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

[Ben Prusia]

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,

 

[Gabe Garfield]

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

 

[Jeff Lawson]

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?

 

[nickgrillo]

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..

 

[brody_clifton]

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:

 

[Matthew Havin]

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.

 

[Ben Prusia]

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?

 

[Amos Magliocco]

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.

 

[Ben Prusia]

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.

 

[nickgrillo]

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..

 

[Scott Olson]

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.

 

[George Tincher]

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

 

[Andrew Revering]

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

 

[George Tincher]

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

 

[Andrew Revering]

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.