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18-20 March 2012 severe prospects


tornadotony

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Judging by the next panel, looks like it's on board with the GFS idea of next Monday being something to watch quite carefully.

Yeah, it seems the models have converged to some degree thanks to the resolution change possibly. Euro would be a big dryline setup on Monday.

But man that GGEM is rather frightening in all honesty...

GFS ensembles on track too, many of them are faster than the OP...

Yes, that is a 989 mb SLP on an ensemble mean...

After that, many solutions lead to a GGEM-esque verbatim, while some others follow the OP/Euro...

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Yeah, it seems the models have converged to some degree thanks to the resolution change possibly. Euro would be a big dryline setup on Monday.

But man that GGEM is rather frightening in all honesty...

GFS ensembles on track too, many of them are faster than the OP...

Yes, that is a 989 mb SLP on an ensemble mean...

After that, many solutions lead to a GGEM-esque verbatim, while some others follow the OP/Euro...

Obviously it is several days out but to see a SLP under 995mb on the ensemble mean is a bit worrisome. Seasonally strong dynamics being put in place with unseasonable thermodynamic environment could spell trouble ahead.

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Obviously it is several days out but to see a SLP under 995mb on the ensemble mean is a bit worrisome. Seasonally strong dynamics being put in place with unseasonable thermodynamic environment could spell trouble ahead.

It's really like late winter dynamics aloft with late spring conditions at the surface. Some pretty volatile ingredients on the table here.

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DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0329 AM CDT MON MAR 12 2012

VALID 151200Z - 201200Z

...DISCUSSION...

LATEST MEDIUM RANGE GUIDANCE CONTINUES TO SUGGEST SIGNIFICANT

TROUGHING WILL DEVELOP ACROSS THE WRN U.S. THIS WEEKEND. THERE ARE

NOTABLE DIFFERENCES BETWEEN THE GFS AND THE ECMWF WITH TIMING OF

STRONGER MID LEVEL FLOW SPREADING INTO THE PLAINS. THE GFS IS

CONSIDERABLY FASTER EJECTING A SIGNIFICANT SHORT-WAVE INTO THE

NRN/CNTRL PLAINS SATURDAY WHILE THE ECMWF MAINTAINS A FULL LATITUDE

TROUGH AND IS SLOWER. GIVEN THESE DIFFERENCES WILL NOT INTRODUCE A

RISK OF ORGANIZED SEVERE THUNDERSTORMS. ADDITIONALLY...WHILE

ISOLATED-SCATTERED THUNDERSTORMS MAY AT TIMES EVOLVE ACROSS PORTIONS

OF THE PLAINS WITHIN THE RECOVERING WARM SECTOR DURING THE LATTER

HALF OF THE WEEK...RELATIVELY WEAK SHEAR AND INCONSISTENCY REGARDING

WEAK IMPULSES LEND TO LOW PREDICTABILITY.

..DARROW.. 03/12/2012

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Just as a point of reference as to how strong this trough could potentially be, this is part of a SWS out of San Diego of all places.

A STRONG COLD PACIFIC STORM SYSTEM IS EXPECTED TO MOVE INLAND

THROUGH CALIFORNIA LATE IN THE WEEK THROUGH EARLY NEXT WEEK WITH THE

MAIN IMPACTS ON SOUTHWEST CALIFORNIA FROM FRIDAY NIGHT THROUGH EARLY

MONDAY. WHILE THERE IS STILL SOME UNCERTAINTY AS TO THE TIMING AND

LOCATION OF THE MORE SIGNIFICANT IMPACTS...THE PERIOD FROM FRIDAY

NIGHT THROUGH EARLY MONDAY SHOULD BE MUCH COOLER...WITH PERIODS OF

STRONG GUSTY WEST WINDS...ESPECIALLY IN THE MOUNTAINS AND

DESERTS...AND PERIODS OF LOCALLY HEAVY PRECIPITATION WITH LOW SNOW

LEVELS.

WEST WINDS IN THE MOUNTAINS AND DESERTS COULD GUST TO 75 MPH AT

TIMES...RAINFALL TOTALS FOR THE FRIDAY NIGHT THROUGH EARLY

MONDAY PERIOD COULD RANGE FROM ONE TO TWO INCHES NEAR THE COAST TO 3

TO 5 INCHES IN THE MOUNTAINS WITH AN INCH OR LESS IN THE DESERTS.

SNOW LEVELS COULD LOWER TO 2500 TO 3000 FEET...POSSIBLY LOWER...WITH

SEVERAL INCHES OF SNOWFALL AT LOWER MOUNTAIN ELEVATIONS POSSIBLE AND

LOCALLY A FEW FEET AT HIGHER ELEVATIONS. THERE IS ALSO THE

POSSIBILITY OF THUNDERSTORMS WITH SMALL HAIL OR GRAUPEL...AND

WATERSPOUTS OVER THE COASTAL WATERS. THIS STORM IS ALSO EXPECTED TO

BRING HIGH SURF TO THE BEACHES.

Needless to say snow levels that low are pretty damn rare any time of the year there.

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It's still too early to know what the evolution of this storm is going to be, so what we've talked about being shown on St. Patrick's Day and beyond has potential for pretty much anywhere between the Appalachians and the Rocky Mountains. As we get closer, we should start being able to pin down specific regions most likely to be affected.

Just curious, normally how far out until you can pretty much say with certainty? The March 2nd outbreak, they were posting information to the public 2-3 days before hand. I know here most people have information long before the public does, so I am curious as to about how long before the event that one would have a pretty decent idea of what area of the nation would be affected.

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Just curious, normally how far out until you can pretty much say with certainty? The March 2nd outbreak, they were posting information to the public 2-3 days before hand. I know here most people have information long before the public does, so I am curious as to about how long before the event that one would have a pretty decent idea of what area of the nation would be affected.

I think it's when the models start to become consistent with location (at least with regards to region) and timing. Even so, considerable uncertainty may remain until the day of, when we can finally see what the mesoscale environment is going to be like.

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18z GFS hammers the Plains repeatedly for at least 3 straight days, by the looks of it. Plenty of moisture/instability and a powerful LLJ on each day. There are some striking similarities between the trough setup here and the setups for May 22nd-24th, 2008; March 13th, 1990 and May 4th/5th, 2007.

Then on day 4, the closed low ejects and creates an event of its own in Texas...

12z Euro ensembles/OP seem to keep the trough more broad-based for a longer period of time and less sharp/amplified, which would probably encourage less strongly meridional flow and create a greater risk for a multi-day event.

To give you an idea at the type of warm sector we may be looking at here for each day, this is the 18z NAM at 51 hrs, keep in mind, the flow from the south is going to intensify significantly ahead of this powerful upper level system, so we could be talking these kind of CAPE values or even higher come the weekend and next week, which is positively nuts for March:

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Not only that, but the capping doesn't look overly impressive considering the amount of instability, this can be attributed to the cold mid level temperatures that you wouldn't see in a late spring/summer setup.

And from what I can tell, the 18z GFS has a repeated dryline setup for the three days prior to the Texas closed low ejection...I'm pretty sure I have never seen that in March, and its a very sharp dryline at that.

So lets see here, on the 18z GFS for all three days synoptically (12z GFS too, essentially), you have:

I) Strong LLJ? Check. (And we all know how the GFS tends to underestimate LL wind response to deepening surface cyclones)

II) Moisture/Instability? Check.

III) Dryline/sfc cold front for forcing? Check.

IV) Non-completely linear shear vectors? Check.

V) Non-thermonuclear cap? Check.

VI) Strong turning in the wind direction with height? Check.

VII) Powerful upper/mid level jet for increased dynamics? Check. (At least for 2 out of the 3 days)

VIII) Vigorous sfc cyclogenesis to help back the sfc winds? Check. (For all three days, there is a sub 1000 mb sfc low)

I don't know about you, but to me that is a pretty hefty list of qualified parameters synoptically for a severe weather threat...

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These setups with really meridional upper flow, and especially ones in which 500 mb is more veered than 200-300 mb, always make me nervous. It's such a fine line between a major tornado outbreak vs. a bunch of junky nontornadic supercells, and sometimes it's almost impossible to discriminate between the two until the event has already started. Right now, both Sunday and Monday look like candidates for days that could walk that fine line. Sunday's directional shear looks better on the GFS soln, but upper support is lacking -- I suppose it would be the May 4, 2007, of this trough's lifecycle, with a high but conditional threat. It would be foolish for me to start picking apart detailed strengths and weaknesses of each day's setup at this timeframe, but I do foresee veer-back-veer profiles becoming one of the major issues to discuss and watch over the next several days -- unless even more wild model swings are on the horizon.

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These setups with really meridional upper flow, and especially ones in which 500 mb is more veered than 200-300 mb, always make me nervous. It's such a fine line between a major tornado outbreak vs. a bunch of junky nontornadic supercells, and sometimes it's almost impossible to discriminate between the two until the event has already started. Right now, both Sunday and Monday look like candidates for days that could walk that fine line. Sunday's directional shear looks better on the GFS soln, but upper support is lacking -- I suppose it would be the May 4, 2007, of this trough's lifecycle, with a high but conditional threat. It would be foolish for me to start picking apart detailed strengths and weaknesses of each day's setup at this timeframe, but I do foresee veer-back-veer profiles becoming one of the major issues to discuss and watch over the next several days -- unless even more wild model swings are on the horizon.

This, although something tells me I do foresee model changes (personally I think that ridge is a bit too amplified on the northwest side, especially with the way it cuts into the 552-534 dm heights of the trough), actually the overnight periods may end up being favorable, given the LLJ really ramps up and there is still plenty of moisture...

Actually, most of the soundings I've checked from around the area, it's mostly just veering with height, I think I've only seen one with a veer-back-veer profile...

That said, given all of this analysis that we've done out of all of the different solutions of this trough, the constant remains, a large longwave trough developing to the west of a very warm, moist and unstable warm sector, which should already set off alarm bells, as Tony mentioned. Given that the main upper level energy hasn't reached the coast yet, I'm thinking the models will continue to be different.

With 3/2, once the UL energy came onshore, the models became much more consolidated with how it was going to evolve, I think the same, or something similar is in store for this one.

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These setups with really meridional upper flow, and especially ones in which 500 mb is more veered than 200-300 mb, always make me nervous. It's such a fine line between a major tornado outbreak vs. a bunch of junky nontornadic supercells, and sometimes it's almost impossible to discriminate between the two until the event has already started. Right now, both Sunday and Monday look like candidates for days that could walk that fine line. Sunday's directional shear looks better on the GFS soln, but upper support is lacking -- I suppose it would be the May 4, 2007, of this trough's lifecycle, with a high but conditional threat. It would be foolish for me to start picking apart detailed strengths and weaknesses of each day's setup at this timeframe, but I do foresee veer-back-veer profiles becoming one of the major issues to discuss and watch over the next several days -- unless even more wild model swings are on the horizon.

I agree 100% with this post. The closest realistic analog we might have to this setup is 3/28/07, in terms of likely trough evolution and time of year. That day even, the whole evolution of the event really hinged on the secondary dryline. If that hadn't formed, you'd have had half the number of tornadoes that ended up occurring, maybe even less. It's probably going to be a nail-biter leading right up to it. I think a major severe threat is realized either way. The question is whether tornadoes or wind/hail will be the dominant threat.

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I agree 100% with this post. The closest realistic analog we might have to this setup is 3/28/07, in terms of likely trough evolution and time of year. That day even, the whole evolution of the event really hinged on the secondary dryline. If that hadn't formed, you'd have had half the number of tornadoes that ended up occurring, maybe even less. It's probably going to be a nail-biter leading right up to it. I think a major severe threat is realized either way. The question is whether tornadoes or wind/hail will be the dominant threat.

Does this threat seem to be more of a Plains threat or will it extend east into the Ohio Valley/Great Lakes?

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Euro looks like it's going to go quite broad based through 96:

You can see compared to the GFS, which concentrates the 528/534 dm heights more around the sfc low in the Pacific, there's more of a ridge between the two impulses on the GFS...

Edit: Scratch that, Euro looks like it is stringing it out by 144, GGEM gets a cutoff by 168/192, quite different solutions now after the relative concensus 00z last night...

I think it might be fairly safe to say that we won't be seeing any outlook in the Day 4-8 from the SPC, not that I really expected one 6+ days out in the first place.

Lol, if this is a time where the NOGAPS is correct... :lmao::whistle:

It appears the GFS has had the most run to run consistency, while the Euro and GGEM have been pretty scattered with their verbatims for the past two days, some really looking ugly, others not so much.

GFS OP is slower than the majority of the ensembles at 144, which translates to a more meridional flow pattern. I think many of them would have better upper level support on Sunday, considering it looks like the majority of them have the core of the incoming jet streak over the warm sector, instead of west of it like the OP, as well as more southwesterly or even, further south, west-southwesterly H5 flow rather than south-southwesterly. Details like this could mean the difference between a major tornado outbreak or not, and I like seeing the fact that the majority of the ensembles place the mid/upper level jet over the warm sector by 132, ensuring good upper level support throughout the day (I.E. less of a conditional threat like Brett mentioned with the GFS OP, but with equally high, or perhaps even higher overall potential):

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There hasn't really been much model consistency from anything...it's a pretty tough call. As per the seasonal trend, the Pacific energy is coming ashore rather disjointedly, which allows for significant amplification of the trough prior to ejection into the Plains. If there is one thing that is consistent, and that we can be more confident on, is that the trough will be rather meridional. All this would tend to decrease the threat east of the Plains, although I would not go as far as 100% confidence given that this is so far out.

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What is quite impressive is how far north the GFS is pegging low to mid 60s dewpoints...the northward return of moisture and how large the sector is really opens my eyes. I also like how around the 19th/20th we see a very potent MLJ/ULJ streak developing at the base of the trough...GFS has a 80-100 kt MLJ streak developing with about 110-120 kt ULJ streak developing. Also looking at 500mb temps of between -15C to -20C with a good EML in place...so 1) we'd be looking at a highly steep lapse rate environment which coupled with temps in the 70s to near 80s and those low to mid 60's dews will lead to some pretty extreme instability this time of year along with great dynamics.

I do agree with some points Jim just mentioned as well...have to really watch for models handle that trough as it ejects through the Plains, if it does amplify too early this would allow for a weaker system and everything to be disjointed...stronger dynamics from stronger instability. While you can't rule out anything east of the Plains as of right now the southern Plains seem like the hot spot...for now.

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Well, the 13/00z ECMWF ens mean is more progressive than the op, but still a lot less so than the GFS and its ensembles. GGEM ens mean is in between, but probably closer to the GFS camp. Right now, the more progressive solutions look more favorable for major severe. I'd say the GFS ensembles look almost incredibly favorable for the southern/central High Plains on both Sunday and Monday. The op Euro would be basically marginal threats until Tue-Wed, at which point the trough comes out very meridional with questionable high-end potential. The other guidance would have legit threats at least one day out of Sun/Mon, if not both.

Next 48 hours or so of runs will probably be crucial. I recall this same dilemma leading up to the 22-23 May 2008 setup, except the ECMWF was the more progressive solution, and it won out. Hmm.

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Surprised nobody posted this.

ZCZC SPCSWOD48 ALL

ACUS48 KWNS 130825

SPC AC 130825

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0325 AM CDT TUE MAR 13 2012

VALID 161200Z - 211200Z

...DISCUSSION...

LATEST GFS AND ECMWF BOTH AGREE THAT A WRN U.S. TROUGH WILL EVOLVE

THIS WEEKEND IN RESPONSE TO A FAIRLY STRONG BLOCKING HIGH THAT WILL

DEVELOP OVER THE ERN U.S. HOWEVER...THERE IS CONSIDERABLE

DISAGREEMENT REGARDING THE EWD MOVEMENT OF STRONGER MID-HIGH LEVEL

FLOW INTO THE PLAINS WHERE STRONGER SHEAR WOULD NOT ONLY SUPPORT BUT

ENHANCE THE PROSPECT FOR SEVERE STORMS GIVEN THE EXPECTED

MOISTURE/INSTABILITY. THE ECMWF IS CONSIDERABLY SLOWER WITH HEIGHT

FALLS ACROSS THE ROCKIES AND THUS STRONGER FLOW IS EXPECTED TO

ADVANCE NO FARTHER THAN WY/CO/NM BY THE END OF THE PERIOD. FOR THIS

REASON WILL NOT INTRODUCE A SEVERE RISK UNTIL TIMING IS RESOLVED

WITHIN THE MODEL GUIDANCE.

..DARROW.. 03/13/2012

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12z GFS is caving to the crappy-looking Euro solution... 582 dm March blocking over the Midwest FTL.

GG. And it shows a semblance of a death ridge popping up afterwards. But yeah, as I said, no consistency whatsoever, just like all the other systems this year. I would say from the tendency for upper lows to close off early over the SW US this year, that this evolution in the modeling has not been surprising.

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