Midwest Mischief as Shortwave Trough and Strong Low Pressure Team Up To Deliver Multiple Days of Trouble

 Oh She Trouble...  

Ahhh.. Yes, the good old fashioned severe weather season has returned. After a rather quiet April, it seems Mother Nature needs to remind folks who's boss as she takes aim at the Midwest and MidAtlantic today, tomorrow, and on Saturday. In particular, its looking like tomorrow may bring her worst as parts of Kentucky, Tennessee, Illinois, and Indiana and others prepare for damaging winds, large hail, and tornadoes. The Storm Prediction Center (SPC) has outlined these areas in a Moderate Risk (Level 4/5) for the possibility of widespread, long lived severe weather with portions of the MidAtlantic (including Virginia) being outlined in a Slight Risk (Level 2/5). 

SPC Day 2 Categorical Risk. Severe Weather is most likely over the Moderate Risk area, which encompasses Missouri, Illinois, and Kentucky

 The Setup: 

A potent shortwave trough and occluding, strong low pressure will slowly eject over the Plains and upper midwest over the next 48 hours or so. In response, strong warm air advection will take place with a rapidly advancing warm front into the Ohio Valley and Missouri Valley during the day tomorrow, leading to a very unstable, moisture loaded atmosphere. Coupled with a moderately strong upper level wind field and cold temperatures aloft, this will promote the development of supercells and cluster of storms capable of all hazards by later afternoon and evening. 

500 Mlb (Midlevel) Height and Wind Chart. Can clearly see midlevel tough or "dip" in the jetstream and strong low pressure over the upper midwest by last afternoon tomorrow. 

The potent low pressure and associated shortwave trough will lead to very stout mass response, or the lifting of more warm, moist air from the gulf northward over the day tomorrow. This warm, moist air will be below very cold temperatures aloft, promoting a very unstable environment. Forecast soundings, as shown below, show Surface-Based Convective Available Potential Energy (SBCAPE) becoming moderate to extreme by late afternoon with widespread 3,000-4,500 J/Kg SBCAPE. 

SBCAPE GFS Forecast. Moderate to extreme SBCAPE values forecasted across the risk area by late afternoon

Digging deeper into the forecast soundings, its easy to see why tomorrow has potential for widespread severe weather. In addition to temps in the 80s, dewpoints in the upper 60s and low 70s, and cold temperatures aloft, low Lifted Condensation Levels (LCLs) and low Level of Free Convection (LFC) will promote lower cloud bases and greater use of energy. Furthermore, looking at the atmospheric profile, there is a very "fat" appearance to the CAPE curve indicating the potential for rapid parcel acceleration (ie very strong updrafts). While wind shear profiles (wind change in speed and direction with height) aren't nearly as impressive, the very strong updrafts should easily compensate by making more efficient use of the wind profiles aloft. Taken together, its easy to see why tomorrow has big potential for an active day. 


But What About Virginia? 

As it turns out, it seems the troubles will not only be confined to the midwest, but they could also spill over into the MidAtlantic as well during the afternoon and overnight on Friday into the day on Saturday. While details are still fuzzy at this time due to the complicated nature of the setup, it appears that multiple rounds of severe storms are possible. Starting with Friday afternoon, a cluster of storms may overspread the region by Friday afternoon into the early evening hours, bringing mainly a damaging wind and hail threat. Then overnight Friday into the early morning hours on Saturday, another cluster or line of storms may cross the Appalachians into Virginia, bringing the chance for damaging winds, hail, and an isolated tornado. If the atmosphere has enough time to recover during the day on Saturday, yet another round of storms is possible by the evening with the exiting of the shortwave trough. In other words,..its complicated. But for now, we will keep watching tomorrow and Saturday for some severe weather around our neck of the region. 

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