I am sorry, but I must be brief as I need to get my things packed for a birthday weekend trip. Anyway onto the weather, almost all guidance is in some sort of agreement that numerous ingredients will come together Friday into Saturday for a widespread severe weather event from the Plains eastward, including almost all of the Southeast US.
A strong upper-level storm system is progressing out of the Four Corners region of the Southwestern United States. As it ejects out of the Rockies/Four Corners region and into the Plains, a strong surface low will develop and begin to tap some of the Gulf moisture available. On Friday, the combination of a strong low-level jet, warm moist air, and cold air aloft with lead to the initiation of an intense squall-line across Tx/Ok that will glide upstream going into Friday night.
By Saturday morning a squall-line is expected to be approaching or very close to the Ms River. At this time, the first surface low will occlude back across the Plains as another low develops around the Little Rock/Memphis area in response to a secondary vort max rotating around the base of the trough. This intensifying surface low, along with the upper-level vort max, will increase the low-level jet across the Ms & Tn Valleys.( As seen above.) By Sat morning, a 40-50kt low-level jet will overspread the region. This combined with a strong diffluent upper-level jet will make for a highly sheared environment for thunderstorms to breed. Also, with the approaching upper-level disturbance, sufficient cooling aloft will increase instability into the 1500-2500j/kg category, which is more than sufficient for severe thunderstorm growth. All modes of severe weather should be expected with tornadoes, (some strong) large hail, and damaging winds.
The highest chances for all these ingredients to come together on Saturday look to be NORTH of I-20 and East of the Ms River. Basically in a circle from Jackson, Ms to Memphis, Tn to Nashville, Tn down to Birmingham, Al. Elsewhere, the threat is still on the moderate side with places like New Orleans, La/Hattiesburg, Ms/Mobile, Al/Montgomery, Al/Meridian, Ms/Fl Panhandle/Atlanta, Ga.
One saving grace that could lead to less overall severe weather is the fact that everything with severe weather events is about timing. Small mesoscale features that we cannot see days in advance can cause differences in timing. If the Friday night squall-line is faster than expected, then the atmosphere out ahead of it on Saturday will not have enough time to destabilize sufficiently; thus, an overall decrease in the severe weather threat should be expected. Also, along the Gulf Coast not enough upper-level cooling aloft may occur leading to a capped atmosphere and very little in the way of severe weather, better yet rain. Many things can go wrong leading to a busted forecast; however, we have seen these parameters come together before and those events saw their fair share of severe weather.
It should also be noted that the SPC has highlighted much of Ms/Al/Tn/Eastern La in a hatched 30% area. This is unheard of for down along the Gulf Coast in a Day 3 forecast. Remember, have your severe weather plan ready for action by Friday evening!
-Zack Fradella
