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2012-12-25 FORECAST: LA/MS

I've been eyeballing the area from Louisiana into Alabama for a few days. It looks poised for a Christmas Day severe event, with low-level helicity in excess of 200 m2/s2 and SBCAPE around 1,000 J/kg suggesting the possibility for tornadoes. A slightly negatively tilted trough brings a potent 500 mb jet core into LA, with diffluence overspreading from LA into AL as the system progresses. This morning's NAMM forecast sounding shows 0-3km CAPE approaching 200 J/kg in Alexandria, LA, migrating eastward.

Bottom line: With the sun setting early, this isn't a long-distance chase event. But it is a concern for the folks in southern and central LA, MS, and perhaps AL--particularly, I think, in a line across central LA into western MS. Where the southeast side of the H5 jet kisses better instability--especially higher 0-3km CAPE--curving hodographs could spell trouble, and I see that the SPC has now issued a moderate risk for part of the area. I'm not sure which Dixie Alley diehards are up for chasing on Christmas Day, but this could be an opportunity, albeit a fast one, with storm motions ranging from fast to screaming, aoa 45 kts.

Frankly, I don't like the thought of Dixie Alley lighting up on Christmas. Besides the fact that people will be travelling, families' guards are apt to be down. No one expects to sustain storm damage, or perhaps worse, on Christmas.
 
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I'm not a dixie-alley diehard by any stretch, in fact I prefer to avoid chasing there but I've been considering the situation a few days now and have decided to position in Natchez, MS and see what happens. But the timing appears to be congealing quite nicely for a daytime event but between the speed, poor line-of-sight and weak road system, it will be difficult at best. I can't roam too far east as I need to get to San Antonio in a few days.
 
I'm undecided whether I will chase this, but my initial target would be near McComb, MS with quick access north/south on I-55 and east/west Hwy 98, both are four-lane and are really your only hopes of getting/staying ahead of these potentially fast moving storms. I can shoot up I-55 from McComb to Brookhaven and catch 4-lane Hwy 84 to the east if necessary. Both 98 and 84 can take you east to I-59, but terrain and visibility are very poor for the most part. I will not chase this after dark and intend to stay ahead of the squall line until I get back home to the FL Panhandle.
 
I'm not at all definite, but I'll be watching storm modes on Tuesday AM to make a decision. Either way, I'm not venturing south to the Tuscaloosa/Birmingham axis with only a couple hours of overcast daylight even if supercells become substantial, and chasing fast-moving systems in coal country north of there is out. I'll see if the warm sector outperforms its anticipated northward boundary and offers chaseable cells in the northern half of Alabama, but I have no desire to surf home on a rampant QLCS in the dark. Initial target would be between Russellville and Moulton, AL, along AL24 which offers some areas of decent visibility and turns NE toward Decatur.
 
I'm not a dixie-alley diehard by any stretch, in fact I prefer to avoid chasing there but I've been considering the situation a few days now and have decided to position in Natchez, MS and see what happens. But the timing appears to be congealing quite nicely for a daytime event but between the speed, poor line-of-sight and weak road system, it will be difficult at best. I can't roam too far east as I need to get to San Antonio in a few days.

You may want to avoid Natchez, from there East to I-55 you have nothing but trees with extremely limited road options. Might want to consider Brookhaven or McComb.

For me, waking up and will do Xmas with the kids and let the storms chase me. If one gets going good near me then ill go into chase mode. Storm motions combined with terrain and limited roads always temper my expectations in chases in this area.

Edit: After looking at the 00z runs the low looks to be coming in a bit farther south, I-10 between Baton Rouge and Mandeville may be the play. Once you get along the I-10 corridor terrain is flat but with trees. Hammond, La wouldn't be the worst place to be with I-55 and I-10 intersecting. This will also be in better instability, NAM showing 0-3 EHI's around 4 in this area. Historically this area hasn't had many tornadoes and fewer strong tornadoes but just farther north near Kentwood, La (near Ms line) gets quite a few. Looks like I'll be tracking the warm front first thing in the morning to determine chasing. GFS drops off instability north of I-10 (500 or less ML) while the NAM squeezes a good bit more juice into SE Ms. HRRR runs in the morning should give a bit more insight.
 
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I just finished looking at a few NAM soundings. I agree, things have dropped south. Baton Rouge is just plain nuts, with CAPE around 1,600, 1 km SRH over 500, and a 12 sigtor/6 EHI. But that's at 00Z, which I'm assuming is after dark down there this time of year. Lake Charles shows some impressive soundings too--not as potent as Baton Rouge, but how potent do you need, after all, and there's daylight to work with.
 
I just finished looking at a few NAM soundings. I agree, things have dropped south. Baton Rouge is just plain nuts, with CAPE around 1,600, 1 km SRH over 500, and a 12 sigtor/6 EHI. But that's at 00Z, which I'm assuming is after dark down there this time of year. Lake Charles shows some impressive soundings too--not as potent as Baton Rouge, but how potent do you need, after all, and there's daylight to work with.

Lake Charles the winds veer some. Going to be a difficult chase this time of the year with it getting dark so early. With this system bombing out wonder if things may get fired up along the warm front earlier in the day. The instability and winds are in place, the difficult part getting tors out of the warm front that far south is keeping storms isolated enough and not turning into a heavy rain event.
 
Don't have much to say forecast wise other than noticing the forecast track of the Low and precipitation estimates have shifted South, which means might get some snow accumulation here. Most everyone around here would love a little snow on Christmas so maybe it will set in just before dark. As far chasing, Land between the Red River and I55 is heavily forested. I've chased a few times to the W of the Red River. Lots of Farmland between Monroe and Vicksburg on down to between Alexandria and Natchez. I would love to catch a good storm in there, but that is a narrow corridor especially with fast moving storms. Never been East of I55 but from satellite views looks like there's not quite as many trees. May be after dark though before it gets past I55. I'll probably drop to highway 190 or I10 at Lake Charles and then try to stay out in front of things till dark.
 
Looking at high res reflectivity from the SSEO page on SPC, looks like cells will really get organized along I-55 as the low continues to strengthen and take on more of a negative tilt this afternoon. The exit region in central Ms late this evening could be seeing multiple isolated long lived supercells in a NE to SW broken line from near Philadelphia, Ms to the gulf coast. If things play out this way, these storms will be screaming at 60+ mph at night. Will not be the least bit surprised to see a high risk at the next update if models continute to indicate discreet cells and there isn't a massive squal line killing cell formation. Parameters in a small area certainly justify it and the overall danger level of this event could turn out to be quite extreme.
 
Don't have much to say forecast wise other than noticing the forecast track of the Low and precipitation estimates have shifted South, which means might get some snow accumulation here. Most everyone around here would love a little snow on Christmas so maybe it will set in just before dark. As far chasing, Land between the Red River and I55 is heavily forested. I've chased a few times to the W of the Red River. Lots of Farmland between Monroe and Vicksburg on down to between Alexandria and Natchez. I would love to catch a good storm in there, but that is a narrow corridor especially with fast moving storms. Never been East of I55 but from satellite views looks like there's not quite as many trees. May be after dark though before it gets past I55. I'll probably drop to highway 190 or I10 at Lake Charles and then try to stay out in front of things till dark.

I just read through this thread again and noticed this ^ That didn't make a bit of sense. I meant Mississippi River. I should wake up good in the morning before I try to write something :)
 
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