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Memorial Day weekend severe threats


jojo762

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00 PM CDT SAT MAY 27 2017  
  
THE NWS STORM PREDICTION CENTER HAS ISSUED A  
  
* TORNADO WATCH FOR PORTIONS OF   
  NORTHERN AND WESTERN ARKANSAS  
  SOUTHERN MISSOURI  
  
* EFFECTIVE THIS SATURDAY NIGHT AND SUNDAY MORNING FROM 700 PM  
  UNTIL 200 AM CDT.  
  
* PRIMARY THREATS INCLUDE...  
  A FEW TORNADOES AND A COUPLE INTENSE TORNADOES POSSIBLE  
  WIDESPREAD DAMAGING WINDS LIKELY WITH ISOLATED SIGNIFICANT GUSTS  
    TO 80 MPH POSSIBLE  
  SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 2.5  
    INCHES IN DIAMETER POSSIBLE  
  
SUMMARY...SEVERE THUNDERSTORMS WILL CONTINUE TO DEVELOP WITHIN A  
HIGHLY UNSTABLE ENVIRONMENT FROM FAR SOUTHERN MISSOURI INTO NORTHERN  
AND WESTERN ARKANSAS. TORNADOES WILL ESPECIALLY BE POSSIBLE WITH ANY  
STORM ALONG A ROUGHLY WEST-EAST OUTFLOW BOUNDARY ALONG THE  
MISSOURI/ARKANSAS BORDER VICINITY, WHILE SEMI-DISCRETE SUPERCELLS OR  
EVOLVING LINE-EMBEDDED MESOVORTICES WOULD ALSO POSE A TORNADO RISK.  
OTHERWISE, WIDESPREAD AND LOCALLY INTENSE DAMAGING WINDS WILL BE  
HIGHLY LIKELY AS STORMS ACCELERATE EAST/SOUTHEASTWARD THIS EVENING.  
  

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5 minutes ago, Memphis Weather said:

Nowata storm trying to latch onto the boundary

This storm is definitely one to watch given what you said... Plus it is discrete. Classic supercell structure appears to be developing, on radar at least.

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Nothing overly impressive at the moment, seems the limited SRH is hurting where many people thought maybe the extreme instability would help to overcome that.

 

EDIT: to clarify I was among those who thought instability would compensate for meager low level helicity

 

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DAY 1 CONVECTIVE OUTLOOK    
NWS STORM PREDICTION CENTER NORMAN OK  
0744 PM CDT SAT MAY 27 2017  
  
VALID 280100Z - 281200Z  
  
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST  
OKLAHOMA TO WESTERN TENNESSEE...  
  
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL  
OKLAHOMA TO THE TENNESSEE VALLEY...  
  
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTH TEXAS  
TO THE MID-ATLANTIC...  
  
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE  
SOUTHERN HIGH PLAINS...  
  
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM  
SOUTHWESTERN TEXAS TO THE ATLANTIC COAST...  
   
..SUMMARY  
  
WIDESPREAD SEVERE WIND GUSTS WILL CONTINUE FROM THE OZARKS TO THE  
TENNESSEE VALLEY THIS EVENING INTO THE OVERNIGHT HOURS.  
ADDITIONALLY, VERY LARGE TO GIANT HAIL AND A FEW TORNADOES REMAIN  
POSSIBLE FROM THE RED RIVER VALLEY NORTHEASTWARD TO THE OZARK  
PLATEAU. A FEW INSTANCES OF DAMAGING WINDS AND LARGE HAIL WILL ALSO  
BE POSSIBLE ACROSS THE MIDDLE OHIO VALLEY, MID-ATLANTIC, AND  
SOUTHERN HIGH PLAINS THIS EVENING.  
   
..OZARKS TO THE TENNESSEE VALLEY  
  
MULTIPLE SEVERE CONVECTIVE SYSTEMS ARE EVOLVING ACROSS THIS REGION  
THIS EVENING, AIDED BY AN AXIS OF AMPLE INSTABILITY ALONG THEIR  
SOUTHERN/EASTERN FRINGE. THE 00Z BNA SOUNDING SAMPLED AN ENVIRONMENT  
CHARACTERIZED BY PLENTIFUL MIXED-LAYER CAPE, SUCH THAT  
DOWNWIND-PROPAGATING MCSS WILL BE MAINTAINED THROUGH MUCH OF THE  
EVENING INTO THE EARLY OVERNIGHT. AS SUCH, THE 45- AND 30-PERCENT  
WIND PROBABILITIES ARE EXPANDED SOUTHEAST. ACROSS THE OZARKS,  
PROPAGATION WILL LIKELY BE ENHANCED BY AN OUTFLOW BOUNDARY  
STRETCHING EAST-WEST ACROSS FAR SOUTHERN MISSOURI. IN TURN, UPSCALE  
GROWTH THIS EVENING SHOULD FOSTER THE EVOLUTION OF A BOWING COMPLEX  
FROM NORTHERN ARKANSAS TO WESTERN TENNESSEE. WITH EVEN GREATER  
INSTABILITY PRESENT HERE, A FEW SIGNIFICANT DAMAGING GUSTS, AS WELL  
AS TORNADOES AND VERY LARGE HAIL, REMAIN POSSIBLE.  
   
..RED RIVER VALLEY TO NORTHEAST OKLAHOMA  
  
SEVERE CONVECTION HAS INITIATED NEAR A DRYLINE CLOSE TO THE I-35  
CORRIDOR, AS WELL AS ALONG A COLD FRONT PUSHING SOUTH ACROSS  
NORTHEAST OKLAHOMA. WITH EXTREME BUOYANCY PRESENT (E.G., 5600 J/KG  
OF MLCAPE FROM THE 00Z OUN SOUNDING), THE POTENTIAL FOR GIANT HAIL  
CONTINUES. ADDITIONALLY, WHILE STORMS HAVE GENERALLY FAILED TO  
DEVELOP ORGANIZED/SUSTAINED LOW-LEVEL MESOCYLONES SO FAR (LIKELY DUE  
TO MODE AND THE UNDERCUTTING COLD FRONT), MORE ROBUST/SEMI-DISCRETE  
DEVELOPMENT CURRENTLY APPEARS UNDERWAY ACROSS THE EASTERN HALF OF  
THE STATE. WITH RICH BOUNDARY-LAYER MOISTURE REMAINING AND SOME  
SLIGHT BACKING OF LOW-LEVEL WINDS ACROSS EASTERN OKLAHOMA, THE  
THREAT FOR A FEW TORNADOES, ONE OR TWO OF WHICH COULD BE STRONG,  
REMAINS.  

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1 minute ago, Buckeye05 said:

Becoming a little more interested in the Paden, OK cell. Overall structure seems to be improving and I see some evidence of rotation trying to develop. 

Will see if it sustains itself though. Nowata cell quickly went upscale into an HP mess. 

Primarily because it got undercut, I believe. Hard to tell if that was just an OFB or the cold front.

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7 minutes ago, jojo762 said:

Primarily because it got undercut, I believe. Hard to tell if that was just an OFB or the cold front.

I don't think it was the cold front. 70+ dews remain at 01z NW of I-44. The cell crossed over into the north side of an outflow boundary and never could quite latch onto it, even though it took a turn right. We chased it for a while and never really saw any kind of wall cloud or focused low-level rotation. Given the rich, boundary layer moisture, convective overturning wasn't enough to completely ruin the environment, but it did create enough CINH to limit updraft organization and disrupt low-level wind fields enough to preclude a greater tornado threat. 

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5 minutes ago, Quincy said:

I don't think it was the cold front. 70+ dews remain at 01z NW of I-44. The cell crossed over into the north side of an outflow boundary and never could quite latch onto it, even though it took a turn right. We chased it for a while and never really saw any kind of wall cloud or focused low-level rotation. Given the rich, boundary layer moisture, convective overturning wasn't enough to completely ruin the environment, but it did create enough CINH to limit updraft organization and disrupt low-level wind fields enough to preclude a greater tornado threat. 

I really didn't think it was either to begin with... As I thought the CF was still north into KS... But Picca in the 01Z discussion mentioned the cold front undercutting the storms in NE OK, so I just went with what he said.

Quote

Severe convection has initiated near a dryline close to the I-35
   corridor, as well as along a cold front pushing south across
   northeast Oklahoma. With extreme buoyancy present (e.g., 5600 J/kg
   of MLCAPE from the 00Z OUN sounding), the potential for giant hail
   continues. Additionally, while storms have generally failed to
   develop organized/sustained low-level mesocylones so far (likely due
   to mode and the undercutting cold front)

 

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