156  
FXUS62 KCAE 181532 AAA  
AFDCAE  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE COLUMBIA SC  
1132 AM EDT FRI AUG 18 2017  
   
SYNOPSIS
 
 
A SURFACE PRESSURE TROUGH WILL LINGER IN THE FORECAST AREA  
THROUGH EARLY NEXT WEEK. UPPER RIDGING OVER THE REGION WILL  
WEAKEN SOMEWHAT TODAY AND SATURDAY, AND THEN BECOME A LITTLE  
STRONGER EARLY NEXT WEEK. THE PATTERN SUPPORTS PARTLY CLOUDY  
SKIES WITH SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS.  
IT WILL BE HOT WITH HEAT INDEX VALUES PEAKING 102 TO 108 TODAY,  
AND 100 TO 105 SATURDAY THROUGH MONDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
MORNING ANALYSIS SHOWED SURFACE HIGH PRESSURE CENTERED ALONG THE  
GULF COAST STATES WITH A SURFACE TROUGH EAST OF THE MOUNTAINS  
AND COLD FRONT EXTENDING FROM EASTERN OHIO SOUTHWARD INTO NORTH  
CENTRAL TENNESSEE. WATER VAPOR IMAGERY SHOWS UPPER RIDGE STILL  
EVIDENT OVER THE AREA BUT WILL BE WEAKENING A BIT TODAY AS  
SHORTWAVE ENERGY TRACKS ACROSS THE OHIO VALLEY INTO THE MID-  
ATLANTIC. THE FRONTAL BOUNDARY TO THE WEST WILL APPROACH THE  
FORECAST AREA BUT WILL NOT ARRIVE UNTIL LATER THIS EVENING.  
 
THROUGH THE AFTERNOON, MODERATE INSTABILITY WILL DEVELOP WITH  
SLIGHTLY BETTER SHEAR BUT DRIER AIR WAS NOTED ON THE MORNING  
UPSTREAM SOUNDINGS AND CURRENT GOES16 PRECIPITABLE WATER  
PRODUCT WITH VALUES AROUND 1.6-1.7 OVER THE FORECAST AREA. THIS  
LOWER MOISTURE ALONG WITH WESTERLY DOWNSLOPING LOW LEVEL FLOW  
SHOULD LIMIT CONVECTION TODAY AND WILL CONTINUE TO ADVERTISE  
GENERALLY SLIGHT CHANCE TO CHANCE POPS MAINLY LATE AFTERNOON  
WITH A FOCUS ON HIGHER POPS IN THE NORTHERN MIDLANDS LATE WHERE  
THE FRONT WILL BE APPROACHING AND THE TAIL UPPER ENERGY RESIDES.  
THE DRIER AIR ALOFT WILL PROVIDE A THREAT OF DAMAGING WIND  
GUSTS FOR STORMS THAT DO DEVELOP TODAY WITH DOWNDRAFT CAPE  
VALUES AROUND 1000 J/KG. FORECAST SOUNDINGS ALSO SHOW A CAPPING  
INVERSION AROUND 700MB WHICH MAY FURTHER INHIBIT CONVECTION  
TODAY. HI-RES MODEL GUIDANCE IN GOOD AGREEMENT WITH DEVELOPING  
CONVECTION LATE AND FOCUSING BETTER POPS IN THE NORTHERN  
MIDLANDS.  
 
TEMPERATURES ARE RISING RAPIDLY ONCE AGAIN WITH COLUMBIA ALREADY  
AT 92 DEGREES AS OF 11 AM AND WITH PLENTY OF SUNSHINE AND LATER  
CONVECTIVE INITIATION EXPECTED THINK SOME LOCATIONS MAY REACH 99  
TO 100 DEGREES THIS AFTERNOON. HEAT INDICES WILL AGAIN BE IN THE  
102 TO 108 DEGREE RANGE AS WELL.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/
 
 
THE MODELS DEPICT SURFACE TROUGHING LINGERING THROUGH SUNDAY.  
HOWEVER, IT MAY BE SLIGHTLY DRIER AS THE MODELS HAVE MORE  
SIGNIFICANT MOISTURE SHIFTED FARTHER EAST AHEAD OF UPPER  
TROUGHING SATURDAY WITH LITTLE RECOVERY SUNDAY BECAUSE OF  
BUILDING RIDGING. MID-LEVEL TEMPERATURES ARE FORECAST TO REMAIN  
RELATIVELY WARM WITH H5 TEMPERATURES NEAR -6 C. THE MOS HAS VERY  
LOW POPS. EXPECT LITTLE THUNDERSTORM COVERAGE. THE SLIGHTLY  
DRIER AIR SHOULD RESULT IN A LITTLE LOWER HEAT INDEX VALUES.  
HOWEVER, IT WILL REMAIN HOT WITH FORECAST MAXIMUM HEAT INDEX  
READINGS 100 TO 105.  
 

 
   
LONG TERM /MONDAY THROUGH THURSDAY/
 
 
THE MODELS SHOW UPPER RIDGING BUILDING OVER THE REGION MONDAY  
AS SURFACE HIGH PRESSURE STRENGTHENS OVER THE WESTERN ATLANTIC.  
LOW-LEVEL MOISTURE SHOULD REMAIN HIGH DUE TO A SOUTHEAST FLOW  
OFF THE OCEAN. THE PATTERN SUPPORTS PARTLY CLOUDY SKIES WITH A  
CHANCE OF MAINLY AFTERNOON THUNDERSTORMS. SIMILAR CONDITIONS  
ARE EXPECTED TUESDAY. A WEAK COLD FRONT IS FORECAST TO  
APPROACH WEDNESDAY AND BE IN THE AREA THURSDAY WHICH MAY BRING  
AN INCREASED CHANCE OF THUNDERSTORMS. THE GFS AND ECMWF MOS HAVE  
POPS 20 TO 30 PERCENT MONDAY AND TUESDAY, AND 30 TO 40 PERCENT  
WEDNESDAY AND THURSDAY. THE MOS SUPPORTS ABOVE NORMAL  
TEMPERATURES LOWERING TO ABOUT NORMAL THURSDAY. EXPECT MAXIMUM  
HEAT INDEX VALUES 100 TO 105 THROUGH THE PERIOD.  
 

 
   
AVIATION /15Z FRIDAY THROUGH TUESDAY/
 
 
GENERALLY VFR CONDITIONS THROUGH THE PERIOD EXCEPT POSSIBLE  
RESTRICTIONS IN THUNDERSTORMS.  
 
MOSTLY CLEAR SKIES ACROSS THE AREA EARLY THIS MORNING. DIURNAL  
CUMULUS CLOUDS STARTING TO DEVELOP WITH STRONG HEATING. WESTERLY  
WINDS AROUND 10 KNOTS WILL SHIFT MORE SOUTHWESTERLY BY AFTERNOON  
AHEAD OF AN APPROACHING FRONTAL BOUNDARY. CONDITIONS FAVOR  
ISOLATED TO SCATTERED CONVECTION EXPECTED LATER IN THE AFTERNOON  
AND FOCUSED MAINLY IN THE UPSTATE INTO THE NORTHERN MIDLANDS  
INITIALLY THEN PUSHING INTO THE MIDLANDS AROUND 00Z. WILL NOT  
INCLUDE A MENTION OF STORMS IN THE FORECAST DUE TO UNCERTAINTY  
ANY WILL AFFECT ANY TERMINAL BUT MAY INCLUDE IN THE 18Z  
FORECAST.  
 
EXTENDED AVIATION OUTLOOK...SCATTERED MAINLY AFTERNOON AND  
EVENING SHOWERS AND THUNDERSTORMS POSSIBLE EACH DAY. ALSO, LOW-  
LEVEL MOISTURE COULD RESULT IN EARLY MORNING FOG AND/OR STRATUS.  
 

 
   
CAE WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...NONE.  
 

 
 

 
 
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