Friday, October 16, 2020

 

 Current Conditions at Sanborn Field


                    

Friday Night
- Mostly clear skies. Low: 42-46

Saturday
- Becoming mostly cloudy by sunset. High: 68-72

Saturday Night -
Becoming cloudy. Low: 46-50

Sunday -
Rain beginning in the afternoon. Temps falling
                  throughout the day. High: 52-56

Monday -
Lingering showers. High: 48-52

 
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Discussion: 
Skies will continue to be mostly clear throughout Friday night. Comfortable temperatures will return on Saturday with increasing clouds throughout the day. Saturday night will bring more clouds ahead of an incoming low pressure system. Sunday, a weak cold front will push through the area, causing temperatures to fall during the day. Much needed rainfall will accompany the front and will continue overnight and into Monday.
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Forecaster: Orr, Vochatzer, Travis
Issued:  5 PM CDT 16 October 2020
 
Technical Discussion (The nerdy stuff we are discussing in class)

A much more "disturbed" flow regime has set up compared to last week. As a result, model continuity with the GFS has been poor the last couple of days, but consensus between the GFS and NAM holds up well. As such went with a blend of the GFS and NAM with SREF and GEFS for temperatures and QPF. The main focus is the much needed rain that is expected to come near the end of the period on Sunday.

Friday night into Saturday looks much the same as the quiet weather we saw last week. The LW trough and an associated jet streak situated over the Upper Midwest and south Central Canada has begun to shift to the NE according to GFS and NAM 250-hPa heights and winds. The northward shift of the jet stream will allow for the retreat of the cold temperature we saw Thursday, Friday morning, and Friday afternoon. As the LW exits a new SW will propagate out of the Upper Midwest causing flow in between the two systems (over mid-Missouri) to turn more zonal. The result will be a slight eastward shift in the low-level and surface anticyclone putting Missouri in low-level southwesterly flow. Both GFS and NAM depict a strong LLJ originating over the Southern Plains and moving into the Mid Mississippi Valley. GFS depicts a 50 knot LLJ over KCOU. This will aid in strong WAA Saturday. GFS and NAM MSLP and 1000-500-hPa thickness reflect this as well with tight gradients and small solenoids beginning Friday night into Saturday. It is possible both the SREF and GEFS may be underestimating the impact from WAA and therefore have trended to the warm side of ensemble guidance.

By Saturday night, clouds will be on the increase out ahead of the aforementioned SW. GFS and NAM 500-hPa vorticity shows circulation moving into the area early Sunday morning in between 09z and 12z. Model Consensus diverges in timing of precip arrival. GFS is much quicker with precip arrival as Skew-Ts show adequate saturation beginning around 18z Sunday. The NAM soundings are slower with saturation not occurring until closer to 22z to 23z Sunday. SREF is even earlier wanting to bring precip in closer to 15z Sunday. More likely is a combination of the GFS and NAM with precip beginning in between 18z and 22z.

Both GFS and NAM soundings want rain persisting into the day Monday continuing into Monday night until the end of our forecast period. Consensus between ensemble members of both the GEFS and SREF breaks down immensely with 40+ degree spreads in high temperatures for Sunday and Monday. Ensemble odel guidance was less weighted on for temperature during these two days with more emphasis being placed on the anticipated synoptic setup. When all is said and done, the GEFS and SREF ensembles have a mean QPF of 0.7 in and 0.5 in respectively. Regardless, much needed rainfall will fall over Columbia.

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