Friday, October 2, 2020

  Current Conditions at Sanborn Field





Friday - Partly cloudy
. Becoming cloudy in the evening. High
: 58-62


Friday Night -
Cloudy. Low: 46-50

Saturday -
Morning rain. Mostly cloudy gradually clearing. High: 52-56
Saturday Night
- Clearing skies. Low: 40-44
 
 

Sunday -
Partly cloudy. High: 60-64

 
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Discussion: 
Pleasant day on Friday starting out with some sunshine but giving way to clouds by Friday evening and highs approaching 60 Friday afternoon. Waking up Saturday morning to scattered rain showers and an overall cloudy day Saturday with highs in the mid-50s. Rainfall amounts are expected to be light in the range of 0.1-0.2 inches. A cold front Saturday night will bring clearing skies and take lows down into the low 40s. Sunday we return to nicer conditions as we see partly sunny skies and highs in the low 60s.
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Forecaster: McGuire, Bongard
Issued:  10 AM CDT 2 October 2020
 
Technical Discussion (The nerdy stuff we are discussing in class)

Initial conditions as the start of the forecast period Friday morning has temperatures beginning to rebound from the upper 30's into the low 40's as insolation begins to warm the region. Diagnostics reveal a long wave ridge-trough pattern across the CONUS with a moderate trough draped over the Northern Plains through New England. This places mid-Missouri just west of the trough axis enjoying northwesterly flow lending to the cold overnight lows and potential for frost. The 06Z GFS will be used for this forecast as the model is handling initial conditions much more accurately than its NAM counterpart. SREF and GEFS plumes will be used as supplemental data along with GFS soundings. 

Upper level modeling is indicative of the ridge-trough pattern across the CONUS seen in diagnostics. The nose of a northwest-southeast jet streak embedded in the western flank of the long wave trough will force its way into the Midwest by Friday evening. The trough over the eastern half of the CONUS will amplify over the course of Friday night and Saturday as a frontal boundary develops just to the northwest of the forecast area. The jet streak will orient in a north-south direction in the upstream flow of the trough by 21Z Saturday. 500-mb vorticity maps reveal vorticity advecting into the region from the northwest as a shortwave treks into the area riding the northwesterly flow. Vorticity will remain over Missouri for much of the forecast period as the shortwave develops into the frontal boundary that is expected to pass through central Missouri by late Saturday night. Vorticity will linger through midday Sunday before vacating the region late Sunday afternoon. The moisture profile in GFS model soundings leaves something to be desired as the column slowly saturates from the top down overnight Friday into Saturday as the boundary encroaches on the region. If with the lower levels moistening up by 12Z Saturday morning PWAT values are paltry meandering between 0.75 -0.85 inches. Some low level forcing will be available during the morning hours Saturday to promote scattered precipitation across the region. The K-index struggles to get above 27 during the crucial part of the forecast period. This evidence suggests the chance for scattered rain showers in the AM hours of Saturday with rainfall accumulations being hampered by the lack of significant moisture. Accumulations will range between 0.1 and 0.2 across the region depending on the locale and where showers trek. The culprit for this lack of moisture seems to be a surface high pressure system over central Texas that is cutting Gulf moisture off from the Midwest thanks to its eastern flank. Therefore the only moisture this frontal system has to work with is riding the northwest flow down from Canada. 

Fropa is expected late Saturday evening potentially into Sunday with not much fanfare outside of falling temperatures. Lows Saturday night into Sunday will fall into the low 40's. Sunday will enjoy a post frontal weather regime with partly cloudy skies and temperatures rebounding only into the low 60's.  

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