910  
ACUS01 KWNS 210055  
SWODY1  
SPC AC 210053  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0653 PM CST MON FEB 20 2017  
 
VALID 210100Z - 211200Z  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS TONIGHT NEAR  
SOUTHEAST LOUISIANA COASTAL AREAS...  
   
..SUMMARY
 
 
A COUPLE OF STRONG THUNDERSTORMS ARE POSSIBLE NEAR SOUTHEASTERN  
LOUISIANA COASTAL AREAS TONIGHT, PERHAPS ACCOMPANIED BY SOME SEVERE  
WEATHER POTENTIAL.  
   
..SYNOPSIS
 
 
MUCH OF NORTH AMERICA REMAINS UNDER THE INFLUENCE OF SPLIT BRANCHES  
OF WESTERLIES EMANATING FROM THE MID-LATITUDE PACIFIC. DESPITE THE  
PRESENCE OF RELATIVELY MILD CONDITIONS ACROSS MUCH OF THE U.S. IN  
ASSOCIATION WITH THIS REGIME, THERMODYNAMIC PROFILES ARE GENERALLY  
STABLE ACROSS MOST AREAS, WITH LOW OR NEGLIGIBLE CONVECTIVE  
POTENTIAL.  
   
..MISSISSIPPI VALLEY/NORTHWESTERN GULF COAST REGION
 
 
A NARROW PLUME OF HIGHER MOISTURE CONTENT AIR HAS RETURNED NORTHWARD  
ACROSS NORTHWESTERN GULF COASTAL AREAS THROUGH THE UPPER MIDWEST,  
AHEAD OF SHEARED/ELONGATED TROUGHING WITHIN THE WESTERLIES. THIS  
TROUGHING WITHIN BOTH THE NORTHERN AND SOUTHERN STREAMS HAS LARGELY  
BEEN IN PHASE AS IT PROGRESSES ACROSS THE PLAINS. BUT THE NORTHERN  
STREAM TROUGHING IS FORECAST TO INCREASINGLY PIVOT NORTHEASTWARD AND  
EASTWARD MORE RAPIDLY THAN THE SOUTHERN STREAM TROUGHING, AS A  
STRONG UPSTREAM MID/UPPER JET STREAK CONTINUES TO NOSE INLAND ACROSS  
NORTHERN CALIFORNIA AND THE NORTHERN GREAT BASIN. WITHIN THE  
SOUTHERN STREAM TROUGHING, MODELS SUGGEST THAT MODEST LOWER/MID  
TROPOSPHERIC CYCLOGENESIS MAY OCCUR TONIGHT ACROSS PARTS OF EASTERN  
TEXAS INTO THE LOWER MISSISSIPPI VALLEY.  
 
ISOLATED TO WIDELY SCATTERED THUNDERSTORM ACTIVITY HAS BEEN  
OCCURRING EARLY THIS EVENING, WITHIN A NARROW CONVECTIVE BAND,  
GENERALLY ALONG THE LEADING EDGE OF REMNANT COMPOSITE OUTFLOW  
GENERATED BY EXTENSIVE CONVECTION LAST NIGHT. IT APPEARS THAT A  
RISK FOR THUNDERSTORMS MAY LINGER ACROSS EASTERN ARKANSAS THROUGH  
PORTIONS OF NORTHEASTERN MISSOURI/WEST CENTRAL ILLINOIS ANOTHER  
COUPLE OF HOURS (INTO THE 02-04Z TIME FRAME). HOWEVER, HIGHEST  
THUNDERSTORM PROBABILITIES PROBABLY WILL BECOME INCREASINGLY  
CONFINED TO PORTIONS OF THE ARK-LA-TEX AND LOWER MISSISSIPPI VALLEY,  
SOUTHWARD INTO THE GULF OF MEXICO, AIDED BY LARGE-SCALE FORCING FOR  
ASCENT ASSOCIATED WITH THE EVOLVING SOUTHERN BRANCH PERTURBATION.  
 
INLAND OF IMMEDIATE COASTAL AREAS, MOST THUNDERSTORM ACTIVITY SEEMS  
LIKELY TO REMAIN ROOTED ABOVE AT LEAST A SHALLOW SURFACE-BASED  
STABLE LAYER, WHICH IS EXPECTED TO MITIGATE ANY APPRECIABLE SEVERE  
WEATHER POTENTIAL. HOWEVER, THE ENVIRONMENT OVER THE OPEN WATERS OF  
THE NORTH CENTRAL GULF OF MEXICO APPEARS AT LEAST MARGINALLY  
SUPPORTIVE OF ORGANIZED CONVECTION, INCLUDING SUPERCELLS. AND  
CONVECTION CAPABLE OF PRODUCING GUSTY WINDS AND/OR A TORNADO MAY NOT  
BE OUT OF THE QUESTION NEAR SOUTHEAST LOUISIANA COASTAL AREAS  
TONIGHT.  
   
..NORTHERN CALIFORNIA
 
 
COOLING ALOFT ASSOCIATED WITH AN INLAND MIGRATING UPPER IMPULSE MAY  
BE ACCOMPANIED BY SOME RISK FOR THUNDERSTORM ACTIVITY ACROSS COASTAL  
AREAS INTO NORTHERN PORTIONS OF THE SACRAMENTO VALLEY BY THE 05-07Z  
TIME FRAME. IN THE VICINITY OF A 100+ KT 500 MB JET STREAK,  
LOW-LEVEL AND DEEP LAYER SHEAR PROBABLY WILL BECOME SUPPORTIVE OF  
ORGANIZED SEVERE STORM DEVELOPMENT, PERHAPS INCLUDING SUPERCELLS,  
GIVEN SUFFICIENT BOUNDARY LAYER DESTABILIZATION. ACROSS AND INLAND  
OF COASTAL AREAS, THIS REMAINS TOO UNCERTAIN FOR AN OUTLOOK OF  
APPRECIABLE SEVERE PROBABILITIES.  
 
..KERR.. 02/21/2017  
 

 
 
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