Friday, November 13, 2020


 Current Conditions at Sanborn Field



Friday Night -
Cloudy. Rain beginning after midnight. Low: 36-40

Saturday -
Cloudy. Scattered showers. High: 58-62

Saturday Night -
Cloudy. Rain ending in the evening. Low: 40-44

Sunday -
Clear skies. Windy. High: 52-56

Monday -
Clear skies. High: 56-60
 
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Discussion: 

The clear skies we saw on Friday will soon give way to increasing clouds and rain beginning around 3 a.m. Friday night out ahead of an approaching cold front. Scattered showers continue on and off all day Saturday, and some areas may hear a few rumbles of thunder. The cold front passes through Saturday night, sending Columbia back down into the low 40s as the rain comes to an end. High pressure builds in behind the cold front keeping skies clear on Sunday, but high winds will be present most of the day. The pleasantly clear skies continue into Monday with temperatures in the upper 50s, making it a nice day to spend outside!
 
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Forecaster: Orr, Travis
Issued: 6 PM CST 13 November 2020
 
Technical Discussion (The nerdy stuff we are discussing in class)
 
Mid-Missouri will once again receive some much needed rain during this forecast period. Temperatures remain seasonable even with the passage of a cold front Saturday night. This forecast was assembled using the 18Z GFS and NAM model output and soundings and the SREF/GEFS plumes. High res models such as the HRRR and NAM Nest were consulted for the possibility of convection.

As of 21Z on Friday, RAP analysis places Missouri underneath a strong jet streak at the 250 mb level. The core of this jet streak moves out of the area Saturday, and by 00Z Sunday the Middle Mississippi Valley region will be dominated by divergence aloft. Missouri will remain under the influence of the jet streak's entrance region for the remainder of the forecast period. Behind it, the flow will return to a more zonal pattern. 
 
On the GFS 500-mb plots of vorticity and height, strong circulation propagates over Missouri out ahead of a longwave trough passing over by 06Z Sunday. The 700-mb plot of heights and relative humidity shows that abundant moisture over Missouri will lead to spotty showers. This is supported by GFS and NAM soundings, showing sufficiently deep saturation and upward motion in the column. Scattered thunderstorms are not out of the question. Model soundings hint at enough instability to support a few rumbles of thunder. NAM and GFS consensus breaks down slightly with respect to instability. NAM soundings are more aggressive with elevated CAPE maximizing near 600 J/kg just before FROPA. The GFS has less CAPE maximizing at only 400 J/kg. Simulated Reflectivity from the HRRR and NAM Nest supports scattered thunderstorms. Both models also support a secondary line of thunderstorms developing just ahead of the passing cold front when the GFS and NAM proper both maximize instability. The moisture in the atmosphere will move out around the same time as the circulation, so rain will end by 03Z Sunday. Dry air builds in behind the exiting precip and remains in mid-Missouri for the remainder of the forecasting period. This and the upper-level zonal flow will contribute to the clear skies and calm conditions on Sunday and Monday. 

A strong 50+ knot LLJ at 850 hPa over COU reveals that Saturday's warmer temperatures will be the result of warm air advection. This is supported by tight solenoids in the MSLP and 1000-500-mb thickness plots. The high winds at 850 hPa mix down to the surface as GFS soundings for Saturday afternoon depict a breezy 20 knot wind at the surface. A shift in winds from southwest to northwest on both the 850-mb and MSLP plot indicate the passage of a cold front around 03Z on Sunday. This front will allow colder air to be pushed into Mid-Missouri, causing the lows on Saturday night to be in the lower 40s. 850-hPa winds remain above 40 knots even after FROPA keeping our surface winds breezy into Sunday. Winds will remain out of the west and northwest after the passage of the front, so the warmer temperatures on Sunday and Monday will be due to daytime heating.

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