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andyhb

April 26th-30th, 2014 Major Tornado Outbreak

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My best guess is still that tomorrow will be a letdown, and I'm fairly surprised (even in this day and age) to see so many northern/Midwest chasers flocking down here, considering the ideal chase target Sunday could be well back to the NE and early in the day.

 

The GFS is the only model showing verbatim what looks to be a potent tornadic supercell environment prior to 01-02z; it has much richer BL moisture and much more backed sfc winds. Looking back at this past Wed, the NAM definitely underforecast low-level backing in a somewhat similar situation, so a GFS-leaning compromise on helicity is probably warranted. As usual, though, I think moisture will be the downfall of any chaser-friendly activity tomorrow. The NAM-4km depicts very well, on a 100 mb mean qr plot, how much better moisture surges into SW OK just after sunset. It initiates a supercell in NW TX between 01z-02z, such that the last twilight would be fading just as things potentially get interesting.

 

Between 00z RAOBS, current sfc obs and the drought factor, I just can't justify buying into the more optimistic side of moisture guidance. I believe pretty strongly (but not with certainty) that the "real" moisture will surge in at dusk or even an hour after that, with any CI likely awaiting it.

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My best guess is still that tomorrow will be a letdown, and I'm fairly surprised (even in this day and age) to see so many northern/Midwest chasers flocking down here, considering the ideal chase target Sunday could be well back to the NE and early in the day.

 

The GFS is the only model showing verbatim what looks to be a potent tornadic supercell environment prior to 01-02z; it has much richer BL moisture and much more backed sfc winds. Looking back at this past Wed, the NAM definitely underforecast low-level backing in a somewhat similar situation, so a GFS-leaning compromise on helicity is probably warranted. As usual, though, I think moisture will be the downfall of any chaser-friendly activity tomorrow. The NAM-4km depicts very well, on a 100 mb mean qr plot, how much better moisture surges into SW OK just after sunset. It initiates a supercell in NW TX between 01z-02z, such that the last twilight would be fading just as things potentially get interesting.

 

Between 00z RAOBS, current sfc obs and the drought factor, I just can't justify buying into the more optimistic side of moisture guidance. I believe pretty strongly (but not with certainty) that the "real" moisture will surge in at dusk or even an hour after that, with any CI likely awaiting it.

 

Based on how the season has gone you're assuming most chasers wouldn't mind chasing after dark. I agree regarding the flock of folks coming down from the north but if they're continuing to Dixie Alley afterwards I can understand it. 

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The 0z RGEM has an impressive look across W OK and N TX saturday evening. The LLJ is coming in perpidicular to the warm front at 40-60kts while surface winds are backed across NE Tx, E NE, KS and OK. Sfc dewpoint max is in the low to mid sixties across S OK and convection appears to get going just after sundown. EC's svr param package is listed below:

post-7879-0-32516800-1398490907_thumb.jp

post-7879-0-58980300-1398490932_thumb.jp

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Full text/prob map for Sunday.

 

cEqwhfJ.gif

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT SAT APR 26 2014

VALID 271200Z - 281200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER AR...FAR NRN LA/NERN TX/ERN
OK/SWRN MO...

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CNTRL
CONUS...

...SUMMARY...
AN OUTBREAK OF SEVERE STORMS IS POSSIBLE ON SUNDAY ACROSS PARTS OF
THE CENTRAL STATES WITH LARGE HAIL...DAMAGING WINDS...AND TORNADOES.
THE GREATEST RISK FOR STRONG TORNADOES APPEARS CENTERED FROM THE
ARK-LA-TEX TO THE LOWER MISSISSIPPI VALLEY.

...SYNOPSIS...
A VIGOROUS SHORTWAVE TROUGH CENTERED IN THE LEE OF THE SRN ROCKIES
AT 12Z/SUN WILL SUBSTANTIALLY SLOW AS IT PROGRESSES TOWARDS NEB. AN
ATTENDANT MID-LEVEL JET /AOA 50 KT AT 500 MB/ WILL
PERSIST FROM THE DESERT SW...CURLING NWD FROM THE RED RIVER TO THE
MO VALLEY. AT THE SURFACE...A CYCLONE SHOULD DRIFT EWD OVER THE
CNTRL PLAINS WITH A WARM FRONT ARCING EWD ACROSS THE CORN BELT TO
THE LOWER OH VALLEY. A DRYLINE/WEAKENING PACIFIC COLD FRONT SHOULD
REACH ERN KS/OK INTO DEEP S TX IN THE LATE AFTERNOON.

...MO VALLEY TO THE WRN GULF COAST...
OVERALL SCENARIO HAS NOT CHANGED MUCH FROM PREVIOUS OUTLOOK WITH
GRADUALLY INCREASING CONFIDENCE IN A POSSIBLE OUTBREAK AMIDST
CONTINUED LIMITING FACTORS.

THE WARM SECTOR WILL BE INCREASINGLY BROAD/MOIST BENEATH AN EML WITH
LOWER 60S SURFACE DEW POINTS BECOMING ESTABLISHED NEAR THE WARM
FRONT AND MIDDLE TO UPPER 60S INTO THE LOWER/MID-MS VALLEYS AND
ARKLATEX BY EARLY EVENING SUN. THIS COMBINED WITH INITIALLY STEEP
MID-LEVEL LAPSE RATES AND MODERATE TO STRONG DEEP-LAYER SHEAR WILL
SUPPORT AN EXPANSIVE AREA OF ORGANIZED SEVERE STORMS.

AREAS OF CONVECTION SHOULD BE ONGOING AT 12Z/SUN FROM PARTS OF IA TO
OK. ALTHOUGH THE BULK THIS ACTIVITY SHOULD BE ELEVATED...IT SHOULD
TRANSITION TO BECOMING SURFACE-BASED AS DOWNSTREAM DIURNAL HEATING
ENSUES. CLUSTERS OF ISOLATED TO SCATTERED SEVERE STORMS WILL BE
POSSIBLE AS THIS LEAD CONVECTION LIKELY DEVELOPS EWD.

THE MOST INTENSE SEVERE STORMS SHOULD DEVELOP ALONG THE DRYLINE AND
REMNANT CONVECTIVE OUTFLOWS IN THE WARM SECTOR DURING THE AFTERNOON.
IN THE WAKE OF EARLY DAY CONVECTION...THERE REMAINS SUBSTANTIAL
UNCERTAINTY IN THE DEGREE OF DESTABILIZATION /ESPECIALLY WITH NRN
EXTENT/. NAM/GFS GUIDANCE IS INSISTENT ON DEVELOPING AT LEAST
MODERATE BUOYANCY WITH MLCAPE AOA 1000 J/KG INTO NERN KS AS
INSOLATION OCCURS ALONG THE DRYLINE AMIDST STEEP MID-LEVEL LAPSE
RATES. IF THIS WERE TO OCCUR...ROBUST MID-LEVEL DCVA WOULD FOSTER
SCATTERED STORMS FORMING BY MID-AFTERNOON INVOF KS/MO BORDER.
ALTHOUGH DEEP-LAYER WIND PROFILES SHOULD BE LARGELY MERIDIONAL
HERE...BACKED LOW-LEVEL WINDS WOULD AID IN SUFFICIENT CURVATURE TO
THE LOW-LEVEL HODOGRAPH FOR SUPERCELLS. LARGE HAIL /SOME
SIGNIFICANT/ AND AT LEAST A FEW TORNADOES APPEAR POSSIBLE. PARTS OF
THIS REGION MAY BE UPGRADED TO MODERATE RISK IN LATER OUTLOOKS IF IT
APPEARS STABILIZING EFFECTS OF EARLY DAY CONVECTION WILL NOT BE TOO
DETRIMENTAL TO THE AFTERNOON THREAT.


FARTHER S...A MORE VOLATILE THERMODYNAMIC ENVIRONMENT SHOULD EXIST S
OF ANY EARLY DAY CONVECTION /INVOF THE ARKLATEX/. WITH SURFACE
TEMPERATURES HEATING INTO THE 80S/90S ALONG/W OF THE DRYLINE IN
TX...MLCAPE SHOULD REACH 2500 J/KG JUST AHEAD OF IT. HODOGRAPHS
APPEAR QUITE CONDUCIVE TO SUPERCELLS...CAPABLE OF PRODUCING VERY
LARGE HAIL AND STRONG TORNADOES. NAM FORECAST SOUNDINGS REMAIN THE
MOST ROBUST WITH THE CO-LOCATION OF STRONG BUOYANCY AND LARGE
CURVING HODOGRAPHS. OTHER GUIDANCE SUGGESTS STRONGER KINEMATIC
FIELDS WILL BE DISPLACED FARTHER EAST /CENTERED OVER THE LOWER MS
VALLEY/. BUT WITH THE DRYLINE STALLING OR SLOWLY MOVING ACROSS NERN
TX SUN NIGHT...TRAINING CONVECTIVE CLUSTERS WITH EMBEDDED SUPERCELLS
MAY CONTINUE WELL INTO THE NIGHT. PARTS OF THIS REGION MAY WARRANT
AN UPGRADE TO HIGH RISK IN LATER OUTLOOKS.


..GRAMS.. 04/26/2014

 

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Monday is yet again a major outbreak on the Euro with a broad 50+ kt LLJ, backed SSE surface winds and broad upper level trough along with a well timed vort max (plentiful moisture/instability of course). Tuesday is also looking potent as the strongest impulse in the trough rounds the base and slams into the SE, I'm not sure the last time I've seen a model showing this level of consistency with such a dangerous severe weather setup for more than one day.

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Monday is yet again a major outbreak on the Euro with a broad 50+ kt LLJ, backed SSE surface winds and broad upper level trough along with a well timed vort max (plentiful moisture/instability of course). Tuesday is also looking potent as the strongest impulse in the trough rounds the base and slams into the SE, I'm not sure the last time I've seen a model showing this level of consistency with such a dangerous severe weather setup for more than one day.

 

How many total tornadoes are you thinking from Saturday evening until Tuesday in total? We should have a game to see who predicts the closest.

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I'm honestly surprised at how dull the Day 1 outlook sounds in regards to the potential for after-dark supercells across NW TX/SW OK. 

 

It seems like they acknowledge decent probabilities that storms will develop in that window, but don't believe the tornado threat is significant. I tend to agree.

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Monday is yet again a major outbreak on the Euro with a broad 50+ kt LLJ, backed SSE surface winds and broad upper level trough along with a well timed vort max (plentiful moisture/instability of course). Tuesday is also looking potent as the strongest impulse in the trough rounds the base and slams into the SE, I'm not sure the last time I've seen a model showing this level of consistency with such a dangerous severe weather setup for more than one day.

 

The 00z UKMET incidentally also shows the same vorticity lobe swinging around the base of the trough during the day Monday, resulting in the strengthening of the low-level jet.  The GFS has slowly trended towards showing this subtle vorticity lobe, but still hasn't caught up with the ECMWF/UKMET camp.  I suspect it will as we get closer to the event.

Taking Sunday and Monday together, I think that this is the most substantial large-scale tornado outbreak threat that we have seen since 2011.  This is definitely not a garden variety spring tornado setup we're dealing with here...

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It seems like they acknowledge decent probabilities that storms will develop in that window, but don't believe the tornado threat is significant. I tend to agree.

 

I agree the tornado threat shouldn't be significant but also that there is the potential for some mischief after dark. Something that could exceed "an isolated tornado". Time will tell but the forecaster sounded like he had a bias that nothing major can really happen after dark in the South Plains. Just my take on it especially compared to the 1730Z Day 2 yesterday. It doesn't really matter since the OKC media will make up their own outlooks anyway haha

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The 00z UKMET incidentally also shows the same vorticity lobe swinging around the base of the trough during the day Monday, resulting in the strengthening of the low-level jet.  The GFS has slowly trended towards showing this subtle vorticity lobe, but still hasn't caught up with the ECMWF/UKMET camp.  I suspect it will as we get closer to the event.

Taking Sunday and Monday together, I think that this is the most substantial large-scale tornado outbreak threat that we have seen since 2011.  This is definitely not a garden variety spring tornado setup we're dealing with here...

 

It's encompassing such a large area too. Scary looking on the models. 

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It's encompassing such a large area too. Scary looking on the models. 

 

I actually think one of the worst parts is that areas that get hit on Monday could take one on the chin on Tuesday as well.

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I actually think one of the worst parts is that areas that get hit on Monday could also take one on the chin on Tuesday as well.

 

I unfortunately won't be able to get out to chase much because of work constraints. But I still think we here in SC KY are right in the mix..

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I actually think one of the worst parts is that areas that get hit on Monday could take one on the chin on Tuesday as well.

This. I think for MS, AL and GA and probably TN too Tuesday could have even higher end potential than Monday/Monday night. On Tuesday the warm sector looks like it likely have time to recover from the overnight convection; h5 flow further strengthens with the jet core at jaw dropping 90-100 kt over western TN and and northern MS at 00z 4/30, LLJ remains strong and the Euro has consistently been hitting secondary low development over the TN valley. Western half of AL featuring over 2000 j/kg of CAPE at 00z 4/30 on the new Euro. Volatile setup and scary to think the results if Sunday through Tuesday all live up to their potential.

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Second time ever that two consecutive day three moderates have been issued.

 

And frankly I think that could become three straight tomorrow night.

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XpCOgWF.gif

   DAY 3 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0235 AM CDT SAT APR 26 2014
 
   VALID 281200Z - 291200Z
 
   ...THERE IS A MDT RISK OF SVR TSTMS FOR NRN/CNTRL MS...WRN TN...FAR
   NERN LA/ERN AR/NWRN AL/SWRN KY...
 
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MIDWEST TO THE CNTRL
   GULF COAST...
 
   ...SUMMARY...
   AN OUTBREAK OF SEVERE STORMS IS POSSIBLE ON MONDAY ACROSS PARTS OF
   THE LOWER MISSISSIPPI VALLEY AND MID-SOUTH. LARGE HAIL...DAMAGING
   WINDS...AND TORNADOES ARE EXPECTED.
 
   ...SYNOPSIS...
   BROAD UPPER-LEVEL TROUGH WILL REMAIN ANCHORED OVER THE CNTRL CONUS
   WITH AN INTENSE MID-LEVEL SPEED MAX /AOA 80 KT AT 500 MB/ ROTATING
   THROUGH THE BASE OF THE TROUGH AND EJECTING ACROSS PARTS OF THE
   MID-SOUTH AND CONFLUENCE OF MS/OH RIVERS BY MON AFTERNOON. SURFACE
   CYCLONE SHOULD REMAIN CENTERED OVER THE MO VALLEY...WITH A WARM
   FRONT DRAPED EWD OVER THE MIDWEST. COMPOSITE DRYLINE/PACIFIC COLD
   FRONT SHOULD EXTEND FROM THE LOWER MO VALLEY TO TX GULF COAST ON MON
   AFTERNOON.
 
   ...MIDWEST TO CNTRL GULF COAST...
   A PLUME OF 60S SURFACE DEW POINTS WILL BE ESTABLISHED FROM THE WARM
   FRONT IN THE MIDWEST S/SWWD TO THE WRN/CNTRL GULF COAST AND PERSIST
   AMIDST STRONG LOW-LEVEL S/SWLYS. ALTHOUGH CONVECTION WILL LIKELY BE
   ONGOING AT 12Z/MON FROM PARTS OF THE MIDWEST TO MID-SOUTH...ROBUST
   DIURNAL HEATING SHOULD OCCUR IN CONVECTIVE-FREE AREAS TO SUPPORT AT
   LEAST MODERATE BUOYANCY OVER MUCH OF THE WARM SECTOR BY AFTERNOON.
   LOW/DEEP-LAYER SHEAR WILL BE QUITE STRONG OWING TO THE
   AFOREMENTIONED SPEED MAX. THIS CO-LOCATION WITH THE ESTABLISHED WARM
   SECTOR YIELDS A LARGE AREA OF ORGANIZED SEVERE POTENTIAL. 
 
   THE MOST CONCENTRATED CORRIDOR FOR HIGH-END SEVERE RISK APPEARS
   CENTERED OVER PARTS OF THE LOWER MS VALLEY TO MID-SOUTH. WIDESPREAD
   STORMS APPEAR PROBABLE DURING THE AFTERNOON...LIKELY EMANATING FROM
   REGENERATIVE CONVECTIVE CLUSTERS ALONG THE DRYLINE/CONVECTIVE
   OUTFLOWS. WITH EFFECTIVE SHEAR AOA 50 KT AND SURFACE DEW POINTS INTO
   THE MIDDLE TO UPPER 60S...SETUP COULD YIELD SEVERAL SUPERCELLS WITH
   STRONG TORNADOES AND LARGE HAIL...EVOLVING INTO BOWS AND WIDESPREAD
   DAMAGING WINDS.
 
   ..GRAMS.. 04/26/2014

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Thread has been moved here given the potential magnitude/areal coverage of this threat.  Make quality posts and try to avoid the one word/one liner/emoticon only stuff. 

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Have awakened just to check this outlook.  Very concerning for persons who experienced 4/27/11 and areas westward.   And thanks for moving the thread since this will probably become an historic outbreak.

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I keep saying that to myself, but I know better. I have only chased once in that area and it was a nightmare. I swore never again, and I've stuck to that so far. I just can't justify it with the **** road network, **** terrain and less than ideal storm motions for chasers. This just isn't worth it to me and a lot of other chasers. There will definitely be some out there chasing this though. I hope they stay safe.

 

If you stay south of Interstate 30 in Arkansas and south of US 70 in OK/TX, the terrain is pretty flat with periodically alternating woods and fields.  It's not the High Plains, but it isn't *awful* chasing territory.  You would have to be insane to chase in Arkansas north of I-30 though.  I'm sure there will be plenty of chasers up in those hills and I hope they stay safe; I won't be one of them.  If I go after this system I'll likely stick to a 50-mile radius around Texarkana.

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kq7Mm4n.gif

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0350 AM CDT SAT APR 26 2014

VALID 291200Z - 041200Z

...DISCUSSION...
THE MULTI-DAY SEVERE WEATHER EPISODE ASSOCIATED WITH THE PERSISTENT
UPPER-LEVEL TROUGH OVER THE CNTRL CONUS SHOULD CONTINUE INTO D4/TUE
AS THE LAST IN A SERIES OF INTENSE MID-LEVEL SPEED MAXIMA EJECTS
THROUGH THE BASE OF THE TROUGH. THIS SHOULD RESULT IN STRONG
KINEMATIC FIELDS OVERSPREADING A GULF WARM SECTOR CHARACTERIZED BY
60S SURFACE DEW POINTS. THE BREADTH OF THE WARM SECTOR WILL PROBABLY
BE CONFINED BY WIDESPREAD ANTECEDENT CONVECTION ON D3.

HOWEVER...GUIDANCE IS FAIRLY CONSISTENT WITH DIURNAL DESTABILIZATION
OCCURRING AHEAD OF THE PACIFIC COLD FRONT/EFFECTIVE DRYLINE. THE
CAPE/SHEAR COMBINATION APPEARS FAVORABLE FOR HIGHER-END SEVERE RISK
FOCUSED FROM THE CNTRL OH VALLEY TO THE CNTRL GULF COAST.


OVERALL KINEMATIC FIELDS SHOULD BE IN A WEAKENING STATE ON D5/WED
AND BECOME INCREASINGLY DISPLACED FROM GREATER BUOYANCY AS THE FRONT
ACCELERATES EWD. NEVERTHELESS...ORGANIZED SEVERE POTENTIAL IS
EVIDENT FROM PARTS OF THE CNTRL APPALACHIANS AND MID-ATLANTIC SWD TO
THE SOUTHEAST...LIKELY YIELDING EVENTUAL SLIGHT RISK DELINEATION.

..GRAMS.. 04/26/2014

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With respect to this evening, the high res short term models are virtually in agreement with little to nothing firing before 00z Sunday. While at least somewhat of a nocturnal threat exists, the setup from Sunday into Tuesday is exceedingly more impressive.

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Closing in on ICT, with a view of the sun rising behind the elevated convection to our east...

y7y2ujem.jpg

uqy8yvy6.jpg

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You should have seen the sunrise on the east side of that elevated convection. The sky was absolutely on fire. 

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Seems like the "multi-day significant severe event" the SPC mentioned days ago is coming to fruition... With back-to-back-to-back D3 MDTS likely, and possibly three straight big tornado days including a chance for three HIGH risks despite how improbable that sounds its a real possibility. Funny how everybody thought this weekend was a bust a few days ago, myself included, albeit todays threat is underwhelming and evening convection COULD be detremental to tomorrows threat. Same works with monday/tuesday... With mondays convection being potentially detremental to tuesday. Nonetheless a significant severe weather outbreak appears probable attm

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