Tuesday, October 12, 2021

Current Conditions at Sanborn Field

Tuesday Night:
Cloudy. Thunderstorms after 3 a.m. Low: 62

Overcast. Rain in the morning. Scattered thunderstorms in the afternoon. High: 77

Wednesday Night:
Overcast. Rain throughout the night, scattered thunderstorms between 1-4 a.m. Low: 62

Cloudy. Rain in the early morning. Conditions begin to clear around noon, scattered showers beginning around 3 p.m. High: 70 

Thursday Night:
Cloudy. Light rain, with possible thunderstorms around 1 a.m. Low: 60
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    There's a few rainy days coming to Missouri. Thunderstorms will begin Tuesday night, around 3am, and cloudy skies will stick around throughout the forecast period. Wednesday begins with rain in the morning, and then scattered thunderstorms in the afternoon. This will be the warmest day in the forecast period, with a high of 77 degrees. In the evening, rain continues, and around the hours of 1-4am, more scattered thunderstorms return. Thursday sees a cooler high temperature of 70 degrees. Rain continues into Thursday morning, but there is a bit of a break from all the precipitation from the late morning until the afternoon. From there, scattered showers will turn to light rain in the evening, with a potential for more thunderstorms in the night. Nighttime low temperatures will stay in the low 60s. 

- VanUnnik, Watts


Forecasters: VanUnnik, Watts, Orr

Date Issued: 10/12/21  06:00 PM CST

Technical discussion:  

    For this busy forecast, the 12Z run of the GFS was chosen. When compared to the NAM, the GFS had better initial conditions and more accurate placement of the lows over both the Great Lakes and Colorado. SREF and GEFS plumes were used to aid in forecasting temperatures and rainfall amounts, and GFS soundings were used to forecast storm potential.

    At 250-mb, Missouri remains under the influence of the jet streak for the majority of the forecast period. Mid-Missouri is under the right exit region of the upper-level jet Tuesday evening, but it moves out by 09Z Wednesday. At this time, high amounts of divergence move into the region. Abundant divergence remains out of the area until 06Z Thursday when Missouri falls under the influence of the right entrance region of the jet streak. This moves out by 18Z Thursday, and divergence remains out of the region for the remainder of the forecast period. 

    At 500-mb, strong vorticity associated with the low pressure system over Colorado begins making its way eastward. Circulations move through Missouri 09Z Wednesday, and are gone by 21Z. Another "wave" of vorticity moves through Missouri around 09Z Thursday, providing another chance for storm development. Abundant circulations remain out of Mid-Missouri for the rest of the forecast period. A trough with strong amounts of vorticity develops in the west around 00Z Friday, and future forecasters should watch for its development.

     700-mb plots show the abundant moisture that dominates the region over the next few days. High RH values move into Mid-Missouri by 09Z Wednesday when Missouri is in the warm sector of the cyclone over Colorado/Nebraska. A steady flow of moisture remains in the region throughout Wednesday until a brief break Thursday at 15Z. This break is short lived as high RH values return by Friday at 03Z.

    850-mb plots show the low pressure system in the west in better form. As the low moves northeastward, a cold front passes over Missouri around 18Z Wednesday. Up until this point, warm and moist air will be pushed into Missouri. A strong LLJ pushes in moisture from the Gulf even after FROPA, and continues to do so until the approach of a trough 12Z Friday. 

    At the surface level, solenoids are seen over Missouri around 09Z Wednesday, a sign of WAA. However, the WAA is short-lived as the cold front passes over Mid-Missouri 18Z Wednesday. Soon after moving through the region, this front stalls, becoming a stationary front over southeastern Missouri. The front remains in that spot until the approaching trough "pushes" it out of Missouri by 15Z Friday. 

    The most favorable opportunities for storms are Tuesday night and Wednesday afternoon/evening. GFS soundings of Tuesday night's storms show MUCAPE of up to 800 J/kg, K Index and TT values favorable for moderate convection potential, and SRH and BRN Shear values favorable for producing strong thunderstorms. The potential for severe storms Tuesday night after midnight should not be ruled out. As for Wednesday, MUCAPE values of up to 850 J/kg are seen around 21Z. This CAPE, accompanied by negative Omega values, TT and K Index values favorable for convection, and 0-1 km and 0-3 km SRH values favorable for strong storm development. Again, severe storms cannot be ruled out. PW values for these events remain in the 1.20" to 1.70" range, so higher amounts of rain around 1" are expected. 


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