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Archive Severe threat April 26-27, 2011

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TimHSV
Posted 23 April 2011 - 04:59 AM

After looking at the ECMWF/GFS/NAM/SREF, this was a strong potential for a Major Tornado Outbreak over several states including AR/MO/TN/MS/AL. We will have several days of a strong, southerly fetch off the GOM,with a powerhouse 500mb trough approaching from the west currently depicted on the models and a high octane boundary layer, very favorable jet structure's at 850mb/500mb/300mb, with long and curved hodographs, with high SRH values over 500 m2/s2 on some forecast soundings. These cells will be possibly discrete in nature due to boundary
 

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smokedevil
Posted 24 April 2011 - 07:35 AM

MEG...


IT STILL LOOKS LIKE WEDNESDAY HAS THE POTENTIAL TO DEVELOP INTO A
MAJOR OUTBREAK. THIS STORM WILL BE ONE OF THE MORE DYNAMIC SYSTEMS
I HAVE SEEN IN A WHILE. FORECAST SOUNDINGS INDICATE INCREDIBLE
0-3KM SRH VALUES OVER 1500M/S2 EARLY WEDNESDAY MORNING...AND MORE
REALISTIC VALUES AROUND 300-600 DURING THE DAY. MODELS ALSO NOW
FEATURE A 80KT LLJ CENTERED OVER MEMPHIS LATE TUESDAY NIGHT. THE
MID LEVEL SHORTWAVE DOES NOT LOOK QUITE AS NEGATIVELY TILTED
THIS..RUN BUT IT IS STILL VERY AMPLIFIED. SURFACE WINDS WILL BACK
AS A SURFACE LOW TRACKS FROM CENTRAL ARKANSAS INTO WESTERN
KENTUCKY RESULTING IN LONG CURVED HODOGRAPHS SUPPORTIVE OF SEVERE
THUNDERSTORMS. TORNADOES...POSSIBLY STRONG LONG TRACKED
TORNADOES...LARGE HAIL AND DAMAGING WIND ARE ALL POSSIBLE ON
WEDNESDAY.
 

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RollTide18
Posted 24 April 2011 - 08:02 AM

I agree i think its possible we could have a tornado outbreak and a flood of this young century in the same storm.
 

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wxfan22
Posted 24 April 2011 - 09:34 AM

I'm a little confused on timing for the mid south. The SPC is showing Tuesday as our greatest threat day and MEG is screaming Wednesday for the major outbreak.....I believe they even say tuesday will be rather uneventful until very very late. Can anyone explain this?
 

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mwbwhorton
Posted 24 April 2011 - 09:52 AM

wxfan22 my local forecast says tuesday night into wednesday morning is our target time ak 8or 9 pm till like 11am or 12 pm wednesday....the afternoon hours after 12pm east of me
in areas toward meridian,birmingham ect....
 

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tennessee storm chaser
Posted 24 April 2011 - 10:48 AM

wxfan22, on 24 April 2011 - 09:34 AM, said:
I'm a little confused on timing for the mid south. The SPC is showing Tuesday as our greatest threat day and MEG is screaming Wednesday for the major outbreak.....I believe they even say tuesday will be rather uneventful until very very late. Can anyone explain this?

for the looks for the meg area. i would suggest late tuesday night into over night, early wed. looks to be prime time for the area. course closer to the event, timing may be tweeked some.
 

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StormStalker
Posted 24 April 2011 - 10:57 AM

From HUN...

Quote

WE HAVE INCREASED POP INTO THE LIKELY RANGE LATE MON NIGHT IN NW
AL...AND TUE AREAWIDE. SVR MCS/QLCS WL BE MOVING EWD INTO THE AREA
LATE MON NIGHT INTO TUE...ALBEIT WEAKENING AS IT LOSES LOW LEVEL
CONVERGENCE AND DIFF VORT ADV WITH HEIGHT FADES. THE MODELS INDICATE
THAT AS THE SYS SLOWS AND BECOMES ORIENTED MORE W-E...A COLD POOL /
BOUNDARY SHOULD BECOME ESTABLISHED WHICH SHOULD BECOME FOCUS FOR
EITHER CONTINUED OR RENEWED DVLPMT INTO TUE NIGHT. WE MAY NEED TO
RAISE THE POP FOR THIS PD IN FUTURE UPDATES...ALONG WITH THE
POTENTIAL FOR +RA GIVEN AMPLE MOISTURE INFLUX ASSOC WITH THE LLJ.
SUPERCELLS MAY BE PSBL AS WELL...SPCLY W OF I-65 ALONG WARM FRONT
GIVEN A GOOD COMBO OF ML-CAPE/6KM BULK SHEAR. 0-1KM SRH VALUES
INCREASE ABOVE 300 M2/S2 SUGGESTIVE OF A TORNADO THREAT AS WELL LATE
TUE NIGHT.


WED LOOKS TO BE A HIGH IMPACT WX DAY...PERHAPS CONTAINING AN ONGOING
MORNING EVENT...FOLLOWED BY A WDSPRD SQLN WED AFTN/EVNG
. WINDY
CONDITIONS ARE LIKELY WED GIVEN A VERY TIGHT PRESSURE GRADIENT...AND
A WIND ADVISORY MAY BE REQUIRED. THE NAM SUGGESTS THE WARM FRONT AND
OVERNIGHT CONVECTION SHOULD LIFT N OF THE AREA BY 12Z. THIS IS STILL
A QUESTION MARK THOUGH. THE GFS PROGS A LARGE MCS MOVG INTO MIDDLE TN
AND PSBLY CLIPPING NRN AL AS WELL. SOMETHING TO WATCH CLOSELY IN
FUTURE SHIFTS AS IT COULD CERTAINLY INCREASE OUR +RA/FLOOD THREAT.
IN ANY EVENT...MODEL SOUNDINGS INDICATE A LOW CLOUD LAYER BENEATH A STRONG
CAPPING INVERSION THRU THE MORNING HRS. THIS SHOULD PROHIBIT PRE-FRONTAL
CONVECTIVE REDVLPMT AND ALLOW FOR DECENT HEATING DURG THE AFTN. A 5H
JET ACCELERATES TO 90-100KT BY MIDDAY INTO THE AFTN...CREATING VERY
STRONG DEEP LAYER SHEAR. WITH A STRONG SHORTWAVE/-DIV Q PROVIDING
AMPLY FORCING ALONG THE COLD FRONT...CONDITIONS APPEAR FAVORABLE FOR
A LONG-LIVED SQLN TO DVLP WED AFTN/EVENING. DAMAGING WINDS AND MESO-
VORTICES / QLCS TORNADOES WL BE CONSIDERABLE THREATS.
 

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Tyler Penland
Posted 24 April 2011 - 11:39 AM

What's the timing on this for the North Georgia area? Based on the NAM it looks like yet another 11PM event.
 

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SD
Posted 24 April 2011 - 11:40 AM

wxfan22, on 24 April 2011 - 09:34 AM, said:

I'm a little confused on timing for the mid south. The SPC is showing Tuesday as our greatest threat day and MEG is screaming Wednesday for the major outbreak.....I believe they even say tuesday will be rather uneventful until very very late. Can anyone explain this?

Its both really. One shortwave mid morning to mid aftn Tuesday then another stronger one on Wednesday.
 

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SD
Posted 24 April 2011 - 11:42 AM

Tyler Penland, on 24 April 2011 - 11:39 AM, said:

What's the timing on this for the North Georgia area? Based on the NAM it looks like yet another 11PM event.

GFS would be a little earlier. Im not sure that 11pm isnt going to be too late in this type of setup.
 

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nohurricane
Posted 24 April 2011 - 11:55 AM

Definitely lots of model differences to still be worked out to determine the ultimate storm mode. Still 3+ days out. NAM and some models are showing a much weaker lead wave that causes wednesday to have significantly higher low level shear and more backed winds. GFS is in the other camp with winds veered more and what would be a higher wind dmg threat/primarily squall line. Also European has been a bit slower and farther north with the strongest forcing. This would lead to a higher tornado threat across the Southeast if it verified with more westerly shear vectors.
 

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AlabamaStormTracker
Posted 24 April 2011 - 12:49 PM

nohurricane, on 24 April 2011 - 11:55 AM, said:

Definitely lots of model differences to still be worked out to determine the ultimate storm mode. Still 3+ days out. NAM and some models are showing a much weaker lead wave that causes wednesday to have significantly higher low level shear and more backed winds. GFS is in the other camp with winds veered more and what would be a higher wind dmg threat/primarily squall line. Also European has been a bit slower and farther north with the strongest forcing. This would lead to a higher tornado threat across the Southeast if it verified with more westerly shear vectors.


With the NAM in camp and the Euro going slightly in that direction, we may be onto something here. The significant lack of low level convergence in the warm sector via the GFS makes this mainly a squall line scenario with the parallel shear vectors as many have stated. If the winds back more....boundaries around from late Tuesday night convection.....that could make for a hellacious time with better low level lift for storms. If anything is able to go in this warm sector it would be a serious situation......much like last week. Probably not as widespread, though.
 

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Fred Gossage
Posted 24 April 2011 - 01:12 PM

Had to delete previous statement. Looking at 12Z data, LCL heights wouldn't be perfect... but would be within climatological adequate range for strong to violent tornadoes... especially north of a line from Livingston to Sylacauga to Roanoke. If you believe the NAM, with low to mid 80s, versus approaching 90 in west AL (seems more realistic with such a strong LLJ and other things), then they are very doable statewide. The shortwave has trended a little more positively tilted and broader based for Wednesday... and this means more mid-level turning, with the shear vectors less parallel to the surface

 

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TimHSV
24 April 2011 - 07:09 PM, said:

KEEP A WATCH HERE....This is gonna get real interesting if the current trends/track pans out DallasFortWorth.png



* AT 622 PM CDT...STORM SPOTTERS AND DOPPLER RADAR OBSERVED A DEVELOPING TORNADO 10 MILES WEST OF GUNSIGHT...MOVING EAST AT 30 MPH.
 

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mwbwhorton
Posted 24 April 2011 - 07:42 PM

TimHSV, on 24 April 2011 - 07:09 PM, said:

KEEP A WATCH HERE....This is gonna get real interesting if the current trends/track pans out



* AT 622 PM CDT...STORM SPOTTERS AND DOPPLER RADAR OBSERVED A DEVELOPING TORNADO 10 MILES WEST OF GUNSIGHT...MOVING EAST AT 30 MPH.

yep id really be on my guard if i lived in Ft Worth especially after St Louis the other day......any updates?
Edited by mwbwhorton, 24 April 2011 - 07:43 PM.

 

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Psalm 148:8
Posted 24 April 2011 - 07:49 PM

Fred Gossage, on 24 April 2011 - 06:51 PM, said:

...And look at two of the dates being thrown around... 00Z 11/11/2002 and 00Z 11/16/1989.

What happened those dates? Regions affected....I was not a weather weenie back then...
 

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Fred Gossage
Posted 24 April 2011 - 07:53 PM

Psalm 148:8, on 24 April 2011 - 07:49 PM, said:

What happened those dates? Regions affected....I was not a weather weenie back then...


The Veteran's Day outbreak of 2002 and the Huntsville tornado of 1989. What that image shows... is that out of the computer system's database of dates and analogs, the setup Wednesday afternoon... in terms of low-level wind structure and thermodyanmics... is similar to those two days.
 

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rlsrlj
Posted 24 April 2011 - 08:00 PM

Very interesting that it would pick 2 "cool" season events. A period when we usually see less instablility compared to April events. Any ideas why?
 

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trency911
Posted 24 April 2011 - 08:02 PM

Psalm 148:8, on 24 April 2011 - 07:49 PM, said:

What happened those dates? Regions affected....I was not a weather weenie back then...


11/2002 This says it all in my opinion.
Note: These weren't all the tornadoes just those rated strong.Hereis total reports off SPC page.
Veterans_Day_Tornado_Outbreak.JPG

 

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Fred Gossage
Posted 24 April 2011 - 08:02 PM
rlsrlj, on 24 April 2011 - 08:00 PM, said:

Very interesting that it would pick 2 "cool" season events. A period when we usually see less instablility compared to April events. Any ideas why?


It seems that just happens to be the closest analogs in the system. The latest run has also triggered on January 24, 1997 as another analog. That was the F2 that hit the Food World in the Tuscaloosa area, and there was an F4 in Murfreesboro, Tennessee. Seeing the system pick kinematic analogs from November - January... but in the presence of late April thermodynamics... is rather unsettling.
 
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