Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 021905 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 305 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 WIGGLE 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/... AT PRESENT...HIGH PRESSURE IS CENTERED OVER THE CENTRAL APPALACHIANS...WITH THE NEXT FRONTAL BOUNDARY STILL LOCATED WELL TO THE NORTHWEST IN THE NORTHERN PLAINS. FOR TONIGHT...THE HIGH WILL REMAIN IN PLACE...AND WITH DRY AIR OVER THE AREA WITH MANY AREAS SEEING DEW POINTS DOWN INTO THE 50S AT PRESENT...RADIATIONAL COOLING SHOULD START QUICKLY AFTER SUNSET. AS WINDS BEGIN TO TURN SOUTHERLY OVERNIGHT WITH THE APPROACH OF THE FRONT TO THE NORTHWEST...DEW POINTS WILL BEGIN TO RISE...AND SHOULD REACH THE LOWER 60S BY MORNING. THIS WILL LIMIT JUST HOW COOL IT CAN GET...BUT ALSO MAY HELP SOME PATCHY FOG TO FORM AWAY FROM THE COASTAL AND METRO AREAS. OTHERWISE...VERY BENIGN WEATHER WITH LIGHT WINDS. FRONT APPROACHES FROM THE NORTHWEST ON MONDAY...BUT WITH FORCING REMAINING WELL NORTHWEST DURING THE DAY AND LIMITED MOISTURE /MOST GUIDANCE KEEPS PW`S BELOW 1.5 INCHES/...GENERALLY WE EXPECT DRY WEATHER THROUGH AFTERNOON. THE PRESSURE GRADIENT WILL TIGHTEN UP SO WE DO EXPECT WINDS TO BECOME A BIT GUSTY...AND THE SOUTHWESTERLY FLOW WILL DRAG WARMER AIR NORTH SO HIGHS WILL RISE SEVERAL DEGREES COMPARED TO TODAY. HOWEVER...WITH A RELATIVE LACK OF MOISTURE /DEW POINTS EXPECTED TO REMAIN IN THE LOW 60S/...HEAT INDICES SHOULD STAY WELL BELOW HEAT ADVISORY CRITERIA AND IN FACT PROBABLY WON`T EVEN CRACK 100 AT OUR RELIABLE REPORTING STATIONS. HIGHS WILL BE IN THE LOW 90S IN MOST AREAS WITH MID 90S IN THE HOTTEST SPOTS. && .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 RECIEVE 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 VICNIITY 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 SATURDAY/... 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 /19Z SUNDAY THROUGH FRIDAY/... GENERALLY VFR CIGS AND VIS THROUGH MONDAY NIGHT. CHANCE OF SUB- VFR CIGS/VIS AT MRB/CHO TONIGHT WITH PATCHY FOG...WITH BEST CHANCE AT CHO...THEN CHANCE OF SUB VFR CIGS/VIS MONDAY NIGHT WITH THUNDERSTORMS IN THE EVENING AND SHOWERS/PATCHY FOG OVERNIGHT. OTHER CONCERN WILL BE WINDS FROM THE SOUTHWEST GUSTING TO AROUND 20 KNOTS AS THE COLD FRONT APPROACHES MONDAY AFTERNOON. 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... 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...AND HAVE KEPT SCA GOING THROUGH MONDAY EVENING ALL WATERS...WITH THE SCA FOR THE BAY AND ADJACENT WATERS CONTINUING THROUGH MONDAY NIGHT. 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 WARRENT 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... ASTRONOMICAL TIDES ARE LOWERING WITH THE FULL MOON NOW BEHIND US...AND ANOMALIES ARE LOW ENOUGH THAT TIDAL FLOODING WILL NOT BE A THREAT THROUGH TONIGHT. 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...RCM SHORT TERM...HAS/RCM LONG TERM...DFH AVIATION...HAS/RCM/DFH MARINE...HAS/RCM/DFH TIDES/COASTAL FLOODING...RCM

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