Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 280051
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
851 PM EDT MON JUL 27 2015

.SYNOPSIS...
WEAK HIGH PRES WILL BUILD OVER THE AREA TONIGHT THROUGH WEDNESDAY.
A COLD FRONT WILL CROSS THE AREA THURSDAY NIGHT AND MOVE INTO THE
SOUTHEAST FRIDAY. WEAK HIGH PRESSURE BUILDS AGAIN FOR THE
WEEKEND.

&&

.NEAR TERM /THROUGH TUESDAY/...
A VERY WARM AND MOIST AIR MASS IS ACROSS THE MID- ATLANTIC THIS
EVENING. DEWPTS RANGE FROM THE UPPER 60S TO LOW 70S. SHOWERS
PERSIST ACROSS THE HIGHLANDS WEST OF THE BLUE RIDGE THIS EVENING
WHILE STRONGER SHOWERS AND THUNDERSTORMS PERSIST ACROSS THE
PIEDMONT/TIDE WATER REGION. THERE IS STILL A SUFFICIENT AMT OF
INSTABILITY ACROSS THE REGION AND OUTFLOW BOUNDARIES FROM PAST
STORMS HAVE ALLOWED FOR NEW CONVECTIVE DEVELOPMENT. SHOWERS AND
THUNDERSTORMS ARE POSSIBLE THIS EVENING INTO THE OVERNIGHT HOURS.
COVERAGE SHOULD BE ISOLATED TO SCATTERED AND WILL PRODUCE HEAVY
RAINFALL RATES. FLASH FLOOD GUIDANCE HAS LOWERED ACROSS THE REGION
IN PLACES THAT RECEIVED RAINFALL TODAY. FLASH FLOODING IS POSSIBLE
BUT DUE TO THE COVERAGE EXPECTED IS AN ISOLATED CONCERN.

THE OTHER STORY TONIGHT IS FOG...WINDS WILL BECOME VARIABLE TO
CALM TONIGHT AND CLEARING WILL CONTINUE TO OCCUR ACROSS MUCH OF
THE AREA. THE WET GROUND WILL ALLOW FOG TO DEVELOPMENT. HOW FAST
IT WILL FORM IS THE QUESTION. LOW LYING AREAS WILL LIKELY SEE FOG
FORMATION THIS EVENING. FOG IS THEN EXPECTED TO FORM ACROSS MUCH
OF THE REGION BY TUESDAY MORNING. FOG MAY BECOME DENSE IN PLACES
SUCH AS THE CENTRAL FOOTHILLS...PIEDMONT AND SHENANDOAH VALLEY.

DRIER AIR WORKS INTO THE AREA TUE WITH RISK OF SHOWERS AND/OR
T-STORMS CONFINED ONLY TO AREAS SOUTH OF I-66.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
SFC HIGH PRESSURE BUILDS IN WED MORNING AS LINGERING FRONTAL
BOUNDARY FROM THE FIRST HALF OF THE WEEK DISSIPATES. MAIN STORY
FOR MID WEEK WILL BE WARMING TEMPS AS UPPER LVL RIDGE BROADENS
ACROSS THE EASTERN US...RESULTING IN RISING HEIGHTS WED INTO
THURS. AT THE SFC...SLY FLOW WILL CONTINUE THE WAA AND MOISTURE
ADVECTION. HIGH TEMPS EXPECTED TO REACH LOWER TO PSBL MID
90S...WHICH COMBINING WITH DEW PTS IN THE UPPER 60S TO LOWER 70S
PRODUCES HEAT INDICES IN THE UPPER 90S TO LOWER 100S. AS THE
VALUES STAND...NO HEAT ADVISORY WOULD BE NEEDED WED. WHILE MOST
THE AREA WILL REMAIN DRY...TERRAIN DRIVEN CONVECTION WILL BE PSBL
IN THE LATE AFTN/EARLY EVENING TIME FRAME.

UPPER LVL RIDGE AXIS SHIFTS FROM THE GREAT LAKES REGION 12Z WED TO
THE NORTHEAST BY 12Z THURS AHEAD OF AN APPROACHING CLOSED
LOW/TROUGH. ASSOCIATED COLD FRONT APPROACHES FROM THE WEST...WITH
THE 12Z MODEL SUITE PROGGING THE FRONTAL PASSAGE SOMETIME LATE THURS
AFTN INTO THE FIRST HALF OF THURS NIGHT. INCRSG SLY FLOW AHEAD OF
THE FRONT WILL KEEP A WARM AND MOIST ATMO IN PLACE...WITH YET
ANOTHER DAY OF HIGHS REACHING THE LOWER TO MID 90S AS 850MB TEMPS
NEAR 20 DEGREES CELSIUS AND DEW PTS AROUND 70. SHEAR REMAINS MEAGER
DURING THE DAY...BUT EXPECTING ENOUGH RESULTING INSTABILITY TO AID
IN GENERATION IN PULSE TSTMS OUT AHEAD OF THE STORM.

FRONT SWINGS THRU THURS NIGHT...WITH PCPN TAPERING OFF WEST TO EAST
BY FRI MORNING. MINIMAL BREAK IN TEMPS...WITH 850MB TEMPS DROPPING
OFF TO AROUND 16 DEGREES CELSIUS IN THE WAKE OF THE FRONT. LOW TEMPS
WILL DROP BACK TO NEAR NORMAL.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
COLD FRONT CROSSING REGION THURSDAY NIGHT. MARGINALLY UNSTABLE SO
CAN`T RULE CONVECTIVE DEVELOPMENT CONTINUING AFTER DARK. SURFACE
HIGH WILL TRANSPORT MUCH DRIER AIR INTO REGION...RH 20 TO 30
PERCENT...FRIDAY. PASSAGE OF WEAK PVA AND QUASI-STATIONARY SURFACE
TROUGH MAY SUPPORT A STRAY THUNDERSTORM OR SHOWER OVER SOUTHEAST
MD SUNDAY.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
VCSH/VCTS POSSIBLE THIS EVENING AT THE TERMINALS. FOG EXPECTED TO
DEVELOP TONIGHT AT CHO-MRB-IAD-BWI AND MAY EXPAND TO DCA-MTN. IFR
VSBYS EXPECTED AT THE FOUR TERMINALS WITH THE POTENTIAL AT ALL THE
TERMINALS. SHRA/TSRA THAT DOES OCCUR AT THE TERMINALS MAY REDUCE
VSBYS TO SUB-VFR DUE TO HEAVY RIAN.

VFR CONDITIONS EXPECTED TUESDAY. DRIER AIR WORKS FURTHER SOUTH
TUE WITH ONLY A RISK OF A T-STORM AT KCHO.

VFR CONDITIONS WED-WED NIGHT. PSBL SUB-VFR CONDITIONS
THURS WITH DVLPNG SHOWERS AND TSTM...MAINLY THURS AFTN/EVENING TIME
FRAME. ANY TSTM COULD PRODUCE GUSTY AND VRB WINDS. VFR CONDITIONS
RETURN THURS NIGHT.

&&

.MARINE...
SRLY WINDS SHOULD CAUSE CHANNELING THIS EVENING FOR THE LOWER
TIDAL POTOMAC AND BAY SOUTH OF NORTH BEACH. WINDS EXPECTED BELOW
SCA TUE- TUE NIGHT. MAIN THREAT IS CG LIGHTNING FROM T-STORMS.

SUB-SCA CONDITIONS EXPECTED WED. PSBL BRIEF PERIOD OF SCA
GUSTS WED EVENING ON THE CHESAPEAKE BAY. SUB-SCA CONDITIONS THEN ON
ALL WATERS THUR MORNING. INCRSG SLY FLOW AHEAD OF THE APPROACHING
COLD FRONT COULD BRING GUSTS BACK TO AROUND 18-20 KTS THURS AFTN AND
NIGHT ON THE CHESAPEAKE BAY.

&&

.TIDES/COASTAL FLOODING...
A COASTAL FLOOD ADVISORY IN EFFECT FOR LATE TONIGHT/EARLY TUESDAY
MORNING FOR ANNE ARUNDEL COUNTY. ANOMALIES OF A HALF TO ONE FOOT
ABOVE NORMAL ARE EXPECTED. THIS SHOULD LIMIT MINOR FLOOD AT OTHER
SPOTS ON THE WESTERN SHORE OF THE CHESPEAKE BAY. WILL MONITOR
TRENDS AT BALTIMORE AND TIDAL POTOMAC NEAR ALEXANDRIA.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...COASTAL FLOOD ADVISORY FROM 2 AM TO 6 AM EDT TUESDAY FOR
     MDZ014.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT TUESDAY FOR ANZ533-534-537-
     541>543.

&&

$$
SYNOPSIS...SEARS
NEAR TERM...HAS/LFR
SHORT TERM...SEARS
LONG TERM...CEM
AVIATION...CEM/SEARS/LFR/HAS
MARINE...CEM/SEARS/LFR/HAS
TIDES/COASTAL FLOODING...HAS



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