940
FXUS61 KAKQ 130812
AFDAKQ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
412 AM EDT TUE AUG 13 2013
.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA LATE THIS AFTERNOON AND TONIGHT.
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH WEDNESDAY
INTO THURSDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
LATEST WX ANALYSIS DEPICTS MAIN AREA OF SFC LOW PRESSURE OVER THE
EASTERN GREAT LAKES WITH A WEAK TROUGH/SFC WARM FRONT EXTENDING SE
INTO THE NORTHERN MID ATLC REGION. THIS HAS PLACED BULK OF THE AKQ
IN BETWEEN ORGANIZED AREAS OF CONVECTION TO THE NORTH IN ADVANCE OF
THE COLD FRONT AND TO THE SOUTH ASSOCIATED W/ WEAK SFC TROUGHING AND
SHORTWAVE ENERGY. MOD EL HAVE GENLY BEEN OVERDOING THE AMOUNT AND
COVERAGE OF PRECIP THUS FAR EARLY THIS MORNING AND WILL MAINTAIN
ONLY SLIGHT CHC TO CHC POPS FOR MOST OF THE REGION THROUGH 12Z. DID
INCLUDE A SMALL AREA OF LIKELY POPS FOR THE NEXT FEW HRS ACRS
INTERIOR NE NC AND INTO FAR SE VA FOR SHOWERS AND POSSIBLY A FEW
EMBEDDED TSTMS.
BELIEVE THERE WILL BE SEVERAL HRS LATER THIS MORNING INTO EARLY THIS
AFTN WITH LITTLE TO NO PRECIPITATION OVER MOST OF TH CWA...IN
GENERAL THINK MODELS ARE TOO FAST WITH ADVECTION OF CURRENT ACTIVITY
OVER FAR SW VA AND ERN TN. THIS SHOULD ALLOW FOR AT LEAST A FEW HRS
OF PARTLY SUNNY SKIES INTO MIDDAY WITH TEMPERATURES RAPIDLY RISING
THROUGH THE 80S TO NEAR 90. MODEL ML CAPES AVG 1000-1500 J/KG N/W
AND 1500-2000 J/KG ACRS FAR S/E VA AND ERN NC BY 18Z. DEEP LAYER
SHEAR OF AROUND 30 KT IS FAIRLY IMPRESSIVE FOR AUGUST AND WILL
SUPPORT STRONG GUSTY WINDS IN AFTN CONVECTION. SPC HAS PLACED ALL
BUT FAR NW COUNTIES IN SLIGHT RISK FOR SEVERE WX TODAY (WIND
THREAT) BUT IN GENERAL THINK THAT BEST COVERAGE OF STORMS (AND
THEREFORE HIGHEST POTENTIAL FOR SEEING SEVERE WX) WILL RESIDE OVER
SE 1/2 OF THE CWA WHERE ML CAPES ARE A BIT HIGHER. LOW LEVEL WIND
DIRECTION IS PROGGED TO AVG ALMOST DUE WESTERLY OVER MUCH OF
CENTRAL VA THIS AFTN WHICH WOULD SUGGEST SOMEWHAT DRIER AIR AND
ONLY SCATTERED COVERAGE OF STORMS. WITH PRECIPITABLE WATERS OF AROUND
2" HAVE LEFT POPS AT LOW END LIKELY THIS AFTN IN CENTRAL VA...BUT
MANY AREAS MAY ONLY SEE A BRIEF SHOWER OR TSTM (ALTHOUGH SHEAR
WILL BE ENOUGH THAT AT LEAST ISOLATED SEVERE STORMS WILL BE POSSIBLE).
FARTHER S/E AS SFC TROUGH DEEPENS WITH AFTN HEATING WILL CARRY A
70% POP AND THIS IS WHERE SEVERAL ROUNDS OF TSTMS ARE MORE
LIKELY...AS WELL AS POTENTIAL FOR LOCALIZED FLOODING. PRECIP WILL
GENLY WANE IN COVERAGE THROUGH THE EVENING HRS ACRS NW
AREAS...WHILE MUCH OF SE VA/NE NC WILL CONTINUE W/ LIKELY POPS
THROUGH MIDNIGHT.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
GFS/NAM IN GOOD AGREEMENT THAT THE SFC COLD FRONT WILL THE FRONT
WILL HAVE PUSHED TO AROUND CAPE HATTERAS BY 12Z/WED...AND WILL
CARRY ONLY A 20% POP IN NE NC EARLY ON. SKIES WILL AVG MOSTLY
SUNNY BY LATE MORNING ONWARD FOR MOST OF VA...PARTLY SUNNY ACRS
THE FAR SE. STRONG UPPER TROUGH SWINGING ACRS NEW ENGLAND WILL
BRING A REFRESHINGLY COOL/DRY AIRMASS TO THE MID ATLC STATES. MOS
DEW PTS ARE PROGGED TO AVG INTO THE UPPER 40S TO LOWER 50S OVER
NORTHERN ZONES BY AFTN AND IN THE 50S OVER THE SOUTH. HIGHS WILL
ONLY TOP OUT IN THE UPPER 70S TO AROUND 80 THROUGHOUT. SFC HIGH
PRESSURE CENTERED OVER THE GREAT LAKES AND OHIO VALLEY WILL RIDGE
SE INTO THE MID ATLC PROVIDING MAINLY CLEAR SKIES WED NIGHT. WENT
CLOSE TO MOS NUMBERS WITH LOWS MAINLY IN THE 50S WELL INLAND AND
60-65 SE COASTAL SECTIONS.
NAM/UKMET LIFT MORE CLOUDS AND SOME MOISTURE BACK NORTH INTO SE VA/NE
NC ON THU WHILE GFS/ECMWF GENLY KEEP THE SFC RIDGING STRONGER WITH
BULK OF CLOUDS AND MOISTURE STAYING ACRS SE NC. THINK THE DRIER
FORECAST IS MORE PROBABLE BUT WILL RETAIN A LOW CHC FOR SHOWERS IN
NE NC...PARTLY TO MOSTLY SUNNY ELSEWHERE. HIGHS REMAIN SEVERAL
DEGREES BELOW AVG IN THE UPPER 70S TO LOWER 80S.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
EXTENDED PERIOD WILL BE HIGHLIGHTED BY A PROLONGED PERIOD OF
UNSETTLED WEATHER WITH BELOW NORMAL DAYTIME TEMPERATURES.
MEDIUM RANGE MODELS IN GOOD AGREEMENT ON HANDLING AMPLIFIED LARGE
SCALE FLOW PATTERN (STRONG RIDGE IN THE WEST AND STRONG TROUGH IN
THE EAST) THRU EARLY NEXT WEEK. SHORTWAVE ENERGY WILL DIVE
DOWN THE BACK SIDE OF THE UPPER TROUGH OVER THE MIDWEST
FRI-SAT...REINFORCING LOWER HEIGHTS OVER THE EAST. ENERGY IS THEN
EXPECTED TO AID IN THE DEVELOPMENT OF AN UPPER LOW POSITIONED OVER
THE MID MS VALLEY SAT. STRONG UPPER BLOCKING RIDGE WILL REMAIN OVER
THE WRN ATLANTIC...KEEPING THE UPPER TROUGH ANCHORED OVER THE EAST
THROUGH THE WEEKEND. STRONG BERMUDA HIGH WILL ALSO BUILD WWD THROUGH
THE WEEKEND...BEFORE STALLING OFF THE SE COAST SUN. THIS WILL PLACE
THE MID ATLANTIC IN FAVORABLE SWLY FLOW ALOFT...ADVECTING ABUNDANT
DEEP MOISTURE INTO THE REGION. MEANWHILE AT THE SFC...MEAN FRONTAL
POSITION EXPECTED TO BE ALONG THE SE COAST INTO THE DEEP SOUTH FRI
AS COOL HIGH PRESSURE REMAINS OVER THE GREAT LAKES REGION. LATEST
ECMWF AND GFS GUIDANCE DIFFERS ON TIMING AND PLACEMENT OF THE
FRONT...MOSTLY RELATING TO HOW FAR SOUTH THE FRONT WILL MAKE IT
DURING THE SHORT TERM. HAVE OPTED TO TREND EXTENDED FORECAST TOWARD
A BLEND OF THE TWO UNTIL DIFFERENCES CAN BE RESOLVED. HIGH PRESSURE
AND DRIER WEATHER EXPECTED FRI WITH THE FRONT TO THE SOUTH. HAVE
OPTED TO PUSH CHANCE POPS FARTHER SOUTH FRI...GENERALLY IN NC. A
TROPICAL WAVE OVER THE ERN GULF IS EXPECTED TO LIFT ALONG THE FRONT
SAT-SUN. MODELS DIFFER ON THE STRENGTH OF THE WAVE...BUT THE RESULT
WILL BE THE SAME...A WET WEEKEND ACROSS THE MID ATLANTIC. A SERIES
OF SHORTWAVES (MAINLY ASSOCIATED WITH THE WAVE) IN THE SWLY FLOW
WILL INTERACT WITH THE FRONT...RESULTING IN SEVERAL ROUNDS OF
RAINFALL (POSSIBLY HEAVY AT TIMES) SAT-SUN. WILL LIMIT TO CHANCE
POPS DUE TO IT STILL BEING DAYS 6-7 AS WELL AS AFOREMENTIONED
FRONTAL DIFFERENCES. THUNDERSTORM POTENTIAL WILL BE RATHER LIMITED
DUE TO ABUNDANT CLOUD COVER AND WIDESPREAD PRECIP. UPPER CLOSED LOW
OVER THE MIDWEST WILL OPEN MON AND EJECT NEWD. MOISTURE WILL BEGIN
TO PUSH OFFSHORE...BUT WILL KEEP MENTION OF CHANCE POPS MON
AFTERNOON DUE TO THE CLOSE PROXIMITY OF THE FRONT AND UPPER LOW.
HEIGHTS AND H85 TEMPS WILL BEGIN TO RECOVER FRI...BUT TEMPS EXPECTED
TO REMAIN IN THE UPPER 70S TO NEAR 80 THANKS TO ONSHORE FLOW.
HEIGHTS AND THICKNESSES WILL CONTINUE TO RECOVER THROUGH THE
WEEKEND...BUT CLOUDS AND PRECIP WILL PREVENT TEMPS FROM REACHING
THEIR FULL POTENTIAL. HAVE GONE UNDER GUIDANCE A FEW DEGS...WITH TEMPS
GENERALLY IN THE LOW TO MID 80S (-1 STD DEV). WITH THE COASTAL FRONT
REMAINING EAST OF THE LOCAL AREA...TRIMMED DEWPOINTS BACK A FEW DEGS
ALONG THE COAST (UPPER 60S/LOW 70S)...AND SEVERAL DEGS OVER THE
PIEDMONT (LOW 60S).
&&
.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
A WARM FRNT REMAINS NORTH OF THE AREA TDY AS A COLD FRNT CURRENTLY
OVER THE OH VALLEY ADVANCES TOWARDS THE AREA. CALM/LGT WINDS AND
MOIST LO-LVLS WILL ALLOW FOR SOME MVFR VSBYS (IFR AT KSBY?). AHEAD
AND ALONG THE FRNT...SCT SHRAS/TSTMS MAY ALSO LEAD TO PERIODIC
IFR/MVFR CONDS LATER TDY. OTW...VFR UNDER A MSTLY CLDY SKY. THE FRNT
CLRS THE AREA TNGT AS WINDS SHIFT FROM SWRLY TO NLY...WITH HI PRES
AND A DRIER AIRMASS MOVING IN FROM THE NORTH. THE FRNT WILL STALL
FOR A FEW DAYS OVER THE CAROLINAS....WHICH WILL KEEP SOME CHC FOR
RAIN ESPECIALLY AT KORF/KECG.
&&
.MARINE...
SUB-SCA CONDS EXPECTED TODAY WITH A WARM FRNT NORTH OF THE AREA AND
A COLD FRNT APPROACHING FROM THE WEST. WINDS WILL SLOWLY SHIFT FROM
SLY TO WLY AT 10-15 KT. THERE COULD BE A BRIEF PERIOD WHERE WINDS
GUST TO JUST OVER 15 KT ACROSS THE SOUTHERN BAY...MOUTH OF THE BAY
AND COASTAL WATERS FROM CAPE CHARLES SOUTH...BUT THIS SHOULD BE
SHORT LIVED FROM LATE MRNG INTO ERLY AFTN.
MODELS ARE IN GOOD AGREEMENT WITH THE TIMING OF THE NEXT COLD FRONT
WHICH WILL MAKE IT INTO THE AREA LATE TNGT AND PUSH SOUTH INTO
NC EARLY WED. WHILE THE INITIAL GRADIENT IS NOT OVERLY
IMPRESSIVE...THERE SHOULD BE A BRIEF SCA EVENT WITH NORTHERLY WINDS
OF 15 TO 20 KT OVER THE BAY AND LWR JAMES AS COLDER AIR ALOFT MOVES
OVER THE WARM WATERS LATE TNGT AND EARLY WED. OTHER RIVER ZONES AND
CURRITUCK SOUND WILL BE CLOSE AS WELL...BUT KEPT THEM OUT OF THE SCA
ATTM. SOME OF THE HIGHER RES MODELS ARE SHOWING THIS SURGE. BY WED
AFTN...WINDS SHOULD SUBSIDE TO 10-15 KT OR LESS. THE COMBINATION OF
SFC HIGH PRESSURE CENTERED OVER NORTHERN PORTIONS OF THE WATERS AND
A TROUGH OF LOW PRESSURE ALONG THE SE COAST WILL LEAD TO PERSISTENT
NE FLOW INTO THU. THIS WILL KEEP SEAS ALONG THE COAST AROUND 3 FT OR
GREATER WITH WAVES 2 FT OVER THE BAY. MODELS DIFFER ON STRENGTH AND
POSITION OF A DEVELOPING COASTAL TROUGH THUS INTO FRI SO UNCERTAINTY
REMAINS IN THE FORECAST LATER IN THE WEEK. WILL CONTINUE TO BUILD
SEAS UP AROUND 4 FT ALONG THE SOUTHERN COASTAL AREAS DUE TO THE
PROLONGED NE FLOW.
&&
.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
NC...NONE.
VA...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 AM TO 4 PM EDT WEDNESDAY FOR
ANZ632-634-638.
SMALL CRAFT ADVISORY FROM 1 AM TO 1 PM EDT WEDNESDAY FOR
ANZ630-631.
&&
$$
SYNOPSIS...LKB
NEAR TERM...LKB
SHORT TERM...LKB
LONG TERM...SAM
AVIATION...MAS
MARINE...MAS/JAO