812  
ACUS02 KWNS 191725  
SWODY2  
SPC AC 191725  
 
DAY 2 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
1225 PM CDT FRI OCT 19 2018  
 
VALID 201200Z - 211200Z  
   
..NO SEVERE THUNDERSTORM AREAS FORECAST
 
 
   
..SUMMARY
 
 
THE RISK FOR SEVERE THUNDERSTORMS APPEARS NEGLIGIBLE ACROSS THE U.S.  
SATURDAY THROUGH SATURDAY NIGHT.  
   
..SYNOPSIS
 
 
WITHIN ONE BRANCH OF WESTERLIES EMANATING FROM THE MID-LATITUDE  
PACIFIC, LARGE-SCALE RIDGING APPEARS LIKELY TO PERSIST ACROSS AND  
INLAND OF THE BRITISH COLUMBIA/PACIFIC NORTHWEST COAST, WHILE  
DOWNSTREAM TROUGHING PREVAILS OVER EASTERN NORTH AMERICA. ONE OR  
TWO EMBEDDED SHORT WAVE TROUGHS EMERGING FROM THE NORTHEAST PACIFIC  
MAY SUPPRESS THE RIDGING ACROSS THE CANADIAN PRAIRIES INTO THE  
CENTRAL CANADIAN/U.S. BORDER AREA SATURDAY THROUGH SATURDAY NIGHT.  
HOWEVER, A VIGOROUS SHORT WAVE TROUGH OF ARCTIC ORIGINS IS FORECAST  
TO DIG SOUTHEAST OF THE UPPER MIDWEST, THROUGH THE MID ATLANTIC  
COAST REGION BY 12Z SUNDAY, AND CONTRIBUTE TO FURTHER AMPLIFICATION  
OF THE LARGER-SCALE TROUGHING. THIS WILL LIKELY LEAD TO CONTINUED  
SUPPRESSION OF MID/UPPER SUBTROPICAL RIDGING ACROSS THE EASTERN GULF  
AND SOUTH ATLANTIC COASTS.  
 
AT THE SAME TIME, WITHIN A BRANCH OF WESTERLIES EMANATING FROM THE  
SUBTROPICAL EASTERN PACIFIC, A BROAD MID-LEVEL LOW MAY CONTINUE TO  
EVOLVE WITHIN LARGER-SCALE TROUGHING NEAR THE CALIFORNIA/NORTHERN  
BAJA COAST.  
 
THIS PATTERN IS EXPECTED TO MAINTAIN GENERALLY STABLE CONDITIONS NOW  
PRESENT ACROSS MUCH OF THE NATION, BUT A FEW AREAS WITH LOW  
PROBABILITIES FOR SCATTERED THUNDERSTORM ACTIVITY MAY DEVELOP  
SATURDAY INTO SATURDAY NIGHT.  
   
..LOWER GREAT LAKES INTO UPPER OHIO VALLEY/ALLEGHENY PLATEAU
 
 
STRONG MID-LEVEL COOLING, ASSOCIATED WITH LARGE-SCALE ASCENT AND  
COLD ADVECTION (TO LESS THAN -30 C AT 500 MB), IS FORECAST TO  
ACCOMPANY THE DIGGING SHORT WAVE TROUGH. DESPITE RELATIVELY  
COOL/LOW MOISTURE CONTENT BOUNDARY LAYER CONDITIONS AHEAD OF THE  
ASSOCIATED REINFORCING COLD FRONT, FORECAST SOUNDINGS SUGGEST THAT  
DAYTIME HEATING MAY CONTRIBUTE TO SUFFICIENT STEEPENING OF LOW-LEVEL  
LAPSE RATES AND CAPE TO SUPPORT LOW-TOPPED CONVECTION CAPABLE OF  
PRODUCING LIGHTNING. THIS POTENTIAL WILL BE MAXIMIZED DURING THE  
MID TO LATE AFTERNOON, AND MAY INCLUDE MUCH OF THE UPPER OHIO VALLEY  
AND ALLEGHENY PLATEAU, IN ADDITION TO COASTAL AREAS DOWNSTREAM  
(SOUTHEAST) OF THE LOWER GREAT LAKES.  
   
..CENTRAL/EASTERN GULF COAST REGION
 
 
ALONG/AHEAD OF AN INITIAL SURFACE FRONT ADVANCING SOUTHWARD ACROSS  
THE REGION, WEAK TO MODERATE BOUNDARY LAYER CAPE MAY PROVIDE SUPPORT  
FOR SCATTERED THUNDERSTORM ACTIVITY SATURDAY AFTERNOON, NEAR THE  
SOUTHERN PERIPHERY OF THE EVOLVING CYCLONIC MID/UPPER FLOW. GIVEN  
THE EXPECTED TENDENCY FOR SUSTAINED CONVECTION TO BE UNDERCUT BY THE  
COLD FRONT, IN THE PRESENCE OF OTHERWISE MODEST TO WEAK SHEAR, ANY  
SEVERE WEATHER POTENTIAL STILL APPEARS NEGLIGIBLE AT THIS TIME.  
   
..PARTS OF SOUTHERN ARIZONA INTO THE COLORADO VALLEY
 
 
MODELS INDICATE THAT A CORRIDOR OF WEAK TO MODERATE INSTABILITY MAY  
DEVELOP NEAR THE LEADING EDGE OF THE MID-LEVEL COOLING ASSOCIATED  
WITH THE EVOLVING UPPER LOW/TROUGH. THIS MAY BECOME SUFFICIENT TO  
INITIATE SCATTERED THUNDERSTORMS SATURDAY INTO SATURDAY NIGHT.  
HOWEVER, AT THIS TIME, THE ENVIRONMENT STILL APPEARS UNLIKELY TO  
SUPPORT AN APPRECIABLE RISK FOR SEVERE STORMS.  
   
..MAXIMUM RISK BY HAZARD
 
 
TORNADO: <2% - NONE  
WIND: <5% - NONE  
HAIL: <5% - NONE  
 
..KERR.. 10/19/2018  
 

 
 
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