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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KILM 191028
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
628 AM EDT SUN MAY 19 2013

.SYNOPSIS...
COMBINATION OF BERMUDA HIGH PRESSURE OFFSHORE...AND WEAK LOW
PRESSURE ALOFT...WILL CREATE INCREASING THUNDERSTORM CHANCES AND
SEASONABLE TEMPS DURING THE NEXT FEW DAYS. A DRYING AND WARMING
TREND WILL FOLLOW FOR THE MIDDLE OF THE WEEK. A COLD FRONT WILL
APPROACH FRIDAY...BRINGING A RENEWED CHANCE FOR
THUNDERSTORMS...AND COOLER TEMPERATURES INTO NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 630 AM SUNDAY...SATELLITE WATER VAPOR ANIMATION THIS MORNING
SHOWS A SWIRL OF VORTICITY MOVING EAST ACROSS THE PEE DEE AND
SANDHILLS REGION OF THE CAROLINAS. THIS IS LIKELY WHAT HAS PRODUCED
THE EXPLOSION OF SLOW MOVING CONVECTIVE SHOWERS ACROSS DARLINGTON
AND FLORENCE COUNTIES IN THE PAST FEW HOURS. RAINFALL ESTIMATES FROM
RADAR ARE AS HIGH AS 1.23 INCHES IN THE STAR FORK BRANCH JUST SOUTH
OF DARLINGTON RACEWAY. SIMILAR TOTALS ARE POSSIBLE IN THE NEXT HOUR
OR TWO ACROSS EASTERN DARLINGTON COUNTY AND ADJACENT PORTIONS OF
SOUTHWESTERN MARLBORO COUNTY.

A WEAK VORTICITY LOBE EXTENDING TO THE SOUTH OF THIS SWIRL ALSO
APPEARS TO BE RESPONSIBLE FOR THE SCATTERED SHOWERS DEVELOPING FROM
MCCLELLANVILLE INTO GEORGETOWN AND ON NORTH INTO MYRTLE BEACH. POPS
FOR THE MORNING HOURS HAVE BEEN RAISED ACROSS THIS AREA AS WELL.

IT IS CURRENTLY NOT KNOWN HOW MUCH (IF ANY) SUBSIDENCE WILL DEVELOP
BEHIND THIS DEPARTING VORTICITY MAXIMUM AND WHAT ITS IMPACT MIGHT BE
ON AFTERNOON CONVECTION. FARTHER UPSTREAM THERE APPEARS TO BE ACTIVE
CONVECTION ONGOING ACROSS NORTH GEORGIA AND EASTERN TENNESSEE THAT
ADVECTION OF THE UPPER FLOW SHOULD BRING TOWARD THIS PART OF THE
CAROLINAS BY LATE IN THE DAY. FOR THIS REASON I HAVE NOT ADJUSTED
AFTERNOON POPS DOWNWARD. NO CHANGES HAVE BEEN MADE TO FORECAST HIGHS
EITHER. PREVIOUS DISCUSSION FROM 300 AM FOLLOWS...

HIGH PRESSURE OFF THE NORTHEAST COAST AND STRONG LOW PRESSURE ACROSS
THE CENTRAL PLAINS IS PRODUCING A SOUTH WIND ACROSS THE CAROLINAS. A
WEAK AND BAGGY UPPER TROUGH ACROSS THE SOUTHERN APPALACHIANS WILL
HELP BRING GOOD CHANCES OF SHOWERS AND THUNDERSTORMS TO THE EASTERN
CAROLINAS THIS AFTERNOON. THIS IS ALMOST A TROPICAL AIRMASS WITH
PRECIPITABLE WATER OVER 1.60 INCHES AND 850 MB TEMPS AROUND
+12C...AND IT WILL NOT TAKE MUCH SUNSHINE TO IGNITE PLENTY OF
SURFACE-BASED CONVECTION TODAY GIVEN NO CAPPING INVERSION ALOFT. THE
BEST COVERAGE OF SHOWERS AND STORMS SHOULD REMAIN INLAND FROM THE
COAST FOLLOWING THE BETTER MID-LEVEL MOISTURE NEAR THE UPPER TROUGH.
ONCE THE AFTERNOON SEABREEZE CIRCULATION CRANKS UP...SUBSIDENCE AND
STABLE AIR FROM THE NEARSHORE OCEAN WATERS SHOULD CREATE A MINIMUM
IN CONVECTIVE COVERAGE ALONG THE COAST. THIS LEAVES THIS MORNING FOR
THE BEST CHANCE OF SHOWERS ALONG THE IMMEDIATE COAST.

FORECAST WIND PROFILES SHOW INSUFFICIENT DIRECTIONAL SHEAR OR WIND
SPEEDS FOR STORM CELL ORGANIZATION. SLOW MOVEMENT AND HIGH
PRECIPITABLE WATER MAY LEAD TO HEAVY RAINFALL HOWEVER. SINCE ANY
BREAKS IN CLOUD COVER SHOULD LEAD TO RAPID CUMULUS DEVELOPMENT...
HIGHS SHOULD ONLY RISE INTO THE LOWER 80S AWAY FROM THE BEACHES.

TONIGHT...CONVECTIVE ACTIVITY WILL DIMINISH IN COVERAGE DURING THE
EVENING BUT WILL NOT END COMPLETELY AS THE DEEPEST MOISTURE WITH THE
WEAK UPPER DISTURBANCE REMAINS ACROSS THE INTERIOR CAROLINAS. LOWS
SHOULD FALL INTO THE MID TO UPPER 60S UNDER MOSTLY CLOUDY SKIES.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 AM SUNDAY...COMBINATION OF BERMUDA HIGH PRESSURE AND WEAK
MID-LEVEL IMPULSE WILL CREATE SCATTERED TO WIDESPREAD CONVECTION
DURING THE FIRST PART OF THE WEEK.

BERMUDA HIGH PRESSURE WHICH HAS BEEN DOMINATING THE SYNOPTIC REGIME
FOR SEVERAL DAYS NOW WILL CONTINUE TO SIT IN PLACE
OFFSHORE...PUMPING WARM MOIST AIR INTO THE CAROLINAS. WHILE THIS
TYPICALLY SUPPORTS TEMPS NEAR TO ABOVE CLIMO...ITS ALSO A SETUP THAT
FEATURES DIURNAL CONVECTION. THIS CASE WILL BE NO DIFFERENT...EXCEPT
THAT TSTMS ARE EXPECTED TO BE MORE WIDESPREAD THAN "TYPICAL" DUE TO
THE PRESENCE OF THE SHORTWAVE ALOFT. SLIGHTLY COOLER MID-LEVEL TEMPS
WILL ENHANCE LAPSE RATES...WHILE MODERATE PVA ASSOCIATED WITH THE
IMPULSE WILL HELP DRIVE LIFT. WITH INSTABILITY PROGGED TO BE 1000 -
2000 J/KG...EVEN WITH AMPLE CLOUD COVER CONVECTION SHOULD TRIGGER
DURING THE EARLY AFTN ALONG THE PIEDMONT TROUGH AND SEA BREEZE
BOUNDARY EACH DAY. ADDITIONALLY...MONDAY NIGHT CONVECTION WILL
LIKELY LINGER MANY HOURS AFTER NIGHTFALL AS RESIDUAL OUTFLOW
BOUNDARIES TAP REMNANT ELEVATED CAPE ALLOWING FOR SHOWERS/TSTMS TO
PERSIST.

WHILE CONVECTION WILL BE LIKELY ON MONDAY...THERE IS SLIGHTLY MORE
UNCERTAINTY TUESDAY DUE TO THE DISAGREEMENT IN MODEL OUTCOMES ON
THE EVOLUTION OF THE SHORTWAVE ALOFT. FEEL THE SLOWER GFS MAY BE
CORRECT DUE TO THE ALREADY SLOW-MOVEMENT OF THIS FEATURE...SO
ANOTHER DAY OF ENHANCED LIFT IS POSSIBLE TUESDAY AND THUS WILL CARRY
HIGH CHC POP TUESDAY AFTN. IF THE FASTER SOLUTION ENDS UP BEING
CORRECT...SOME SUBSIDENCE BEHIND THE VORT MAY LIMIT OVERALL
CONVECTIVE COVERAGE TUESDAY.

TEMPS MON/TUE WILL BE AROUND CLIMO...TEMPERED SLIGHTLY BY CLOUD
COVER. EXPECT HIGHS IN THE LOW 80S AWAY FROM THE IMMEDIATE COAST
MONDAY...AND THEN A FEW DEGREES WARMER TUESDAY. LOWS WILL BE HELD UP
BY CLOUD COVER...FALLING ONLY INTO THE UPPER 60S BOTH NIGHTS.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 300 AM SUNDAY...BUILDING HEIGHTS ALOFT AND BERMUDA-TYPE
SURFACE HIGH OFFSHORE WILL CREATE SUMMER LIKE CONDITIONS THROUGH THE
MAJORITY OF NEXT WEEK. WHILE THE FIRST TWO DAYS...WED/THU...ARE
LIKELY TO BE THE WARMEST...THERE IS SOME UNCERTAINTY DUE TO THE
PRESENCE OF A DEPARTING SHORTWAVE ALOFT. ATTM EXPECT THE IMPULSE TO
BE OFFSHORE...SO SOME SUBSIDENCE BEHIND THIS FEATURE AND BENEATH
BUILDING 1000-500MB THICKNESSES WILL BUMP TEMPS AND LOWER OVERALL
CONVECTIVE POTENTIAL. HOWEVER...WITH THETA-E RIDGING CONTINUING AND
TEMPS RISING INTO THE MID 80S...TSTMS WILL STILL BE POSSIBLE EACH
DAY. ALTHOUGH CONVECTION SHOULD NOT BE WIDESPREAD WED/THU...AND
FOCUSED ON THE USUAL BOUNDARIES (SEA BREEZE FRONT AND PIEDMONT
TROUGH)...WILL CARRY SCHC POP ACROSS THE ENTIRETY OF THE CWA SINCE
IT WOULD BE SUPERFLUOUS TO TRY TO NAIL DOWN SPATIAL EXTENT OF
COVERAGE THIS FAR OUT.

LATE IN THE WEEK...FULL LATITUDE TROUGH WILL BEGIN TO DISPLACE THE
UPPER RIDGE ACROSS THE EAST...LEADING TO INCREASING CONVECTIVE
POTENTIAL FRI AHEAD OF A COLD FRONT WHICH IS CURRENTLY PROGGED TO
CROSS FRIDAY AFTN. WOULD EXPECT FROPA TO SLOW WITH LATER MODEL RUNS
DUE TO DEEP SOUTHERLY FLOW AHEAD OF IT AND THE KNOWN MODEL BIAS TO
BREAK DOWN RIDGES TOO QUICKLY. WILL CONTINUE INHERITED LOW-CHC POP
FRIDAY AND SCHC SATURDAY...BUT IT IS POSSIBLE THAT COOLER AND DRIER
AIR WILL WORK INTO THE REGION BY NEXT WEEKEND.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AS OF 06Z...SCATTERED MAINLY LIGHT SHOWERS ARE POSSIBLE THROUGH
DAYBREAK AT FLO/LBT WITHIN A BAND OF THICKER MID-LEVEL MOISTURE LEFT
OVER FROM SATURDAY`S INLAND THUNDERSTORM ACTIVITY. PLENTY OF BKN
MID-LEVEL CLOUDS COULD BECOME ACCOMPANIED BY SCATTERED LOW CLOUDS AS
SURFACE TEMPERATURES APPROACH DEWPOINT TEMPERATURES OVER THE NEXT
FEW HOURS. THE ATMOSPHERE APPEARS SET FOR ANOTHER ROUND OF INLAND
SHOWERS AND STORMS SUNDAY AFTERNOON. BIGGEST THREAT WILL BE REDUCED
VSBY IN HEAVY RAINFALL. LESSER CHANCES FOR SHOWERS AND STORMS ARE
EXPECTED AT THE COAST ALTHOUGH THERE ARE SOME INDICATIONS IF
ANYTHING AFFECTS THE ILM/CRE/MYR IT COULD BE A LATE MORNING EVENT
RATHER THAN AFTERNOON LIKE FARTHER INLAND. OTHERWISE GENERALLY SOUTH
SURFACE WINDS WILL INCREASE TO AROUND 10 KT DURING THE DAY.

EXTENDED OUTLOOK...AFTN SHOWERS/TSTMS POSSIBLE AGAIN MONDAY.
OTHERWISE PREVAILING VFR.

&&

.MARINE...
-- Changed Discussion --
NEAR TERM /THROUGH TONIGHT/...
AS OF 630 AM SUNDAY...NO SIGNIFICANT CHANGES HAVE BEEN MADE TO THE
FORECAST THIS MORNING. PREVIOUS DISCUSSION FROM 300 AM FOLLOWS...

HIGH PRESSURE RIDGING SOUTHWARD ACROSS THE WESTERN ATLANTIC FROM ITS
CENTER OVER NEWFOUNDLAND CANADA...AND LOW PRESSURE OVER NEBRASKA
WILL BOTH MOVE LITTLE THROUGH TONIGHT. THIS WILL MAINTAIN A
SOUTHERLY WIND ACROSS THE CAROLINA COASTAL WATERS... WITH WIND
SPEEDS GENERALLY 10-15 KNOTS. SCATTERED SHOWERS THIS MORNING MAY
DIMINISH IN COVERAGE THIS AFTERNOON DUE TO SINKING AIR BEHIND THE
DAYTIME SEABREEZE FRONT. CHANCES FOR SHOWERS AND THUNDERSTORMS WILL
RETURN TONIGHT AS A WEAK UPPER LEVEL DISTURBANCE BEGINS TO DRIFT
EAST OVER THE INTERIOR CAROLINAS.

SEAS CURRENTLY ARE AROUND 2 FEET...BUT MAY BUILD TO 3 AND EVEN 4 FT
OUT AT 20 MILES DISTANCE FROM SHORE BY THIS EVENING...ALL DUE TO
PERSISTENT SOUTH WINDS ACROSS THE WESTERN ATLANTIC. SPECTRAL WAVE
DATA FROM THE FRYING PAN SHOALS BUOY SHOWS THE BULK OF THE WAVE
ENERGY CURRENTLY IS EMBODIED IN A 9 SECOND SOUTHEAST SWELL...WHICH
WILL CONTINUE INTO TONIGHT AS THE 4-5 SECOND SOUTH WIND WAVES BUILD
ON TOP.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 300 AM SUNDAY...LITTLE VARIABILITY IN MARINE CONDITIONS FOR
THE EARLY PART OF THE WEEK AS BERMUDA HIGH PRESSURE RETAINS ITS
CONTROL OVER THE SYNOPTIC REGIME. THIS MANIFESTS ITSELF AS
PERSISTENT S/SW WINDS OF 10-15 KTS...WITH LITTLE FLUCTUATION DURING
THE PERIOD. WHILE THESE WINDS WILL CREATE A SOUTHERLY 5 SEC WIND
CHOP OF 3-4 FT...THE LONGEVITY OF THIS BERMUDA HIGH HAS ALLOWED A
2FT/10SEC SE SWELL TO DEVELOP IN THE WAVE SPECTRUM AS WELL. THESE
TWO WAVE GROUPS WILL COMBINE TO CREATE 2-4 FT SEAS THROUGH THE
PERIOD.

LONG TERM /WEDNESDAY THROUGH THURSDAY/...
AS OF 300 AM SUNDAY...PERSISTENT BERMUDA HIGH OFFSHORE WILL MAINTAIN
ITS POSITION THROUGH THE EXTENDED...KEEPING S/SW RETURN FLOW ONGOING
ACROSS THE WATERS AT 10-15 KTS. WHILE A WEAK SE SWELL WILL BE
EVIDENT WITHIN THE WAVE SPECTRUM THROUGH MID-WEEK...IT WILL FEATURE
A SLOWLY DECAYING AMPLITUDE...ALLOWING SEAS TO BECOME MORE WIND-WAVE
DOMINATED WITH A SHORTER AVERAGE PERIOD. AS THE SWELL DECAYS...3-6
FT SOUTHERLY WIND WAVES BECOME DOMINANT...AND THESE SHORTER PERIODS
HELP WAVE AMPLITUDES GROW WITHIN THE COASTAL WATERS. SEAS INITIALLY
OF 2-4 FT WILL INCREASE LATE THURSDAY AHEAD OF A COLD FRONT
ADVANCING FROM THE WEST...AND MAY APPROACH SMALL CRAFT ADVISORY
THRESHOLDS LATE.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...JDW
NEAR TERM...TRA
SHORT TERM...JDW
LONG TERM...JDW
AVIATION...TRA