Significant severe weather threats 4/8-10

[brettjrob]

Monday looks like such a beautiful, classic chase day on the 00z GFS, where moderate to high instability is complimented by nicely-curved hodos that still promote manageable storm motion. It's really a shame the models are still in such a state of flux, and that the trend is toward a lower-amplitude trough in which shortwave timing will make or break the potential. Tuesday is looking more and more like an Arklatex/Ozarks event, possibly back toward I-35, where the magnitude of the threat will hinge on the degree of low-level veering.

[OKpowdah]

Verbatim, 00z GFS appears to be 3-6" of snow on top of a tornado-ravaged landscape by next Wednesday..

[brettjrob]

Just for posterity's sake.

 

[Stebo]

Just for posterity's sake.

 

kduc.png

 

Incredible sounding there.

[OKpowdah]

Just for fun ... OUN goes from a classic tornado outbreak sounding to light snow in 45 hours

 

[andyhb]

SPC hitting the less capped area in KS harder on Monday with a D5.

DAY 4-8 CONVECTIVE OUTLOOK   NWS STORM PREDICTION CENTER NORMAN OK  0340 AM CDT THU APR 04 2013     VALID 071200Z - 121200Z       ..DISCUSSION      ..SUNDAY/D4 - NERN OK INTO THE LOWER MO VALLEY    MODELS ARE IN GOOD AGREEMENT IN MOVING A LOW AMPLITUDE SHORTWAVE  TROUGH FROM THE ROCKIES EWD ACROSS THE CNTRL PLAINS DURING THE DAY  AND TO THE MS RIVER BY 12Z MON. THIS PATTERN WILL ALLOW LOW LEVEL  MOISTURE TO INCREASE ON SLY FLOW AROUND THE WRN ATLANTIC  ANTICYCLONE...WITH MID TO UPPER 50S F DEWPOINTS INTO KS AND MO BY  00Z. ISENTROPIC LIFT N OF THE WARM FRONT WILL BE ENHANCED BY THE  SHORTWAVE TROUGH...AND SCATTERED THUNDERSTORMS ARE EXPECTED TO LIFT  NEWD ACROSS ERN KS...MO...IA...AND IL DURING THE EVENING AND  OVERNIGHT. COOL TEMPERATURE PROFILES ALOFT AND ADEQUATE CLOUD  BEARING SHEAR MAY SUPPORT SOME MARGINALLY SEVERE HAIL.      ..MONDAY/D5 - CNTRL AND WRN KS...NWRN OK    MODELS INDICATE THE WRN TROUGH AMPLIFYING ON MON WITH A 90 KT  MIDLEVEL SPEED MAX DIGGING SEWD ACROSS CA AND NOSING INTO THE SRN  HIGH PLAINS BY TUE MORNING WITH STRONG HEIGHT FALLS. AT THE  SURFACE...LOW PRESSURE IS FORECAST TO DEEPEN SOMEWHERE NEAR THE  TX/OK PANHANDLE AREA...WITH A WARM FRONT EXTENDING EWD ACROSS KS AND  INTO MO. A DRYLINE SHOULD EXTEND SWD NEAR THE TX/WRN OK BORDER AS  WELL. LOWER 60S F BOUNDARY LAYER DEWPOINTS SHOULD EXIST ACROSS MUCH  OF THE WARM SECTOR...WITH MID 60S F TO THE RED RIVER. WITH COOL  TEMPERATURES ALOFT...THIS WILL RESULT IN MODERATE INSTABILITY  LEVELS.      THE MOST LIKELY AREA FOR CONCENTRATED SEVERE STORMS APPEARS TO BE  OVER SWRN KS...WHERE COOLER AIR ALOFT WILL RESULT IN THE LEAST  AMOUNT OF CAPPING POTENTIAL AND WHERE SFC CONVERGENCE WILL BE  MAXIMIZED ALONG WITH HEATING. WIND PROFILES WILL BE DECIDEDLY  SUPERCELLULAR WITH EXTREME HAIL POSSIBLE AS WELL AS A FEW TORNADOES.  DURING THE EVENING...WARM ADVECTION WITH THE NOCTURNAL LOW LEVEL JET  WILL BE MAXIMIZED AND MAY INCREASE STORM COVERAGE. THE MAIN MODEL  DIFFERENCE IS HOW THE EVENING STORMS MAY BE FORCED. THE GFS  INDICATES A COLD FRONT SURGING SWD. IF THIS OCCURS...INITIAL  SUPERCELLS COULD EVENTUALLY MERGE INTO AN MCS. THE ECMWF SOLUTION IS  MORE SUPPORTIVE OF CONTINUED SUPERCELLS AFTER DARK WITH THE BOUNDARY  REMAINING STATIONARY ACROSS NRN KS.    MORE ISOLATED STORMS ARE LIKELY SWD INTO WRN OK/TX ALONG THE  DRYLINE...BUT THIS THREAT AREA COULD BE CONFINED TO A NARROW ZONE AS  CAPPING INCREASES TO THE E. RECENT HEAVY RAINS AND DECREASED SURFACE  ALBEDO MAY PROVIDE A FEEDBACK MECHANISM FOR COOLER TEMPERATURES AS  WELL.     ...TUESDAY/D6 TO THURSDAY/D8 - ERN OK/ARKLATEX INTO THE MIDDLE AND  LOWER MS VALLEY...  AFOREMENTIONED COLD FRONT DEPICTED BY GFS IS FORECAST TO SURGE SWD  AND WILL BECOME A PRIMARY FOCUS FOR CONVECTION FROM NRN IL INTO MO  AND OK...LINKING WITH THE DRYLINE OVER N CNTRL TX. BY  TUESDAY...SUBSTANTIAL BOUNDARY LAYER MOISTURE WILL BE IN PLACE WITH  UPPER 60S F DEWPOINTS AHEAD OF THE FRONT.     MEANWHILE...THE ECMWF SOLUTION KEEPS THE SYNOPTIC FRONT STATIONARY  ACROSS SRN NEB INTO NRN IL/IND DURING THE DAY ON TUE...WITH THE  DRYLINE FROM CNTRL KS INTO OK AND CNTRL TX. THIS MODEL ALSO  INDICATES SUBSTANTIAL MOISTURE AND INSTABILITY POTENTIAL FROM  KS/OK/TX INTO THE LOWER MS VALLEY.    GIVEN THESE MODEL DIFFERENCES...PREDICTABILITY IS TOO LOW FOR AN  AREA ON TUE/D6...ALTHOUGH THERE IS THE POTENTIAL FOR SIGNIFICANT  SEVERE INCLUDING TORNADOES. THE THREAT SHOULD PERSIST INTO WED/D7  ACROSS THE LOWER MS VALLEY. AREAS ARE LIKELY TO BE INTRODUCED AS  PREDICTABILITY INCREASES IN SUBSEQUENT OUTLOOKS.    ..JEWELL.. 04/04/2013

[Ed Lizard]

So far no luck, but I'm trying to angle my boss into sending me to Southwest Wichita County (Texas) for a project starting Monday, although a quick look at GFS suggests a freezing rain threat mid-week is about equal probability to a tornado threat.

[It's Always Sunny]

Monday looks like such a beautiful, classic chase day on the 00z GFS, where moderate to high instability is complimented by nicely-curved hodos that still promote manageable storm motion. It's really a shame the models are still in such a state of flux, and that the trend is toward a lower-amplitude trough in which shortwave timing will make or break the potential. Tuesday is looking more and more like an Arklatex/Ozarks event, possibly back toward I-35, where the magnitude of the threat will hinge on the degree of low-level veering.

Central OK looking favorable on Monday late afternoon

[OKpowdah]

I may start leaning toward Tuesday as a bigger day for many in OK

[andyhb]

Tuesday could be a nasty day across a large area if the GFS is on the right track.

[baroclinic_instability]

I may start leaning toward Tuesday as a bigger day for many in OK

Absolutely, right now as modeled by all the major modeling centers, Tue is the day across the southern plains. GFS would be kinematically favored over the ECMWF with the bulk of the stronger 500 flow in the ECMWF farther W over the Continental Divide/western high plains. But those are small details not resolvable at this tme frame.

 

I have been thoroughly impressed with the general consistency of the GFS and GEFS, especially compared to the ECMWF (and others including the CMC which has been laughably bad).

[Chicago Storm]

It's nice to see the trough/energy more consolidated on the past few runs of guidance...Mon/Tues looking good.

[OKpowdah]

Absolutely, right now as modeled by all the major modeling centers, Tue is the day across the southern plains. GFS would be kinematically favored over the ECMWF with the bulk of the stronger 500 flow in the ECMWF farther W over the Continental Divide/western high plains. But those are small details not resolvable at this tme frame.

I have been thoroughly impressed with the general consistency of the GFS and GEFS, especially compared to the ECMWF (and others including the CMC which has been laughably bad).

The main problem I see with Tuesday is the s/w breaks northward, with nothing to the northeast to block it. All the good stuff surges into Kansas, north of the instability, and we get this disconnect between kinematics and thermodynamics. I'd like to see something suppress heights over the GL and NE a little more.

Looks more like an environment for an MCS / squall line by late Tuesday afternoon

[baroclinic_instability]

The main problem I see with Tuesday is the s/w breaks northward, with nothing to the northeast to block it. All the good stuff surges into Kansas, north of the instability, and we get this disconnect between kinematics and thermodynamics. I'd like to see something suppress heights over the GL and NE a little more.

Looks more like an environment for an MCS / squall line by late Tuesday afternoon

I certainly won't disagree with that. It certainly is not a perfect setup verbatim GFS, but Tue certainly looks like the most impressive day synoptically. But even in weaker solutions the kinematics will be there across the warm sector, although the 12z GFS would be too SSW/parallel to the dryline for long lived supercell activity. But I am always leery of getting to caught up in details of wave ejection day 5-6 lee of the Rockies....they never handle it well. Even a slightly southward/stronger PV ejection could dramatically alter the low level backing/mass fields and subsequent storm motions and storm modes with this scenario. 

[MichelleH]

What's the thoughts on this system as it moves eastward into Dixie Alley on Wed/Thurs? Thanks!

[brettjrob]

Disclaimer: I have a huge personal bias between Monday and Tuesday. The former I have a chance at chasing; the latter I have none at all. That being said, I still prefer Monday for overall chase quality as of now, but I admit there's a bit of a trend that could change that. Anyone who's chased much will tell you that when a Plains setup is straddling days, the famed "day before the day" has a knack for pulling out the best-quality storms and tornadoes, even if the second day is still significant somewhere.

 

Basically, Monday all comes down to initiation and the cap. There's increasing agreement that significant lee cyclogenesis and backing of low-level winds will occur in time to yield favorable hodographs along the dryline by Monday afternoon/evening, but forcing is subtle and height tendencies are ~neutral, casting doubt on the ability of updrafts to penetrate the bottom of the EML. Some of these same questions plagued April 14 last year, though the trough axis certainly had progressed more for that event and H5 heights did fall during the day in the region with storms. Regardless, if a setup is going to have one glaring concern, I always prefer it to be the cap rather than instability or shear quality.

[It's Always Sunny]

From what I've looked at I'm now leaning towards Tuesday as well for Oklahoma. Nice dry line/cold front set up with dews in the 70's Tuesday afternoon.

[OKpowdah]

From what I've looked at I'm now leaning towards Tuesday as well for Oklahoma. Nice dry line/cold front set up with dews in the 70's Tuesday afternoon.

I wouldn't go quite as far as 70s.....

[patrick7032]

Looking at point soundings at work...and conferring with others there...our basic thoughts are for a few discrete supercells to form along the intensifying dryline Moday afternoon and evening. Like brett said...upper dynamics/ascent are lagging behind. However...the 1.5 PV analomy surface shows an elongated piece of energy crossing the Red River Valley at 00z. This may help from an ascent point of view...if it verifies. Tuesday still looks good. As on Monday...strong low level shear will promote supercell development...but backing winds above 700mb makes us believe the discrete supercell window will be short lived as the profiles would favor a QLCS forming with embedded supercells. With the energy fueling this system having left the Asain Coast yesterday...and it not forecast to come ashore along the west coast until 00z Monday...I imagine things will perhaps slightly but potentially significantly change once the system is sampled by the UA network.

[baroclinic_instability]

Disclaimer: I have a huge personal bias between Monday and Tuesday. The former I have a chance at chasing; the latter I have none at all. That being said, I still prefer Monday for overall chase quality as of now, but I admit there's a bit of a trend that could change that. Anyone who's chased much will tell you that when a Plains setup is straddling days, the famed "day before the day" has a knack for pulling out the best-quality storms and tornadoes, even if the second day is still significant somewhere.

 

Basically, Monday all comes down to initiation and the cap. There's increasing agreement that significant lee cyclogenesis and backing of low-level winds will occur in time to yield favorable hodographs along the dryline by Monday afternoon/evening, but forcing is subtle and height tendencies are ~neutral, casting doubt on the ability of updrafts to penetrate the bottom of the EML. Some of these same questions plagued April 14 last year, though the trough axis certainly had progressed more for that event and H5 heights did fall during the day in the region with storms. Regardless, if a setup is going to have one glaring concern, I always prefer it to be the cap rather than instability or shear quality.

00z GFS came in a bit faster with the upper trough for Monday...and overspreads more subtle DCVA/ height falls east than the 12z run was progging. Still doesn't show much in the way of initiation, but warm sector soundings depict little to no leftover EML.

[brettjrob]

00z GFS came in a bit faster with the upper trough for Monday...and overspreads more subtle DCVA/ height falls east than the 12z run was progging. Still doesn't show much in the way of initiation, but warm sector soundings depict little to no leftover EML.

 

An absolute powderkeg along the dryline with the current model consensus. In broad terms, these questionable capping events are how you end up with dryline days like Arnett/Greensburg (5/4/07). One can find several such explosive cases where global and mesoscale models were stingy on QPF for the most part leading up. Of course, there are plenty more cases where the paltry QPF turns out to be warranted and it cap busts. Regardless, the ceiling of potential for Monday is incredibly high for so early in the spring in this region.

 

GFS, GGEM and UKMET are remarkably similar at H5 and the surface at 96 hrs. A 987 sfc low centered over the CO/KS border. Textbook stuff.

[David Reimer]

FWIW, the 0Z GFS precipitation parameters do show indications of convection just west of Interstate 35 in Central Oklahoma by late afternoon on Monday.

[andyhb]

FWIW, the 0Z GFS precipitation parameters do show indications of convection just west of Interstate 35 in Central Oklahoma. 

 

The 00z OKC sounding had a 0-1 km EHI of 6.6 along with MLLCL heights below 1000 m with a classic sickle shaped hodograph waiting for anything that can initiate.

[LocoAko]

The 00z OKC sounding had a 0-1 km EHI of 6.6 along with MLLCL heights below 1000 m with a classic sickle shaped hodograph waiting for anything that can initiate.

 

I'm seeing 7.7 EHI for OKC (not that it really even matters at this point). Nasty stuff. 

 

[andyhb]

I'm seeing 7.7 EHI for OKC (not that it really even matters at this point). Nasty stuff. 

 

SKT_GFS__KOKC.png

 

I was just referring to the 0-1 km layer, which is to the right of the MLLCL.

 

Regardless, that is a pretty classic Plains significant tornado sounding, assuming initiation of course.

[Stebo]

 

 

DAY 4-8 CONVECTIVE OUTLOOK     

NWS STORM PREDICTION CENTER NORMAN OK    0354 AM CDT FRI APR 05 2013       

VALID 081200Z - 131200Z       

 

...DISCUSSION...   

...SEVERE WEATHER APPEARS LIKELY EARLY NEXT WEEK FROM THE CNTRL/SRN    PLAINS TO THE MID/LOWER MS VALLEY...      

 

  WHILE RICH GULF MOISTURE HAS BECOME CONFINED TO THE SWRN PORTION OF    THE BASIN IN THE WAKE OF A COLD FRONT THAT HAS REACHED THE YUCATAN    PENINSULA...AIR MASS MODIFICATION WILL OCCUR THIS WEEKEND AND    ESPECIALLY EARLY NEXT WEEK AHEAD OF AN AMPLIFIED UPPER-LEVEL TROUGH    OVER THE WEST. THE WRN TROUGH WILL EJECT INTO THE CNTRL CONUS BY    MID-WEEK AS A POTENT MID-LEVEL JET STREAK ROUNDS THE BASE OF THE    TROUGH. BY THIS TIME...SEASONABLY RICH GULF MOISTURE WILL BE PRESENT    ALONG THE DRYLINE AND EVENTUAL COLD FRONT THAT WILL PUSH EWD TOWARDS    THE MS VALLEY. WITH SEVERAL DAYS OF MOISTURE RETURN OCCURRING    BENEATH A STOUT EML...A MODERATE TO STRONGLY UNSTABLE AIR MASS WILL    LIKELY DEVELOP.      

 

DESPITE AVERAGE DIFFERENCES BETWEEN MODELS WITH REGARD TO    TIMING/PLACEMENT OF THE KEY SYNOPTIC FEATURES BY D5-6...INCREASING    FORCING FOR ASCENT ALONG WITH STEEP MID-LEVEL LAPSE RATES AND    STRENGTHENING DEEP-LAYER SHEAR SHOULD RENDER A SETUP FAVORABLE FOR    POTENTIALLY SIGNIFICANT AND WIDESPREAD SEVERE WEATHER DURING THIS    TIME FRAME. GREATEST DISCRETE SUPERCELL POTENTIAL WITH PRIMARILY    VERY LARGE HAIL AND TORNADOES SHOULD EXIST ON D5 AHEAD OF THE    DRYLINE. AS A PACIFIC COLD FRONT MERGES WITH THE DRYLINE...AN    EXTENSIVE SQUALL LINE SHOULD FORM AND DEVELOP EWD TOWARDS THE MS    VALLEY WITH PRIMARY RISKS BECOMING DAMAGING WINDS AND TORNADOES ON    D6. PRIOR TO D5...A LOCALIZED BUT ENHANCED RISK FOR VERY LARGE    HAIL/FEW TORNADOES SHOULD EXIST NEAR THE DRYLINE/WARM FRONT    INTERSECTION EXPECTED TO BE INVOF NWRN KS ON MON EVENING.

 

[It's Always Sunny]

I wouldn't go quite as far as 70s.....

There was a nice little weenie pocket on the GFS FWIW. There's room for hope. Otherwise, widespread 60's.

[It's Always Sunny]

I certainly won't disagree with that. It certainly is not a perfect setup verbatim GFS, but Tue certainly looks like the most impressive day synoptically. But even in weaker solutions the kinematics will be there across the warm sector, although the 12z GFS would be too SSW/parallel to the dryline for long lived supercell activity. But I am always leery of getting to caught up in details of wave ejection day 5-6 lee of the Rockies....they never handle it well. Even a slightly southward/stronger PV ejection could dramatically alter the low level backing/mass fields and subsequent storm motions and storm modes with this scenario. 

Winds actually veer more west on 00Z GFS which would aid the supercell duration hopefully in central Texas. SFC-500 mb bulk shear is pretty decent too at 50-60 kt.

[CoastalWx]

Man, all systems go on the euro for eastern KS down towards OKC Tuesday evening.

[CoastalWx]

The only thing I'm not a huge fan of, is the lack of a good concise s/w really kicking out east from the Rockies..but may not matter too much. If anything..may favor KS.