Small Craft Advisory 79, NWS Wakefield, VA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
359 PM EDT SUN JUN 12 2011

.SYNOPSIS...
A COLD FRONT ASSOCIATED WITH A LOW OVER SOUTHERN QUEBEC WILL CROSS
THE AREA TONIGHT. HIGH PRESSURE WILL THEN BUILD IN FROM THE GREAT
LAKES REGION AND LEAD TO DRY AND COOLER CONDITIONS FOR MONDAY INTO
WEDNESDAY. ANOTHER LOW WILL AFFECT THE MID-ATLANTIC REGION LATER IN
THE WORK WEEK.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
SEVERE THUNDERSTORM WATCH NUMBER 467 ISSUED UNTIL 00Z FOR THE ENTIRE
CWA EXCEPT THE EASTERN SHORES...TIDEWATER...AND NE NORTH CAROLINA.
TEMPS HAVE RISEN TO THE UPPER 80S AND LOWER 90S TODAY WITH THE
MOSTLY SUNNY SKIES IN PLACE WELL SOUTH OF A WARM FRONT ACROSS PA
AND NJ. WARM SECTOR ENVIRONMENT HAS PROMOTED MODERATE
DESTABILIZATION...1500-2000 J/KG MLCAPES. EVEN THOUGH SHEAR
REMAINS VERY WEAK (15-20 KT FROM 0-6 KM)...LOW-LEVEL LAPSE RATES
ARE VERY STEEP (DRY-ADIABATIC UP TO 800-850 MB). SO A SIMILAR
SITUATION AS YESTERDAY WITH GOOD INSTABILITY AND WEAK SHEAR...WITH
CONVECTION EXPECTED TO EASILY DEVELOP ALONG SFC BOUNDARIES. LATEST
LAPS ANALYSIS SHOWING DECENT CONVERGENCE THROUGH THE MID-SECTION
OF THE CWA...WITH A WIND SHIFT EVIDENT. STORMS ARE ALREADY
STARTING TO THE ENTER THE NORTHWEST PART OF THE CWA...WITH MORE TO
THE WEST ASSOCIATED WITH A COLD FRONT STRETCHING DOWN FROM
CENTRAL PA TO EASTERN KY. WEAK H5 SHORTWAVE OVER EASTERN KY AS
WELL. THESE FEATURES WILL CONTINUE TO ADVANCE EASTWARD AND COULD HELP
SHOWERS AND STORMS STAY ACTIVE INTO THE NIGHTTIME HOURS. DAMAGING
WINDS ARE THE MAIN THREAT DUE TO DCAPE VALUES >1000 J/KG AND SFC TO
MID-LEVEL THETA-E DIFFERENCES GREATER THAN 30 C. HEAVY RAIN WILL
ALSO ACCOMPANY THESE STORMS WITH THE WEAK STEERING FLOW ALOFT AND
PWATS AVERAGING AROUND 1.75 IN.

CHANCE OF SHOWERS AND STORMS WILL LINGER INTO THE OVERNIGHT HOURS...THOUGH
THE SEVERITY AND COVERAGE WILL SLOWLY DIMINISH WITH THE LOSS OF
DAYTIME HEATING. LOW TEMPS WILL BE ABOUT NORMAL...MID 60S. COLD
FROPA OVERNIGHT WILL SHIFT SW WINDS TO OUT OF THE NNW.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
SHORT TERM PERIOD CHARACTERIZED BY AN UPPER LOW SOUTH OF JAMES BAY
SLOWLY PROGRESSING TO THE SOUTHEAST AND CLOSING OFF OVER THE GULF OF
MAINE BY WEDNESDAY. SUBSEQUENTLY...DECREASING HEIGHTS OVER THE
MID-ATLANTIC REGION AND A BREAK FROM THE HEAT. HIGH TEMPS FROM
MONDAY THROUGH WEDNESDAY WILL BE SEASONABLE...LOW TO MID 80S IN
MOST SPOTS WITH UPPER 70S OVER COASTAL AREAS. PARTLY TO MOSTLY SUNNY
SKIES. A SHORTWAVE TROUGH WILL PASS THROUGH THE UPPER CONUS
THROUGH THE PERIOD...AND START TO KICK THE AFOREMENTIONED CUTOFF
LOW OFF TO THE NORTHEAST INTO THE CANADIAN MARITIMES ON WEDNESDAY.
AS SUCH...TEMPS MAY BE A BIT WARMER ON WEDNESDAY THAN EARLIER IN
THE WEEK. A SFC LOW MAY DEVELOP OVER THE OH/TN VALLEYS...AND GFS
SHOWS PRECIP EXTENDING EAST OF THIS LOW TOWARDS VA. CURRENTLY KEPT
THIS PRECIP OUT OF THE FORECAST HOWEVER AS THE EURO/NAM/CMC ARE
KEEPING CONDITIONS DRY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
UNCERTAINTY ABOUNDS IN THE EXTENDED RANGE AS THE MODELS TRY TO
RESOLVE THE MOVEMENT OF A CLOSED LOW THROUGH THE NORTHERN PLAINS
TO THE EAST COAST THURSDAY INTO SATURDAY. THE GFS SHOWS THAT THIS
LOW GETS LOST IN THE FLOW SOME AND LINGERS OVER THE NRN OHIO
VALLEY BEFORE GRADUALLY WASHING OUT BY THE WEEKEND WITH NW FLOW
LINGER THROUGH THE PERIOD. THE ECMWF ON THE OTHER HAND ALLOWS THIS
CLOSE LOW TO CONTINUE TO SLIDE EAST AS THE UPPER RIDGE DEVELOPING
OVER THE CENTRAL PLAINS BUILDS EASTWARD WITH TIME...PUSHING THIS
FEATURE OFF THE COAST IN THE VOID LEFT BY THE LONGWAVE TROUGH THAT
PULLS OFF THE COAST EARLIER IN THE WEEK. WITH THE OVERALL
PROGESSIVE NATURE OF THE SYNOPTIC PATTERN...FELT THAT THE GFS
SCENARIO JUST LEAVING THE UPPER LOW BEHIND IS NOT REPRESENTATIVE
SO HAVE LEANED MUCH MORE TOWARD THE ECMWF. WITH THIS PATTERN
SHOULD SEE A WEAK WARM FROM PUSH THROUGH OR DISSOLVE OVER THE AREA
ON THURSDAY. THIS LIGHT FORCING COULD PRODUCE SOME SCATTERED
CONVECTION AS THE LOW LEVEL MOISTURE RETURNS. THEN AS THE LOW
PASSES TO THE NORTH ON FRIDAY...WILL SEE A WEAK COLD FRONT SLIDE
THROUGH AGAIN PRODUCING A SCATTERING OF CONVECTION. OVER THE
WEEKEND...WILL BEGIN TO SEE THE UPPER RIDGE BUILD EASTWARD INTO
THE REGION WHICH WILL LIMIT ANY CONVECTION AND ALSO BEGIN TO SEE A
WARMING TREND.

FOR TEMPERATURES HAVE GENERALLY STAYED CLOSE TO HPC NUMBERS
THURSDAY INTO FRIDAY BUT THEN WENT HIGHER THAN THE MEX/HPC NUMBERS
OVER THE WEEKEND.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
THUNDERSTORMS ARE APPROACHING THE FA FROM THE WNW. THESE STORMS
HAVE THE POTENTIAL TO PRODUCE STRONG AND ERRATIC WIND GUSTS ALONG
WITH SIGNIFICANTLY REDUCED VISIBILITY IN HEAVY RAIN. A COLD FRONT
WILL PUSH THROUGH THE AREA LATE SUNDAY EVENING WITH HIGH PRESSURE
BUILDING INTO THE REGION MONDAY.

MOSTLY VFR CONDITIONS WILL PREVAIL THROUGH WEDNESDAY WITH HIGH
PRESSURE IN PLACE. A SW WIND AHEAD OF THE FRONT WILL SHIFT TO NW
THEN N BEHIND THE FRONT.

&&

.MARINE...
HAVE GENERAL LIGHT SOUTHERLY FLOW IN PLACE AHEAD OF THE COLD FRONT
THIS EVENING. EXPECT SCATTERED CONVECTION IN ADVANCE OF THIS FRONT
WITH MAINLY GUSTY WINDS BEING THE MAIN THREAT. THE FRONT SHOULD
CROSS THE REGION BETWEEN 3Z AND 9Z. BEHIND THE FRONT...WILL SEE A
BRIEF SURGE OF WINDS AROUND 20 KTS MOVING DOWN THE BAY AND
OFFSHORE. THIS SURGE SHOULD BE A SHORT LIVED BETWEEN ABOUT 9Z AND
15Z. SO HAVE RAISED A SCA FOR THE BAY WITH THE 20 KTS WINDS. ONCE
THE SURGE HAS PASSED...HIGH PRESSURE BEGINS TO BUILD INTO THE
REGION...BUT A LINGERING CLOSED LOW OFF THE NE COAST...WILL
CONTINUE TO SEE A LIGHT NW TO NRLY FLOW MONDAY NIGHT ALL THE WAY
INTO WEDNESDAY. THE UPPER TROUGH PULLS AWAY FROM THE COAST ON WED
EVENING AND A WARM FRONT ASSOCIATED WITH A LOW OVER THE GREAT
LAKES WILL SWING ACROSS THE AREA. THIS WILL TURN THE FLOW OUT OF
THE SOUTH...BUT SHOULD REMAIN WELL BELOW SCA LEVELS. THE COLD
FRONT ASSOCIATED WITH THIS SYSTEM SWINGS THROUGH ON FRIDAY AND
COULD PROVIDE SOME THUNDERSTORMS WITH GUSTY WINDS.

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
NC...AIR QUALITY ALERT UNTIL 3 PM EDT MONDAY FOR NCZ017-102.
VA...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 AM TO 1 PM EDT MONDAY FOR
     ANZ630>632-634.

&&

SYNOPSIS...MAS
NEAR TERM...MAS
SHORT TERM...MAS
LONG TERM...ESS
AVIATION...AJZ/DAP
MARINE...ESS

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