04/29/05 FCST: OK/MO/AR/IL/KY/TN

Edit at 10:07AM CDT - 4/26 : Changed subject line

I know this is still very far away, but the GFS has been pretty consistent with showing a really deep upper level Low Pressure system that will be moving somewhere through the Plains States or nearby during the day on Friday. Looking at the 18Z GFS, there is an upper level Low Pressure (under 996mb) centered at the Colorado/Kansas border at 0Z Saturday. The GFS also shows a wide swath of precipitation breaking out to the north and east of the Low Pressure. I feel that there could be a chance of severe weather coming into the central and southern Plains during that day, but my confidence is still lacking because from what I have seen on the 12Z GFS on UCAR, moisture return could be a problem with this system (as temperatures in Kansas will maintain around 65-70 all week, Oklahoma in the lower 70s), but I am still new to forecasting and still not that much in the know abou moisture return. The system right now looks really potent, and could add up to some severe weather in the Plains states during the end of next week. Storms could linger into the day on Saturday, April 30th, but that will be found on a seperate forecast thread, but it appears by the 18Z GFS that the Low pressure will track through the Sunflower State or like in previous runs, through the northern and central portions of Oklahoma. It is still very far out for a forecast for Saturday as the GFS has not been consistent with keeping a set location.

Graphic for this forecast can be found on my "Chase Forecasts" link on my signature line,
 
Definitely looks like a doozy, if it verifies...I'm not too worried about moisture return, provided the Gulf doesn't get hosed after this weekend. That should be enough time to get a least decently juicy air up into the S. Plains. This is a fast flow, low amplitude wave setup, which tends to be quite good for severe weather. Also, we're starting to enter the climatological max. period for tornadoes in the S. Plains. We shall see...

Gabe
 
I'd be very, very, very pessimistic about decent moisture return for the Central Plains by then. The GFS doesn't bring the next front to the Gulf, but it does make it to near the KS/OK state line before getting hung up. The ECMWF is in the neighborhood.

Of course, we're talking 130 hours here, so who knows?
 
The GFS has been pretty consistant with a upper level low pressure system for the past week, in the 28th-30th period. I'm excited about this system, because this is the first system this year that I WILL be chasing, as I leave on the 27th, and I'll be down there... And I'm getting really excited as this system draws closer and I'm also looking towards the 30th as well, where the low will shift eastward into the Upper Mississipi Valley, and we'll have 60F dew points as far north as South Bend, IN... I might start a thread for this soon...

There is still a great amount of uncertainty of where it's gonna land... But I'd set my sights from Kansas into Texas, at this point, although it is still too early to tell... And I'm not gonna even go into too many details because it's so far out. But the GFS has been consistant with the same solution for quite a few runs, now, and this would be severe weather potential for parts of the Central and Southern Plains....

Outlook (hard to pin this down, but...):
http://midwestchase.com/wxforecasts/04_29-30_05.gif

..Nick..
 
Edited 4/24/05 10:55pm est: GFS now moving this event forward a day
to the 4/30/05 and 5/1/05 timeframe.


Definiately a long ways out to tell for sure right now, but 4/29 is looking to have good potential for supercells during daylight hours over SE KS, eastern OK, and NE TX, with the GFS currently having a 998mb surface low positioned in the TX panhandle area by 04/30 00Z, 50-60KT 500mbsouthwesterlies over the area, and the approach of 80-100+ kt 250mb winds. Moisture for the 29th is not looking to be great, but the GFS is indicating low 60s dps up to the KS/OK border, with mid 60s farther down in SE OK, NE TX.
My nephew, Jeff, and I land in OKC at 3pm on the 29th, and the way it looks now we will need to really hurry it up to get the rental vehicle together and get on the road asap..
The current GFS forecast for the afternoon/evening of the 30th is looking even more potent atm over the lower MS river valley area, with mid-60s DPs, a 50-60KT low level jet streak, 80+kt 500mb streak, and strongly divergent 250mb flow over the area :shock:
 
Okay....nobody has chatted on this subject for a while, so I'll throw in an update for the nite types.

After looking at the 00Z runs of the NAM, GFS, and the Canadian,
the event is back on for Friday the 29. The GFS and NAM are in fairly good agreement of a 1001mb low over SC OK at 12Z Fri... then the GFS moves it to Jonesboro, AR by 00Z Sat. The Canadian is a tick west at 00Z with the low hanging west a good 150+ miles. Nonetheless... the event Friday (96 hours out) looks to affect NE AR, W TN, W KY, and the Bootheel of MO....... of course everything can and will change before then.

The GFS spins the low down to 999mb as the upper trough moves through NE OK/NW AR. CAPE comes out to 2000-2500 over NE AR/W TN, with 0-3 km helicity values in front of the low above 300.

EDIT: 06Z NAM supports the Canadian spin on things... GFS is too fast.
Has 995mb (yey) low at 18Z over NE OK... putting the action over SC-SE MO/NC-NE AR in the 21Z-00Z timeframe.
 
GFS just took the fun away for anything to happen on Saturday...but the 6Z GFS shows an upper level Low Pressure system centered near Oklahoma City at 0Z Saturday. The Low Pressure is progged under 1000mb, but of course, the NAM is showing a much better solution with an upper level Low Pressure centered under 996mb at the Missouri/Oklahoma/Arkansas borders at 18Z Friday. So far, the NAM (now waiting for the 12Z run) is speeding up the system from the GFS model, but has it deeper. Should the NAM model pan out, the chances for severe weather in the Plains states diminishes (boo!).

Big problem with this system is the availability of moisture and the ability to get it up as far as northern Oklahoma during the day on Friday. GFS is showing poor moisture return. Is it possible?
 
The biggest problem with the 29th (and the days immediately around it) is the influence of a strong shortwave that develops in the wake of the Canadian low (formerly known as the "Great Lakes Cyclone" per one SPC outlook a few days ago). As this massive low moves north over eastern Ontario, then begins tracking westward, a large disturbance seperates from the eastern periphery and slings out over New England. This is a powerful feature and the GFS is in agreement with last night's NAM over the evolution.

This New England low competes with features working their way into the plains during the period. An interesting case is Wednesday, when the NAM backs 850s in the plains temporarily, until the 850 leeside low is caught up in the pattern and the winds veer hard out of the west again. They stay veered for several days, according to last night's run, along with the surface winds.

On Thursday (0Z Friday), which otherwise might look like an interesting chase day, a double-barrel surface low is progged by both models, one in southeast CO and northeast NM forming on the nose of a jet streak riding the zonal flow into the plains, and the other well east, centered somewhere around southern Illinois and serving to veer surface flow in much of the warm sector.

Friday the 29th suffers much the same fate per the GFS: strong west winds at 850 and at the surface through much of southern Oklahoma and Texas.

EDIT: This morning's 12z NAM shows a much more vigorous shorwave on Friday moving from the plains into the lower Mississippi Valley. Areas of eastern AR, eastern MO, west-central and southwest Illinois could be of interest now.
 
The 12Z NAM is showing a very powerful upper level storm system to be centered in southeast Missouri at 0Z Saturday. At 12Z Friday, this storm system is centered in eastern Oklahoma with a reading of 997mb. As the storm system moves into Missouri, the system will strengthen, abd by 0Z has a progged reading of 994mb. Dewpoints in SE Missouri could reach as high at 65-70 degrees, along with instability values of up to 3000 J/Kg in extreme northeastern Arkansas. Helicity will be high to the east and southeast of the Low Pressure, it appears that valus can reach 400-500 between 18Z and 22Z in the bootheel of Missouri. LI in southeastern Missouri/northeastern Arkansas is progged to be at -6. Upper level winds, although, may be too strong and could cause this system to end up "squall-lining". The terrain down in southcentral/southeastern Missouri and northcentral/northeastern Arkansas is a little rough for casual storm chasing, and the road networks are about the same (Mark Twain National Forest is down there). I am going to monitor this throughout the days, today, tomorrow, and Thursday, to look for changes.

Right now, I believe the best chances for severe weather during the day on Friday will be in the Show-Me State. Temperatures and dewpoints in this area will be close by, leading to lower LCL's. Also being close to the Low Pressure System, areas around Poplar Bluff should be watching the skies come Friday.

Graphic for this forecast can be found at the "My Chase Forecasts" link on my signature.
 
I'm becoming more and more intrested in Friday. Haven't checked all the data just yet, but the 12Z NAM and is looking very good! The latest data indicates a deepening low pressure (now 994mb) system centered in Missouri, with good wind fields at 850-700MB, and much better moisture, compared to yesterdays runs. It's showing dew points rising to >65F across Eastern AR/MO (>60F even in IN), with strong low-level shear of >250 m2/s2 SRH (wild >500 m2/s2 SRH in IL). This is all combined with CAPES in excess of 3000J/KG, so the chances appear to be very good, possibly for supercells/tornadoes, especially across Eastern AR/MO (and perhaps into Southern IL).

I didn't go into too much detail since it's still 3+ days away, but it's looking really good... Here's an outlook map I created for Friday: http://midwestchase.com/wxforecasts/04_29_05-1332.gif

..Nick..
 
The 12z NAM and GFS put a deep low in SE Missouri at 0Z Saturday, the 18z GFS slows this down a bit going for SC Missouri. Both models indicate upwards of mid 50's and low 60's tds. With instability of up to 3000 j/kg that is located in up to 400 m/s of helicity. Moisture should begin pushing into this region on Thursday night so I do not believe there will be to much conditional problems on the forecasted moisture verifiying. I couldn't chase this setup if I wanted to due to prior arrangements. That whole area around southern Missouri is un-chaseable (except extreme SE and extreme parts of SW). Now if the low could contuntie to slow down then we can be in some business.

P.S. Still three days out so all bets are off.

-Scott.
 
Looking at the new ETA, it seems the threat area has shifted ever so slightly eastward. Based on this run, I would expect the most intense weather that day to be confined to areas along and S of the Ohio River and along and E of the MS River. Right now, I like SRN IL, SRN IN, WRN KY, WRN TN, ERN AR, and much of LA and MS.

The biggest downsides I see are obviously the location (not great as far as chasing goes), the forward movement of the storms (likely 50-60 knts) and a bit less CAPE progged on the NRN extent of the above mentioned area than I would like to see. However, we know the models never do well with forecasting CAPE accurately this far out.

On the other hand, helicity is very high (500 m2/s2) shown on 72 hr ETA across the NRN portions of the threat area. And we are talking a fairly large area. With strong upper jet punching into the area, a nice powerful LLJ transporting moisture into the area, good directional and speed shear and an unstable atmosphere with a source of strong lift, I don't see how this area would fail to explode if things hold as they are.

The question is, with all of that forcing, can anything that fires remain discreet for very long? I think the window for isolated cells is pretty short. But even so, with helicity as high as it is, I would expect embedded supercells within the eventual line that will form to continue at least an isolated tornado threat as it moves to the E that evening. And with the dynamics, we might see a bit of everything....LEWP's w/ bowing segments, rotating commaheads, etc.

As of right now, it appears Friday has the potential for a significant severe weather event, if you buy the ETA solution. Of course the exact placement and severity will have to wait to be determined. To be honest, I hate to even attempt a forecast this far out. But since this one looked good, I thought I'd bite. But my guess, areas around Evansville, IN...Paducah, KY, Owensboro, KY.....Memphis, TN.....Jackson, TN..... Pine Bluff, AR.....Jonesboro, AR....Jackson, MS.....and Monroe, LA better be on guard Friday afternoon and evening. If this pans out, it could be a pretty significant event.

-George
 
I write a daily severe weather forecast discussion, and I have to say I'm quite excited about Friday. This is my first time posting to Target Area, and I wanted my first post to be about something big. I think this would be the event.

Friday, a developing low pressure center will be located in Northwest Arkansas by mid-day. The associated boundaries with this system will include a warm front stretching from the low into the Ohio River Valley; a very strong dryline extending from the low down into far NW LA and stretching SSW into Southern Texas; and a cold front draping south west of the low and then arching back up to the Texas Panhandle and into Colorado.

I find it interesting how strong and how far east the dryline appears to be. Notice the location of the 70 degree dew point line, and the strong moisture gradient in Texas. Then compare that location to the nose of the thermal axis in Texas where temperatures get as high as in the low 100s in South Texas.

The moisture depth looks very good, but seems to be concentrated at mid-day over Arkansas. Perhaps this is indicative of the area of intiation, nearest the low in NW AR.

Instability looks favorable for at least a Moderate risk day over much of Arkansas, and perhaps Northern Louisiana, as seen by the Lifted Indices and SBCAPE.

The low level jet winds look crazy good with over 50-60 knots of speed by early afternoon. The low level shear and upper level shear look great for nicely tilted updrafts. The 6km shear also looks excellent with 60-70 kts of deep layer shear. This should be a great setup for really put together supercells.

One concern with such a dynamic system is how fast it will squall out. This setup has everything going for it, or so it seems by model guidance. There is great dry intrusion at 500mb and 700mb, so we're not overly saturated, and the shear parameters look excellent for keeping the cells descreet, at least for a time. Vertical motion would be the only concern. If there is too much of that, storms may go "blobular" too fast, however, as long as there is broad vertical motion that isn't too intense, we may have the perfect setup.

Vertical motion is one thing that models have a real hard time forecasting. However, when it's forecasted well, it's probably one of the best parameters for determining updraft strength and overall synoptic forcing. Given that the model output in this situation has a HUGE area of positive vertical motion, I'd say its a fair likelihood that this can be counted on. In the region of greatest interest (Arkansas and Louisiana), the vertical motion is quite good over the entire region.

The capping parameters seem favorable, at least ahead of the dryline. Lid strength and Convective Inhibition look good in the area by 18z.

I'd say explosive initiation would be likely by early afternoon. Perhaps even by late morning.

A cell or two near the low firing in NW Arkansas around Noon could be one of many significant supercells. However, that one could have a rapid storm motion that would parallel the warm front. If a cell gets rooted in that, and gobbles up that 300-500 3km Helicity, we would probably be looking at some great long-tracked tornadic supercells.

I think for a major city concern, Memphis may be under the gun on this one. Little Rock as well.

I'm sure we're looking at a Moderate Risk event, if not High Risk, with a significant threat for tornadoes.

Andy
 
Andy,

Welcome to Target Area! Glad to see you posting in here. I subscribe to your daily forecasts and always love to hear everyone's thoughts.

With that said, it seems the SPC Day 3 is in pretty good agreement with what you said above (and in some cases with what I said). They have a 25% hatched area over ERN AR, the Bootheel of MO, WRN TN/KY and the SRN most tip of IL. It seems everything is coming together. How it all interacts and manifests is yet to be seen. But I certainly agree, this is moderate risk material at least, with or without tornadoes. With winds aloft as strong as they appear to be, some of that will get transported down to earth. But I think there is good tornadic potential, especially if the storms can remain isolated.

After looking this over again, here's are my concerns:

1. Will convection be ongoing early in the period or break out before maximum heating?

2. What is the the storm mode likely to be?

3. What will be the actual storm speed?

I think the storms will likely be hauling to the NE, especially the farther N you go. But anything going up there should be likely to become tornadic. Helicity is just nuts in that area. Perhaps the storms farther S will be more isolated and move slower, but have less helicity to work with. However, the more abundant CAPE values farther S should make up for lesser helicity.

Oh well, even with a few uncertainties, it still looks as good as any setup I've seen all year and better than most. I suppose any system will always have a few "ifs" to sort out. But I wouldn't at all be surprised to see some tornadic activity in the vicinity of Paducah, Little Rock, Jonesboro, and Memphis especially. And if CAPE is a bit higher than currently forecasted farther N, this could be a one Jim Dandy of a tornado event. Hopefully things will become a bit more clear as we progress closer to the date.

-George
 
Well I think it's quite literally, way too good to be true. My proprietary indexes are now starting to show blips of severe showing up in south-central Missouri as early as 12z. Although I'm not entirely sure I believe that, I do think it's indicative of the early convection threat.

Given how fast this system is going to deepen and scream off to the Northeast, it seems apparent that early and fast development will be likely. I don't think that's necessarily going to mean that this event won't be as severe as we've been talking.

We still have plenty of dry mid levels to keep storms refiring along the boundaries. This should help with getting some sunshine in as well to increase the instability. Another thought is that instability isn't necessarily completely dependent on sunshine. With the proper profile and good advection, you can get a lot of instability, even under a cloud deck. This may be a good example of the best of both worlds.

What remains a very interesting fact for those concerned about ongoing convection is how the models continue to indicate little precip, keeping the bulk of it north of the warm front. If there is any truth to this, the warm sector may just go bonkers in the classic, textbook sense.

I think more important than high amounts of whole atmosphere CAPE is the amount of low-level CAPE. In this situation there seems to be a broad area of good low-level CAPE, and regardless how much whole atmosphere CAPE we end up with, the low LFC and LCL heights would probably still exist, and therefore better our chances at fair amounts of 3km CAPE. Same goes for the strong low level lapse rates which also show up in this situation. That's saying a lot for this far east geographically.

I definately think that storm mode will be big supercells. Again, if the synoptic forcing can be held down, that mode will last a little longer. Storms going linear is inevitable. It happens every time. The question is how long will they remain supercells. Right now I think they could go a while, but perhaps thats wishcasting. With the dry mid-levels, dynamic forcing being strong, but not insane...and the model precip output being minimal in the warm sector, perhaps these are indications that the supercellular mode will last a while.

Storm motion will be fast. As always, if you can get on a tower from being visible on satellite to just showing up as a blip on radar, it's motion will be nearly stationary until it gets rooted into the mean steering winds. However they will likely take off pretty fast since the 50 knot winds look to be as low as 900mb. But given shear vector, storm motion shouldn't be quite that fast. I'd say starting out moving at initiation to the ENE at 30 and eventually picking up to NE @ 45.

Given what I hear about that chase territory, I'd stay home and watch the event unfold with Gibson Ridge.

I really have a concern for Memphis. It's going to be a rough afternoon at Elvis World.
 
Ben here at the hospital waiting for the baby! But while I am waiting, I am doing some more glancing at the system for Friday:

6Z NAM is showing a much more powerful upper level storm system (991mb) that will move through the Ozarks during the day on Friday. By the NAM, the storm system should be centered near Cape Girardeau, Missouri at 0Z Saturday. At 18Z Friday, the storm system should be centered in northwest Arkansas near Eureka Springs. I feel that the best chances for severe weather will develop along and to the east of the surface Low Pressure, which will give the best chances to southcentral and southeastern Missouri, along with northcentral and northeastern Arkansas. The cities of Memphis, TN, Poplar Bluff, MO, Jonesboro, AR, and Cape Girardeau, MO are all in the path of the storm system. With dewpoints reaching into the upper 60's in the area close to the Mississippi River, along with instability values of up to 2500 J/Kg, this area could see some dangerous thunderstorms developing. With helicity values highest nearest and to the east of the surface low, there could be a good chance for tornadoes. Only problems I can see with this storm system is that with the upper level winds, this storm system may end up producing a squall line (after a little time with discrete cells) instead of the isolated discrete supercell situations. This may turn into a derecho event with extremely high winds. Most likely, I may be chasing this system, but I will not chase through the forests and hills of southcentral Missouri, rather, I will be targetting the Poplar Bluff area (eastern edge of the Ozark Mountains) and head east from there as storms develop. Given the fast storm speed, the flatlands of extreme SE Missouri might be my best bet. I agree with Andrew on every point he made about the forecast, I am just hoping there isn't much early convection to hinder any chances for good development.

Graphic for this forecast can be found at the "My Chase Forecasts" link on my signature.
 
I was becoming increasingly concerned as I was doing a national outlook last night, for an significantly severe event on a moderately sized scale (150-300 reports) from Arkansas and Southern Missouri through the Ohio/Tennessee Valleys.

I would readily agree with all who said primary convective mode will be supercells although given mean flow sfc:400 millibars being roughly parallel to the warm front and excellent large-scale ascent traveling along the boundary, I would watch for the low-topped supercells over MO/S IL/W KY to eventually evolve into a damaging bow echo(es). Meanwhile across SC KY into N MS/N AL, looks like the mode should be supercells through much of the duration of the event, perhaps evolving into a squall line with numerous embedded tornadoes.

The parameters look almost deceivingly good, and therefore I am apprehensive about blowing this out of proportion. However if things keep looking the same over the next 2-3 model runs I would say we could have a considerable number of tornadoes to chase on Friday.

...Alex Lamers...
 
Well, this event certainly has the potential, assuming the NAM/GFS at least mostly verify, to be a signficant severe weather outbreak... Rich Gulf moisture (aside: what's Gulf moisture? I seem to remember it from last year, but I'd be darned if I've seen it this year... :roll: ) will stream northward into the area of concern ahead of an initial low progged to weak Thursday evening and overnight. NAM is forecasting CAPEs in the 1500-2500 j/kg range across a large portion of the forecast area. LCLs should be sufficiently low, with T-Td deficits in the 10-15 degree range (upper 70s / near 80 + mid-upper 60 Tds). Low-level shear will be ridiculous 35-60kts at 850mb and 45-65kts at 700mb with a gradually veering profile. The cold front / dryline takes on a NE-SW orientation by evening, which could lead to a transition from supercell mode to squall line as the NAM is forecasting 0-6km deep-layer shear vector to be out of the SW (parallel to the front) along and immediately behind the front, though shear orientation is more normal to the front (westerly) a tad farther east.

Right now, the only down side that I can see is veered surface winds. With the expected boundary orientation, it appears that winds will veer to the SSW or SW immediately ahead of the front across AR, western MS, LA, and western TN. This seems a little odd since we should see a little more isollabaric contribution from the slowly deepening surface low(998mb at 12z, 997mb at 18z, 995mb a 0z, 991mb at 6z), which may result in a slightly more backed surface flow pattern. As of now, that's really the only main thing that I can find that would limit tornado potential Friday (well, that and storm mode). Only time will tell I suppose...

For what it's worth, the Jackson MS morning AFD reads like a page out of the forecasters diary... LOL. http://kamala.cod.edu/offs/KJAN/0504270930.fxus64.html
 
I agree with others that this is a powerful setup with the potential for numerous reports of wind damage and tornadoes. I'm curious how others evaluate the rapidly veering low level wind fields, as the surface and lower-level low pressure centers (sfc-850) get caught up in the Great Canadian Pinwheel and zip off to the Ohio River. By 0z Saturday, the sfc low is practically in London...lol.

At 18z, it looks like supercells to me, and along the warm front in N AR/MO bootheel, I think storm motions are even such (~35-40 knots) that you could actually "chase" these for a small period of time. Anything faster (in that terrain), and the strategy is nothing but pick a spot with a view and wait for them to parade on by. People have seen tornadoes that way too. But even the 18z cells won't play nice for long as they head for the Ohio River Valley.

My sense is that around 21-22z, the mode will rapidly transition to linear convection, albeit with a continued threat of large hail, damaging winds, and isolated tornadoes from embedded sups in the line.
 
If I decide to go chasing on Friday I would be setting up in the NE corner of Arkansas or along the far West side of the Missouri bootheel depending on the exact position of the surface low and associated warm front. CAPE should be around 2000-2500J/KG. Helicity is forecast to increase throughout the afternoon with values forecasted to be greater than 400m2/s2. Deep layer shear will be good at 60kts. Low level shear will be very good. Dewpoints of 60-65 can be expected throughout the target area. LCL and LFC heights will be low enough to get the job done.
The only concerns I have are early morning precip./cloud cover and the amount of time supercells will remain discrete. Storm motion has come down a bit over the last couple of runs, but >40kts is a sure thing. With good road networks this would be very challenging. With poor road networks your'e screwed. If the models verify, I would expect to see several strong tornadoes and possibly one or two significant tornadoes, assuming the storms remain somewhat discrete for several hours. I think the best chance for strong long-track tornadoes will be along the warm front where backed surface winds will increase tornado potential. I would love to get out chasing for this, but I am flirting with disaster in a couple classes if I don't stay home and do homework this weekend. If things are still looking really good tomorrow though, I will probably buckle.

edit- I forgot to mention that the storm motion greater than 40kts is kind of deceiving considering they should slow down once they turn right. I am sure 99% of you already knew that, but I just figured I had better throw it in.
 
The setup for Friday is still looking very healthy per the latest model solutions and I'm beginning to think that a severe MCS or bow echo evolving from low-topped supercells is likely up the Ohio River. The setup is pretty classic and the +75 knot MLJ will help. The only thing that is concerning with this event is poor environmental lapse rates on the NAM which have ruined many-a-good event thus far this year, primarily when concerning potential tornado outbreak situations.

...Alex Lamers...
 
One interesting feature of the NAM is that it places the jet streak maxima with diffluence over the lower MS valley at around 0Z. This could boost storms in that area -- but would also place the AR/TN/AL area in the rightfront converging quadrant of the jet. This could help keep storms that pop up in this region from going linear.

Another to note if you're chasing on Friday: (bunkers) storm motion is progged to be VERY FAST. >50 knots to the ENE.
 
The 0z NAM output continues to look relatively similar on the large-scale, with very strong shear and moderate instability across the region of concern. It does appear that the veered surface flow invof the front will likely limit tornado threat to the south of the surface low, as seen by the fact that model forecast helicities are stronger farther east across central and eastern MS, well removed from the instability axis, which, at 0z, is progged to be near the MS/AR border area.

I'm quite surprised to see only a SLT risk on the new Day 2 outlook. The reason stated is that there is still much question regarding storm mode (linear vs. discrete). Regardless, I think the relatively widespread coverage of severe weather expected supports a MDT risk, even if we "only" end up with a fast-moving, intense squall line. I was thinking that the linear vs. discrete argument may be most valid in the debate between MDT and HIGH, though the lack of real intense instability will probably preclude the issuance of such a grand risk. At any rate, I'd be incredibly surprised if we don't see a MDT risk out by tomorrow... The magnitude of the flow and the moderate instability will at least support a risk of widespread, very damaging winds...
 
Jeff, agreed. Regardless of the mode, there will still be a significant severe weather threat. With dynamics as strong as they are, this would warrant a moderate IMHO even if it was all expected to be a wind threat. That is some very, very strong shear. Some of that is bound to be transported down to the sfc with these storms. However, even if it quickly goes linear, I would expect a little bit of everything in the way of severe weather. There will likely be bowing segments with rotating comma heads, embedded sups, etc. So this stuff IMO will maintain an isolated tornado threat well into the evening.

I would expect them to likely go MOD by 1730. More so than the storm mode, something tells me they are a little less confident in cloud cover and precip over part of the area. Edwards made mention to the possibility that there may be a rather weak or non-existent cap over some of the area, allowing stuff to fire very early. This may have been the main reason to avoid a MOD for the time being.

Still, with a 25% hatched area, an upgrade seems highly likely by 1730z unless there are drastic changes (which is always a possibility).
 
Explosive initiation near Danville & Mount Ida, AR around Noon Central time. Storms will explode along the boundary and to the east of there, but the biggest storms look to develop from the initiation point and track ENE at about 50 MPH to Little Rock and Conway, AR and on right through Memphis. If this forecast holds, the major metro areas of Little Rock and Memphis may have some very nasty weather they need to be concerned about on Friday. Right now I think Moderate risk is a given, potentially a high risk. However, instability could be better for a high risk, so I'm not entirely sold on that just yet. On the other hand, the insane low level jet and great winds aloft along with the vertical motion may be more than enough to compensate and bring this risk to what one might consider a high risk category. Another factor to consider is mode of storms. I think initially they will be supercells with tornadoes, however, by 6-7 PM they should start to line out in Arkansas and begin to bow. The risk from that point on will be a high wind event from the squall line. The fact that two major metro areas are in the direct path of the nastiest part of this system (from what I can tell) I think too should be a consideration in the risk given. We'll see what the pros at the SPC do with this.

My target for initiation is Mount Ida, AR... with Little Rock and Memphis both in the direct path of the worst storms farther downstream.
 
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