Current Conditions at Sanborn Field
Thursday Night - Rain stopping around 9pm. Low: 44-48
Friday - Mostly Sunny. High: 72-76
Friday Night - Increasing clouds throughout the night. Low: 48-52
Saturday - Widespread rain. High: 54-58
Sunday - Mostly sunny. High: 66-70
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Discussion:
Two low pressure systems pass through the Columbia area this weekend, one on Thursday and the other on Saturday. Thursday's system slowly moves out of the area Thursday night taking the rain with it. Friday's winds arrive from the SW bringing us warmer temperatures. The second low pressure system moves in Saturday morning and brings the moisture back along with moisture from the Gulf, giving us clouds and more rain for a majority of the day. A cold front is associated with this system, dropping our temperatures back down for the day before warming back up on Sunday as the low pressure leaves our area. The atmosphere then dries out leaving us with clear skies and pleasant weather as we enter next week.
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Forecaster: Nixon, Cochran, Travis
Issued: 5:00 PM CST 08 April 2021
Technical Discussion (The nerdy stuff we are discussing in class):
The GFS20 was chosen as the primary model used for today’s forecast based on it’s placement of the low pressure system approaching Missouri. GEFS and SREF plumes were referenced for temperatures and total QPF over the weekend. GFS soundings were also used for sky conditions. The main focus for this forecasting period is the LPS passing over northern Missouri on Thursday night and the trough that follows Saturday afternoon.
The LPS that has been moving across the western portion of the U.S. reaches our area at the beginning of this period and can be seen on the 250mb plots of height, wind, and divergence. This system moves north and is engulfed into an upper level trough centered in Iowa. This trough absorbs the LPS but then shortly after, develops again into an almost-closed system on Saturday. The highest levels of divergence associated with the system stay SE of Missouri and is concentrated around the eastern border of Arkansas, but our forecast area still sees some elevated levels of divergence aloft with the passage of this system.
The two low pressure systems are also seen on the 500mb plots of height and vorticity. The vort max seen from the first LPS encompasses most of the central United States, these high values of rotation associated with the slowly-moving LPS attribute to the rain and cloudy sky conditions seen throughout Thursday. The vorticity leaves mid-Missouri just briefly on Friday and then returns with the passage of the second LPS. Expect more rainy conditions as the vorticity reaches a maximum again on Saturday at 15Z. We are then left with a short period of zonal flow that will carry out the rest of this period resulting in a more dry and calm atmosphere.
The majority of the moisture in the atmosphere on the 700mb plots of height and RH can be seen moving in accordance with the low pressure systems, but this is aided from moist air travelling up from the Gulf transported by the LLJ. These saturated conditions support more widespread rain as the system passes over Columbia on Saturday. Total QPF plumes expect around 1.0in of rain throughout the weekend and 0.65in of that accumulation occurring on Saturday. This layer does however dry up after the system passes and leaves us with clear skies as the weekend closes.
The 850mb plot of winds and temperatures show Missouri with westerly winds as the first LPS passes on Thursday and keeps this direction until Friday at 21Z where the winds shift southerly. They then shift from NNW and back to the westerly as the second system passes and stay from that direction as we enter the next week. A cold front sweeps through Columbia with the system on Saturday causing that to be our coolest day, however we do warm up again as we will be under the influence of a shortwave ridge with the exodus of the system and then enter zonal flow on Sunday.
GFS soundings do not detect any significant CAPE values throughout the entirety of the forecast period, so the threat of storms over the weekend is small. However, large amounts of UVM are depicted in the lower levels on Saturday with a saturated atmosphere in the lower levels as well, contributing to the widespread rain we will experience on Saturday.
The next forecasting shift should continue to watch Saturday’s LPS move through the area as well as the cold front it brings with it.
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