4/02/09 FCST: MS/AL/FL/GA/SC/NC/TN

[Marc Austin]

Well I thought I would go ahead an start this thread up. If models verify (very unlikely), this could be a big severe weather event. Ample instability along with 0-1km and 0-3km SRH AOA 200m2/s2 and decent shear for the southeast should provide a nice environment for supercells. the SREF on SPC shows a bull's eye sig-tor of 6 at 21Z over SE AL. A large area encompassing much of AL and WRN GA is highlighted in a supercell composite of 12 at the same time. Now I know neither of these parameters is a tell-all for severe weather forecasting, but I thought it was pretty impressive and might generate some thoughts. Anyone have anything to add to this forecast discussion? I do plan on chasing this setup if it ends up turning out anywhere near this good. I have yet to see a tornado in the southeast and I've lived here all my life!

Significant Tornado April 4 2100Z

Supercell Composite

 

[Fred Gossage]

In my opinion, the big differences I've noticed so far between this setup and the setup last week is that the sub-tropical jet looks a touch further north this time, and that may help to put the right (subsidence) semi-circle of the cyclonically curved jet streak over the coast instead of the divergent left-front quadrant like last week. It also looks that there could be a substantial capping inversion along the coast. However, after last week... I'm not really ready to jump on this yet, just watching it nervously.

 

[Paul Austin]

Much like last week's setup, I wonder what effects pre-existing and ongoing convection will have on instability and low-level flow/wind vectors, as well as potential cloud cover. As mentioned in SPC's 730z Day 3 Outlook, models appear to disagree WRT the speed and track of a 500mb low in concert with the approaching shortwave. This development bears close watching as its effects will likely play a role in the warm front position and movement, as well as the LLJ and sfc wind development. If things continue to look interesting, I'll be joining Marc in AL/GA.

 

[Jeff Russell]

Nam 12z run showing 8-9 inches of rain in SE AL, SW GA, FL panhandle. Rivers already running high, this could be the final nail in the coffin. Picture is 60hr total thur 00Z Friday.

 

[Matthew Crowther]

I am almost completely certain that north GA will see little if any severe weather with this system- the NAM (which handled the last storm better with the severe details)
shows the typical bunch of convection over central and south GA during the day- robbing us of all of the surface instability. It still looks like a second round of severe storms will get going back in MS and SW Alabama around 21Z or so, but even back there the convection closer to the Gulf may reduce the chances of a significant outbreak. Here in the ATL I expect the usual heavy rain and a few rumbles of thunder during the day, and round two overnight will be a dying squall line with again only a minimal severe threat.

 

[Derek Weston]

Looking like a fairly potent severe setup may be unfolding here. Looks like we'll have a shot at CAPE > 2000 J/kg in southern Mississippi and Alabama. Though, shear seems a bit unidirectional in this area -- a bit further north we flip that situation with lower CAPE and a better directional shear setup. NAM is putting earlier day convection across the northern half of Mississippi and Alabama... while things look reasonable clear to the south. Should be interesting.

 

[Paul Austin]

SPC put out a rather large Moderate risk area for primarily MS and AL in the 6z Day 2 outlook, mentioning "strong/long-track tornadoes" in the discussion. Strong shear of 60-70 kts maximized over MLCAPE values of 2000-3000 J/Kg and extra lift provided by the approaching cold front make severe storms, some with rotation, a virtual certainty. The greatest uncertainty is storm mode. The effects of morning/early afternoon convection along the warm front coupled with somewhat unidirectional wind fields and strong forcing along the cold front could favor more linear storm modes with embedded supercells, LEWPs, bowing segments, etc. If early cloud cover can erode away early enough and return flow strengthen ahead of approaching low, more discrete cells could develop ahead of the greater forcing in the warm sector. Regardless, tornadoes appear quite likely with this system.

http://www.spc.noaa.gov/products/outlook/day2otlk.html

I had already decided to chase this setup and pegged an area from west central AL to around Montgomery and back up toward Tuscaloosa as a very general initial target area. It's looking more and more like initiation will begin in MS. Hmmmmm Here's hoping for something discrete. We had some semi-discrete sups with T-warnings yesterday even associated with the MCS in GA/n FL. So it's a little more than wishing.

 

[Kevin Askew]

Watching close

Be interesting to see how far north the SLP will come. Definantly looks like another warm front position. Winds will back here with a deeper SLP. So comes down to Last hours event surely this far north. Wait & hold my breath again. I think W. KY will get in on this again. Tentatively targeting Madisonville KY.-Paris TN

 

[Lisa Post]

This is about the time of year I wish I lived just a *little* further south. Grr...ah well, my state's time is coming.

 

[Paul Knightley]

Cross-posted from my blog:

Well, Spring is well and truly here now, so it should come as no suprise to see a series of powerful troughs pushing through the USA, bringing rounds of severe weather. Some of these in recent days have not had huge amounts of Gulf moisture to feast on, meaning fairly low-end severe events. However, on Thursday, such a trough will be accompanied by plenty of moisture, as strong return flow from an open Gulf streams into portions of the south and south-east.

Basically anywhere from around the Mississippi Delta region eastwards, and northwards towards Tennessee is at risk from severe weather as the potent upper trough and associated surface low move through the area. 500-1500 J/Kg of CAPE are expected, along with strong 0-6 and 0-1km shear values - more than sufficient for supercell structures, although given the intense forcing, a fairly complex scenario is expected. Also, surface winds are expected to be a little veered - however, I recall seeing something similar on the Super Tuesday outbreak of Feb 2008, and there were numerous strong tornadoes, and very long-track tornadoes.

The warm front currently looks like lying through central Alabama (E-W, ish!) by around 21z/close to peak heating. Should this occur, low-level helicity would be maximised just ahead of the front. Storms crossing this front would have an enhance chance of producing tornadoes, although could become more elevated as they continue to move NE into the cooler air.

At this stage, although a large area is at risk, I would place the Birmingham - Montgomery - Columbus area of Alabama in the highest risk area for strong tornadoes Thursday afternoon/evening, although anywhere from Mississippi eastwards could be in for a rough ride.

 

[Eric Graham]

Targeting the same area as last Saturday in Kentucky. Looking at Evansville, IN to Hopkinsville, Ky line. Looks like a descent chase suppose to be in the mid 60's low 70's. Figguring that it'll be the same type of setup as was Saturday. Cells start to fire along a line and immedetally go severe or tornado warned. Time of initiantion anywhere between late afternoon early evening.

 

[beaudodson]

If the NAM is correct on its track then I believe the KPAH region will see a tornado threat and the SPC could move the moderate risk north a bit. Assuming the NAM track is correct - high CAPE values and helicity readings over West TN and West KY pose a serious threat for tornadoes. Similar to last Saturday's event.

Beau

 

[Dave Marshall]

That 30 days was up just in time!

I've been watching the models pretty closely on this one since Sunday evening, and things have been remarkably consistent. Right now I'm liking the SE Alabama area south of I-85 and east of I-65 during the early evening hours.

The one thing that has me concerned is what looks to be a pretty dry area SE of Montgomery at 21z, as seen on the 12z GFS today. Surface moisture is good, but there's a little bullseye of very dry air at 700mb. I'm hoping that feature fades in the 18z and 00z runs, maybe just a fluke.

The SPC backed off of their language just a bit on the 1730z update, and are now mentioning the potential for a cap across much of the warm sector. That could be good, that could be bad. Atleast we shouldn't have another one of those blasted MCSes getting in the way of all the fun this time.

I guess I'll just have to wait until the 06z model runs tomorrow to make my final call on a target.

 

[Angie Norris]

Looks like it could be an interesting day in the southeast again tomorrow.

Strongly negatively tilted trough at 500mb again, with northern MS and AL progged to be under a 75-80kt max in the exit region of the jet. Tds progged to be in the mid 60s with temps in the 70s by 0Z should give nice LCL heights, SBCAPE progged to be ~2800J/kg and MUCAPE progged to be ~2400J/kg over central MS by 18Z. There's a nice theta-e ridge over central MS/AL and an interesting area of surface wind convergence on the MS/AL border around 0Z.

I'd put a little triangle around the Jackson, MS/Huntsville, AL/Columbus, GA area, and if I could be there, I think I'd be sitting in the Columbus, MS area (final target subject to change with subsequent runs of the WRF, of course).

This is climatologically prime time for Dixie Alley, and is 24 hours short of the 35th anniversary of the Superoutbreak. All you Dixie chasers keep safe tomorrow.

 

[Chip Redmond]

I was very concerned about the lack of a cap in AL/MS after looking at the forecast soundings earlier. I am hoping a good cape will delay anything from the south that may mess up anything at my target area of Elizabethtown, KY that has a great option N/S and E/W. Shear looks great both speed and directional coupled with a very promising CAPE values 1500+, being at the nose of a LLJ with dewpoints approaching the mid-60s and LI's approaching -5.

So far this year, this setup has the best potential that I've seen. What is even more promising is storm motions of 15-20knts! Finally a system without racing supercells impossible to keep up with!

Good luck to all out and about tomorrow!

Chip