Current Conditions at Sanborn Field         

 

Friday Night - Clear. Low: 38-42

Saturday - Clear skies. High: 62-66

Saturday Night - Brief partly cloudiness. Then becoming clear. Low: 36-40

Sunday - Clear. High: 46-50

Monday - Clear skies. High: 56-60

 

 

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Discussion: 

Friday night will bring clear skies and seasonal temperatures compared to Friday morning's winter-like lows. Clear skies persist into Saturday with temperatures warming into the mid 60s, creating perfect conditions for Halloween festivities. Brief cloudiness and cooler temperatures will move in Saturday night with the passage of a cold front around 10pm. Sunday, skies clear out and temperatures will return to near average for early November. Clear skies continue into Monday as temperatures return to above average.

 

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Forecaster: Orr, Travis

Issued:  5:30 PM CDT 30 October 2020

 

Technical Discussion (The nerdy stuff we are discussing in class)

 

Clear and pleasant weather will persist for the duration of the forecast period. The main issue is tracking a dry cold front that will pass late Saturday night, knocking temperatures back down to near average. Good consensus between the GFS and NAM meant that a blend of the two was used alongside consultation with the GEFS and SREF ensembles for temperatures. 

The cutoff, upper-level low that plagued the western CONUS has since deamplified and has moved off to the northeast according to RAP analysis of 250 hPa. Missouri currently sits in the rear inflection point between a broad upper-level ridge to the west, and a longwave to the east. With the exiting longwave, Missouri sits in the right exit region of the associated jet streak indicating DVM dominates the column. This is backed up by the crystal clear skies that the entire state of Missouri is experiencing as shown by the GOES visible band. 

 

Prognostics of GFS upper-level flow show that the pattern transitions from the meridional flow regime the CONUS has been experiencing for the past several days to a zonal regime until the approach of the next system. This is supported well at the 500 hPa level with little to no tight circulations present west of the Mississippi River. Zonal flow persists until both GFS and NAM show a shortwave at 500 hPa digging in from the Upper Midwest. A broad ribbon of circulation stretching from the Middle Mississippi Valley to the Southern California coast tightens as it wraps into the approaching shortwave. The result is a decent display of cyclogenesis in the Upper Midwest. However, the moisture supply to the developing system is dismal at best. Prognostics of 700-hPa RH and low-level 850-hPa flow show that moisture will be in extremely short supply. As the wave approaches, strong SW flow at 850 hPa will result in WAA dominating Saturday during the day. This will allow daytime high's to reach into the mid to upper 60s, very pleasant for the last day of October. A moderate to strong LLJ originating out of the desert SW will set up and aid in both WAA and dry air advection. GFS and NAM soundings show only a brief, low-level cloud deck setting up in between 00z and 03z Saturday. By 09z, winds shift from the SW to the NW with the passing cold front. The cold front quickly pushes out any small amounts of moisture that was able to advect in.

By Sunday, upper-level flow returns to an extremely similar pattern to Friday's. By Monday, GFS and NAM 250-hPa plots of height and winds show upper-level flow shifting more zonal once again as a ridge builds in behind the amplifying shortwave exiting the region to the NE. Using a combination of persistence and analog forecasting, it is very likely that Sunday will see similar conditions to Friday with temperature once again warming up to above normal by Monday. However, with 850-hPa winds showing low-level flow still out of the WNW into Monday, it is unlikely WAA will dominate, preventing Monday highs from getting as high as Saturday. Monday morning's shift should look at changes in model guidance and adjust the daytime high accordingly.