Wednesday, April 8, 2020

Severe Thunderstorm Watch in effect from 3:05pm until 9:00pm.

Wednesday Night- Decreasing clouds, severe thunderstorms possible 
early evening. Low: 40-44

Thursday- Partly cloudy. High: 54-58

Thursday Night- Mostly clear. Low: 28-32

Friday- Mostly sunny. High: 54-58

Saturday- Mostly cloudy with rain possible. High: 56-60

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A severe thunderstorm watch remains in effect until 9 PM. This evening, scattered thunderstorms -- some severe -- will form along a cold front passing over central Missouri. After it passes through, clouds will move out and temperatures will drop. These colder temperatures, courtesy of northerly winds behind the front, will stay with us over the next several days as a high pressure system builds in. Even though we will experience cooler temperatures, that high pressure system will maintain mostly sunny skies. Go out and enjoy the sunny skies, because Saturday will bring our next chance for rain and cloudy skies as winds become southerly and begin to bring in moisture.
Forecasters: Vanderpool, Pauley, Heaven
Issued: 5:00pm April 8, 2020

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

Model Diagnostics from the WPC recommends a general model blend of the GFS/NAM/ECMWF.

The biggest issues in the near term include very warm temperatures and the risk for severe weather in central MO. A severe thunderstorm watch is in effect until 9 pm CDT for Columbia and points east. Plenty of agitated cumulus are showing up on visible satellite in mid-MO, with a developing line of convection approximately 30 miles northwest of Columbia as of 4:15 pm CDT. 

20z RAP analysis reveals a very unstable atmosphere in central MO. MUCAPE values near 3000 J/Kg - maximized over Columbia - are coincident with minor veering in the lower layers of the atmosphere. Hodographs suggest storm motion from the WNW at ~25 kt, which appears to be verifying based upon latest WSR-88D data. Convection is currently limited to a few showers developing along the frontal boundary to the northwest of Columbia, but given very high CAPE and relatively calm winds (< 50 kt) below 500-mb, these will likely grow upscale into scattered, fully-fledged thunderstorms over the next hour or two. Not every storm will become severe, and many may struggle somewhat to reach severe levels. However, upscale growth will continue to be fed by a narrow corridor of low-level moisture pooling ahead of the approaching cold front. Primary threats will be large hail and damaging winds, with emphasis on the damaging downburst winds considering the substantial amount of dry air present in the lower and middle troposphere. Hail up to a couple inches in diameter is also possible, especially when taking into account evaporative cooling in the storm downdrafts and the very large CAPE values in place. It is possible that convection may become cold-pool dominant within a few hours after formation, which would lead to a transition towards a greater wind threat later on in the evening. Should this occur, it would likely be after storms clear the Columbia area. Short-range CAMs including the HRRR and NAM 3-km validate this prognosis, with the 20z HRRR forecasting rapid convective development in the severe watch area between 22z and 00z. 

Prognostically, high-res models show that the incoming front is rather messy and ill-defined. The 20z HRRR and 18z NAM 3-km both agree that surface moisture should scour out between 00z and 02z. Thus, the true sfc FROPA will probably occur sometime within that time frame. Convection is likely to grow upscale between now and then, with some storms becoming severe, before moving out of the Columbia area around or shortly after 00z. 

Tonight, the aforementioned cold front -- associated with a positively-tilted trough axis at the surface -- will move southeast, firmly entrenching mid-MO in a regime of strong cold air advection. It will be strong enough to cause a 40+ degree drop between daytime highs today (Wednesday) and early-morning lows tonight. 

For Thursday and Friday, high temperatures will hover in the 50s -- about 5-10 degrees below climatological averages -- with mostly sunny skies. This chilly and tranquil weather will be brought into the region courtesy of a strong surface high with a Canadian origin. Current indications are that continued cold air advection and radiational cooling will cause temperatures to drop below freezing (and possibly several degrees below freezing) for Thursday night, which appears to be our coldest night of the forecast period. 

On Saturday, things will get a bit more interesting as lee cyclogenesis produces a panhandle hook type low pressure system. Out ahead of this low, temperatures should warm into the upper 50s to lower 60s for highs as warm air advection kicks in. This will also support overcast skies and a decent chance for rain. Currently, instability looks rather lacking, so this activity is unlikely to be severe. February-like weather looks to return on the backside of this low, with an extended period of much below normal temperatures likely beginning early next week. 

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