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April 12th/13th and 15-16th Severe Weather Thread


andyhb

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It looks a little faster to me compared to last night, and certainly higher-amplitude as the trough comes onshore. The SLP placement and low-level flow look a lot better along the dryline Thu-Fri, too, though I'm sure there will be some capping issues. Still, given a well-timed shortwave, I think either of those days could be explosive roughly along the 100th meridian per this run verbatim.

SPC agrees, highlights both Thursday and Friday roughly around the area you mentioned and the bigger potential on Saturday...Saturday just looks nasty on most of the models/ensembles. What's kind of scary is that at least half of the 00z GFS ensemble members are stronger than the OP with the mid level circulation and therefore, the resulting SLP. Some of them bomb the Saturday system well sub-990 mb.

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0359 AM CDT MON APR 09 2012

VALID 121200Z - 171200Z

...DISCUSSION...

MEDIUM RANGE MODELS CONTINUE TO INDICATE A PATTERN CHANGE...WHICH

EXPECTED TO START ON D3/WED...WILL PROGRESS THROUGH MUCH OF THE

EXTENDED FORECAST PERIOD. THIS WILL RESULT IN THE DEVELOPMENT OF

SWLY MID-UPPER LEVEL FLOW FROM THE SWRN STATES THROUGH OK AND

CENTRAL PLAINS TO THE UPPER MS VALLEY/GREAT LAKES REGION AS A DEEP

LONGWAVE TROUGH EVOLVES IN THE WEST.

MODELS REMAIN CONSISTENT IN FORECASTING AN INCREASE IN SEVERE

WEATHER ACROSS PARTS OF THE SRN AND CENTRAL PLAINS DURING D4/THU

THROUGH D6/SAT. SLY LOW LEVEL WINDS TO THE EAST OF A SURFACE LOW

DEVELOPING OVER WRN KS WILL RESULT IN RICH MOISTURE RETURN INTO

OK/KS ON D4/D5 AND THEN EXTENDING INTO PARTS OF THE MID/UPPER MS

VALLEY ON D6. THIS COMBINED WITH ENEWD EXTENSION OF STEEP MIDLEVEL

LAPSE RATES WILL RESULT IN MODERATE TO STRONG INSTABILITY DEVELOPING

THROUGH D6. SWLY MIDLEVEL WINDS WILL STRENGTHEN FROM MID TO LATE

THIS WEEK ACROSS THE REGIONAL SEVERE WEATHER THREAT AREAS SUCH THAT

ORGANIZED STORMS INCLUDING SUPERCELLS CAN BE EXPECTED DURING

D4...D5...AND D6. THE STRONGEST BULK SHEAR IS EXPECTED ON D6/SAT

WITH THE SEVERE WEATHER THREAT AREA ALSO EXPANDING SWD SOME INTO N

TX AND NEWD INTO SWRN IA.

BEYOND D6...THE SEVERE WEATHER THREAT MAY CONTINUE ACROSS THE SRN

PLAINS...BUT MODEL UNCERTAINTIES PRECLUDE THE INCLUSION OF ANY

ADDITIONAL REGIONAL SEVERE WEATHER THREAT AREAS.

..PETERS.. 04/09/2012

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12z GFS are you kidding me?

Huge, very intense trough and shifted the threat east on Friday/Saturday...incredible wind fields juxtaposed with 60+ sfc dews and H85 dews >10 degrees throughout showing up across the Ozarks/Mid South. Got the H5 barb of death showing up within the mid level jet streak.

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12z GFS are you kidding me?

Huge, very intense trough and shifted the threat east on Friday/Saturday...incredible wind fields juxtaposed with 60+ sfc dews and H85 dews >10 degrees throughout showing up across the Ozarks/Mid South. Got the H5 barb of death showing up within the mid level jet streak.

Instability isn't all the impressive though. I'm sure it would get the job done.

From a hodo stanpoint between here and Springfield, that's impressive.

GFS_3_2012040912_F108_37.0000N_94.0000W_HODO.png

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Instability isn't all the impressive though. I'm sure it would get the job done.

From a hodo stanpoint between here and Springfield, that's impressive.

I'm not going to be too surprised if the GFS is underdoing surface temps and therefore instability here, and with substantial moisture in place, that would be a very dangerous combination.

I'm not sure what kind of analogs are going to pop up on SPC MARS for this run, but there are probably some well known dates.

Areas further north need to watch the triple point on both days, since the GFS is pooling moisture around it.

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12z Euro at 120.

For reference, here's the 12z GFS at 120.

Will repost this from tennesseewx, the GFS 6 hr precip at 132 hrs looks to possibly have a string of intense supercells setting up across the Eastern Plains and Ozarks/Mid MS Valley.

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Still a long ways to go until the event, but I'm starting to lean towards Saturday as having the biggest potential. The GFS runs over the last day have shown the trough splitting, with one vort max ejecting out into the Plains on Saturday with the other lagging behind, and the 12z ECMWF shows this as well. The large-scale pattern over the several-day window looks good for a possible outbreak, and the broadness of the trough itself gives me a little more confidence than usual (this far in advance) that something significant will result from this. However, the specifics regarding the trough evolution and the shortwaves that spin off and eject eastward are going to be crucial and remain highly uncertain at this point.

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Concerning the northern extent of the severe threat on Sat, the 09/0z runs of the Euro and GFS were somewhat similar with the surface features (timing differences aside), that went out the window with the 09/12z runs. The 12z GFS now sneaks the surface high down from Canada and pushes most of the precip on the weekend south of MN, the Euro on the other hand has held true to its previous idea. With the strength of this western trough and the energy that it was ejecting on both the Euro and GFS runs as of 0z, I'm not sure I'm buying into the GFS 12z solution. Seems to me that the strength of the surface low developing and moving into the Upper Mississippi Valley should be strong enough to hold the Canadian surface high to north until we get on the back side of the surface low. As of now I'm sticking with the higher resolution ECMWF I admit that 20-25% of that statement might be wish casting, well than so be it, our lake levels are down 2-3ft from last fall, and topsoil moisture is some area's is non existent. But still the Euro makes more sense to me.

So guys and gals who wins this one??? anyone want to venture a guess?

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Still a long ways to go until the event, but I'm starting to lean towards Saturday as having the biggest potential. The GFS runs over the last day have shown the trough splitting, with one vort max ejecting out into the Plains on Saturday with the other lagging behind, and the 12z ECMWF shows this as well. The large-scale pattern over the several-day window looks good for a possible outbreak, and the broadness of the trough itself gives me a little more confidence than usual (this far in advance) that something significant will result from this. However, the specifics regarding the trough evolution and the shortwaves that spin off and eject eastward are going to be crucial and remain highly uncertain at this point.

Good to have you on board.

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The 12Z CMC verbatim looked nasty, but that solution is still somewhat of an outlier at this moment as most guidance splits the trough (to some degree) across the west before ejecting it as a smaller piece (and more compact) of energy. BUt we will see, a CMC solution is not off the table...even the GFS has shown a few runs similar to it.

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Latest 96 hr OPC 500 mb analysis shows a very large/strong upper trough on the West Coast.

mtmqlu.jpg

Lately they had a survey of sorts on the OPC FB page wondering if they should take away the prior paths in their surface plots. I can understand them doing this for the 24/48hr plots, but because of the lag between 48/96, I feel they should leave that in there.

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The 12Z CMC verbatim looked nasty, but that solution is still somewhat of an outlier at this moment as most guidance splits the trough (to some degree) across the west before ejecting it as a smaller piece (and more compact) of energy. BUt we will see, a CMC solution is not off the table...even the GFS has shown a few runs similar to it.

It was the "overphaser" this winter for sure with the ULL's that came thru the CONUS.

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The 12Z CMC verbatim looked nasty, but that solution is still somewhat of an outlier at this moment as most guidance splits the trough (to some degree) across the west before ejecting it as a smaller piece (and more compact) of energy. BUt we will see, a CMC solution is not off the table...even the GFS has shown a few runs similar to it.

I'd still say the ones that do split the trough are substantial threats on Saturday considering the intensity of the initial vort max that ejects.

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It was the "overphaser" this winter for sure with the ULL's that came thru the CONUS.

I don't particularly remember it having any bias towards too much upper level phasing. FWIW, this scenario isn't a phasing of two waves creating the powerful ULL the CMC eventually simulates. In fact, the GFS and EC really never "split" the lead wave day 3 from the western jet stream day 5. 18Z GFS just forms one elongated jet stream which limits cyclogenesis while the CMC digs that jet energy into Mexico and deepens across the 4 corners before ejecting.

Pretty dramatic differences between the 12z/18z GFS. 12Z GFS would be much more favorable for low level cyclogenesis with a sharper pertubation along the jet max. The 18Z GFS almost has no curvature along the jet stream punching through the plains/ozarks,

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I'd still say the ones that do split the trough are substantial threats on Saturday considering the intensity of the initial vort max that ejects.

Depends, either way there will be some potentially sig severe Saturday given the low level wind fields in even the weakest simulations (18z GFS), but it would still be more favorable to have a larger degree of cyclogenesis associated with a stronger/deeper perturbation along the jet stream.

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One thing I did like about the 18z run was the larger extent of moisture return compared to the 12z run, with a greater area of 65+ dews. With sfc and low level flow directly out of the Caribbean and Central/Western Gulf, moisture return looks like a non issue for the most part towards next weekend, which when you combine with seasonably strong winds aloft, tends to always result is some sort of trouble.

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Thursday looks fairly interesting across western KS on the NAM, but I'm concerned about the moisture situation. It pools lower 60s dew points, but indicates nasty moisture holes developing farther south, with low-mid 50s prevalent down the dryline in the Panhandles. In my experience, this often means the moisture will end up mixing out farther north anyway, too. If some of the forecast soundings did verify for areas like DDC-GCK and points north up to I-70, there would definitely be a tornadic supercell threat, though.

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Note the intensity of the upper/mid level jet that it is digging on the west coast at the end of its run too.

Actually another thing I find interesting is that the 12z CMC ensembles are all in relative agreement with the OP's dangerous solution, considering we rarely see a lot of agreement from that particular ensemble set this far out.

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