussion:
The GFS was used for today’s forecast based on its superior handling of the location and timing of the low pressure system moving in on Sunday. GFS soundings as well as GEFS & SREF plumes were also referenced for temperature and cloud cover. The LPS and the storms that will accompany it will be the main focus fore this forecast period.
To start out the period, Missouri will be in a transition zone at the 250-mb level between a trough-ridge pattern with a deep upper-level ridge making its way into the area. This will remain until Sunday morning when a small shortwave moves over the state causing elevated upper-level divergence. Once this disturbance moves through, we move into zonal flow to finish out the forecast period.
On the 500-mb plot of heights and vorticity, the circulations associated with the trough quickly push off to the east as the ridge moves in. Missouri does not experience more circulations until Sunday morning when the LPS reaches the area and brings more circulations to help fuel the active weather we will experience on Sunday. We again then return to zonal flow at this level to finish off the day.
The 700-mb plot of heights and RH does not depict any moisture in the area until Friday afternoon. We then experience a large influx of moisture from the Gulf with the LPS also contributing some moisture once it reaches the area going into Sunday morning. This influx of moisture will bring some increasing cloud cover and possible showers into the area. The low pressure as well as the moisture pushes northeast and we remain dry for the rest of the period.
The 850-mb plot of heights, winds, and temperature have us in a moderate NW flow until a shift occurs on Saturday morning giving us significant SW flow contributing to rising temperatures. The LPS reaches the area at this level early Sunday morning which is when the heaviest rain and possible storms are expected to occur. Once the precipitation moves out of the area we return to a weak northerly flow with increasing pressure.
At the surface, we are under the influence of a large high pressure system until Saturday when the pressure begins to drop as the LPS moves towards the state. The low pressure center reaches us early Sunday morning which lines up well with the timing of when the most active weather is expected.
GFS soundings suggest a very dry atmosphere with a backing wind until late Friday evening when the lower levels begin to saturate with some rising motions suggested near the surface during this time. Some light rain will be likely in the area for a brief time period going into Saturday morning. By Sunday, we still see some saturation near the surface with a slight inversion causing a cap at around the 750-mb level. Significant upward motion is depicted near the surface at this time. Very strong CAPE values up to about 2100 J/Kg are being shown early Sunday morning with the K-index over 30 and TT-index staying around 55 which supports storm development during this time. If the air parcels push through the cap, expect some heavy rain at times and some thunderstorms lasting until about 11a.m. on Sunday. The absence of any strong wind shear during this time is reason to believe these storms will not become severe. The atmosphere once again dries out for the remainder of the forecast period by early Sunday afternoon.
The next forecast period should focus on the incoming low pressure system moving towards the area from the NW United States.
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