Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 161754 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 154 PM EDT THU APR 16 2015 .SYNOPSIS...
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HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST THROUGH TONIGHT. A WEAK COLD FRONT WILL PASS THROUGH THE REGION FRIDAY AND HIGH PRESSURE WILL RETURN FOR SATURDAY. THE HIGH WILL MOVE OFF THE COAST SUNDAY AND A WARM FRONT WILL MOVE INTO THE AREA SUNDAY NIGHT INTO MONDAY. A COLD FRONT WILL PASS THROUGH LATE MONDAY INTO MONDAY NIGHT BEFORE HIGH PRESSURE RETURNS FOR THE MIDDLE PORTION OF NEXT WEEK.
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&& .NEAR TERM /THROUGH FRIDAY/...
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ANALYSIS THIS AFTERNOON SHOWS HIGH PRESSURE ALONG THE NEW ENGLAND COAST AND A SURFACE RIDGE AXIS EXTENDING FROM THIS HIGH INTO THE MID-ATLANTIC. AN UPPER-LEVEL RIDGE IS ALSO LOCATED ACROSS NEW ENGLAND SOUTH TOWARD THE MID-ATLANTIC COAST. SURFACE LOW PRESSURE REMAINS OFF THE SOUTHEAST COAST AND AN UPPER-LEVEL DISTURBANCE IS MOVING THROUGH THE OHIO VALLEY. THE RETURN FLOW AROUND THE HIGH HAS COMBINED WITH THE UPPER-LEVEL DISTURBANCE TO BRING PLENTY OF CLOUDS AND EVEN SOME SHOWERS TO CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS. HOWEVER...THESE CLOUDS HAVE BEEN DISSIPATING AS THEY RUN INTO THE RIDGE AXIS TOWARD THE METROPOLITAN AREAS NORTH AND EAST. THE UPPER-LEVEL RIDGE WILL CONTINUE TO MOVE OFF TO OUR EAST THROUGH THIS EVENING AND THE SURFACE HIGH WILL ALSO SHIFT OFF THE NEW ENGLAND COAST. THIS WILL CAUSE HIGH AND MID-LEVEL CLOUDS TO SHIFT EAST ACROSS THE REST OF THE AREA. HOWEVER...PRECIPITATION WILL LIKELY REMAIN ACROSS CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS...WHERE MOISTURE IS DEEPER. HAVE LEFT THE FORECAST DRY FOR THE REST OF THE AREA THIS AFTERNOON AND EVENING...BUT A FEW SPRINKLES CANNOT BE RULED OUT AS THE UPPER-LEVEL DISTURBANCE SWINGS THROUGH. THERE IS A TIGHT GRADIENT IN TEMPERATURES THIS AFTERNOON DUE CLOUDS AND PRECIP VS. SUNSHINE. MAX TEMPS IN THE LOWER TO MIDDLE 70S ARE EXPECTED ACROSS THE METROPOLITAN AREAS INTO NORTHERN MARYLAND...BUT MAX TEMPS IN THE 50S ARE EXPECTED ACROSS THE CENTRAL SHENANDOAH VALLEY INTO THE POTOMAC HIGHLANDS WHERE MORE CLOUDS AND PRECIP ARE. THE UPPER-LEVEL DISTURBANCE WILL MOVE OFF TO OUR EAST LATER THIS EVENING...BUT A SOUTHERLY FLOW WILL CONTINUE TO INCREASE MOISTURE ACROSS OUR AREA...RESULTING IN PLENTY OF CLOUDS. MOST LOCATIONS MAY END UP DRY DUE TO A LACK OF FORCING...BUT THERE MAY BE A FEW SHOWERS ACROSS CENTRAL VIRGINIA INTO THE ALLEGHENY AND POTOMAC HIGHLANDS WHERE MOISTURE IS DEEPEST. A COLD FRONT WILL APPROACH FROM THE WEST LATE TONIGHT. WITH PLENTY OF MOISTURE IN PLACE THERE WILL BE SOME SHOWERS THAT BREAK OUT AHEAD OF THE FRONT...ESPECIALLY ACROSS NORTHERN AND WESTERN PORTIONS OF THE CWA CLOSER TO THE BOUNDARY. LIFT WITH THIS SYSTEM WILL BE WEAK SO PRECIPITATION AMOUNTS WILL BE LIGHT. MILD CONDITIONS ARE EXPECTED AHEAD OF THE FRONT. LEANED TOWARD THE WARMER GUIDANCE DUE TO THE SOUTHERLY FLOW AND INCREASED CLOUD COVER. THE COLD FRONT WILL MOVE INTO THE REGION FRIDAY. THE TEMPERATURE GRADIENT WILL BE WEAK ALONG THE FRONT...SO WARM CONDITIONS ARE EXPECTED EVERYWHERE. LEANED TOWARD THE WARMER GUIDANCE...WITH THE THINKING THAT SOME SUNSHINE WILL BREAK OUT AS DRIER AIR ALOFT CLEARS OUT ANY HIGH AND MID-LEVEL CLOUDS LEAVING JUST A SCT TO BKN CU DECK. MAX TEMPS WILL RANGE FROM THE 60S IN THE MOUNTAINS TO THE MID AND UPPER 70S NEAR WASHINGTON AND BALTIMORE INTO CENTRAL VIRGINIA. THE WARM AND RELATIVELY MOIST CONDITIONS WILL CAUSE SOME INSTABILITY TO DEVELOP. THIS MAY BE ENOUGH FOR A FEW SHOWERS AND POSSIBLY EVEN A THUNDERSTORM...ESPECIALLY LATER IN THE AFTERNOON EAST OF THE BOUNDARY FOR LOCATIONS NEAR AND EAST OF THE BLUE RIDGE MOUNTAINS. THE THREAT FOR SEVERE WEATHER IS LOW DUE TO LIMITED INSTABILITY...WEAK SHEAR PROFILES AND A LACK OF A SIGNIFICANT LIFTING MECHANISM SINCE FORCING ON THE FRONT WILL BE WEAK.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
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THE FRONT WILL MOVE OFF TO THE EAST FRIDAY EVENING. ANY LEFTOVER SHOWERS FRIDAY EVENING NEAR AND EAST OF INTERSTATE 95 WILL DISSIPATE OVERNIGHT AS DRIER AIR MOVES IN FROM THE NORTHWEST. LEANED TOWARD THE WARMER GUIDANCE DUE TO A NORTHWEST WIND INCREASING MIXING BEHIND THE FRONT...PREVENTING RADIATIONAL COOLING. HIGH PRESSURE WILL CONTINUE TO BUILD OVERHEAD SATURDAY THROUGH SATURDAY NIGHT. DRY AND SEASONABLE CONDITIONS ARE EXPECTED.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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A LARGE AND SLOW-MOVING UPPER-LEVEL TROUGH WILL APPROACH THE REGION FROM THE UPPER MIDWEST DURING THE SECOND HALF OF THE WEEKEND. RAIN CHANCES WILL INCREASE FROM SOUTHWEST TO NORTHEAST AHEAD OF A WARM FRONT DURING THE DAY SUNDAY. AN INCREASING LOW- LEVEL JET WILL USHER PLENTIFUL MOISTURE INTO THE REGION...IN TANDEM WITH UPPER-LEVEL DIVERGENCE FROM THE RIGHT ENTRANCE REGION OF AN 250 MB JET. THIS SHOULD SET THE STAGE FOR A WIDESPREAD SOAKING RAIN SUNDAY NIGHT...SOME OF WHICH MAY BE HEAVY. NOT ENOUGH CONFIDENCE AT THIS TIME TO INCLUDE ANY FLOODING MENTION IN THE HWO BUT AT LEAST SPOTTY NUISANCE FLOODING COULD BE POSSIBLE DURING THIS TIME. PARTS OF THE AREA MAY WARM SECTOR MONDAY...BUT THAT DEPENDS ON HOW FAR NORTH THE WARM FRONT CAN GET GIVEN RAIN-COOLED AIR AND CLOUD DEBRIS. AT LEAST ISOLATED ELEVATED THUNDER IS POSSIBLE LATE SUNDAY NIGHT INTO MONDAY EVENING THOUGH. RAIN CHANCES SLOWLY DIMINISH AS A COLD FRONT/TROUGH AXIS PIVOT THROUGH THE AREA LATER MONDAY NIGHT. HIGH PRESSURE BRIEFLY RETURNS LATE TUESDAY INTO WEDNESDAY...BEFORE ANOTHER SYSTEM APPROACHES FROM THE WEST BY LATE NEXT WEEK.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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VFR CONDITIONS ARE EXPECTED THROUGH THIS EVENING. A FEW SHOWERS MAY IMPACT KCHO DURING THIS TIME. HIGH AND MID-LEVEL CLOUDS WILL INCREASE ELSEWHERE. SOUTH TO SOUTHEAST WINDS WILL GUST AROUND 15 TO 20 KNOTS THIS AFTERNOON BEFORE DIMINISHING TOWARD SUNSET. A FEW SHOWERS ARE POSSIBLE LATE TONIGHT INTO FRIDAY MORNING...ESPECIALLY ACROSS THE NORTHERN TERMINALS. CIGS/VSBYS MAY APPROACH MVFR LEVELS AT THIS TIME. THE BEST CHANCE FOR MVFR LEVELS WILL BE AT KCHO DUE TO DEEPER MOISTURE. A COLD FRONT WILL PASS THROUGH THE TERMINALS LATER FRIDAY INTO FRIDAY EVENING. A FEW SHOWERS AND PERHAPS A THUNDERSTORM ARE POSSIBLE. VFR CONDITIONS ARE EXPECTED BEHIND THE FRONT FRIDAY NIGHT. VFR W/ NLY FLOW 10 KT SAT-SAT NIGHT. FLOW BECOMES ELY 10- 15 KT SUN-SUN NIGHT W/ LWR CIGS/RA LEADING TO SUB-VFR. FLOW BECOMES SLY INTO MON AND INCREASES 10-20 KT. SUB-VFR CONDS MAY BECOME MORE SCTD DURING THIS TIME.
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&& .MARINE...
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HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST TODAY. A DEEPER MIXING LAYER HAS CAUSED WINDS TO INCREASE AWAY FROM THE WATERS THIS AFTERNOON. HOWEVER...THE MIXING LAYER IS NOT AS DEEP OVERHEAD DUE TO THE RELATIVELY COOLER WATERS. THE MIXING LAYER MAY INCREASE SOME LATE THIS AFTERNOON BEFORE WINDS DECREASE THIS EVENING. WILL CONTINUE WITH THE SMALL CRAFT ADVISORY FOR THIS REASON...BUT CONFIDENCE IS HIGHER ACROSS THE EDGES OF THE WATERS WHERE TEMPS ARE BIT WARMER. SOUTHERLY WINDS WILL CONTINUE TONIGHT...BUT THE GRADIENT WILL BE WEAK ENOUGH FOR SUBSCA CONDITIONS. A COLD FRONT WILL PASS THROUGH THE WATERS LATE FRIDAY INTO FRIDAY EVENING. SOUTH TO SOUTHWEST WINDS AHEAD OF THE FRONT WILL SHIFT TO THE NORTHWEST BEHIND THE FRONT. WINDS SHOULD REMAIN BELOW SCA CRITERIA. THERE MAY BE A FEW SHOWERS AND EVEN A COUPLE THUNDERSTORMS AHEAD OF THE FRONT FRIDAY AFTERNOON. SHOULD THUNDERSTORMS DEVELOP...THEY WILL BE CAPABLE OF PRODUCING LOCALLY GUSTY WINDS. MARGINAL SCA GUSTS POSSIBLE SAT-SAT NIGHT IN NLY CHANNELING...THEN ELY FLOW AS HIGH PRESSURE ESTABLISHES ITSELF TO THE NORTH AND A WARM FRONT DEVELOPS TO THE SOUTH...INCREASING THE GRADIENT. SCA LIKELY SUN-MON...W/ OUTSIDE CHANCE OF GALE BUT NOT ENOUGH CONFIDENCE FOR HWO MENTION JUST YET GIVEN HIGHEST LLJ OVERNIGHT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL/DFH LONG TERM...DFH AVIATION...BJL/DFH MARINE...BJL/DFH

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