153
FXUS62 KILM 131020
AFDILM
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
620 AM EDT TUE AUG 13 2013
.SYNOPSIS...
WARM AND MOIST HIGH PRESSURE WILL PERSIST THROUGH TONIGHT AHEAD OF
A COLD FRONT WHICH WILL MOVE SLOWLY ACROSS THE AREA TONIGHT. THIS
FRONT WILL BECOME STATIONARY JUST SOUTH OF THE LOCAL AREA
WEDNESDAY THROUGH FRIDAY...BEFORE LIFTING BACK NORTH AS A WARM
FRONT DURING THE WEEKEND. PERIODS OF HEAVY RAIN ARE LIKELY THROUGH
THE WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 615 AM TUESDAY...CLUSTERS OF CONVECTION EARLY THIS MORNING
HAVE EVADED THE MAJORITY OF THE ILM CWA. HOWEVER...LATEST 88D
READOUTS INDICATE...1 OF THESE CLUSTERS THAT MOVED ACROSS
WILLIAMSBURG AND SOUTHERN FLORENCE COUNTIES...WILL SLOWLY DISSIPATE
AS IT PUSHES TO THE NORTHEAST.
THE PIEDMONT SFC TROF ORIENTED NE-SW ACROSS THE CENTRAL
CAROLINAS...AND THE SEA BREEZE CIRCULATION LATER THIS MORNING
THROUGH THE AFTERNOON...WILL BOTH BE A FORCING SOURCE FOR
CONVECTION TO DEVELOP. THE SEA BREEZE WILL LIKELY PUSH VERY LITTLE
INLAND...IE. SOMEWHAT PINNED...DUE TO THE STRONGER WINDS ALOFT
JUST OFF THE SFC. THE EXPANDING LONGWAVE UPPER TROF TO THE SOUTH
ACROSS THE EASTERN 1/3RD TO 1/2 OF THE U.S. WILL RESULT WITH
SOME DECREASING TEMPS ALOFT...THAT WILL PRODUCE SOME STEEPER LAPSE
RATES COMPARED TO THE PAST SEVERAL DAYS. OVERALL...THIS WILL AID
CONVECTIVE DEVELOPMENT. IN ADDITION...LATER TONIGHT A S/W TROF
EMBEDDED IN THE LONGWAVE UPPER TROF...WILL PARTIALLY PUSH ACROSS
THE FA DURING THE PRE-DAWN WED HOURS. AND YET ANOTHER AID FOR
CONVECTIVE DEVELOPMENT...WILL BE THE APPROACH OF THE SFC COLD
FRONT FROM THE NW...THAT WILL MERGE WITH THE PIEDMONT TROF. MODELS
INDICATE THIS MERGED BOUNDARY TO REACH THE IMMEDIATE COAST OF THE
ILM CWA BY DAYBREAK WEDNESDAY. AS FOR POPS...HAVE GONE WITH GOOD
CHANCE TO LIKELY CATEGORIES BY MIDDAY TODAY...AND CONTINUING THEM
WELL INTO TONIGHT. VIA SPC DAY1 CONVECTIVE OUTLOOK...HAVE
HIGHLIGHTED JUST THE NC PORTION OF THE ILM CWA WITH ISOLATED
DAMAGING WIND GUSTS POSSIBLE FROM THE DAYS/NIGHTS CONVECTION.
THE AMOUNT OF THE DAYS INSOLATION REACHING THE SFC WILL BE
SOMEWHAT LOWER THAN PREVIOUS DAYS...AND THEREFORE WILL LEAN TOWARD
MODEL MOS GUIDANCE THAT ILLUSTRATES LOWER MAX TEMPS COMPARED TO
THE OTHERS. IN THIS CASE...WILL LEAN TOWARD THE LOWER NAM MOS. TO
OFFSET THE LOWER MAX TEMPS...WILL BE SLIGHTLY HIER SFC DEWPOINTS
ACROSS THE FA COMPARED TO THE PAST SEVERAL DAYS. ALL THIS POINTS
TO HEAT INDICES ONCE AGAIN REACHING THE 100 TO 104 RANGE...JUST
SHY OF AN ADVISORY. AS FOR TONIGHTS MINS...LOW 70S INLAND TO MID
AND UPPER 70S ALONG THE IMMEDIATE COAST. MODELS SOMEWHAT DELAY THE
OCCURRENCE OF CAA AFTER THE CFP LATE TONIGHT.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
AS OF 300 AM TUESDAY...PATTERN SETTING UP FOR WHAT SHOULD BE AN
EXCEEDINGLY WET PERIOD WED/THU ACROSS THE CAROLINAS.
IT STARTS WITH AN ANOMALOUSLY STRONG 5H TROUGH WHICH WILL DIG ACROSS
THE EASTERN CONUS. THIS WILL SERVE A DUAL-PURPOSE TO AIDING RAINFALL
POTENTIAL. FIRST...IT INCREASES THE LOW-LEVEL LAPSE RATES LEADING TO
ENHANCED INSTABILITY. SECOND...AS THE TROUGH AXIS REMAINS WEST OF
THE CWA...SW FLOW ABOVE 850MB PERSISTS...PUMPING COPIOUS GULF
MOISTURE INTO THE COLUMN...AND PWATS RISE TO WELL ABOVE TWO INCHES
THROUGH THE SHORT TERM. AT THE SURFACE...A COLD FRONT WILL CROSS THE
AREA WEDNESDAY BEFORE STALLING ALONG OR JUST SE OF THE COAST ON
THURSDAY. THIS PROVIDES SURFACE CONVERGENCE FOR ENHANCED LIFT WITHIN
THIS MOIST ENVIRONMENT. TO MAKE THE ENVIRONMENT EVEN MORE CONDUCIVE
FOR HEAVY RAINFALL...300MB JETTING INCREASES ON EASTERN SIDE OF THE
LONGWAVE TROUGH...AND REMAINS NEARLY STATIONARY ACROSS THE
NORTHEAST. THIS LEAVES THE CAROLINAS BENEATH THE RRQ /FAVORABLE
DIFFLUENT REGION/ WHICH WILL ONLY AID AS A LIFTING
MECHANISM...COMBINING WITH PVA AHEAD OF 5H AND 7H IMPULSES ROTATING
THROUGH ALOFT.
ALL OF THESE PARAMETERS REMAIN IN PLACE FOR THE DURATION OF THE
PERIOD AS THE MID-LEVEL FLOW BECOMES INCREASINGLY AMPLIFIED WHICH
CAUSES NEARLY NO LONGITUDINAL PROGRESSION OF THE FEATURES. THIS
CREATES A SITUATION WHERE A LONG-PERIOD OF CONVECTION WITH EMBEDDED
VERY HEAVY RAINFALL WILL OCCUR ACROSS THE REGION. THE ONLY LIMITING
FACTOR EVIDENT IS THE SURFACE FRONT...WHICH MAY DRIFT FAR ENOUGH TO
THE SOUTH THAT SOME RESIDUAL DRYING WORKS INTO THE NORTHWEST HALF OF
THE AREA. THIS IS EVIDENT CLEARLY IN 850MB MOISTURE TRANSPORT
VECTORS WHICH ARE AIMED SQUARELY ALONG THE COAST...AND MUCH DRIER
MID-LEVEL AIR IN FORECAST SOUNDINGS NEAR I-95 VS THE CAPE FEAR
COAST. WILL CONTINUE THE HIGH-LIKELY POP FOR THE COAST THROUGH THE
PERIOD...BUT AGREE WITH INHERITED HIGH-CHC INLAND ON THURSDAY WHERE
QPF MAY NOT BE AS SIGNIFICANT. STILL...THE POTENTIAL EXISTS FOR
SIGNIFICANT RAINFALL ACROSS THE AREA THROUGH THE SHORT TERM...WHICH
MAY CAUSE LOCALIZED FLOODING AT TIMES.
TEMPS WILL BE SIGNIFICANTLY IMPACTED BY CLOUDS AND RAIN...AND HIGHS
WILL AVERAGE 4-8 DEGREES BELOW NORMAL...WITH THURSDAY BEING THE
COOLEST DAY. DIURNAL RANGES WILL BE LIMITED AS WELL...AND EXPECT
ONLY ABOUT 10 DEGREE DIFFERENCES BETWEEN MAX AND MIN DURING THE
PERIOD. HIGHS WILL BE IN THE LOW/MID 80S WED...AND AROUND 80 ON THU.
LOWS WILL FALL TO AROUND 70 BOTH NIGHTS...COOLER INLAND ON THU NIGHT.
&&
.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 300 AM TUESDAY...CONTINUED WET PERIOD TO START THE LONG
TERM...BUT IMPROVEMENTS ARE POSSIBLE LATE...INTO NEXT WEEK.
MID-LEVEL TROUGH AND SURFACE COLD FRONT WILL REMAIN IN PLACE FRIDAY
INTO THE WEEKEND. THIS WILL OCCUR IN AN ENVIRONMENT CHARACTERIZED BY
PWATS OVER TWO INCHES...AND HENCE SCATTERED TO WIDESPREAD
SHOWERS/TSTMS ARE EXPECTED. HOWEVER...FRIDAY MAY END UP BEING
SLIGHTLY LESS ACTIVE AS THE FRONT WILL WAVER JUST OFFSHORE...WITH
SOME DRIER AIR EVIDENT ON FORECAST SOUNDINGS DURING FRIDAY. AS THE
MID-LEVEL TROUGH SHARPENS FURTHER DURING THE WKND...A 5H LOW WILL
TRY TO CLOSE OFF ACROSS THE TN VLY. THIS HAS A TWO-PRONGED EFFECT ON
THE AREA. IT WILL FIRST PULL THE FRONT BACK NORTH CREATING A RENEWED
ROUND OF CONVECTION SATURDAY...AND THEN MORE TYPICAL SUMMERTIME
CONVECTION ON SUNDAY AS THE FRONT STAYS NORTH OF THE AREA...ALLOWING
FOR A WARMER AND MORE HUMID AIR MASS TO FLOOD INTO THE REGION.
TOWARDS THE END OF THE PERIOD...THE MID-LEVEL RIDGE OFFSHORE WILL
RETROGRADE WESTWARD BACK TOWARDS THE COAST...THANKS IN PART TO THE
CLOSING OF THE 5H LOW AND EXPANSION OF THE RIDGE ITSELF. THIS WILL
CAUSE SOMEWHAT DRIER AIR TO WORK INTO THE CAROLINAS...BUT TYPICAL
SUMMERTIME WEATHER IS EXPECTED FOR EARLY NEXT WEEK.
TEMPS WILL START WELL BELOW CLIMO FRI/SAT...BEFORE WARMING TO MORE
SEASONABLE LEVELS SUNDAY AND ESPECIALLY ON MONDAY.
&&
.AVIATION /10Z TUESDAY THROUGH SATURDAY/...
AS OF 06Z...EXPECT VFR OVERNIGHT AT THE COASTAL TERMS WITH
OCCASIONAL CONVECTIVE DEBRIS CLOUDINESS FROM UPSTREAM. FOR THE
INLAND TERMS...FLO AND LBT...A CLUSTER OF STORMS FROM ROUGHLY
FLORENCE NORTHWARD TO ROCKINGHAM WILL PUSH TO THE ENE AND CROSS
BOTH INLAND TERMS DURING THE NEXT 1 TO 2 HOURS. HAVE INCLUDED MVFR
CONDITIONS FROM THIS CONVECTION...WITH THE BEST CHANCE FOR IFR
WILL BE THE NORTHERN PORTIONS OF THIS CLUSTER WHICH SHOULD REMAIN
NORTH OF THE ILM CWA. AFTERWARDS...DEBRIS CLOUDS AND ACTIVE LOW-
LEVEL WINDS SHOULD INHIBIT ANY FOG FORMATION. BY MIDDAY TUESDAY...
SEA BREEZE CIRCULATION SHOULD HAVE DEVELOPED...ALONG WITH
T-STORMS ALONG THIS BOUNDARY AS A RESULT OF DAYTIME HEATING...A
MOIST AIR MASS IN PLACE WITH PWS 2+ INCHES...AND WITH LIFT
PROVIDED BY THE SEA BREEZE. AT THIS POINT...WILL INCLUDE VCTS FOR
THE COASTAL TERMS BY LATE MORNING THROUGH THE AFTN HOURS. AT
KFLO/KLBT...PCPN CHANCES INCREASE AFTER 19Z WITH AN APPROACHING
BOUNDARY RESULTING FROM THE MERGER OF A COLD FRONT WITH THE
PIEDMONT TROF. THE TIGHTENING GRADIENT WILL RESULT IN SW-WSW
WINDS INCREASING TO 10-15 KTS AND GUSTS UP TO 20 KTS DURING THE
DAY. THE COASTAL TERMS WILL OBSERVE SSW-SW WINDS AT THE SAME
PREVIOUSLY MENTIONED SPEEDS. WILL ALSO INCLUDE VCTS AT ALL TERMS
DURING THE NIGHT...THROUGH THE END OF THE 06Z TAF ISSUANCE
PERIOD.
EXTENDED OUTLOOK...EXPECT NUMEROUS SHOWERS AND T-STORMS WEDNESDAY
THROUGH SATURDAY...WITH LOCALIZED PERIODS OF MVFR/IFR/LIFR
POSSIBLE DUE TO HEAVY RAINFALL.
&&
.MARINE...
NEAR TERM /THROUGH TONIGHT/...
AS OF 615 AM TUESDAY...SCEC HAS BEEN RAISED FOR ALL 4 COASTAL WATERS
ZONES FROM MID-MORNING TODAY THROUGH DAYBREAK WEDNESDAY.
SCEC CONDITIONS TO DEVELOP TODAY AND PERSIST THROUGH TONIGHT UP
UNTIL A PARTIAL CFP SLATED AROUND DAYBREAK WEDNESDAY. THE SFC
PRESSURE PATTERN AND GRADIENT AHEAD OF THE COLD FRONT WILL PRODUCE
A SW-WSW WIND DIRECTION ACROSS THE WATERS WITH SPEEDS INCREASING
TO 15 TO 20 KT...WITH FEW GUSTS UP TO 25 KT POSSIBLE DURING LATE
TODAY THRU TONIGHT.
SIGNIFICANT SEAS WILL BUILD TO 3 TO 5 FT LATER THIS MORNING...AND
PERSIST AT THESE HEIGHTS THRU TONIGHT. THE WIND DRIVEN 4 TO 6
SECOND PERIOD WIND WAVES WILL DOMINATE THE WAVE SPECTRUM...WITH A
1 TO 2 FOOT EASTERLY GROUND SWELL AT 9-10 SECOND PERIODS REMAINING
IDENTIFIABLE.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 300 AM
TUESDAY...COLD FRONT WILL CROSS THE WATERS SLOWLY ON
WEDNESDAY...TURNING WINDS FROM SW TO NE DURING THE AFTN.
REGARDLESS OF DIRECTION...SPEEDS WILL BE QUITE LIGHT...10 KTS OR
LESS ON WEDNESDAY. AS FRONT PUSHES SOUTH OF THE WATERS...A NE
SURGE WILL OCCUR ON THURSDAY AND WINDS WILL INCREASE RAPIDLY TO
AROUND 15 KTS...POSSIBLY UP TO 20 KTS NEAR THE 20NM BOUNDARY. SEAS
BECOME PRIMARILY WIND-WAVE DOMINATED...2-4 FT WEDNESDAY...GROWING
TO 3-4 FT WITH ISOLATED 5 FTERS POSSIBLE THURSDAY THANKS TO THE
INCREASED NE WINDS.
LONG TERM /FRIDAY THROUGH SATURDAY/...
AS OF 300 AM TUESDAY...COLD FRONT SOUTH OF THE WATERS FRIDAY WILL
LEAVE NE WINDS OF 10-15 KTS IN ITS WAKE ACROSS THE WATERS. THESE
WINDS WILL REMAIN FROM THE NE ALL OF FRIDAY INTO SATURDAY...BEFORE
THE FRONT LIFTS BACK TO THE NORTH DURING SATURDAY...WITH WINDS
TURNING TO THE SE AT 10 KTS OR LESS. SEAS START 2-4 FT EARLY FRIDAY
WITH A NE WIND CHOP PREDOMINANT IN THE WAVE SPECTRUM. AS WINDS EASE
THROUGH THE PERIOD WAVE HEIGHTS WILL FALL TO 2-3 FT...AND THEN 1-2
FT LATE SATURDAY.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...NONE.
&&
$$
SYNOPSIS...JDW
NEAR TERM...DCH
SHORT TERM...JDW
LONG TERM...JDW
AVIATION...DCH/BJR