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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