04/10/09 FCST:AL/GA/KY/TN

[Jeff Russell]

Surprise no one has start a thread on the possible severe weather Friday in the southeast.

Based on the 18z NAM at 54 hours, 00z 04/11. An outbreak of severe weather looks probable from Lexington, KY through CNTRL TN, down to Northern AL.

A broad area of 1500-2000 J CAPE, H7 jet max of 60 kts, cold air aloft with H7 temps of -5 C and H5 temps of -17 C, surface winds out of the South with temps of ~70 F and DP of ~65 F. EHI (0-1km) 2.5 and EHI (0-3km) 4.7. LCL heights should be around 500-750ft. Helicity (0-1km) 250 and (0-3km) 400-500. LI's of -7. Storm speeds will be a concern as currently showing 260@35kts.

Current target would be somewhere around Murfreesboro, TN.

This is my first post to a forecast thread, go easy on me.

Jeff

 

[Wes Carter]

Although the GFS puts it a bit ahead, it generally agrees at 18z+48. The lifted index is showing -6 to -8. I am also concerned with the 35kt storm motions, but that is par for the course in this neck of the woods.

As of right now I will be looking at anywhere from Columbia, TN down to Huntsville to start with.

 

[Brett Adair]

I believe that moisture is the biggest question. I'm not sure how far north we get the 65+ dewpoints before the system moves on through. Also, I'm not sold that the best upper dynamics will line up with the afternoon instability. That's something that has yet to really come in line across this part of the world this season.

 

[Dave Marshall]

I tend to agree with Brett. The GFS is very generous with the moisture compared to the NAM, but its less optimistic regarding shear. The GFS must be the model the SPC is sticking with this time, it seems to be the best match to their discussion.

Both the NAM and the GFS seem to be in agreement that as the day progresses, south and east will be the place to be for the best shear, with instability being the big limiter early on. By 00z instability improves across Georgia a good bit, comes into alignment with decent low level shear, and I'd favor an area from the Atlanta Metro area south to Forsyth and east to the SC line. The progression towards nicely curved hodographs as the evening goes on south of Atlanta has been consistent for 48 hours now.

Things will start off in TN and northern AL, but the NAM in particular has been very steady bringing dynamics into central and northern GA in the 21-00z timeframe. I think anything that can get established south of I-20 from 21z on will bear watching.

 

[Jeff Russell]

What a difference 12 hours make. NAM and GFS both have the low further east and south. Shear looks terrible over CNTRL TN at 00z. Also, the surface low is out running the cold pool aloft.

The SPC 2 day outlook pretty much agreed with my forecast, but it will be very interesting to see what they say in their 1730z update.

 

[Dave Marshall]

Well, stay home guys. The SPC just mentioned the potential for a moderate risk. Forget the High Risk Curse, the SPC has determined the most effective means of protecting the public from severe weather is to get all the storm chasers fired up about the event well in advance. The resulting hot air acts to dry the mid levels and reduce the threat.

I'm a little discouraged that the models continue to modify fairly dramatically run to run, but I'm still feeling like the event will reach further south than they're discussing. Chasing after dark in Georgia is even worse than doing so in the plains though.

EDIT: The 18z model runs are encouraging. Shear, helicity, instability, lift, and perhaps even a reasonable amount of moisture (the big limiter so far) look to converge in an east to west line across the state south of Atlanta. Alot of it could be after dark, but I think it might be worth chasing either way.

 

[Dave Gallaher]

Thinking of the threads here regarding the 'poverty' of the 2009 season so far, I have to say that I've had more opportunities in Dixie Alley than the past few seasons have offered.

However, my work report time in Birmingham has been upped to 5pm and that will limit my north AL chase, unless we get some good early action. The MC in the forecast will probably include a good batch of our regular spring soup, limiting visibility. The 1800UTC forecast shows a tantalizing precip-free zone across NW AL--maybe there will be a break in clouds as well.

 

[Dave Marshall]

Obviously, I'm not going to make concrete plans until tomorrow morning, but I'll be available after about 16z. The NAM and GFS seem to be in good agreement about the location of the various features, but the GFS is being far more conservative in nearly every respect. The NAM really does seem to be playing this thing up big just to the southwest of Atlanta in the 21z-00z timeframe. GFS seems a little more generous with moisture throughout the air column, but isn't quite so optimistic about shear and helicity.

I should be on the road with Cliff Morey headed north towards the Newnan, GA area, with a call on exact staging location made somewhere on the way.

 

[Jeff Russell]

Based on the 00z runs, my initial staging area will be Carrollton in W GA along I-20. Hoping to move south, rather then north. Will make final target tomorrow morning.

 

[Bill Hark]

I am less optimistic for tornadoes on Friday April 10th after examining the 00Z model outputs for April 10th especially for Georgia. The GFS
shows the surface low tracking across Kentucky. It reaches Virginia overnight. The best areas for backed winds are in Kentucky, maybe the TN/KY border
and northwestern NC. The NAM/WRF has the low weakening and shifting slightly southeast. The 850 mb winds are also veered. Predicted dewpoints are marginal and CAPE is predicted to be around 500 for central TN/KY. The better CAPE remains south into GA. I'd like the higher 500mb winds to a be a bit farther north. The SW 50-60 knot winds are mainly in TN and GA and rapidly drop off into TN for both the NAM and GFS. Right now, I'd stay in Cookeville, TN (a town east of Nasville) and check data in the morning. I like the area slightly to the north of Cookeville but there are no major towns. I am not familiar with the area though I suspect it is terrible chase country. As for Georgia, there will be storms though tornadoes less likely due to veered surface winds. The NAM does show surface winds with a more southerly component in northern Georgia. Dalton in northwestern Georgia would be an alternative target if one wants to believe the NAM/WRF and try what I believe is slightly better chase territory.

Bill Hark

 

[Wes Carter]

Although Dr. Hark is not familiar with the territory, he is 100% correct. The whole area up there is curvy winding roads with hills and trees galore. Tennessee is a difficult area to chase in. Even where it is flat it is usually pretty heavily wooded. IMHO the best area to chase in Middle TN is along Route 64 on the southern border. And it's not that great. Couple that with our normally high dewpoints and low cloud bases and it makes it a very dangerous area to chase if you get tornadic storms. Often it's hard to see a tornado until it's right on you.

The area he is referring to has a few small towns like Livingston, Jamestown, Byrdstown, and Livingston (which was devastated in the Super Tuesday Outbreak last year). I live close but I'm not going to try to chase up there. I'll stay here and head out if things look a bit more promising down towards the Alabama border.

And on the GFS it looks like the Cumberland Plateau will be the hot spot if there is one IMHO. (It runs from Chattanooga up into Eastern KY).

 

[Dave Marshall]

Pending the 1300z SPC discussion update, I'm headed for the I-20 corridor west of Atlanta. I'll start in Douglasville and figure something out from there. Should be in the area NLT 1430.

I like the dynamics. Wish they were a bit further south. Both the NAM and the GFS have backed off on the instability just a bit, but the other dynamics still seem to be there. Hopefully we get the cloud breaks they're predicting and that instability is enough to work with.

EDIT: Hey, for once the SPC was smart enough to go with MY forecast. They've moved the best chances further south on the 13z discussion.

 

[Randall Marable]

Surprise no one has start a thread on the possible severe weather Friday in the southeast.

Based on the 18z NAM at 54 hours, 00z 04/11. An outbreak of severe weather looks probable from Lexington, KY through CNTRL TN, down to Northern AL.

A broad area of 1500-2000 J CAPE, H7 jet max of 60 kts, cold air aloft with H7 temps of -5 C and H5 temps of -17 C, surface winds out of the South with temps of ~70 F and DP of ~65 F. EHI (0-1km) 2.5 and EHI (0-3km) 4.7. LCL heights should be around 500-750ft. Helicity (0-1km) 250 and (0-3km) 400-500. LI's of -7. Storm speeds will be a concern as currently showing 260@35kts.

Current target would be somewhere around Murfreesboro, TN.

This is my first post to a forecast thread, go easy on me.

Jeff

A little off-topic but I would have to say not bad at all for a 'first forecast thread'. No one should give you a hard time in the future regarding forecast threads. Good job on this one.