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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