Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 030115 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 915 PM EDT SUN AUG 2 2015 .SYNOPSIS... HIGH PRESSURE WILL DOMINATE THROUGH TONIGHT. A COLD FRONT WILL APPROACH FROM THE NORTHWEST ON MONDAY AND ENTER THE AREA MONDAY NIGHT. THE FRONT WILL STALL IN THE AREA TUESDAY...SLIDE SOUTHEAST WEDNESDAY...THEN LIFT BACK NORTH THURSDAY. A WAVE OF LOW PRESSURE WILL THEN RIDE EAST ALONG THE FRONT FRIDAY. AFTER THIS LOW PASSES THE FRONT WILL SLIP SOUTH OF THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH MONDAY/... HIGH PRESSURE EXTENDS ACROSS THE MID-ATLANTIC AND CENTRAL APPALACHIANS THIS EVENING. A COLD FRONT IS DROPPING THROUGH THE GREAT LAKES. AS THE PATCH OF DENSER CIRRUS EXITS TO THE EAST...THE BULK OF THE NIGHT WILL BE MAINLY CLEAR...ALTHOUGH SOME ADDITIONAL HIGH CLOUDS COULD ENTER FROM THE WEST LATE. COMBINED WITH LIGHT WINDS...THIS COULD LEAD TO SOME PATCHY FOG IN THE TYPICAL SPOTS IN CENTRAL VA AND THE WESTERN VALLEYS...BUT THE DRY AIRMASS LOOKS TO HOLD FIRM AND LIMIT THIS POTENTIAL. IT LOOKS LIKE IF THERE IS DEW POINT ADVECTION...IT WILL BE INTO THE SOUTHEASTERN COUNTIES...SO SOME OF THE VALLEYS COULD STILL RADIATE OUT INTO THE 50S. OTHERWISE 60S FOR MOST AND 70S URBAN CENTERS/BAYSHORE. ALTHOUGH THE FRONT WILL APPROACH US MONDAY...THE ATMOSPHERE WILL NOT MOISTEN APPRECIABLY (WESTERLY FLOW EXCEPT AT THE LOW LEVELS) AND THE BULK OF THE FORCING WILL REMAIN TO THE NORTH. DEPENDING ON THE MODEL OF CHOICE...SOME CONVECTION MAY SNEAK INTO THE NORTHERN POTOMAC HIGHLANDS (TO PERHAPS AS FAR EAST AS THE MARTINSBURG AREA) BY MID TO LATE AFTERNOON. IF ANYTHING DOES HOLD TOGETHER FROM THE NORTHWEST...THE TIME OF ARRIVAL LOOKS TO BE MORE IN THE EVENING TIME FRAME THOUGH. THE PRESSURE GRADIENT WILL TIGHTEN UP SO THERE COULD BE SOME GUSTS AROUND 20-25 MPH. THE SOUTHWESTERLY FLOW WILL DRAG WARMER AIR NORTH SO HIGHS WILL RISE SEVERAL DEGREES COMPARED TO TODAY. HIGHS WILL BE IN THE LOW 90S IN MOST AREAS WITH MID 90S IN THE HOTTEST SPOTS. HOWEVER DEW POINTS WILL ONLY RISE INTO THE LOWER TO MID 60S SO THE HEAT INDICES WILL ONLY BE A FEW DEGREES HIGHER THAN THE AIR TEMPERATURES. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... FRONT MOVES IN MONDAY NIGHT. SHEAR DOES INCREASE...HOWEVER...MOISTURE WILL STILL BE RELATIVELY LIMITED AND THIS WILL IN TURN LIMIT CAPE...SO THIS SHOULD RESULT IN THUNDERSTORM ACTIVITY HAVING TO ADVECT INTO THE AREA RATHER THAN DEVELOP LOCALLY. BEST FORCING ALOFT WILL STAY NORTH. THUS...IT APPEARS THAT STORMS WHICH DEVELOP TO OUR NORTHWEST WILL ENTER THE CWA DURING THE EVENING...BUT APPEAR LIKELY TO DIMINISH TO SHOWERS OVERNIGHT...POSSIBLY EVEN BEFORE REACHING THE METRO AREA. THE INCREASED CLOUD COVER SHOULD HOLD LOWS UP A BIT WARMER THAN TONIGHT`S READINGS. PLACES THAT RECEIVE ANY RAIN COULD ALSO SEE PATCHY FOG OVERNIGHT IF SOME BREAKS IN THE CLOUDS DEVELOP. LOW PRESSURE IN SOUTHERN QUEBEC WILL BE MOVING NORTHWARD WHILE A BERMUDA HIGH PERSISTS IN THE ATLANTIC TUESDAY. A COLD FRONT WILL BE STALLED ACROSS THE MID-ATLANTIC IN THE VICINITY OF THE I-95 CORRIDOR TUESDAY. DUE TO THE TIME OF YEAR...THE TEMPERATURE GRADIENT IS WEAK BUT DRIER AIR WILL BE MOVING INTO THE POTOMAC HIGHLANDS. IN VICINITY OF THE FRONT AND IN THE WARM/MOIST SECTOR ISO-SCT SHOWERS AND THUNDERSTORMS ARE POSSIBLE. FCST SOUNDINGS AT DCA-NHK SHOW 1-2K J/KG OF SBCAPE WITH UNIDIRECTIONAL SHEAR. A STABLE LAYER WILL LIKELY BE OVERCOME BY LATE AFTERNOON AND SOME STORMS MAY PRODUCE GUSTY WINDS ESPECIALLY ACROSS S MD AND SURROUNDING WATERS. THE COLD FRONT MOVES OFF THE COAST TUESDAY NIGHT AS HIGH PRESSURE BUILDS INTO THE REGION FROM THE SW. DRY CONDITIONS EXPECTED WEDNESDAY. WARM AIR ADVECTION WILL BEGIN WEDNESDAY AFTERNOON AS THE NEXT SYSTEM APPROACHES. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... MEDIUM RANGE GUIDANCE IS GRADUALLY COMING INTO BETTER AGREEMENT WITH THE TIMING OF A WAVE OF LOW PRESSURE MOVING ALONG A STALLED BOUNDARY ACROSS THE CWA WEDNESDAY NIGHT INTO THURSDAY. WHILE FINER SCALE DETAILS REMAIN TO BE SEEN...FELT CONFIDENT ENOUGH TO GO WITH HIGH CHANCE POPS AS THE WAVE PASSES. CONVECTION POTENTIAL WILL DEPEND ON EXACT TIMING/PLACEMENT OF THE WAVE. GUIDANCE DIVERGES AFTER THURSDAY...WITH SOME SOLUTIONS SUGGESTING THE FRONT SAGS FAR ENOUGH SOUTH TO LEAVE THE AREA DRY...WHILE OTHER SOLUTIONS KEEP THE FRONT STALLED OVER THE AREA WITH A SECOND WAVE OF LOW PRESSURE FRIDAY INTO SATURDAY. CLIMATOLOGY WOULD SUGGEST A SLOWER SOUTHWARD PROGRESSION OF THE FRONT...AND AS SUCH HAVE KEPT CHANCE POPS IN THE FORECAST THROUGH THE END OF THE WEEK. HIGH PRESSURE SHOULD ATTEMPT TO MAKE A RETURN NEXT WEEKEND. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... HIGH PRESSURE CENTERED OVER THE AREA TONIGHT. DO NOT HAVE VERY HIGH CONFIDENCE OF VSBY REDUCTIONS IN BR AT THE WESTERN TERMINALS BUT IF IT DOES OCCUR CHO WOULD HAVE THE HIGHEST CHANCE. A FRONT WILL APPROACH FROM THE NW MONDAY...RESULTING IN INCREASING S/SW WIND GUSTS TO AROUND 15-20 KT...BUT OTHERWISE NO AVIATION IMPACTS WITH VFR CONDITIONS EXPECTED THROUGH THE DAY. MRB WILL HAVE THE HIGHEST CHANCE OF A SHOWER/STORM BY EARLY MONDAY EVENING. LOW CONFIDENCE ON HOW FAR S/E (I.E. THE METRO SITES) THIS ACTIVITY MAKES IT BEFORE WEAKENING. IF IT DOES HOLD TOGETHER...SUB- VFR CONDITIONS WOULD BE POSSIBLE. THERE IS A LOW CHANCE OF BR LATE MONDAY NIGHT AT MRB/CHO AS WELL AS ANY LOCATION WHICH SEES RAIN. A STALLED COLD FRONT WILL BE NEAR THE I-95 TERMINALS TUESDAY AND SHRA/TSRA POSSIBLE THROUGH TUESDAY EVENING. SUB-VFR POSSIBLE IN LWR CIGS/VSBYS ASSOCIATED W/ SHWRS/TSTMS WED NIGHT- THU. WIND DIRECTION FORECAST UNCERTAIN AND DEPENDS ON PLACEMENT OF STALLED FRONT...BUT SPEEDS SHOULD BE LIGHT AOB 10 KT. && .MARINE... GUSTIEST WINDS (UP TO 15 KT) THIS EVENING ARE OVER NORTHERN SECTIONS OF THE BAY. ALTHOUGH WINDS OVERNIGHT SHOULD BE FAIRLY LIGHT WITH HIGH PRESSURE IN CONTROL...THERE MAY BE A FEW CONTINUED GUSTS TO 15 KT DUE TO SOUTHERLY FLOW OVER THE BAY. WINDS WILL STRENGTHEN FROM THE SOUTH ON MONDAY AS THE PRESSURE GRADIENT TIGHTENS AHEAD OF AN APPROACHING COLD FRONT. THIS WILL HELP WINDS TO REACH SCA LEVELS BY AFTERNOON. HAVE KEPT SCA GOING THROUGH MONDAY EVENING ALL WATERS...WITH THE SCA FOR THE BAY AND ADJACENT WATERS CONTINUING THROUGH MONDAY NIGHT. THUNDERSTORMS MAY APPROACH THE WATERS FROM THE NW MONDAY EVENING...BUT SHOULD BE ON A WEAKENING TREND IF THEY DO. A STALLED COLD FRONT WILL BE NEAR THE WATERS TUESDAY AND SHOWERS AND THUNDERSTORMS ARE POSSIBLE IN THE AFTERNOON AND EARLY EVENING. SOME STORMS MAY PRODUCE GUSTY WINDS THAT MAY WARRANT A SMW. DEPENDING ON THE LOCATION OF THE GRADIENT...A SCA MAY BE NEEDED TUESDAY AFTERNOON FOR PORTIONS OF THE WATERS. WINDS SHOULD REMAIN BELOW SCA LEVELS WEDNESDAY AND WEDNESDAY NIGHT. SHOWERS AND SCATTERED THUNDERSTORMS ARE POSSIBLE MAINLY ON THURSDAY AS A WAVE OF LOW PRESSURE APPROACHES THE WATERS ALONG THE FRONT. SHOULD THIS WAVE OF LOW PRESSURE BE STRONGER THAN WHAT THE CURRENT CONSENSUS SUGGEST THEN THERE IS A CHANCE OF SCA GUSTS THURSDAY...BUT CONFIDENCE IN ANY ONE SOLUTION IS LOW AT THIS TIME GIVEN MODEL SPREAD. && .TIDES/COASTAL FLOODING... TIDAL ANOMALIES REMAIN BELOW A HALF FOOT THIS EVENING. SOUTHERLY FLOW AHEAD OF THE NEXT FRONT WILL ELEVATE TIDAL ANOMALIES ON MONDAY...BUT AT THIS POINT WE ARE NOT EXPECTING MINOR FLOODING. THIS POSSIBILITY WILL REQUIRE MONITORING HOWEVER. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM NOON MONDAY TO 6 AM EDT TUESDAY FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY FROM 3 PM MONDAY TO MIDNIGHT EDT MONDAY NIGHT FOR ANZ535-536. && $$ SYNOPSIS...RCM NEAR TERM...ADS/RCM SHORT TERM...HAS/RCM LONG TERM...DFH AVIATION...ADS/HAS/DFH MARINE...ADS/HAS/RCM/DFH TIDES/COASTAL FLOODING...ADS/RCM

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