Wednesday, May 5, 2021

 

Current Conditions at Sanborn Field


Wednesday Night: Partly cloudy. Low: 46-50.

Thursday: Mostly cloudy. AM rain possible. High: 60-64.


Thursday Night: Mostly clear. Low: 40-44. 


Friday:  Partly cloudy. High: 62-66. 


Saturday: Overcast. Rain likely with thunderstorms also possible. High: 56-60.
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Discussion: 
 

Though there is a slight chance of rain overnight on Wednesday into Thursday, the end of our work week looks rather pleasant as temperatures will remain relatively cool and the skies will remain sunny.  Conditions, unfortunately will change on Saturday as we will receive rain through moist of the day with increasing chances for thunderstorms as we go through the evening.  The system moving into our area on Saturday could provide us with anywhere between 0.5 in and 1.5 in of rain.   

 

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Forecaster: Gasch, Vanderpool
Issued: 5:00 PM CDT May 5, 2021

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

A calm afternoon has been noted across mid-MO, with light winds and mild temperatures beneath mainly sunny skies. However, 18 UTC WPC sfc analysis reveals a low pressure system centered over southeastern SD, with a trailing cold front extending to its south. This front has generated scattered storms over central NE and far north central KS as of 20:30 UTC, with some of this convection pushing or exceeding severe limits. 

In the near term, the main focus for COU will be on small rain chances late tonight into Thursday as a cold front pushes into mid-MO. The 12 UTC GFS prognostic forecast at 250-mb indicates that a longwave trough will swing through the Midwest over the next 36 hours, with an embedded shortwave responsible for the aforementioned surface low and resultant convection. This embedded shortwave will propagate along the edge of this upper trough, thus causing the low and its associated cold front to track east and south throughout the overnight hours. Thus, partly to mostly cloudy skies are anticipated overnight with FROPA likely at COU around or just before sunrise Thursday. As the front moves through, there are indications that enough moisture may be present for some scattered showers. SREF means for MUCAPE also sit at ~470 j/kg Thursday morning, so a clap or two of thunder is not out of the question. Moisture will be limited, however, so only brief rainfall is expected if it occurs at all. 

Much of Thursday should remain dry and partly to mostly cloudy behind the cold front. The clouds and CAA will ensure that temperatures are significantly lower than Wednesday; highs will probably only reach the low 60s. Conditions will also probably be quite breezy, with NW winds gusting upwards of 25 mph.

Thursday night will see clearing skies and continued light CAA as the surface high passes just to the south of COU. These will create ideal conditions for a cool-down; lows should bottom out in the lower 40s. 

For Friday, current thinking is that return flow on the backside of the surface high will allow modest WAA to bring temperatures back up. Additionally, sunshine through at least the first half of the day will likely be enough to lift temperatures into the middle and upper 60s, if not the lower 70s. However, our next storm system will be gathering steam to the west, and this one looks well-organized and powerful. Out ahead of an approaching upper level longwave trough, a region of upper level moisture will create the chance for a shield of clouds to move east into mid-MO Friday afternoon and evening, which would reduce temperatures.

Friday night into Saturday, ridging will briefly develop at 500-mb and 250-mb. This ridging should allow for moisture advection and weak WAA throughout the column. Lee cyclogenesis is likely to begin Saturday morning in southeastern CO and southwestern KS, with the developing sfc cyclone giving rise to a warm/stationary front that will likely stretch somewhere into mid-MO. That will likely create chances of rain through much of the day Saturday. The GFS places this stationary/warm front just south of COU and keeps mid-MO in the cold sector, but extreme surface temperature spread in the GEFS members indicates that this is definitely not a decided solution. There will be the potential for both severe weather and widespread heavy rain with this system, as the GFS closes the surface low and creates a rather powerful cyclone over KS by Saturday evening. Where this front sets up will determine which (if any) hazard types COU receives. Right now, GEFS mean QPF through Saturday night at midnight are sitting at just shy of an inch, with rapidly rising means continuing beyond that. Future shifts will definitely want to pay close attention to this system.

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