125  
FXUS62 KCHS 221956  
AFDCHS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHARLESTON SC  
356 PM EDT MON MAY 22 2017  
   
SYNOPSIS
 
 
A SERIES OF DISTURBANCES WILL TRACK ACROSS THE SOUTHEAST THROUGH  
MIDWEEK. A COLD FRONT WILL PUSH OFFSHORE WEDNESDAY NIGHT INTO  
THURSDAY. HIGH PRESSURE WILL THEN PREVAIL THIS WEEKEND.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
NUMEROUS SHOWERS AND TSTMS HAVE DEVELOPED THIS AFTERNOON ACROSS  
PORTIONS OF SOUTHERN SC AND GA, MOSTLY PROPAGATING NNE. PWS OF  
1.8 TO 1.9" SUPPORTING LOCALLY HEAVY RAINFALL WITH THE  
CONVECTION. THE SEABREEZE HAS BEGUN TO DEVELOP BASED ON COASTAL  
WIND DIRECTIONS AND THE EROSION OF CUMULUS RIGHT AT THE COAST.  
THIS, PLUS THE CONCENTRATION OF UPPER VORTICITY ENERGY OVER  
INLAND AREAS WILL TEND TO PUSH THE GREATEST CONVECTION COVERAGE  
AWAY FROM THE COAST AND TOWARD INLAND AREAS. THUS WE HAVE THE  
LIKELY POPS OVER INLAND AREAS THROUGH EARLY THIS EVENING.  
 
A LULL IS EXPECTED FROM MID TO LATE EVENING BEFORE SPEED  
CONVERGENCE IN LOW-LEVEL JETTING OVER THE WATERS INDUCES NEW  
SHOWER AND TSTM DEVELOPMENT OFFSHORE. ADDITIONAL SHOWERS AND  
TSTMS SHOULD DEVELOP LATER TONIGHT ACROSS INLAND AREAS AS  
GREATER PVA SHIFTS OVER THE AREA AHEAD OF MORE SHORTWAVE  
ACTIVITY. INSTABILITY WILL REMAIN FAIRLY WEAK SO SEVERE WX IS  
NOT MUCH OF A CONCERN, THOUGH LOCALIZED FLOODING IS POSSIBLE  
GIVEN THE HIGH PWS.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/
 
 
ON TUESDAY, A COLD FRONT IS EXPECTED TO RUN ACROSS THE PIEDMONT  
OF THE CAROLINAS AND GA. SHORT RANGE GUIDANCE INDICATES THAT A  
FRONT WAVE WILL DEVELOP ALONG THE COLD FRONT ACROSS GA OR SC.  
THE FRONT WAVE IS FORECAST TO TRACK NE ALONG THE FRONT DURING  
THE DAYLIGHT HOURS ON TUESDAY. MODEL FORECAST SOUNDINGS SUGGEST  
THAT LFC LEVELS WILL REMAIN BELOW 2 KFT WITH PW VALUES AROUND  
1.9 INCHES. IN ADDITION, A WIDE FIELD OF 1500-2000 J/KG CAPE  
WILL DEVELOP ALONG AND EAST OF THE FRONT/WAVE. CONVECTION SHOULD  
EASILY FORM NEAR THE FRONTAL WAVE, SUPPORTING CATEGORICAL POPS  
FOR SHOWERS AND THUNDERSTORMS. SHEAR BETWEEN 0-6 KM WILL LIKELY  
RANGE AROUND 40 KTS, YIELDING LOOSELY ORGANIZED CLUSTERS OR  
BANDS OF THUNDERSTORMS. IT IS POSSIBLE TO SEE A FEW DAMAGING  
WIND EVENTS WITH THE STRONGER STORMS. PERHAPS MORE LIKELY,  
RAINFALL RATES MAY BECOME QUITE HEAVY DURING THE PASSAGE OF  
THUNDERSTORM CLUSTERS, SEE TIDE SECTION BELOW. HIGH TEMPERATURES  
SHOULD VERIFY WITHIN A DEGREE OR TWO OF 80 DEGREES ON TUESDAY.  
BASED ON THE TIMING OF THE FRONTAL WAVE, COVERAGE OF DEEP  
CONVECTION SHOULD SHIFT NE DURING THE EVENING HOURS. IT APPEARS  
THAT A NOTEWORTHY DECREASE IN COVERAGE OF SHOWERS AND  
THUNDERSTORMS WILL OCCUR ACROSS FORECAST AREA TUESDAY NIGHT,  
HIGHLIGHT WITH POPS DECREASING TO CHC. LOWS TUESDAY NIGHT ARE  
FORECAST TO RANGE IN THE UPPER 60S TO LOW 70S.  
 
WEDNESDAY, DEEP SFC LOW PRESSURE SHOULD ORGANIZE ACROSS THE OHIO  
RIVER VALLEY. SHORT RANGE GUIDANCE INDICATES THAT A COLD FRONT  
WILL APPROACH FROM THE WEST DURING THE DAYLIGHT HOURS. AT THE  
MID LEVEL, H5 TROUGH WILL SWING ACROSS THE DEEP SOUTH DURING THE  
AFTERNOON, GFS1DEG SHOWS A WIDE FIELD OF H5 Q-VECTOR CONVERGENCE  
WILL SPREAD WEST TO EAST ACROSS THE CWA. THE ENVIRONMENT AHEAD  
OF THE COLD FRONT IS FORECAST TO SEE CAPE VALUES POOL TO 1500  
J/KG WITH SWEAT PEAKING NEAR 400. I WOULD EXPECT THAT A BAND OF  
DEEP CONVECTION WILL FORM ALONG AND AHEAD OF THE COLD FRONT.  
GIVEN THE SYNOPTIC SCALE FORCING, INSTABILITY, AND SHEAR, THE  
SEVERE RISK COULD PEAK WED AFTERNOON AND EVENING. HIGH TEMPS  
SHOULD RANGE VERY CLOSE TO VALUES EXPECTED FOR TUESDAY. DRY AIR  
WILL SPREAD EAST ACROSS THE REGION WEDNESDAY NIGHT.  
 
THURSDAY, LARGE LOW PRESSURE WILL CIRCULATE ACROSS THE MID WEST  
AND GREAT LAKES REGIONS AS HIGH PRESSURE BUILDS OVER THE GULF  
OF MEXICO. THE SFC PRESSURE GRADIENT IS FORECAST TO RANGE FROM  
2-3 MBS ACROSS THE FORECAST AREA. WSW WINDS SHOULD REMAIN GUSTY  
ACROSS FORECAST AREA, ESPECIALLY DURING THE MORNING.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/
 
 
A RIDGE BUILDING ACROSS THE EAST COAST COMBINED WITH SURFACE HIGH  
PRESSURE WILL PROVIDE DRY WEATHER IN THE LONG TERM ALONG WITH A  
GRADUAL WARMING TREND EACH DAY.  
 

 
   
AVIATION /19Z MONDAY THROUGH SATURDAY/
 
 
THE GREATEST CHANCE FOR CONVECTION WILL GRADUALLY SHIFT WEST OF  
THE TERMINALS AS THE SEA BREEZE PUSHES INLAND. HOWEVER, SCATTERED  
COVERAGE ACROSS SOUTHEAST GA MAY AFFECT KSAV BEFORE 6 PM.  
SCATTERED SHOWERS POSSIBLE OVERNIGHT AT KCHS AS SOME ACTIVITY  
DEVELOPS AHEAD OF ANOTHER SHORTWAVE.  
 
ANOTHER ROUND OF CONVECTION EXPECTED DURING THE DAY TUESDAY BUT  
WITH THE BEST COVERAGE INLAND WE DID NOT MENTION CONVECTION AT  
EITHER TERMINAL.  
 
EXTENDED AVIATION OUTLOOK: AN UNSETTLED WEATHER PATTERN WILL BRING  
PERIODS OF FLIGHT RESTRICTIONS THROUGH WEDNESDAY NIGHT.  
 

 
   
MARINE
 
 
LOW-LEVEL JET STRENGTHENS LATER TONIGHT AS SHORTWAVE ENERGY  
APPROACHES THE AREA. SUSTAINED WINDS WILL INCREASE TO 15-20 KT  
LATER TONIGHT WITH SOME GUSTS APPROACHING 25 KT OVER OUTER  
PORTIONS.  
 
TUESDAY THROUGH WEDNESDAY NIGHT: WEAK LOW PRESSURE WILL TRACK NE  
ALONG A SFC FRONT ACROSS DURING THE DAYLIGHT HOURS TUESDAY. SW WINDS  
ACROSS THE MARINE ZONES WILL INCREASE THROUGH DAY. GUSTS ACROSS  
AMZ350 AND 374 ARE FORECAST TO EXCEED 25 KTS BY THE AFTERNOON. WAVE  
HEIGHTS ARE FORECAST TO BUILD TO 3-4 FEET WITHIN 20 NM AND AROUND 5  
FEET ACROSS AMZ374. SMALL CRAFT ADVISORIES MAY BE NEEDED FOR  
TUESDAY. IN ADDITION, ROUNDS OF THUNDERSTORMS ARE FORECAST ACROSS  
THE MARINE ZONES ON TUESDAY. WINDS MAY DECREASE SLIGHT TUESDAY  
NIGHT, HOWEVER, WAVE HEIGHTS ARE FORECAST TO GRADUALLY BUILD THROUGH  
THE NIGHT.  
 
WEDNESDAY THROUGH WEDNESDAY NIGHT, SW WINDS WILL INCREASE AS A COLD  
FRONT APPROACHES FROM THE WEST. SCA CONDITIONS ARE EXPECTED. MARINE  
ZONES SHOULD SEE COMMON GUSTS TO 25 KTS WITHIN 20 NM AND AROUND 30  
KTS BEYOND 20 NM. WAVE HEIGHTS ARE FORECAST TO PEAK WEDNESDAY NIGHT,  
WITH 6 FEET POSSIBLE WITHIN 20 NM AND UP TO 9 FEET ACROSS EASTERN  
AMZ374. THEN, WINDS/SEAS SHOULD RELAX SIGNIFICANTLY BY FRIDAY.  
 

 
   
TIDES/COASTAL FLOODING
 
 
EVENING HIGH TIDE LEVELS WILL TREND HIGHER EACH DAY APPROACH  
THE NEW MOON PERIGEE THIS FRIDAY. THE MEAN LOWER LOW WATER  
(MLLW) LEVELS ARE FORECAST TO REMAIN BELOW FLOOD STAGE. HOWEVER,  
IT IS POSSIBLE THAT THUNDERSTORMS COULD PASS OVER URBAN COAST  
AREAS DURING THE EVENING HIGH TIDE CYCLE. RAINFALL RATES COULD  
EXCEED 0.75/HR DURING ANY THUNDERSTORM. THE COMBINATION OF  
ELEVATED MLLW WATER LEVELS AND HEAVY DOWNPOURS COULD RESULT IN  
DEEP STREET AND SIDEWALK WATER.  
 

 
   
CHS WATCHES/WARNINGS/ADVISORIES
 
 
GA...NONE.  
SC...NONE.  
MARINE...NONE.  
 

 
 

 
NEAR TERM...JRL  
SHORT TERM...NED  
LONG TERM...MS  
AVIATION...JRL/NED  
MARINE...JRL/NED  
TIDES/COASTAL FLOODING...NED  
 
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