441  
FXUS62 KILM 241534  
AFDILM  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE WILMINGTON NC  
1134 AM EDT SUN OCT 24 2021  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL MOVE OFF THE MID ATLANTIC COAST TODAY.  
SCATTERED SHOWERS AND THUNDERSTORMS MAY DEVELOP AS A COLD FRONT  
MOVES ACROSS THE CAROLINAS MONDAY AND MONDAY NIGHT. HIGH  
PRESSURE WILL BUILD IN TUESDAY AND WEDNESDAY, BUT WILL BE  
QUICKLY PUSHED OFFSHORE THURSDAY AS STRONG LOW PRESSURE  
APPROACHES THE AREA WITH INCREASING WINDS AND RAIN CHANCES.  
 

 
   
UPDATE
 
 
NO SIGNIFICANT CHANGES WITH THIS UPDATE.  
 

 
   
NEAR TERM /THROUGH MONDAY/
 
 
SURFACE HIGH PRESSURE ACROSS THE MID ATLANTIC REGION WILL MOVE  
OFFSHORE. THIS WILL VEER OUR SURFACE WINDS EASTERLY THIS  
MORNING, THEN SOUTHEASTERLY LATER TODAY. DEWPOINTS SHOULD SOAR  
INTO THE 60S ALONG THE COAST, LIKELY HELPING DEVELOP A SCATTERED  
CUMULUS CLOUD DECK THIS AFTERNOON. HIGHS ARE EXPECTED TO REACH  
THE LOWER 80S INLAND WITH UPPER 70S AT THE BEACHES.  
 
A SHORTWAVE TROUGH ACROSS THE GULF COAST WILL MOVE EASTWARD  
TONIGHT, HELPING INDUCE SURFACE LOW PRESSURE TO DEVELOP OFF THE  
SOUTH CAROLINA COAST MONDAY MORNING. A SLUG OF MID AND HIGH  
LEVEL MOISTURE AHEAD OF THE TROUGH WILL LEAD TO SKIES BECOMING  
CLOUDIER LATE TONIGHT. ISENTROPIC ANALYSIS WITHIN THIS CLOUD  
LAYER 10-15KFT ALOFT SHOWS SUFFICIENT LIFT FOR RAIN TO DEVELOP  
AFTER 09Z (5 AM EDT) MONDAY, HOWEVER A SUBSTANTIAL LAYER OF DRY  
AIR BETWEEN THE CLOUD BASE AND THE SURFACE SHOULD EVAPORATE A  
GOOD DEAL OF THE LIGHT PRECIPITATION ON ITS WAY DOWN. I'M  
FORECASTING POPS LATE TONIGHT INTO MONDAY MORNING 30-40 PERCENT  
ALONG THE COAST, BUT ONLY 10 PERCENT ALONG THE I-95 CORRIDOR.  
THIS IS MIDWAY BETWEEN THE WETTER GFS AND THE DRIER NAM AND  
ECMWF. FORECAST LOWS RANGE FROM 60 INLAND TO THE MID 60S ON THE  
COAST.  
 
THE UPPER DISTURBANCE SHOULD MOVE OFF THE COAST BY LATE MONDAY  
MORNING, ALLOWING PARTIAL CLEARING TO DEVELOP. SURFACE LOW  
PRESSURE SHOULD CONTINUE TO DEEPEN OFFSHORE AHEAD OF THE UPPER  
DISTURBANCE, PERHAPS INTERRUPTING THE FLOW OF LOW LEVEL MOISTURE  
ACROSS THE EASTERN CAROLINAS AHEAD OF A COLD FRONT MOVING IN  
FROM THE WEST. IT APPEARS THIS MAY PARTIALLY (OR FULLY) DELAY  
THE ONSET OF SHOWERS AND T-STORMS UNTIL THE FRONT ACTUALLY  
ARRIVES MONDAY NIGHT. I'VE BACKED OFF ON RAIN CHANCES MONDAY  
AFTERNOON, BUT CAN'T BRING MYSELF TO FORECAST DRY CONDITIONS  
GIVEN HREF ENSEMBLE CAPE AT OR ABOVE 1000 J/KG AND NAM SOUNDINGS  
SHOWING NO CONVECTIVE CAP PRESENT.  
 

 
   
SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/
 
 
A LINE OF SHOWERS AND THUNDERSTORMS APPROACH FROM THE WEST  
MONDAY EVENING AHEAD OF A COLD FRONT AS AN UPPER LEVEL TROUGH  
MOVES ACROSS THE MID ATLANTIC. STRONG SHEAR ASSOCIATED WITH THE  
TROUGH COMBINED WITH A MOIST AIRMASS WITH DEWPOINTS IN THE UPPER  
60S WILL INCREASE THE THREAT OF SEVERE WEATHER AS THE STORMS  
MOVE ACROSS THE AREA LATE MONDAY EVENING INTO EARLY OVERNIGHT  
HOURS. WITH 0-6 KM SHEAR AROUND 40-60 KTS, DAMAGING WIND GUSTS  
WILL BE THE PRIMARY CONCERN. TORNADO THREAT CANNOT BE DISCOUNTED  
GIVEN FORECASTED LOW LEVEL HELICITY VALUES, BUT STILL UNCERTAIN  
HOW FAVORABLE THE ENVIRONMENT WILL BE, ESPECIALLY WITH THE  
NOCTURNAL TIMING OF THE EVENT.  
 
COLD FRONT MOVES OFFSHORE TUESDAY MORNING WITH DRY AND COOL AIR  
MOVING IN FOR TUESDAY AND TUESDAY NIGHT. WINDS REMAIN A BIT  
BREEZY BEHIND EXITING LOW PRESSURE TO THE NORTHEAST DURING THE  
DAY TUESDAY BEFORE HIGH PRESSURE BUILDS IN FROM THE NORTH  
TUESDAY NIGHT. ABOVE NORMAL LOW TEMPS MONDAY NIGHT AROUND 60,  
COOLER INLAND WHERE CLOUDS WILL CLEAR OUT QUICKER. HIGH TEMPS  
TUESDAY IN THE LOW 70S WITH LOWS TUESDAY NIGHT IN THE UPPER 40S  
AWAY FROM THE COAST.  
 

 
   
LONG TERM /WEDNESDAY THROUGH SUNDAY/
 
 
COOL AND DRY WEATHER CONTINUES WEDNESDAY THROUGH EARLY THURSDAY  
DUE TO BRIEF RIDGING FROM SURFACE HIGH PRESSURE TO THE NORTH.  
ALOFT, A STRONG TROUGH DIGS DOWN INTO TEXAS ON WEDNESDAY BEFORE  
BECOMING A CUTOFF LOW ON THURSDAY. THE STACKED LOW SLOWLY MOVES  
EASTWARD, ENCOMPASSING MOST OF THE EASTERN US ON FRIDAY AND  
SATURDAY. WARM FRONT LIFTS NORTH ACROSS THE AREA LATE THURSDAY  
FOLLOWED BY A COLD FRONT FRIDAY. RAIN CHANCES HIGHEST THURSDAY  
AFTERNOON INTO THURSDAY NIGHT ASSOCIATED WITH THE WARM FRONT.  
THE WIND PROFILE ASSOCIATED WITH THE TROUGH IS QUITE STRONG, BUT  
DECENT INSTABILITY REMAINS HARD TO FIND WITH AMPLE CLOUD COVER.  
SEVERE WEATHER THREAT IS POSSIBLE LATE THURSDAY, BUT LARGE  
UNCERTAINTY STILL EXISTS THIS FAR OUT.  
 
RAIN CHANCES DECREASE FRIDAY, AND EVEN MORESO SATURDAY, AS DRY  
AIR ALOFT MOVES IN. HOWEVER, WITH STACKED LOW TO OUR NORTH AND  
LOW LEVEL MOISTURE LINGERING, FORECASTED POPS ARE SLOW TO  
DIMINISH. WINDS MAY BE A BIT BREEZY FRIDAY AND SATURDAY  
AFTERNOONS DUE TO TIGHTENED PRESSURE GRADIENT AROUND THE LOW.  
TEMPS NEAR NORMAL FOR THE PERIOD, WITH EXCEPTION OF SLIGHTLY  
WARMER TEMPS THURSDAY AND THURSDAY NIGHT.  
 

 
   
AVIATION /17Z SUNDAY THROUGH THURSDAY/
 
 
TRICKY FORECAST ON THE BACK END AS MOISTURE IS EXPECTED TO  
REBOUND OVERNIGHT. GIVEN THAT DEWPOINTS ARE WELL ABOVE GUIDANCE  
AT THIS TIME, THINK CONVECTION MAY BEGIN A BIT EARLIER THAN  
MODEL GUIDANCE, PARTICULARLY AT THE MYRTLES. MONDAY,  
INTERMITTENT SHOWERS WITH PREDOMINATELY MVFR CONDITIONS.  
 
EXTENDED OUTLOOK...CLOUDS AND SHOWERS COULD BRING MVFR  
CONDITIONS MONDAY MORNING. THERE IS A LOW CHANCE OF FLIGHT  
CATEGORY RESTRICTIONS MONDAY NIGHT IN CONVECTIVE SHOWERS.  
LOW CLOUDS, SHOWERS, AND LOW LEVEL WIND SHEAR CONDITIONS COULD  
DEVELOP THURSDAY AS STRONG LOW PRESSURE APPROACHES FROM THE  
WEST.  
 

 
   
MARINE
 
 
THROUGH MONDAY...HIGH PRESSURE OVER THE MID ATLANTIC STATES  
WILL MOVE OFFSHORE TODAY, ALLOWING OUR SURFACE WINDS TO BECOME  
EASTERLY THIS MORNING, THEN SOUTHEASTERLY THIS AFTERNOON. LOW  
PRESSURE IS EXPECTED TO DEVELOP 75- 100 MILES OFF THE SOUTH  
CAROLINA COAST MONDAY MORNING, THEN MOVE NORTHEASTWARD AND AWAY  
FROM THE AREA MONDAY AFTERNOON. THIS LOW SHOULD SPREAD SHOWERS  
ACROSS THE AREA, MAINLY MONDAY MORNING. THE LOW MAY ALSO HELP  
KEEP WIND SPEEDS LOWER THAN THEY OTHERWISE WOULD BE AS A COLD  
FRONT APPROACHES FROM THE WEST. AT THIS TIME IT APPEARS WIND  
SPEEDS SHOULD REMAIN 12 KNOTS OR LESS THROUGH THE PERIOD. SEAS  
AROUND 2 FEET TODAY SHOULD BUILD TO 2-3 FEET MONDAY.  
 
MONDAY NIGHT THROUGH THURSDAY...A COLD FRONT APPROACHES COASTAL  
WATERS EARLY MONDAY NIGHT AND MOVES AWAY FROM COASTAL WATERS BY  
TUESDAY MORNING. LINE OF STORMS ASSOCIATED WITH THE FRONT IS  
EXPECTED TO MOVE ACROSS THE WATERS OVERNIGHT MONDAY, WITH STRONG  
WINDS AND BRIEF WATERSPOUT POSSIBLE. WINDS SPEEDS INCREASE TO  
15-20 KTS OUT OF THE SW AROUND MIDNIGHT, VEERING TO WNW BY  
TUESDAY MORNING. GUSTS TO 25 KTS FORECASTED, PARTICULARLY FOR  
OUTER COASTAL WATERS OFF SE NC, AND A BRIEF SCA MAY BE NEEDED.  
SEAS 3 TO 5 FT MONDAY NIGHT THROUGH TUESDAY AFTERNOON, MIX OF  
WIND CHOP AND A 2-3 FT 7 SEC SE SWELL.  
 
NORTHWEST WINDS REMAIN BREEZY AROUND 15-20 KTS TUESDAY AFTERNOON  
THROUGH EARLY WEDNESDAY DUE TO TIGHTENED PRESSURE GRADIENT AROUND  
EXITING LOW PRESSURE. SEAS 3 TO 4 FT TUESDAY AFTERNOON AND NIGHT.  
HIGH PRESSURE BUILDS IN BRIEFLY FROM THE NORTH WEDNESDAY, DROPPING  
WINDS TO 10 KTS OR LESS BY WEDNESDAY NIGHT. SEAS 2 TO 3 FT WEDNESDAY  
AND WED NIGHT. NEXT SYSTEM APPROACHES ON THURSDAY, STRENGTHENING  
SOUTHERLY WINDS BY LATE THURSDAY AND INCREASING SEAS TO NEAR SCA  
CONDITIONS BY THURSDAY EVENING.  
 

 
   
ILM WATCHES/WARNINGS/ADVISORIES
 
 
SC...NONE.  
NC...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...ILM  
UPDATE...21  
NEAR TERM...TRA  
SHORT TERM...VAO  
LONG TERM...VAO  
AVIATION...43  
MARINE...TRA/VAO  
 
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