18-20 March 2012 severe prospects

[JoMo]

A cutoff low that retrogrades in March. How.. odd.

[DBriedis]

Way this year is, its par for the course.

[andyhb]

Keep an eye on David's website as this threat approaches:

http://texasstormchasers.com/2012/03/15/severe-weather-outbreak-sunday-monday-includes-texas/

[Minnesota Meso]

It's way to early, and I don't know for sure if this will verify, but my gut feeling is this. Looking at several different indicies, including 925mb VV, 850mb VV and 700mb VV, coupled with EHI values and cape values, throw in K IIdex values and 0-6km shear values of 30-40knots, I am begining to set my focus on southeast OK. If I were a storm chaser for my living, I would focus on SE OK, bordered by I-35 on the west, I-40 on the north, the Ark. border on the east side and Dallas on the south side, for Monday. Call me nuts if you want to but the ECMWF is showning this well in it's last three runs, but I can't post the maps. Good luck to the chaser's....stay safe

[SmokeEater]

Snippet from Lubbock's AFD.

"ANALOG GUIDANCE FOR SUNDAY DEPICTED SEVERAL HISTORICAL EVENTS THAT RESULTED IN WIDESPREAD SEVERE ACTIVITY."

[BeauDodson]

Browsing through some of the analogs from the St Louis site

Seems like a decent chance for some heavy rain, as well - over parts of the Missouri Valley down into the Arklatex region.

http://www.eas.slu.e...COLD/analog.php

Also - this is just incredible. I don't ever recall such a long lasting warm spell during the month of March - with temps from 10-40 degrees above normal over a large part of the nation.

[andyhb]

It's way to early, and I don't know for sure if this will verify, but my gut feeling is this. Looking at several different indicies, including 925mb VV, 850mb VV and 700mb VV, coupled with EHI values and cape values, throw in K IIdex values and 0-6km shear values of 30-40knots, I am begining to set my focus on southeast OK. If I were a storm chaser for my living, I would focus on SE OK, bordered by I-35 on the west, I-40 on the north, the Ark. border on the east side and Dallas on the south side, for Monday. Call me nuts if you want to but the ECMWF is showning this well in it's last three runs, but I can't post the maps. Good luck to the chaser's....stay safe

I would be very weary of trusting stuff like this, for one, given the very steep lapse rates likely to be in place (H5 temps are -10 degrees and less across the entire area and at the surface the temps are likely to be in the 70s and 80s and dews are likely to be in the 60s), the instability will probably be more widespread/stronger than one would think. Models tend to not be very good at taking these kinds of factors into account when they create their solutions. K index values are not very reliable for this type of forecasting, if you read that article I posted in the March general discussion/obs. thread. Secondly, we all know that the models tend to underdo low level shear and helicity at this range, and even up till the last minute and there's still 300 m2/s2 0-3 km SRH already showing up at 78 hours on the 18z NAM in Central KS.

I guess what I'm trying to say is I'd be careful in setting targets at this range considering right now this is looking like quite a widespread event. Veer-back-veer profiles seem to be really losing their prevalence across the warm sector right now on the models, which only increases the risk for tornadic supercells.

On another, more concerning note, JoMo, you may want to tell people around you that they should keep their eyes on the weather on Monday.

[JoMo]

On another, more concerning note, JoMo, you may want to tell people around you that they should keep their eyes on the weather on Monday.

Why's that? I have been busy with other stuff lately and haven't been watching this unfold, what's it look like?

[andyhb]

Why's that? I have been busy with other stuff lately and haven't been watching this unfold, what's it look like?

Eastern OK into the Ozarks looks pretty favorable for activity on Monday, and potentially tornadic activity.

Hodograph for Joplin at 00z from the 18z GFS:

[brettjrob]

Though it understandably hasn't been mentioned yet due to the isolated and conditional nature, tomorrow will hold potential for surface-based supercells across much of W TX from I-10 up to the Panhandles. A small shortwave currently propagating ENE across northern Mexico will arrive mid-late afternoon and likely induce discrete initiation in a high-CAPE, modest-shear environment. Between high LCLs and the anemic shear profiles, the tornado threat will be low, albeit nonzero. However, it should be the first real daytime convective event for this region, and I know plenty of chasers (including myself) will take the opportunity to dust off the gear in preparation for Sunday.

As for Sunday itself, I've seen nothing but positive trends on the last 24 h of modeling. The NAM in particular depicts a very progressive and open/broad trend to the trough, with H5 winds Sunday afternoon-evening now progged to be nearly due SW over the Panhandles and SW KS. Though LCLs and the possibility of modest backing above H5 remain concerns, I still think the ceiling of potential for this event is rather high (especially for the High Plains in March). If you assume LCLs can remain in the 1000-1250 m range in the eastern TX PH and that the hodographs above 5 km can at least straighten out some more (rather than curl back due to backing wtih height), this event looks on par with several significant early-season tornado events from the Panhandles in recent memory.

[andyhb]

I also think the potential may extend further east (Central KS/Western OK in particular) on Sunday as well, depending on how far the convection can initiate ahead of the dryline. Wind profiles look even better in this area, with also possibly less LCL issues to work with.

[tornadotony]

I'm kinda hesitant to say this because it really bucks climo for the plains, but if it's gonna happen, it's likelier to happen in the early spring. I think any tornado threat with this system might actually peak between 03z-12z Monday. Prior to that point, I think LCLs are probably going to be a substantial issue, as will large-scale forcing for ascent. After 00z, LCLs lower, and though you get a low-level inversion, I suspect the 50-60kt low-level jet will likely allow for enough mechanical forcing for ascent in the low-levels that will allow storms to be tornadic after dark, perhaps well after dark. There's a long way to go until we have a clear idea of what might potentially happen with this, but this is a feeling I'm starting to get.

[Amped]

Odd setup. Winds at H5 don't have as much of a westerly component as they normally do and the low cuts off. This maybe more of a flood setup than a tornado setup.

I'm Not to say there won't be some Tornados, I just don't think it will be the biggest outbreak of the month .

[andyhb]

Odd setup. Winds at H5 don't have as much of a westerly component as they normally do and the low cuts off. This maybe more of a flood setup than a tornado setup.

We've seen outbreaks in the past where the H5 flow was nearly due south, also the low doesn't cut off until at least Tuesday (beyond if you believe the 00z GFS).

Personally, I think the threat on Sunday may end up being a bit further east than the current Day 4. And I'll still say that Eastern OK/Northeast and North Central Texas/Southeast Kansas eastward into the Ozarks look quite favorable on Monday, assuming that overnight convection doesn't throw a wrench in the system. Another sign I'm seeing is that the models seem to be progressively broadening the base of the trough towards the east, which may indicate a more eastward shift in the dryline/SLP.

Also, what's incredible through all of this, and the cut off later next week, the Gulf emerges virtually unscathed, just a juiced as before the system.

[andyhb]

Euro goes negatively tilted on Monday:

[andyhb]

Day 3, 30% sig-hatched but no mention of tornadoes, probably due primarily to LCL heights and lack of low level shear showing up on the models, although for the latter point they may be playing with a bit of fire considering the models' notoriety for underestimating said parameter.

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0230 AM CDT FRI MAR 16 2012

VALID 181200Z - 191200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE

PLAINS STATES...

...SYNOPSIS...

WITH LARGE-SCALE RIDGING TO FURTHER INCREASE ACROSS THE ERN HALF OF

THE U.S. THIS PERIOD...PRIMARY FOCUS IN TERMS OF SEVERE WEATHER

POTENTIAL WILL SHIFT WWD TO THE PLAINS REGION.

THIS SEVERE POTENTIAL WILL BE ASSOCIATED WITH THE ADVANCE OF A

LARGE/SHARP TROUGH COVERING MUCH OF WRN NOAM. AS THIS TROUGH

ADVANCES SLOWLY BUT STEADILY EWD...A SURFACE COLD FRONT WILL EXIT

THE ROCKIES AND EMERGE INTO THE HIGH PLAINS DURING THE SECOND HALF

OF THE PERIOD...PRECEDED BY A DRYLINE. THE DRYLINE -- AND LATER THE

COLD FRONT -- SHOULD FOCUS A SLOWLY-MOVING AXIS OF STRONG/SEVERE

CONVECTION FROM EVENING INTO THE OVERNIGHT HOURS.

...THE PLAINS...

AS THE UPPER TROUGH ADVANCES AND A COLD FRONT BEGINS SHIFTING INTO

THE HIGH PLAINS...LOW-LEVEL MOISTURE WILL CONTINUE TO ADVECT NWD

WITHIN THE PRE-FRONTAL/PRE-DRYLINE BOUNDARY LAYER. THIS COMBINED

WITH STEEP LAPSE RATES AND DIURNAL HEATING WILL RESULT IN MODERATE

DESTABILIZATION...THOUGH CAPPING SHOULD HINDER CONVECTIVE

DEVELOPMENT INTO THE AFTERNOON.

EVENTUALLY HOWEVER...EXPECT STORM DEVELOPMENT TO OCCUR -- AIDED BY

THE WEAKENING CAP AS HEIGHT FALLS ALOFT OVERSPREAD THE REGION

ENHANCING LOW-LEVEL CONVERGENCE.

AS STORMS DEVELOP...STRENGTHENING FLOW FIELD ALOFT WILL RESULT IN

FAVORABLE SHEAR FOR SUPERCELLS...AND THUS STORMS SHOULD QUICKLY

ORGANIZE/BECOME SEVERE. ATTM...MODEST MOISTURE /DEWPOINTS ONLY IN

THE UPPER 50S TO NEAR 60 IN MOST AREAS/ AND ASSOCIATED/FAIRLY DEEP

BOUNDARY LAYER SUGGESTS PRIMARY SEVERE POTENTIAL WILL BE VERY LARGE

HAIL AND LOCALLY DAMAGING WINDS. WHILE OVERALL STORM COVERAGE MAY

REMAIN FAIRLY ISOLATED THROUGH THE AFTERNOON...AN INCREASE IN

CONVECTION INTO THE EVENING COMBINED WITH SLOW EWD MOVEMENT OF THE

FRONT/DRYLINE SUGGEST EVENTUAL COVERAGE OF SEVERE EVENTS SHOULD

WARRANT 30% SEVERE PROBABILITY LINES.

..GOSS.. 03/16/2012

[andyhb]

Monday's Day 4 (actually hints at further risks later in the week). As of right now, I think this may be the bigger day for tornado outbreak potential.

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0347 AM CDT FRI MAR 16 2012

VALID 191200Z - 241200Z

...DISCUSSION...

MEDIUM-RANGE MODELS IN FAIRLY GOOD GENERAL AGREEMENT THROUGH DAY 4

/MON 3-19/...BUT BEGIN TO DIVERGE DAY 5 /TUE 3-20/ AS THE GFS CLOSES

OFF A LOW IN THE BASE OF THE SLOWLY ADVANCING LARGE SCALE

TROUGH...WHILE THE ECMWF KEEPS THE SYSTEM OPEN.

THE ECMWF EVENTUALLY DEVELOPS A LOW DAY 6...BUT IS MUCH MORE

PROGRESSIVE WITH THE LOW AS COMPARED TO THE GFS -- WHICH KEEPS THIS

FEATURE INVOF OK FOR ROUGHLY 48 HOURS. WHILE A VARYING DEGREE OF

SEVERE POTENTIAL WOULD EXIST DAY 5 -- AND PERHAPS BEYOND -- IN

EITHER MODEL SOLUTION...DUE TO THESE DIFFERENCES WILL REFRAIN FROM

HIGHLIGHTING ANY THREAT AREAS BEYOND DAY 4.

THE PRIMARY SEVERE THREAT DAY 4 IS EXPECTED TO RESIDE OVER ROUGHLY

THE ERN HALF OF THE SRN PLAINS...AS THE INITIAL COLD FRONT ADVANCES

WITH TIME. WHILE SOME THREAT WILL LIKELY EXTEND MUCH FARTHER NWD

AHEAD OF THE FRONT...PERSISTENT CONVECTION MAKING VERY SLOW EWD

PROGRESS DUE TO VERY STRONG MERIDIONAL FLOW ALOFT SHOULD LIMIT

INSTABILITY WITH NWD EXTENT.

FARTHER S HOWEVER...A MORE SWLY BELT OF FLOW ALOFT -- AND THUS MORE

FAVORABLE DIRECTIONAL SHEAR WITH HEIGHT -- IS PROGGED. AS THE FRONT

ADVANCES ACROSS TX/OK INTO A DESTABILIZING AFTERNOON

AIRMASS...SEVERE STORM DEVELOPMENT APPEARS LIKELY. WITH THREATS FOR

HAIL...DAMAGING WINDS...AND POSSIBLY TORNADOES APPARENT ATTM...WILL

MAINTAIN THE ONGOING SEVERE THREAT AREA ACROSS PARTS OF THE SRN

PLAINS REGION -- WHERE THE MOST WIDESPREAD/SUBSTANTIAL THREAT

APPEARS TO EXIST.

..GOSS.. 03/16/2012

Some impressive numbers showing up on the 00z SPC MARS run:

72:

96:

120:

[Minnesota Meso]

I would be very weary of trusting stuff like this, for one, given the very steep lapse rates likely to be in place (H5 temps are -10 degrees and less across the entire area and at the surface the temps are likely to be in the 70s and 80s and dews are likely to be in the 60s), the instability will probably be more widespread/stronger than one would think. Models tend to not be very good at taking these kinds of factors into account when they create their solutions. K index values are not very reliable for this type of forecasting, if you read that article I posted in the March general discussion/obs. thread. Secondly, we all know that the models tend to underdo low level shear and helicity at this range, and even up till the last minute and there's still 300 m2/s2 0-3 km SRH already showing up at 78 hours on the 18z NAM in Central KS.

I guess what I'm trying to say is I'd be careful in setting targets at this range considering right now this is looking like quite a widespread event. Veer-back-veer profiles seem to be really losing their prevalence across the warm sector right now on the models, which only increases the risk for tornadic supercells.

On another, more concerning note, JoMo, you may want to tell people around you that they should keep their eyes on the weather on Monday.

andy: Thanks on the K Index info, of course like any index, it can't be taken on its own merit. If one notices a strong K value its time to dig. Does it make sense? What are the Helicity Values, EHI, Lapse Rates etc, etc....

I also agree that the best Tornadic day will be Monday.

[andyhb]

06z GFS/NAM (00z runs of most models largely do as well) paint Oklahoma and Texas (especially Texas, virtually the entire state in all honesty) as ground zero Sunday evening/overnight and Monday. Favorable shear profiles (not a lot of veer-back-veer, especially on the GFS), plenty of moisture/instability, 40-60+ kt LLJ (there are already impressive SRH values showing up on the NAM), backing surface winds and very little LCL problems to speak of, increasing large scale ascent as the upper/mid jet energy approaches and a trigger for both days.

I'm sure David will have some great analysis on his website by tomorrow, because right now, this is looking like one of the more substantial/potentially significant severe threats I've seen in some time for the state. Much of the state is also essentially a chaser's dream too...

[nrgjeff]

Looks like a multi-day event mainly Sunday and Monday, but perhaps not a huge outbreak. Sunday should start out isolated with some capping (Goldilocks strength?) in place, but it will go. Sunday night storms should be more numerous. Monday less capping may promote more widespread thunder, which can be a crap shoot in convective chaos. I figure there will still be a smaller area one could storm chase on Monday.

Might consider the central High Plains Sunday and Texas Monday. Sunday could be west of SPC if a lee-tough can act as the DL. I'm concerned central Plains QPF might be overcast showers, but maybe precip there would set a outflow boundary OFB for cells starting farther west in the High Plains. An OFB enhancing low level shear would be helpful. Monday Texas may offer a nice combo of perhaps more isolated cells under what's left of a cap, turning with height 0-6 km, and a good push of moisture off the Gulf on southeast sfc winds. Any OFB from Sunday night rain could also enhance 0-1 km shear Monday.

It is a little early to pin down specifics. When the whole trough gets onshore in California model sampling will improve. Pattern recognition does however point to the multi-day, at least 2-day, event.

[Chinook]

I'm kinda hesitant to say this because it really bucks climo for the plains, but if it's gonna happen, it's likelier to happen in the early spring. I think any tornado threat with this system might actually peak between 03z-12z Monday.

Did you mean, "but if it's gonna happen, it's likelier to happen in the early morning."

?

That could be a significant statement.

The SREF (09z) does point to some tornado ingredients at 09z Monday. (significant tornado ingredients)

[andyhb]

Ozarks looking potentially in the game by 00z Monday, especially if the GFS is underdoing instability, some really nasty wind profiles showing up on the 12z GFS...

SGF at 00z, there are forecast hodos like this through AR into LA too, 0-1 km shear is 35-50 knots, 0-6 km shear 40-50 knots and oriented WSW to SW (fairly favorable for discrete supercells), if we get discrete cells ahead of the line, this is also a potentially dangerous situation (even within the line, I could see it being full of QLCS and embedded supercellular circulations (ala April 25th of last year):

NAM is a bit slower than the GFS and would probably shift the threat towards the Ozarks after dark.

[tornadotony]

Did you mean, "but if it's gonna happen, it's likelier to happen in the early morning."

?

That could be a significant statement.

The SREF (09z) does point to some tornado ingredients at 09z Monday. (significant tornado ingredients)

Nope, I meant what I said. It's rare for these events on the plains to be after dark, but if it's gonna happen, this is probably the time of year it's most likely.

[Chinook]

It looks like we have some pretty good severe potential in the Big Bend and Pecos region right now. There's a bulge of moist easterly winds down there. It is uncapped in southwest Oklahoma, also with decent EHI up there, and a severe watch. Dryline northeast of Amarillo. In fact, it seems to be uncapped all the way from Texas up to Wisconsin and southern Michigan.

[tornadotony]

The 12z GFS seems much more supportive of tornadoes in wrn OK and NW TX on Sunday evening, and would probably be quite a major threat.

[thewxmann]

RIght now I'd say maybe 5-10 tornadoes touch down, combined both days. Too many issues with moisture depth and quality, as well as the meridional flow. (Notably though, both issues would be reduced if low-level flow backs more than currently indicated and/or if the dryline does not mix as far east.) I would think Sunday has vastly more potential, but both the GFS and NAM indicate a shortwave that sparks off a round of thunderstorms before peak heating, which reduces instability. Given the stout cap, I'm not sure how that will transpire, but it's something to watch out.

[tornadotony]

RIght now I'd say maybe 5-10 tornadoes touch down, combined both days. Too many issues with moisture depth and quality, as well as the meridional flow. (Notably though, both issues would be reduced if low-level flow backs more than currently indicated and/or if the dryline does not mix as far east.) I would think Sunday has vastly more potential, but both the GFS and NAM indicate a shortwave that sparks off a round of thunderstorms before peak heating, which reduces instability. Given the stout cap, I'm not sure how that will transpire, but it's something to watch out.

A couple notes. I agree with most of what you said. However, I think the backing of the low-level flow, given the rather dramatic pressure falls progged for the area, is probably at least slightly underdone. The GFS I think might be picking up on that with better BL moisture on today's runs than in previous days'. With regards to the final point, I think there is a good shot that convection forms by 18-20z on Sunday, but what effect it will have overall I think is quite questionable. That comment made me think back to 5/5/07, which featured early initiation in a meridional flow setup that evolved into the largest recorded 24h plains tornado event since official record began. Obviously I'm not saying that will happen, but if initiation does occur early with a lead shortwave, it would likely ride close to the dryline, limiting the overall effects on the atmosphere. Additionally, areas south of that shortwave at that initiation time will feature some enhanced subsidence, which could promote further destabilization ahead of the main energy.

One other quick note. Given the issues that it has had with intense systems this year and the isallobaric low-level wind, the NAM may never be the model of choice leading up to this event. Moreso even than the other big events this year, this one will rely very greatly on isallobaric response to drive it, especially with moisture return being key given the part of the country where this threat is.

[andyhb]

However, I think the backing of the low-level flow, given the rather dramatic pressure falls progged for the area, is probably at least slightly underdone. The GFS I think might be picking up on that with better BL moisture on today's runs than in previous days'.

This very strongly.

[Thundersnow12]

However, I think the backing of the low-level flow, given the rather dramatic pressure falls progged for the area, is probably at least slightly underdone.

pretty impressive response to the pressure falls between 18-0z on Sunday on the 18z GFS as the sfc winds really back on and just east of the dryline.

[Thundersnow12]

Altus, OK off the 18z GFS