Special Weather Statement, NWS Wakefield, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
421 PM EDT WED AUG 8 2012

.SYNOPSIS...
A FRONTAL BOUNDARY WILL DISSIPATE LATE TONIGHT...AS HIGH PRESSURE
REMAINS CENTERED OFF THE MID ATLANTIC AND SOUTHEAST COASTS. A MORE
SUBSTANTIAL LOW PRESSURE SYSTEM WILL DEVELOP OVER THE OHIO VALLEY
THURSDAY NIGHT...AND BEGIN TO IMPACT THE MID ATLANTIC REGION
FRIDAY INTO SATURDAY.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
THUNDERSTORMS HAVE FORMED ALONG AND JUST BEHIND A 700 MB TROUGH
STRETCHING FROM THE EASTERN PIEDMONT REGION DOWN INTO THE TN/NC
PANHANDLE THIS AFTERNOON. PER INFRARED SATELLITE IMAGERY...CLOUD
TOPS HAVE COOLED FURTHER WITHIN THIS LINE WITH ADDITIONAL COOLING
MOVING UP AHEAD OF IT AND INTO NE NC/SE VA. A WEAK JET STREAK
ROTATING INTO THE ENHANCED LINE IS ALSO PROMOTING LIFT DUE TO ITS
PROXIMITY TO THE LEFT ENTRANCE REGION. UNFORTUNATELY...THE JET
STREAK IS NOT STRONG ENOUGH TO OVERCOME WEAK STEERING FLOW FROM THE
SURFACE UP TO AROUND 750 MB (OR 8 KFT). THEREFORE VERY SLOW MOVING
THUNDERSTORMS (GENERALLY 5 MPH) ACCOMPANIED BY HEAVY RAIN...FREQUENT
LIGHTNING...AND TRAINING OF STORM CORES MAY CREATE LOCALIZED
FLOODING ISSUES. A SMALL STREAM FLOOD ADVISORY HAS ALREADY BEEN
ISSUED FOR NW LUNENBURG AND SRN PRINCE EDWARD COUNTIES FOR MINOR
FLOODING AND ADDITIONAL HEADLINES MAY BE NEEDED. WILL HIGHLIGHT
MINOR FLOOD POTENTIAL IN THE HAZARDOUS WEATHER OUTLOOK AS WELL.

STORMS SHOULD GRADUALLY TAPER OFF AFTER SUNSET WHEN SUPPORT FROM
DAYTIME HEATING IS LOST AND AS THE TROUGH AND ASSOCIATED SHORTWAVE
ENERGY MOVE NE AND AWAY FROM THE MID ATLANTIC COAST.

CONDITIONS SHOULD THEN BECOME DRY OVERNIGHT. PATCHY FOG IS POSSIBLE
MAINLY INLAND WITH SKIES CLEARING FROM WEST TO EAST LATE
TONIGHT...BUT MOST ESPECIALLY IN AREAS THAT SEE RAINFALL THIS
EVENING. MEANWHILE...AN UPPER LEVEL TROUGH OVER THE MANITOBA/ONTARIO
BORDER IN CANADA BEGINS TO DIG INTO THE UPPER MS VALLEY LATER
TONIGHT.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
THE AFOREMENTIONED CANADIAN TROUGH DIGS INTO THE GREAT LAKES REGION
ON THURSDAY THUS AMPLIFYING WEAK RIDGING OVER THE MID ATLANTIC.
MEANWHILE...A SHORTWAVE MOVING UP FROM THE SOUTHWEST WEAKENS OVER
THE REGION THROUGH THE DAY AS IT MOVES TO THE NORTHEAST. THE
COMBINATION OF THIS FEATURE IN ADDITIONS TO A WEAK BERMUDA RIDGE
ALOFT AND WARMING LOW LEVEL THICKNESSES WILL DEVELOP A LEE TROUGH
OVER THE AREA BY THE AFTERNOON. THE PRESENCE OF THE LEE TROUGH AND
BREEZY SOUTHWEST WINDS BY MID-DAY WILL HELP TO BOOST TEMPERATURES
SLIGHTLY ABOVE NORMAL (LOWER 90S INLAND...UPPER 80S IMMEDIATE
COAST). OTHER THAN THE LEE TROUGH...THERE STILL WILL NOT BE MUCH OF
A TRIGGER FOR PRECIP SO WILL CONTINUE PREVIOUS FORECAST THINKING OF
LIMITING 20% POPS TO THE AFTN/EVENING HOURS. SEABREEZE BOUNDARIES
WEST OF CHES BAY AND DOWN INTO NE NC MAY TRIGGER ADDITIONAL
THUNDERSTORM DEVELOPMENT AND KEPT POPS AROUND 30%...INCLUDING IN THE
NW PIEDMONT WHERE HIGHEST CAPE/LOW LVL INSTABILITY VALUES RESIDE.
EXPECT PRECIP TO TAPER OFF AFTER MIDNIGHT AS THE WAKEFIELD CWA WILL
BE IN BETWEEN DEEPER MSTR OFF THE COAST AND APPROACHING/AMPLIFYING
SYSTEM ACRS THE TN/OH VALLEYS.

FRIDAY CONTINUES TO BE A CHALLENGING FORECAST AS A MORE SUBSTANTIAL
SURFACE LOW PRESSURE SYSTEM APPROACHES THE REGION FROM THE TN/OH
VALLEYS. 12Z MODEL DATA IS STILL ON TREND WITH THE GFS BEING A BIT
TOO FAST WITH PRECIP/FRONTAL TIMING AND THEREFORE CONTINUE TO FAVOR
A SLIGHTLY SLOWER NAM/ECMWF SOLUTION. ALL MODELS GENERATE QPF BY
10/1800Z SO WILL CARRY 40% POPS WEST OF I-95 IN THE MORNING (20-30%
POP EAST OF THE TRAVEL CORRIDOR)...WITH 50-60% POPS ACROSS THE AREA
BY THE AFTERNOON. BULK SHEAR BECOMES FAIRLY IMPRESSIVE (30 KT OR
GREATER) BY AFTN/EVENING. SHEAR PROFILE IS MOSTLY UNIDIRECTIONAL
WITH SOME LOW LEVEL VEERING WITH HEIGHT...THEREFORE A FEW STORMS
COULD BECOME SEVERE WITH LOCALLY DAMAGING WINDS. A FEW CAVEATS TO
CONSIDER ARE THE POSSIBILITY OF SHOWER ACTIVITY EARLY FRIDAY MORNING
AND INCREASING MID-HIGH CLOUDS LATE IN THE MORNING...BOTH OF WHICH
COULD HAMPER CONVECTIVE DEVELOPMENT. TIMING WILL BE EVERYTHING AND
WILL CONTINUE TO MONITOR THIS WX SITUATION CLOSELY. SPC IS
MAINTAINING A SLIGHT RISK AREA FOR THE MID ATLANTIC REGION FOR
FRIDAY...AND WILL CARRY MENTION OF THIS IN THE HWO.

RAINFALL WILL BECOME MORE WIDESPREAD FRIDAY NIGHT INTO SATURDAY
MORNING...GRADUALLY TAPERING OFF FROM WEST TO EAST LATER SATURDAY
AFTN INTO THE EVENING AS A COLD FRONT FINALLY CROSSES THROUGH THE
MID ATLANTIC REGION. HEAVY RAIN WILL CONTINUE TO BE THE MAIN
IMPACT IN THIS WX PATTERN.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
UPR-LVL LO PRES OVER THE GREAT LAKES REGION SAT WILL PULL NE INTO SE
CANADA SAT NGT AND SUN...DRAGGING A COLD FRNT THRU THE MID ATLANTIC
REGION BY SAT NGT. THEREFORE...CHC FOR RAIN (MAINLY 20-40% POPS)
CONTINUE SAT NGT DUE TO DEEP MOISTURE...FRNTAL FORCING...AND THE RFQ
OF AN UPR-LVL JET STREAK. SUN WILL THEN FEATURE DRY CONDITIONS AND A
MSTLY SNY SKY AS HI PRES BLDS IN FROM THE WEST. JUST A SLGT CHC
FOR RAIN MON THRU WED DUE TO SFC BNDRYS AND WEAK CYCLONIC FLOW
ALOFT. NO MAJOR SYSTEMS EXPECTED.

TEMPS NEAR NORMAL THRU THE PERIOD...HIGHS IN THE MID 80S TO LOW 90S
WITH LOWS IN THE MID 60S TO LOW 70S.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
A WEAK SURFACE PRESSURE PATTERN WAS KEEPING LOW LEVEL MOISTURE FROM
GETTING MIXED OUT. AS A RESULT...MUCH OF THE MID ATLANTIC REGION HAD
MVFR CONDITIONS THROUGH THE MORNING HOURS. KEPT A TEMPO GROUP FOR
THIS FOR THE FIRST FEW HOURS OF THE 18Z TAF PERIOD.

WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WERE DEVELOPING ALONG
THE PIEDMONT OF VIRGINIA AND NORTH CAROLINA. NONE OF THESE WERE
IMMINENTLY THREATENING THE TAF SITES BUT WILL MONITOR FOR THE NEED
OF UPDATES. KRIC IS THE MOST LIKELY SITE TO BE AFFECTED DURING THE
AFTERNOON.

WILL NEED TO MONITOR HIGH CLOUD COVERAGE AND AREAS OF RECENT
RAINFALL FOR FOG POTENTIAL THURSDAY MORNING. KEPT IFR OUT OF THE
FORECAST EXCEPT AT RIC. INCLUDED MVFR STATUS AT ALL LOCATIONS
SIMILAR TO THIS MORNING. IF SKIES CLEAR...PHF IN PARTICULAR MAY SEE
IFR VSBYS DUE TO SIGNIFICANT RAINFALL TUESDAY EVENING.

THURSDAY SHOULD SEE SIMILAR WEATHER TO TODAY...PERHAPS A LITTLE
QUICKER END TO THE MORNING LOW CEILINGS DUE TO BETTER MIXING. TSTMS
WILL BE POSSIBLE IN THE AFTERNOON.

OUTLOOK...NO APPRECIABLE CHANGE IN THE WX PATTERN IS EXPECTED FOR
THE NEXT SEVERAL DAYS. SHOWER AND THUNDERSTORM CHANCES INCREASE
ACROSS THE AREA FOR FRIDAY AND SATURDAY AS A MORE SUBSTANTIAL LOW
PRESSURE SYSTEM IMPACTS THE MID ATLANTIC REGION.

&&

.MARINE...
STATIONARY BNDRY LOCATED ACROSS THE NORTHERN WATERS PERSISTS...
AND WILL DIMINISH BY THIS EVNG AS BENIGN MARINE CONDITIONS
CONTINUE. SOUTH WNDS GENERALLY AOB 10 KT THIS EVNG WILL BECOME
SOUTHWESTERLY OVRNGT. WNDS SLGTLY HIER (10-15 KT) THU AHEAD OF AN
APPROACHING COLD FRNT. A FEW GUSTS TO 20 KTS WILL BE POSSIBLE...
HOWEVER CONDITIONS SHUD GENERALLY STAY SUB-SCA. SEAS WILL SLOWLY
BLD EACH DAY FROM 2-3 FT THU...TO 3-4 FT FRI...TO 4-6 FT SAT. WNDS
WILL LIKEWISE APPROACH AND POSSIBLY EXCEED SCA CRITERIA BY LATE
FRI. COLD FROPA OCCURS OVER THE WATERS LATE SAT/SAT NGT. QUIET
MARINE CONDITIONS RETURN SUN THRU WED AS SFC HI PRES BLDS IN FROM
THE WEST BEHIND THE FRNT.

&&

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

&&

SYNOPSIS...BMD/MAM
NEAR TERM...BMD
SHORT TERM...BMD/LKB
LONG TERM...MAS
AVIATION...LSA
MARINE...MAS

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