Area Forecast Discussion
Issued by NWS Wakefield, VA

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000
FXUS61 KAKQ 200117
AFDAKQ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
917 PM EDT TUE AUG 19 2014

.SYNOPSIS...
LOW PRESSURE OFF THE VIRGINIA COAST WILL PULL AWAY FROM THE COAST
TONIGHT...WHILE A WEAK FRONT SLOWLY SINKS SOUTH ACROSS SOUTHERN
VA. THE FRONT RETURNS AS A WARM FRONT ON WEDNESDAY...AND REMAINS
STALLED ACROSS THE AREA THROUGH THE COMING WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
THE SLOW MOVING LOW PRESSURE SYSTEM OFF THE VA CAPES CONTINUES TO
SLOWLY PULL AWAY FROM THE COAST THIS AFTERNOON. STILL SEEING SOME
BANDS OF SHOWERS OVER THE LOWER DELMARVA. THE MODELS SHOW THAT
THIS AREA OF RAIN SHOULD GRADUALLY DIMINISH OVER THE NEXT COUPLE
OF HOURS AS THE LOW MOVES AWAY AND CONVERGENCE ZONE WEAKENS.
MEANWHILE...THE NEXT SHORTWAVE MOVING ACROSS UPSTATE SC CONTINUES
TO LIFT ENE AND MAY PROVIDE ENOUGH FORCING TO GENERATE SOME
CONVECTION ACROSS NERN NC LATE THIS AFTERNOON AND THIS EVENING.
BUT LOOKING A CURRENT RADAR AND WATER VAPOR...THIS WAVE MAY REMAIN
JUST SOUTH OF THE AREA. SO FOR NOW HAVE GONE WITH A LOW CHANCE POP
THROUGH 3Z. BY 3Z...SHOULD SEE THE WEAK FRONT OVER SRN VA CONTINUE
TO GET DRUG SOUTHWARD AND INTO NRN NC WITH WEAK HIGH PRESSURE
CENTERED OVER THE NERN US PUSHING SOUTHWARD. THIS WILL PROVIDE A
PERIOD OF DRY WEATHER AND SOME CLEARING. THIS SHOULD ALLOW
TEMPERATURES TO DROP A FEW MORE DEGREES THAN LAST NIGHT WITH
READINGS IN THE MID TO UPPER 60S IN NRN PORTIONS OF THE CWA AND
LOW 70S SOUTH.

ON WEDNESDAY...THE UPPER LOW OVER THE GREAT LAKES BEGINS TO DIG
INTO THE MID ATLANTIC STATES WITH A COLD FRONT PUSHING INTO THE
OHIO VALLEY. THIS WILL FORCE THE FRONT SOUTH OF THE AREA TO LIFT
BACK NORTH AS A WARM FRONT. WITH SOME DAYTIME HEATING AND THE
RESIDUAL LOW LEVEL MOISTURE STILL AROUND...SHOULD SEE SOME
AFTERNOON TO EVENING CONVECTION FORM IN THE PIEDMONT AND THEN HEAD
EASTWARD WITH THE WARM FRONT. THE 12Z NAM IS MORE EXCITED AND MUCH
MORE LIFT THAN THE GFS OR ECMWF. THE MODELS TEND TO AGREE ON AREAS
ACROSS NORTHERN VA FOR RAIN BUT NOT AS MUCH FURTHER SOUTH SO HAVE
TAPERED POPS A BIT LOWER IN THE SOUTH. FOR TEMPERATURES HAVE
LEANED TOWARD THE MET NUMBERS AS THE MAV HAVE BEEN TOO WARM...BUT
SHOULD SEE MID TO UPPER 80S WITH MORE SUNSHINE.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
THE OVERALL PATTERN IS AGREED UPON IN THE MID RANGE PART OF THE
FORECAST AS THE UPPER LOW OVER THE GREAT LAKES SLIDES INTO THE
EAST AND THE UPPER RIDGE OVER THE MS VALLEY BUILDS
NORTHWARD...SETTING UP NW OVER OF THE MID ATLANTIC REGION.
HOWEVER...BEYOND THE THAT...THE TIMING OF INDIVIDUAL WAVES AND THE
POTENTIAL FOR CONVECTIVE COMPLEXES MAKES THE TIMING OF PRECIPITATION
VERY UNCERTAIN FOR THURSDAY AND FRIDAY. AT THE SURFACE...THE
FRONTAL BOUNDARY THAT WILL BE IN THE VICINITY SHOULD BE SOME
STATIONARY AND PARALLEL TO THE FLOW ALOFT AND COULD ALSO BE A
FOCUS FOR CONVECTION. AT THIS POINT...WITH THE UNCERTAINTY...LEANED
MORE TOWARD CLIMATOLOGY WITH BEST CHANCES IN THE PIEDMONT EARLY IN
THE AFTERNOON AND THEN AREA WIDE IN LATE AFTERNOON THROUGH ABOUT
MIDNIGHT. SUCCEEDING MODEL RUNS WILL HOPEFULLY IMPROVE THE
CONFIDENCE IN THE TIMING OF THE INDIVIDUAL WAVES AND COMPLEXES.

FOR TEMPERATURES...CONTINUED A SLOW WARMING TREND FOR THURSDAY AND
FRIDAY...BUT DID NOT GO AS WARM AS THE MAV NUMBERS...LEANING
TOWARD THE MET NUMBERS WHICH LEANED TOWARD THE UPPER 80S TO LOW
90S ON THURSDAY AND SLIGHTLY COOLER ON FRIDAY WITH MORE CLOUDS
POSSIBLE. FOR LOWS HAVE LEANED WARM THAN GUIDANCE THINKING MORE
CLOUDS AROUND AND A MORE HUMID AIR MASS LIMITING THE COOLING.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
UNSETTLED WEATHER PATTERN CONTINUES INTO THE EXTENDED PERIOD IN NWLY
FLOW ALOFT...BUT DRIER CONDITIONS EXPECTED BY EARLY NEXT WEEK. TEMPS
WILL BE SLIGHTLY BELOW SEASONABLE...LATE SUMMER NORMS TO BEGIN THE
EXTENDED BEFORE RETURNING TO NEAR NORMAL EARLY NEXT WEEK.

UPPER LEVEL FLOW DURING THE EXTENDED IS HIGHLIGHTED BY SPLIT/BLOCKY
FLOW OFF THE ERN CANADA AND NERN US COAST AND AMPLIFYING HIGH
PRESSURE OVER THE SRN CONUS. THIS PLACES THE MID-ATLANTIC REGION IN
NWLY FLOW ALOFT. ASSOCIATED BACK DOOR FRONT WILL PUSH SOUTH OF THE
LOCAL AREA SATURDAY MORNING. SFC HIGH PRESSURE PROGGED OVER THE NE
WILL RIDGE SWWD ALONG THE COAST AND INTO CNTRL VA. NLY LOW-LEVEL
FLOW INDICATED IN MEDIUM RANGE GUIDANCE WILL DRIVE DEWPOINTS
DOWNWARD INTO THE MID 60S. HOWEVER...MODEL DERIVED PWATS REMAIN
AROUND 1.8 TO 2.0 INCHES. COMBINED WITH PERTURBATIONS IN THE NWLY
FLOW...WILL MAINTAIN CHANCE POPS FOR DIURNALLY DRIVEN
SHOWERS/THUNDERSTORMS. WILL ALSO NEED TO WATCH FOR POSSIBLE MCS
DEVELOPMENT UPSTREAM...ROUNDING THE RIDGE AND DROPPING INTO THE
REGION OVERNIGHT THRU THE WEEKEND. BY EARLY NEXT WEEK THE RIDGE AXIS
WILL BEGIN TO BUILD INTO THE REGION AS SFC HIGH PRESSURE IS PROGGED
TO LOCATE OFF THE COAST. BLOCK WILL REMAIN OFF THE NE COAST...BUT
MOISTURE FEED WILL BE CUT OFF. DECREASING MOISTURE AND INCREASING
SUBSIDENCE WILL LIKELY RESULT IN DRY CONDITIONS.
HOWEVER...CONFIDENCE IS NOT HIGH ATTM...SO WILL LEAVE POPS SILENT.

NORTH OF THE BOUNDARY...THICKNESSES AND GUIDANCE YIELD TEMPS IN THE
LOW TO MID 80S THRU MONDAY (AROUND -1 STD DEV). OVERNIGHT LOWS
GENERALLY IN THE UPPER 60S TO LOW 70S NEAR THE WATER. WARMING BACK
UP TO NEAR SEASONABLE NORMS TOWARD THE MIDDLE OF NEXT WEEK.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
HIGH PRESSURE BRIEFLY BUILDS OVER THE AREA FROM THE NORTH BEHIND
DEPARTING LOW PRESSURE SYSTEM. UPPER LEVEL SHORT WAVES IN A W/NW
FLOW WILL KEEP CONDITIONS UNSETTLED FOR THE NEXT SEVERAL DAYS. MOIST
GROUND AND LOW LEVEL CONDITIONS WILL MAINTAIN THE CHC FOR ISSUES
WITH CIG/VSBY EACH MORNING.

AS OF 00Z...NE WINDS PREVAILED AT THE TAF SITES WITH NO PCPN
EXPECTED OVERNIGHT. SKY CONDITIONS WILL BE VARIABLE WITH GRADUAL
LOWERING OF CIGS AND VSBYS. THE MAIN LIMITATION IS INDICATED TO BE
CIGS BUT VSBYS ARE NOT OFF THE TABLE. USED THE RESULTS OF THE
PREVIOUS OVERNIGHT AS A PARTIAL GUIDE AND A MIX OF MOS GUIDANCE TO
MAKE A PLAN FOR THE CURRENT TAF. DESPITE ECG HAVING THE CLOSEST T/TD
SPREAD...EXPERIENCE FROM THIS MORNING WOULD INDICATE THEY WILL NOT
GO DOWN TO IFR FOR A WHILE (I.E. AROUND 12Z) AND MAY HAVE NO LOWER
THAN MVFR. HAVE RIC/PHF WITH SOME PERIODS OF IFR. SBY MOS IS BIASED
BY TEMPERATURES THAT ARE TOO LOW. KEPT ORF OUT OF IFR DUE TO
CLIMATOLOGY.

CONDITIONS SHOULD BE VFR BY AROUND 14-15Z. ON WEDNESDAY...THERE WILL
BE A CHC FOR LATE AFTN/EVENING TSTMS...ESPECIALLY NORTH PORTIONS.
WINDS VEER TOWARD E/SE.

OUTLOOK...CHC FOR AFTN TSTMS THURSDAY THROUGH SATURDAY. SOME
MVFR/IFR PSBL NEAR SUNRISE EACH MORNING. CURRENT FORECAST IS DRY ON
SUNDAY.

&&

.MARINE...
SUB-SCA CONDITIONS PREVAIL THRU THE FORECAST PERIOD. LOW PRESSURE
HAS JUST LOCATED OFF THE VA CAPES THIS AFTERNOON WITH A FRONTAL
BOUNDARY EXTENDING WWD OVER SRN VA. GENERALLY ONSHORE FLOW 10-15 KT
OVER THE WATERS...NORTH OF THE LOW. SEAS HAVE ALSO BUILT TO 3-4 FT
IN THE NRN WATERS. WAVES GENERALLY 1-2 FT. LOW PRESSURE PUSHES
SLOWLY OFFSHORE TONIGHT AS WEAK HIGH PRESSURE RIDGES OVER THE NRN
WATERS. LOW PRESSURE REMAINS JUST OFFSHORE THRU THE END OF THE WEEK
AS A WEAK BOUNDARY REMAINS OVER THE WATERS. HIGH PRESSURE BUILDS
OVER NEW ENGLAND...RIDGING SWD OVER THE LOCAL AREA. THE RESULT WILL
BE PERSISTENT ONSHORE FLOW...AVG AROUND 10 KT. SEAS REMAIN 2-3 FT.
BY THE WEEKEND...THE GRADIENT TIGHTENS WITH NELY WINDS INCREASING TO
10-15 KT. WILL PUSH SEAS IN THE NRN WATERS TO 3-4 FT...WITH 5 FT
POSSIBLE 20NM OUT. FRONT PUSHES SOUTH OF THE WATERS SAT AS HIGH
PRESSURE BUILDS BACK OVER THE WATERS.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
NC...NONE.
VA...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...ESS
NEAR TERM...ESS
SHORT TERM...ESS
LONG TERM...SAM
AVIATION...LSA
MARINE...SAM





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