More Severe Weather Chances...

Another Thursday, another chance of severe weather. Currently, as of 5:50 PM Wednesday, there are twin-tornado-warned supercells in southwestern Oklahoma, as seen below...

Here locally in the GTR, we've seen a mixture of sun and clouds the past couple of days, with temperatures in the 80s with dew point temperatures already into the middle 60s. This has essentially "primed" us up for severe weather chances for tomorrow late afternoon into tomorrow evening.

This is the convective outlook from SPC valid for 12z tomorrow thru 12z Friday - 7 AM to 7 AM. Notice an enhanced moderate risk in place from Vicksburg up to near Elkhart, IN. Inside this moderate circle, there's a 45% chance of severe weather within 25 miles of a point, which is very significant probabilities. 

This a surface temperature/pressure map valid for 21z / 4pm tomorrow. Notice a very strong frontal zone across central parts of Arkansas, with backed winds ahead of it out of the SSE. This front will be one of many factors that produce lift to get thunderstorms going. The backing wind profile will allow for enhanced helicity in the lowest 1km of the atmosphere, which favors tornado development. Of course other ingredients are needed for tornadogenesis, but extra shear is certainly aiding in tornado potential.

Here's a chart of surface-based CAPE (convective available potential energy) valid at 4pm tomorrow. Notice values around 2000 J/KG over a large part of central Mississippi. At least during the late afternoon into the early evening hours, there won't be a shortage of instability/buoyancy in the atmosphere...this is another critical ingredient to thunderstorms and severe storms.

Here's a chart depicting surface dew point temperature and surface lifted index at 4pm tomorrow. According to weatheronline.co.uk: The Lifted Index (LI) is defined as a rising parcel's temperature when it reaches the 500 millibars level (at about 5,500m or 18,000 feet asl), subtracted from the actual temperature of the environmental air at 500 mbar. Greater negative numbers are associated with greater instability. Values across Mississippi range from -4 to -7 C which is fairly substantial. Moisture also will also be copious; dew point temperatures will at least be in the mid 60s F throughout the day and night tomorrow.

Given all these ingredients, some supercells would be possible ahead of the frontal zone tomorrow afternoon across west-central into north-central Mississippi. However, it is expected that we will have some warming aloft, in the low/mid levels that will act to "cap" off any storms from developing. Therefore, we'll have to wait on the front and an approaching upper-level jet streak to provide the necessary forcing to remove the capping inversion and allow storms to grow/develop.

***Bottom line***

All this being said, it appears many ingredients are coming together for a fairly stout severe weather episode across the Mid-South region into north Mississippi tomorrow afternoon and tomorrow evening. This is why SPC has went moderate risk on their day 2 convective outlook.

Expect an intense squall line to be ahead of the frontal boundary, moving east into northwest/west Mississippi late tomorrow afternoon between 5-8 PM. It is likely that this line will be capable of producing significant wind gusts as well as embedded tornadoes. Any breaks in the line will favor a little higher tornado threat. Any bowing segments will favor enhanced damaging wind gusts. Like I talked about earlier though, the threat for pre-frontal supercells is fairly low...however...if any are able to form, they would have the highest chance at producing a tornado and perhaps be capable of producing a strong tornado. Any severe weather threat for Mississippi should be over by 3 AM Friday morning.

If you live anywhere in the red-circled regions above (SPC moderate risk) as well as the yellow shaded areas surrounding it, please be weather aware tomorrow all day as changes can be rapid and short-noticed.

Stay safe out there, and God Bless!
IW