Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 200132
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
932 PM EDT TUE AUG 19 2014

.SYNOPSIS...
LOW PRESSURE WILL CONTINUE TO DRIFT EAST FROM NORTHEASTERN NORTH
CAROLINA THROUGH TONIGHT...WITH AN ONSHORE FLOW PERSISTING INTO
THURSDAY NIGHT. A COLD FRONT WILL MOVE THROUGH THE AREA FROM THE
NORTHWEST FRIDAY WITH MORE ONSHORE FLOW FRIDAY NIGHT INTO NEXT
WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 01Z...1009MB SFC LOW IS OFFSHORE FROM THE VA/NC BORDER AND
DRIFTING EAST. A LIGHT ONSHORE/SELY FLOW IS ACROSS THE CENTRAL
MID-ATLANTIC. UPSTREAM...A SHORTWAVE IS MOVING EAST THROUGH THE
MIDWEST STATES WITH AN MCS PUSHING EAST OVER LAKE ERIE (CURRENTLY
NEAR CLEVELAND).

WILL NEED TO MONITOR DEVELOPMENT ALONG THE SOUTHERN END OF THE MCS
(CURRENTLY OVER COLUMBUS)...FOR DOWNSTREAM AREAS LIKE CUMBERLAND
MD OVERNIGHT. HOWEVER...THE LOW IS OCCLUDED AND EASTWARD PROGRESS
SHOULD BE SOMEWHAT LIMITED. THE 22Z HRRR SUGGEST A SUPPLEMENTAL
VORT LOBE SHIFTS ACTIVITY EAST INTO NWRN PARTS OF THE CWA
WEDNESDAY MORNING. TOOK THIS APPROACH IN THE GRIDS WITH CHANCE
POPS ENTERING THE NORTHWEST AFTER 6 AM.

SHEAR INCREASES OVER THE AREA WEDNESDAY AHEAD OF THE LOW THAT WILL
CONTINUE DRIFTING EAST ACROSS THE GREAT LAKES. TIMING OF VORT
MAX/TROUGH PASSAGE EAST FROM THE SHENANDOAH VALLEY SHOULD BE
CLOSE TO PRIME DIURNAL HEATING...SO MORE ACTIVITY IS EXPECTED THAN
RECENT DAYS. HOWEVER...THE ONSHORE FLOW SHOULD CONTINUE TO LIMIT
STORMS EAST FROM THE BLUE RIDGE. MAINTAINED LIKELY POPS FOR LATE
AFTERNOON/EARLY EVENING FOR NRN SECTIONS OF THE CWA...MAINLY WEST
OF I-95. MAX TEMPS MID TO UPR 80S DEPENDING ON MID LEVEL CLOUD
COVER CLEARING.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/...
THE DISTURBANCE WILL MOVE OFF THE COAST LATE WEDNESDAY NIGHT AND
SHOWERS MAY LINGER EAST OF THE BLUE RIDGE INTO THURSDAY. NORTHWEST
FLOW ALOFT WILL ALLOW A UPPER LOW TO APPROACH THE REGION AND MOVE
ACROSS THE NORTHEAST THURSDAY. THUNDERSTORMS ARE POSSIBLE THURSDAY
AFTERNOON WEST OF THE BLUE RIDGE AS THE EXIT REGION OF AN UPPER
LEVEL JET APPROACHES. SFC FLOW IS LIGHT AND WESTERLY WHICH WILL
KEEP DEWPTS IN THE LOW TO MID 60S THURSDAY. INSTABILITY WILL BE
BASED ON CLOUD COVER WHICH IS HARD TO SAY RIGHT NOW BUT THE MORE
BREAKS THE GREATER THE INSTABILITY. MARGINAL SHEAR OF 25 KTS IS
EXPECTED AT THIS TIME. AT THIS TIME...SVR STORM POTENTIAL IS LOW.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
AN UPPER LEVEL LOW RIDING AROUND THE EAST SIDE OF A DEVELOPING
SUBTROPICAL RIDGE WILL CROSS JUST NORTH OF THE AREA THURSDAY NIGHT
AND FRIDAY. MANY LOCATIONS...PARTICULARLY IN MARYLAND...COULD SEE
PERIODS OF HEAVY RAIN AND AN ISOLATED THUNDERSTORM THROUGH THE NIGHT
THURSDAY. THE COLLOCATION OF ENHANCED LIFT FROM THE LEFT EXIT REGION
OF A JET STREAK ROUNDING THE SOUTHWESTERN SIDE OF THE UPPER LEVEL
LOW LATE THURSDAY NIGHT AS WELL AS A STALLED BOUNDARY AT THE SURFACE
WILL FURTHER ENHANCE THE POTENTIAL FOR RAINFALL ACROSS THE AREA.
OVERALL HAVE HIGHEST POPS ACROSS MARYLAND WITH SHOWERS AND ISOLATED
THUNDERSTORMS THURSDAY NIGHT AND INTO FRIDAY MORNING.

THE AFOREMENTIONED SURFACE BOUNDARY WILL REMAIN NEAR THE AREA
THROUGH FRIDAY AFTERNOON AS A COASTAL LOW FORMS OFF OF CAPE
HATTERAS. WITH MODEST MOISTURE ADVECTION OCCURRING IN THE LOW AND
MID LEVELS...SHOWERS AND ISOLATED THUNDERSTORMS REMAIN POSSIBLE
FRIDAY EVENING...ESPECIALLY OVER THE EASTERN HALF OF THE CWA.
OVERALL RAINFALL COVERAGE SHOULD BE SIGNIFICANTLY LESS FRIDAY
EVENING THAN THURSDAY NIGHT.

HIGH PRESSURE WILL RIDGE DOWN INTO THE AREA BEGINNING FRIDAY NIGHT.
THIS WILL WORK WITH THE LOW PARKED OFF THE SOUTHEAST COAST TO BRING
ONSHORE FLOW INTO THE AREA. THIS MARINE AIRMASS WILL KEEP MOST OF
THE AREA...PARTICULARLY EAST OF THE BLUE RIDGE...CLOUDY HUMID AND
COOL THROUGH THE WEEKEND AND LIKELY INTO THE BEGINNING OF NEXT WEEK.
THUNDERSTORMS ARE UNLIKELY WITH THIS AIRMASS...BUT ISOLATED LIGHT
RAIN WILL BE POSSIBLE MOSTLY SATURDAY...PARTICULARLY IN AREAS WHERE
THERE IS AN UPSLOPE COMPONENT TO THE FLOW. EXPECT MORE BREAKS IN
THE CLOUDS WEST OF THE BLUE RIDGE...THOUGH LIGHT RAIN REMAINS
POSSIBLE SATURDAY AND SUNDAY THERE AS WELL.

HIGH PRESSURE EXTENDING DOWN THE EAST COAST WILL WEAKEN EARLY NEXT
WEEK AS A COLD FRONT APPROACHES FROM THE WEST. THIS WILL LIKELY
SIGNAL THE RETURN OF SOUTHERLY FLOW AND TEMPERATURES BECOMING MORE
SEASONABLE. OVERALL THE COOLER THAN NORMAL TREND OF THE SUMMER WILL
CONTINUE THROUGH THE LONG TERM WITH HIGHS MOSTLY IN THE UPPER 70S AS
THE COOL MARINE AIRMASS COVERS THE AREA FOR THE WEEKEND AND MONDAY.
TUESDAY WILL SEE HIGHS IN THE LOWER 80S AS WEAK WARM AIR ADVECTION
BEGINS OVER THE REGION.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
ONSHORE FLOW CONTINUES AND MVFR/IFR CIGS EXPECTED LATE TONIGHT.
IFR CIGS/VSBYS MOST LIKELY AT CHO AND MRB WEDNESDAY MORNING. A
DISTURBANCE MOVES ACROSS THE REGION WEDNESDAY AND SHRA AND VCTS
ARE POSSIBLE. AT THIS TIME...THREAT OF TS IS LOW AND THEREFORE NOT
IN THE TAFS. ANOTHER DISTURBANCE APPROACHES THURSDAY AND SHRA AND
TSRA IS POSSIBLE IN THE AFTERNOON.

PERIODS OF LOW CEILINGS ARE EXPECTED AS AN UPPER LEVEL DISTURBANCE
CROSSES THE AREA THURSDAY NIGHT AND THEN AGAIN OVER THE WEEKEND AND
INTO EARLY NEXT WEEK AS A MARINE AIRMASS SETTLES INTO THE AREA.

&&

.MARINE...
LIGHT ONSHORE FLOW CONTINUES THROUGH THURSDAY AND WILL STAY BELOW
SCA CRITERIA. SHOWERS AND ISOLATED THUNDERSTORMS ARE POSSIBLE
WEDNESDAY AFTERNOON AND EVENING AND AGAIN THURSDAY AFTERNOON.

CONFIDENCE IS LOW IN THE OCCURRENCE OF ANY MARINE HAZARDS THROUGH
THE LONG TERM.

&&

.TIDES/COASTAL FLOODING...
AN ONSHORE FLOW WILL CONTINUE THROUGH TONIGHT...BUT IT WILL REMAIN
WEAK. TIDAL ANOMALIES AROUND ONE-HALF FOOT ABOVE NORMAL WILL
PERSIST THROUGH TONIGHT. WATER LEVELS WILL BE CLOSE TO MINOR
FLOODING THRESHOLDS DURING THE HIGH TIDE CYCLE LATE TONIGHT BUT
EXPECTATION IS THAT WATER LEVELS WILL REMAIN BELOW MINOR FLOODING
THRESHOLDS SINCE THE ONSHORE FLOW IS WEAK.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...BAJ/HAS
NEAR TERM...BAJ
SHORT TERM...HAS
LONG TERM...CEB
AVIATION...BAJ/HAS/CEB
MARINE...BAJ/HAS/CEB
TIDES/COASTAL FLOODING...LWX






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