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andyhb

April 26th-30th, 2014 Major Tornado Outbreak

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The 00z Euro once again shows a major tornado outbreak for the Monday event, with a strong 850 mb jet of over 50 knots.  This is about the 6th or so consecutive run that has shown this intensification of the LLJ on Monday in response to a subtle vorticity maximum and upper jet rounding the base of the broad trough.  The GFS has been much weaker with this LLJ feature, although it does try to intensify the LLJ somewhat on Tuesday.

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The 00z Euro once again shows a major tornado outbreak for the Monday event, with a strong 850 mb jet of over 50 knots.  This is about the 6th or so consecutive run that has shown this intensification of the LLJ on Monday in response to a subtle vorticity maximum and upper jet rounding the base of the broad trough.  The GFS has been much weaker with this LLJ feature, although it does try to intensify the LLJ somewhat on Tuesday.

1500-2000 J/kg of CAPE w/850 mb flow ~200° @ 50-55 kt at 06z Tues along an axis from HSV/DCU to TCL/BHM.

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I don't know if it has been discussed with the mods but considering this is a multi day and multi regional event. I think it might be a good idea to take this thread and put it in the main forum, we can use this thread as a collection for the entire event so we don't have to go to multiple subforums especially for Sunday/Monday/Tuesday.

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Day 3 moderate for Sunday...wow.

This appears to be the 11th day 3 moderate risk issued, using the current 45% threshold.

Previous day 3 moderates by issued for dates:

4/24/2007

6/6/2007, 6/7/2007

10/18/2007* added thanks to Hoosier

4/10/2008

5/13/2009

4/10/2011

4/27/2011

4/14/2012

4/17/2013

Based off of info from http://www.pmarshwx.com/blog/2012/04/12/spc-day-3-moderates-in-context-what-do-they-become/

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zjnDrDP.gif

   DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0351 AM CDT FRI APR 25 2014
 
   VALID 281200Z - 031200Z
 
   ...DISCUSSION...
   ...MULTI-DAY SEVERE EPISODE SHOULD CONTINUE INTO AT LEAST TUESDAY
   FROM THE OH VALLEY TO THE CNTRL GULF COAST. POTENTIAL EXISTS FOR A
   SEVERE WEATHER OUTBREAK INCLUDING STRONG TORNADOES...
 
   ACTIVE SEVERE WEATHER PATTERN WILL PERSIST WITH A BROAD UPPER-LEVEL
   TROUGH CENTERED OVER THE CNTRL CONUS. ECMWF/GFS/UKMET/CMC ARE RATHER
   CONSISTENT WITH THE EVOLUTION OF INTENSE MID-LEVEL SPEED MAXIMA
   ROTATING THROUGH THE BASE OF THE TROUGH INTO D5/TUE. THESE WINDS
   WILL OVERSPREAD PARTS OF A BROAD WARM/MOIST SECTOR CHARACTERIZED BY
   60S SURFACE DEW POINTS. DESPITE MULTIPLE DAYS OF EXTENSIVE WARM
   SECTOR CONVECTION...DIURNAL HEATING COUPLED WITH W/SWLYS IN THE
   MID-LEVELS SHOULD RECHARGE/STEEPEN LAPSE RATES...POTENTIALLY
   YIELDING MODERATE TO STRONG INSTABILITY EACH AFTERNOON. OF THE TWO
   DAYS HIGHLIGHTED...D5/TUE APPEARS TO HAVE SLIGHTLY GREATER OUTBREAK
   POTENTIAL WITH A 90+ KT 500-MB JET EJECTING OUT OF THE BASE OF THE
   TROUGH.
 
   ..GRAMS.. 04/25/2014

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I'm new here, but if the dry line stalls a bit west of I-35 could this possibly cause trouble for DFW? 

 

If that were to happen then I would say yes, it could possibly cause issues for the DFW area.

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Is there tornado potential in southeast Nebraska at 00Z on Sunday or am I just seeing things...?

there is a possible cold core setup with this however the wind profiles look veer-back-veer which usually doesn't favor well for tornadogenesis. the better chance of strong tornadoes is down south ahead of dryline. most chasers are avoiding this because of the awful terrain

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Have to take this with a grain of salt obviously (being the NAM), but the significant tornado parameter pegs at 10+ around the Arklatex area overnight Sunday into early Monday:
post-533-0-17573800-1398437137_thumb.gif

Edit: The parameters overall look more impressive closer to 00z, as the winds are more backed near the surface. The 06z forecast soundings show considerably less directional shear in the boundary layer.

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there is a possible cold core setup with this however the wind profiles look veer-back-veer which usually doesn't favor well for tornadogenesis. the better chance of strong tornadoes is down south ahead of dryline. most chasers are avoiding this because of the awful terrain

You're talking for Saturday night right?  Because that's the day I'm asking about.

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there is a possible cold core setup with this however the wind profiles look veer-back-veer which usually doesn't favor well for tornadogenesis. the better chance of strong tornadoes is down south ahead of dryline. most chasers are avoiding this because of the awful terrain

 

He is talking about Saturday evening

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He is talking about Saturday evening

oh early morning brain...lol...forgot 0z sun is sat night. but yea if moisture return is going to be as paltry as they are saying for Saturday I don't see the northern play turning out very well. with the jet influence coming in from the SW the first area to experience cooling aloft and some lift would be down into SW Oklahoma. up north you would be depending on moisture convergence along the boundary to fire a storm and with good quality moisture not making it up there I am unsure of this panning out.

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12z NAM is even spookier showing an area of 75+kt 0-6km bulk shear at 8pm Sunday evening in that same area.

I pulled the KTXK forecast sounding for 00z Monday. Here are some of the NAM projections:

0-6km shear: 73.2 kts

SBCAPE: 2938 J/kg, MLCAPE: 2146 J/kg

CINH: -5.4 J/kg

0-1km SRH: 348 m2/s2

STP 11.9 (might be from the old formula, but still, wow)

ML LCL: 690 m

 

Pretty impressive.

http://beta.wxcaster.com/cgi-bin/parse_skewt_trace1.cgi?model=NAM&fcsthr=060&STATIONID=KTXK

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12z GFS for just north of Lawton,OK at 00z on Saturday evening. Very close to where the model initiates convection very shortly after 00z. Surface winds back substantially at this time, with strong convergence along the dryline. This run has a decent window for a tornado threat Saturday evening, and I still think above normal potential for a significant nocturnal severe event.

 

post-128-0-17901300-1398441316_thumb.gif

 

post-128-0-11712700-1398441322_thumb.gif

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12z GFS for just north of Lawton,OK at 00z on Saturday evening. Very close to where the model initiates convection very shortly after 00z. Surface winds back substantially at this time, with strong convergence along the dryline. This run has a decent window for a tornado threat Saturday evening, and I still think above normal potential for a significant nocturnal severe event.

 

It also appears this run of the GFS has slightly better moisture return Saturday evening, along with a little increase in upper level support.  Interesting to see the trend of lower moisture with each consecutive GFS run come to an end, especially considering there are fire weather concerns in Oklahoma today. 

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12z GFS for just north of Lawton,OK at 00z on Saturday evening. Very close to where the model initiates convection very shortly after 00z. Surface winds back substantially at this time, with strong convergence along the dryline. This run has a decent window for a tornado threat Saturday evening, and I still think above normal potential for a significant nocturnal severe event.

Just comparing the 00z-06z-12z GFS with respect to instability, shear and moisture, the last three runs have trended just a bit faster/further east and more ramped up. It will only take a little nudge to produce a small tornado window before the sun goes down. I think we can all unanimously agree that we would rather not see a nocturnal event. For the sake of everyone, chasers included, let's hope these subtle trends continue.

 

Edit: 06z Sunday the GFS now brings >65F dew-points into south-central KS with a LI down to -9C just ahead of the dryline in western OK.

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Observations are hinting that moisture is not going to be near the problem we feared for Saturday night. And the GFS is a bit faster. Someone is going to get a nice sup at sunset.

Sent from my LG-LS980 using Tapatalk

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Observations are hinting that moisture is not going to be near the problem we feared for Saturday night. And the GFS is a bit faster. Someone is going to get a nice sup at sunset.

Sent from my LG-LS980

I hope you are right. but doesn't it seem like that cf with the current system is taking its sweet time getting across the northern gulf. I am hoping it doesn't scour out the moisture too bad. last night just inside the Texas coast, the dews were flirting with 70. so that air should be able to pull north but how fast is the big question

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