3/27/09 FCST - AR/LA/MS/TN/AL

[Marc Austin]

Things seem to be coming together for a widespread severe weather event. SPC even mentions "significant" tornado event if models varify and possible upgrades to MOD and HIGH. Moisture return seems good with dews in the 60 to 70 range as well as CAPE estimates of 2500J/Kg + combined with ample speed and directional shear make this day very chaseable, even from Florida. As of now, the GFS places a surface low over WRN AR around 18Z Friday. I'm liking SRN AR/NRN LA/ NW MS for the better shear/CAPE combinations. TN is also a potential play depending on the placement of the low/warm front. I'm really surprised no one has posted anything on this yet. Well here ya go, have at it! I'm sure many of you will want to discuss this one.

 

[Marc Austin]

MODS, feel free to add FCST: to this thread as I forgot to when I put it up. Thanks

 

[Clarence Bennett]

Someone is likely to get something on this one. It just depends on which model to believe. The 12z GFS had the low placed further to the SE supressing the best stuff south of the TN state line into southern AR and into central MS. Model madness prevails and this one is driving me crazy.

 

[beaudodson]

I have been waiting for someone to start a thread - not as many chasers down in this region as there are out west.

GFS is furthest west with the track of the primary low. It has been fairly consistent with showing a track through Arkansas and Southeast MO - has actually trended a bit west over the last few runs. NAM is further to the south and east and takes the primary low through MS. GFS seems to occlude fairly early, as well.

Several rounds of severe weather will be possible with this system and this will make Fridays forecast more difficult and could even jeopardize the significance of the outbreak. Complicating matters will be system 1 tonight - system 2 tomorrow night and Friday morning and then round 3 on Friday afternoon into Saturday.

The models have been slowly catching up with how the low level jet will unfold - with SREF showing high numbers on the "tornado ingredients" prog for the last few days. SREF has a bullseye over Southeast AR/LA/MS into AL with the above mentioned prog. Seems to peak Friday night (late) over LA and southwest MS and then a second peak between 3 pm and 10 pm over much of MS and extending northward into West TN and then into Alabama, as well. SREF is showing 30-50% bullseye for Friday. Again it has been showing this for several days now - with little change in numbers. I always find it more important to see consistent numbers - day after day leading up to an event.

Track of the low is critical for the placement of the highest tornado potential. Winds should back to the southeast during Friday afternoon over portions of MS and AL - TN. 850 wind fields of 40-60 knots - depending on your model of choice - are showing up over the same region. A strong 500 mb wind max also pushes into the TN Valley on Friday night. Speeds of 100-120 knots are indicated by the GFS over the Arklatex region into southeast AR/North LA. Neutral tilt turns negative on Friday night into Saturday.

CAPE readings have been consistently showing up in the 1000-3000+ range over a large portion of the SPC outlooked area for several days now. GFS has been indicating very high CAPE readings for a number of days now and has shown little change this afternoon. Dew point readings from the middle to upper 60s (even some 70s) push all the way into Arkansas/Mississippi on most models.

There appears to be some question on just how much wind shear is realized with differing opinions from one model to the next. If the low actually does deepen as being depicted by the GFS and some other models then common sense would say that a strong low level jet will develop in response to the deepening low.

I would pick a line from Memphis, TN to Florence, AL and then back down towards Jackson, MS and perhaps southeast AR. This appears to be where the best dynamics will come together, although northern LA and southern AR could see higher CAPE values. Timing of day could be an issue, as well. Although the warm sector is rather broad and the potential for several lines and areas of severe weather will exist. The Memphis, TN - Jackson, MS - Birmingham, AL NWS Offices have been hitting the potential pretty hard in the area forecast discussions and hazardous weather outlooks.

If the low does move further south and east then I would prob try a Jackson - Mobile - Birmingham triangle.

Highest instability being progged for Friday afternoon and evening is actually over AR and Northern LA - CAPE values exceeding 3000 are and have been showing up on the models. Potential for some very large hail will exist in portions of the SPC outlook. Tough chasing in AR, though.

Another question is whether or not a couple of supercells can form closer to the low and along the warm front - if that were to happen then the tornado risk would be enhanced closer to NE AR and into the MO Bootheel and NW TN (assuming the track of the low is close to what the GFS is indicating). Obviously this has greater implications for my region and has been of interest to me since last Friday. Right now it appears most of the KPAH region will be out of the highest risk zone and perhaps will have to deal with elevated convection or some secondary risk on Saturday (see NAM with spiked instability for Saturdays event).

KGWO (BUFKIT) in MS shows CAPE values of 2700+ at 7 pm and 2500+ at 10 pm/ KI of 40+/ sweat index of 600+/ TT of 55+/ BRN of 21-23/ 850 winds increase from 18 knots at 1 pm to 55+ knots by 7-10 pm period/ significant tornado index is greater than 5/ supercell index is greater than 6/ all between the same hours mentioned above. Also noticed on BUFKIT that winds at low levels could actually be east/southeast with plenty of turning with height.

Way too early to determine how Thursday nights activity will come into play - will there still be a lot of cloud debris around on Friday morning or will it clear out of the region in time for destabilization to occur on Friday morning into the afternoon hours? Placement of boundaries? Will the low actually deepen as much as the GFS is indicating? Another question on the table.

A second peak of instability is being shown by the NAM over KY and TN on Saturday afternoon - just southeast of the deep low.

The potential for Friday's event is pretty high - the signal for this event has been on the models for more than 5 days now. It appears SPC is talking about at least a moderate risk and hinted at even higher for Friday. However, with the event still be 48 hours away there should probably be a lot of caution used in trying to pinpoint how this unfolds. Thursday nights thunderstorm complex will be important in how Friday evolves and could really reduce the severe weather threat.

Good luck to anyone chasing - not the best area to chase storms.

EDIT: Developmental RUC now comes in with a low even further west and stronger - showing the primary low passing into eastern Oklahoma. 0z NAM is now further east and south taking the main low through southeast AR and into MS. Cutting the differences between all models would give a track through AR and into MO/IL/KY.

Edit: Also the new day 2 is a large slight - mainly because of some of the factors listed above. The first round of thunderstorms on Thursday night and Friday morning could really complicate how Friday afternoon evolves.

 

[Kevin Askew]

Great post

Nice Beau. Everything on us chasing comes down to Memphis area, if W. TN is in the game we are there even W. AR. & N Mississippi we will chase. So if the SE Low track comes to play we may not go. if it stays with other 2 solutions we in the game. Prefferably with the SLP moving through AR/MO/IL. Very interesting 48hrs coming up!
Kev

 

[Dave Gallaher]

I've got an eye on this one as well. For once, I have Friday off and north Mississippi looks tempting. Central Mississippi has been active Wednesday night/Thursday morning with quite a few TOR warnings posted.

 

[beaudodson]

It looks like all of the morning data is moving away from a deep low pressure area and more towards a broad area of low pressure over AR/LA that pushes into MS/TN on Friday night and Saturday with some tightening during that period.

Pretty much everything is pointing towards a messy complex of thunderstorms over the outlook area on Thursday night and Friday morning - with several rounds of ongoing precip.

Believe SPC questioning of just how much instability recovery will occur is a good one. Several waves/disturbances moving along the front over the next 24 hours. Looks like Friday will be an interesting nowcasting day with trying to place boundaries/recovery/cloud cover/ongoing convection. Questions remain as to just how organized the low pressure will be, as well.

This pick from last night still looks good, though - "I would pick a line from Memphis, TN to Florence, AL and then back down towards Jackson, MS and perhaps southeast AR. This appears to be where the best dynamics will come together, although northern LA and southern AR could see higher CAPE values. Timing of day could be an issue, as well. Although the warm sector is rather broad and the potential for several lines and areas of severe weather will exist. The Memphis, TN - Jackson, MS - Birmingham, AL NWS Offices have been hitting the potential pretty hard in the area forecast discussions and hazardous weather outlooks."

With each run of the models, though, it appears to be less and less of a "big" event. Will be interesting to see if Saturday ends up being the bigger day/event.

Also looks like flash flooding will be a concern in some areas - 5"+ of rainfall for some counties of LA/MS/AL.

SREF shows the morning precip
http://w1.spc.woc.noaa.gov/exper/sref/gifs/2009032609/SREF_precip_MAX_6hr_f030.gif

 

[Matt Gingery]

This event does look much more interesting than 3/23. I like the latest MDT risk area posted by SPC as of late. With CAPE values from 1000-3000 J per KG and strong LLJ I don't believe I can pass this event up either. I will likely play further to the west and catch cells as they initiate near Little Rock on south to Shreveport. I will likely head to Pine Bluff, Ark. tomorrow. I'll head out of SGF around 12z and be in Pine Bluff around 18z. I haven't seen this much CAPE this year and this should be a classified "outbreak" once it is all said and done. Tomorrow is the day to see tubes if anyone is gonna head out. The last day of spring break for myself, so I intend on catching a few tubes tomorrow and taking a break from chasing outside of my local area of SW Missouri until May. Good luck everyone on the chase. I will be in my usual white ford f150 with vortex anemometer and WxWorks. Anybody in SGF that intends on chasing this, send me an IM and maybe we can team up!!!


After going over the model runs and noticing that the front won't make it to the MDT risk area until later in the evening I believe I will hang back and play the Arklatex region early and parallel to the NE up to Little Rock area.

 

[AndyGabrielson]

Chaseable areas are probably hard to come by but I might leave tonight and make the journey depending on what I see. The ongoing stuff in the morning is my biggest concern. However places east and south of I-40 in AR, parts of TN/MS/LA are probably looking at a major outbreak tommorow with strong tornadoes. This is much more likely to produce as mentioned than the 23rd. We have ample moisture, cape unlike most setups so far this season. the only thing I think anyone was to be concerned about is the ongoing stuff in the morning...

Star City, AR is my target tommorow if I make this crazy journey!

 

[Dave Gallaher]

I'm seriously contemplating the run to north Mississippi for this one, as our local action here will be well after dark (and perhaps mostly linear by the time the lines get here). I'm awaiting the 0600Z SWODY 1 to see what the thought is there, and am thinking of setting up in Grenada or Montgomery County and chase back toward home while daylight lasts.

 

[cdcollura]

Good day all,

Appears there is a potent MCS sweeping through the area and SPC has under Moderate with 10% hatrched tornado prob in its wake.

Recovery is going to be a big issue here as well as how fast the cold front approaches from the west.

Chasing, ofcourse, in these areas may require a chain-saw (trees) ;-)

 

[Gabe Garfield]

With a fairly decent maritime tropical airmass hanging out nearby, very cold air aloft being advected from the west, and a deepening surface low to the west, the stage is being set for a fairly active severe weather day across the Arklatex region and into the lower MS valley regions. Right now, it appears that the best threat for tornadoes will manifest during the mid-afternoon in NE TX (and areas downstream, if isolated storms manage to form ahead of the strongest forcing).

The 4 km WRF from both SPC and NSSL shows isolated development early, switching -- eventually -- to a linear storm mode across NE LA into W MS after dark. The SPC WRF is the most"bullish" model: it develops a N/S line of semi-discrete supercells that advances across western LA into central LA by 00z. Should moderate instability develop northward -- as forecast by the GFS -- these storms would have the potential for producing tornadoes. Strong tornadoes are possible after ~21 UTC, when the low-level wind field is forecast to become more vigorous.

I expect several tornadoes today and tonight, with the most intense tornadoes after dark in MS.

 

[Chad Cowan]

I think today has some violent tornado potential given the amazing directional shear and very moist boundary layer. We'll likely see the highest CAPE values of the year so far thanks to the juicy Gulf-modified air mass finally in the warm sector. Tornado climatology definitely favors this area at this point in the season.

Take a look at this RUC forecast skew-t for Alexandria, LA @ 21z, this is where I would camp out: