Multi-day tornado outbreak likely (April 9-11)

[TropicalAnalystwx13]

After our [near] historic dip of the Arctic Oscillation, things sure have turned around...quickly. We're well on our way to the positive phase of the AO, and accordingly, the chances for severe weather are already going up.

More specifically...if the model guidance continues to hold true, a multi-day severe weather and tornado outbreak starting in Texas/Oklahoma and continuing eastward into North Carolina-Florida is likely.

Monday and Tuesday (April 10/11) in particular seem particularly dangerous across Texas and Oklahoma.

SPC's take:

MODELS INDICATE AN UPPER TROUGH DEVELOPING OVER THE WRN STATES
BEGINNING ON SUN/D5 AS A POWERFUL JET DIVES SEWD ALONG THE PACIFIC
COAST. HOWEVER...THE SPEED AT WHICH THE LEADING SHORTWAVE EJECTS
INTO THE PLAINS IS IN QUESTION...WITH MUCH MODEL VARIABILITY.

THE GFS IS SLOWER AND FARTHER S WITH THE TROUGH...AND INDICATES A
COOLER AND MORE MOIST BOUNDARY LAYER WITH RECEDING DRYLINE MON
EVENING. THE ECMWF RAPIDLY EJECTS A SHORTWAVE ACROSS THE CNTRL AND
SRN PLAINS AND SHOWS ONLY A NARROW RIBBON OF LOWER 60S F DEWPOINTS
AHEAD OF A DRYLINE. ASIDE FROM TIMING OF THE TROUGH...MOISTURE
QUALITY WILL DETERMINE STORM SEVERITY AS SHEAR IS LIKELY TO BE
FAVORABLE REGARDLESS. THEREFORE...WHILE SEVERE WEATHER IS LIKELY
SOMEWHERE FROM KS INTO OK AND TX ON MON/D6...TIMING AND EXACT
LOCATION IS TOO UNPREDICTABLE FOR A SEVERE AREA.

FARTHER E ON TUE/D7...MODEL DIFFERENCES PERSIST...BUT LOW LEVEL
MOISTURE SHOULD BE MORE ROBUST ACROSS THE ARKLATEX/LOWER MS VALLEY
REGION. THIS SUGGESTS THE POTENTIAL FOR SIGNIFICANT SEVERE WHERE
FORCING AND SHEAR LINE UP...BUT PREDICTABILITY IS CURRENTLY TOO LOW
TO DELINEATE A SPECIFIC AREA. THE SEVERE THREAT MAY PERSIST INTO
WED/D8 FARTHER E ACROSS THE GULF COAST STATES AND TN/OH VALLEYS
DEPENDING ON WHERE THE TROUGH IS.

[Texas Snowman]

Monday and Tuesday (April 10/11) in particular seem particularly dangerous across Texas and Oklahoma.

Someone on the Texas Spring thread mentioned that some are comparing Monday to the April 10, 1979 Red River outbreak that produced the violent killer tornado in Wichita Falls, Tx (a mile and a half wide multi-vortex F4 that produced 42 deaths) and in nearby Vernon, Tx (11 deaths from a large wedge) and Lawton, Okla. (three deaths).

In reference to the idea that the potential severe weather setup for early next week resembles the one from April 1979, I came across this interesting tweet earlier today from the Fort Worth NWS:

“@NWSFortWorth: The high at DFW today was 55F at 1:39 am CDT. This ties the record lowest high temperature for Apr 3, set previously in 1979. #dfwwx #txwx”

[TropicalAnalystwx13]

I should make a correction...I meant Monday (April 10) and Wednesday (April 12), not Tuesday (April 11).



Ouch.

[cycloneye]

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

[apocalypt-flyer]

I was about to start a thread with regards to this earlier but was hesistant considering it wasn't particularly set in stone yet a few days ago. Would be great if a mod or admin could include the dates in the title.

Yeah, looks like the start to the peak of the season might be quite explosive.

[TwisterFanatic]

Ugh. Haven't been able to keep up with the weather. We've already had a Tornado here in Sallisaw this year.

[TropicalAnalystwx13]

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.

..GRAMS.. 04/05/2013

[apocalypt-flyer]

Had a look at the 06 gfs and then the updated nws prediction. OUCH. That doesn't look fun, especially on Tuesday.

[Ntxw]

I still have some doubt and question about instability. The gulf has yet to warm up and feed the warm front with good 60-70+ dewpoints. It's been cool in most of these areas and warm over cool is not a strong signal for major outbreaks. Kansas and Oklahoma into Arkansas stand a good chance briefly before the cold front sends a linear line and cleans everything out. It will depend on initiation on the dry line, but there really isn't a massive warm air mass/front ahead of it to keep those storms going for long track tornadoes. This is likely the first widespread severe weather event with some tornadoes, something not unusual for spring, I wouldn't quite hype it up to anything historic yet.

[CrazyC83]

Still a lot of uncertainty, but many signs point to a major outbreak, especially Tuesday into Tuesday night.

[TwisterFanatic]

I don't think instability will be a question come Tuesday. 4 days of flow off of the Gulf will result in 60+ dewpoints nearing Nebraska.

[Ntxw]

I don't think instability will be a question come Tuesday. 4 days of flow off of the Gulf will result in 60+ dewpoints nearing Nebraska.

There will be good dewpoints at various locations. But there is also a strong attending cold front that if it moves quickly will scour out anything that forms with a linear line of hail and wind. All will depend on the dry line initiation of super cells and if the air mass allows them to continue before the main line. Here is a good latest discussion from the SPC. I think I like the idea of western Oklahoma and western Kansas for such cells then merge east with the cold front in a squall line. Latest model guidance has trended into the more positive/neutral trough look (linear mode) than the classic negative tilt that is associated with major outbreaks for tornadoes.


DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0345 AM CDT SAT APR 06 2013

VALID 091200Z - 141200Z

...DISCUSSION...
MULTI-DAY SEVERE WEATHER EPISODE IS EXPECTED ACROSS PARTS OF THE
S-CNTRL AND PERHAPS EVENTUALLY THE SERN CONUS IN ASSOCIATION WITH AN
UPPER-LEVEL TROUGH PROGRESSING EWD FROM THE WRN CONUS. PRECEDING
DAYS OF SLY RETURN FLOW OF A MODIFIED GULF AIR MASS BENEATH A STOUT
EML SHOULD YIELD AT LEAST MODERATELY UNSTABLE CONDITIONS AHEAD OF
THE PLAINS DRYLINE BEING OVERTAKEN BY A COLD FRONT THAT WILL
PROGRESS EWD DURING THE PERIOD. WITH STRENGTHENING OF MID-LEVEL
SWLYS AS THE SPEED MAX EJECTS FROM THE BASE OF THE WRN CONUS
TROUGH...SETUP SHOULD BE FAVORABLE FOR SUPERCELLS AND AN EVENTUAL
SQUALL LINE WITH ALL MODES OF SEVERE /SOME SIGNIFICANT/ PROBABLE
DURING D4-5. STILL...CONFIDENCE IS ONLY AVERAGE FOR HIGHLIGHTING
CORRIDORS OF ENHANCED COVERAGE PROBABILITIES /AOA 30 PERCENT/ AS
MODELS REMAIN MODERATELY DIVERGENT WITH TIMING OF THE KEY SYNOPTIC
FEATURES DURING THIS TIME FRAME. DISCREPANCIES WITH EVOLUTION OF THE
UPPER-LEVEL TROUGH AND ATTENDANT COLD FRONT BECOME EVEN GREATER BY
D6-7...WHERE SEVERE WEATHER AREAS COULD EVENTUALLY BE WARRANTED IN
PARTS OF THE SOUTHEAST.

[TropicalAnalystwx13]

The forecast has always been for this trough to be positively-tilted. Even in the very long range it was depicted as such.

My main concern for Monday is the strength of the cap. If it holds, there will be little storms, but if it doesn't, there could be some significant severe weather across western Kansas. As for Tuesday, that looks like the big day. Strong tornadoes, large hail, and damaging winds all appear possible.

[EF-5bigj]

So Tuesday is the big day then are we talking long tracked tornadoes?

[apocalypt-flyer]

There's a fair chance Tuesday could be quite severe BUT models are still disagreeing on timing and depending on that the NWS SPC is obviously hesisant about going too big on upgraded warnings too soon. Hence a SLIGHT for such a huge area.

[cheezyWXguy]

There's a fair chance Tuesday could be quite severe BUT models are still disagreeing on timing and depending on that the NWS SPC is obviously hesisant about going too big on upgraded warnings too soon. Hence a SLIGHT for such a huge area.

It does appear that there is still some uncertainty with this event, but a day 3 MDT is something that's really rare. Ive seen day 3 slight risks turn into day 1 high risks. As far as I've seen, only the worst outbreaks with very high certainty get anything above a slight risk all the way out at day 3. While this one is likely to be a big severe weather event, I don't know if we were ever looking at something of that level here.

[EF-5bigj]

A lot of unknown's at this point will the CAPE break? I guess we will know more on Monday

[apocalypt-flyer]

CAPE's the Convective Available energy.

If anything breaks it'll be the cap.

[EF-5bigj]

I agree with that we will learn more on Monday im guessing.

[TexasF6]

Local met, a newbie on keye 42 Austin, used the term superstorm in description of this weeks storm. What does he mean SUPERSTORM?!!! granted, I trust our forum mets more than this kid, it should be noted.