Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 030830 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 330 AM EST WED FEB 3 2016 .SYNOPSIS...
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A COLD FRONT WILL APPROACH THE AREA TODAY BEFORE PASSING THROUGH TONIGHT. A WAVE OF LOW PRESSURE DEVELOPS ALONG THE BOUNDARY THURSDAY BEFORE PASSING BY WELL TO OUR EAST THURSDAY NIGHT INTO FRIDAY. HIGH PRESSURE WILL RETURN FOR FRIDAY AFTERNOON INTO SATURDAY. COASTAL LOW PRESSURE WILL PASS BY WELL TO OUR SOUTH AND EAST SUNDAY. ANOTHER LOW PRESSURE SYSTEM MAY IMPACT THE AREA EARLY NEXT WEEK.
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&& .NEAR TERM /THROUGH TODAY/...
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AREA OF LOW PRESSURE CENTERED OVER THE GREAT LAKES THIS MORNING WILL MOVE INTO SOUTHERN CANADA THROUGH TODAY. THIS WILL DRAG A COLD FRONT TOWARDS THE REGION LATER TODAY AND TONIGHT. DEEP SOUTHWEST FLOW CONTINUES OUT AHEAD OF THE FRONTAL BOUNDARY WITH PRECIPITABLE WATERS APPROACHING 1.5" AND WARM CLOUD DEPTHS POSSIBLY EXCEEDING 11K FEET BY THE AFTERNOON. THIS WILL SET THE STAGE FOR A PERIOD OF MODERATE TO LOCALLY HEAVY RAINFALL LATER TODAY. BULK OF RAIN TO START THE DAY WILL REMAIN WEST OF THE APPALACHIAN MOUNTAINS WITH SOME LOW CLOUDS/DRIZZLE OUT AHEAD OF IT FROM DC WESTWARD. HOWEVER...AREA OF RAIN WILL SPREAD EASTWARD THROUGH THE DAY...PEAKING BETWEEN 18Z-00Z FOR MOST OF THE REGION. AS FAR AS FLOOD THREAT...WIDESPREAD RAINFALL AMOUNTS OF 0.5-1 INCH EXPECTED...WITH LOCALLY HIGHER AMOUNTS UP TO 1.5 INCHES IN ANY CONVECTION. THIS COMBINED WITH 1-2 INCHES OF LIQUID EQUIVALENT SITTING IN ANY REMAINING SNOW PACK WILL LEAD TO FLOODING CONCERNS THIS AFTERNOON AND TONIGHT IN URBAN AREAS AND SMALL STREAMS/RIVERS...AND THEN LARGER BASINS INTO THURSDAY. SEE HYDROLOGY SECTION FOR MORE INFORMATION. FOR THUNDER POTENTIAL...SHOWALTER INDICIES ARE PROGGED TO GO NEGATIVE LATE THIS MORNING AND INTO THE AFTERNOON INDICATIVE OF ELEVATED CONVECTION...SO DID PUT IN CHANCES FOR THUNDER ACROSS MUCH OF THE REGION. THINKING A CONVECTIVE FINE LINE IS LIKELY...MUCH LIKE WHAT IS CURRENTLY BEING SEEN ACROSS PARTS OF THE OHIO VALLEY. WITH LACK OF SURFACE BASED CAPE...NOT CURRENTLY THINKING SEVERE POTENTIAL...BUT SOME OF THE STRONG LOW LEVEL JET MAY BE ABLE TO MIX DOWN IN THE HEAVIER SHOWERS/POSSIBLE THUNDERSTORMS WITH GUSTS TO 40 MPH. WITH AFOREMENTIONED LOW LEVEL JET OF 60-70 KNOTS AT 850MB...WILL ALSO LEAVE WIND ADVISORY IN PLACE FOR THE HIGHER TERRAIN OF THE ALLEGHENY FRONT AND BLUE RIDGE. LACK OF MIXING SHOULD KEEP IT FROM BECOMING A LOWER ELEVATION CONCERN. OTHERWISE...HIGH TEMPS TODAY WILL RANGE FROM THE LOW 50S IN THE FAR NORTHWEST ZONES WHERE SOME COOLER AIR GETS TRAPPED...TO UPPER 60S ACROSS CENTRAL VIRGINIA AND SOUTHERN VIRGINIA.
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&& .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
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HEAVIEST AND MOST WIDESPREAD RAIN SHOULD BE EXITING THE REGION BY 03Z...HOWEVER ACTUAL BAROCLINIC ZONE IS HELD UP IN CONTINUED DEEP SOUTHWEST FLOW. THUS WILL SEE CONTINUED RAIN SHOWER CHANCES OVERNIGHT...ESPECIALLY ACROSS SOUTHEASTERN ZONES. SOME PATCHY FOG ALSO POSSIBLE. WITH DEVELOPING WESTERLY FLOW...MAY SEE SOME UPSLOPE RAIN/SNOW SHOWERS DEVELOP TOWARDS MORNING ALONG THE ALLEGHENY FRONT. LOWS IN THE 30S/40S. FRONTAL ZONE STILL SLOW TO MOVE EASTWARD ON THURSDAY/THURSDAY NIGHT SO HAVE KEPT CHANCES IN FOR SOUTHEASTERN MARYLAND. MORE PRONOUNCED NORTHWEST FLOW WILL BE DEVELOPING SO ALSO HAVE CHANCES FOR UPSLOPE RAIN/SNOW SHOWERS ALONG THE ALLEGHENY FRONT. WILL BE LOOKING AT HIGHS IN THE 40S TO LOW 50S. HIGH PRESSURE WILL FINALLY BUILD INTO THE REGION ON FRIDAY WITH SKIES CLEARING. WILL SEE NEAR NORMAL TEMPERATURES WITH HIGHS IN THE 40S FOR MOST.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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A POTENTIALLY ACTIVE WEATHER PATTERN MAY SETUP FOR THE PERIOD...BUT UNCERTAINTY IN THE DETAILS REMAINS HIGH THIS FAR OUT. A POTENT UPPER-LEVEL RIDGE OF HIGH PRESSURE WILL DEVELOP OVER THE WESTERN CONUS AND THIS WILL ALLOW FOR A STRONG UPPER-LEVEL TROUGH TO CARVE OUT OVER THE CENTRAL AND EASTERN CONUS. SHORTWAVE ENERGY DIVING INTO THE TROUGH WILL ENHANCE THE CHANCE FOR COASTAL STORMS TO DEVELOP WHILE COLDER AIR REMAINS IN PLACE. FOR SATURDAY...HIGH PRESSURE WILL REMAIN OVERHEAD BRINGING DRY AND SEASONABLY CHILLY CONDITIONS. HOWEVER...COASTAL LOW PRESSURE WILL LIKELY DEVELOP SATURDAY NIGHT OFF THE SOUTHEAST COAST AS SHORTWAVE ENERGY IN THE SOUTHERN STREAM OF THE JET DIGS DOWN AND INTERACTS WITH THE BAROCLINIC ZONE ALONG THE COAST. IT DOES APPEAR THAT THIS SYSTEM WILL DEVELOP TOO LATE TO HAVE A SIGNIFICANT IMPACT ON OUR WEATHER. THAT IS BECAUSE MORE SHORTWAVE ENERGY WILL BE DIVING INTO THE CENTRAL CONUS...ALLOWING THIS SYSTEM TO PUSH FARTHER EAST THAN NORTH. THIS WOULD KEEP THE LOW TOO FAR TO OUR SOUTH BUT THIS WILL HAVE TO BE MONITORED SINCE IT IS STILL SEVERAL DAYS OUT. THE SYSTEM DIVING INTO THE CENTRAL CONUS SUNDAY MAY DEVELOP INTO A COASTAL LOW DURING THE EARLY PORTION OF NEXT WEEK. LATEST DETERMINISTIC GFS AND ECMWF SHOW THIS HAVING A BETTER CHANCE OF IMPACTING OUR AREA. THE GEFS MEAN SHOWS A STRONG UPPER-LEVEL TROUGH OVERHEAD WHICH WOULD ALSO SUPPORT THE POSSIBILITY OF A COASTAL LOW. CONFIDENCE IS HIGH FOR A HIGH AMPLITUDE PATTERN WITH A POTENT UPPER- LEVEL TROUGH OVERHEAD SATURDAY THROUGH TUESDAY...BUT THE DETAILS AND TIMING OF THE SHORTWAVE ENERGY ARE HIGHLY UNCERTAIN WHICH LEADS TO A LOW CONFIDENCE FORECAST. HOWEVER...AS OF NOW IT APPEARS THAT SATURDAY AND SUNDAY WILL TURN OUT DRY AND SEASONABLY CHILLY. A COASTAL STORM MAY BRING THE CHANCE FOR WINTRY PRECIPITATION TO THE AREA EARLY NEXT WEEK.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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MOSTLY VFR CONDITIONS TO START THE PERIOD WILL TREND DOWNWARD INTO MVFR/IFR...INITIALLY IN LOW CLOUDS AND AREAS OF DRIZZLE IN THE EARLY TO MID MORNING HOURS...FOLLOWED BY RAIN AND POSSIBLY A FEW ISOLATED THUNDERSTORMS THIS AFTERNOON/EVENING. LOW LEVEL WIND SHEAR ALSO A CONCERN THIS MORNING WITH WINDS FROM 40-50 KNOTS AT 2000 FEET. WINDS WILL THEN GUST OUT OF THE SOUTH UP TO 25 KNOTS THIS AFTERNOON...ENDING ANY LLWS THREAT. LOCALLY HIGHER GUSTS ARE POSSIBLE IN ANY ISOLATED THUNDERSTORMS. RAIN WILL TAPER OFF TO SHOWERS LATER THIS EVENING AND TONIGHT. THERE MAY BE LINGERING AREAS OF LOW CEILINGS AND VISIBILITIES...BUT SHOWING A GENERAL IMPROVEMENT FOR NOW. WINDS WILL TURN WEST-NORTHWESTERLY BY THURSDAY MORNING. WIDESPREAD VFR WILL DEVELOP FOR THURSDAY AND FRIDAY...PERSISTING INTO SATURDAY AND SUNDAY. LOW PRESSURE MAY IMPACT THE TERMINALS EARLY NEXT WEEK. DETAILS ARE HIGHLY UNCERTAIN AT THIS TIME.
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&& .MARINE...
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STILL SEEING SUB-SCA CONDITIONS EARLY THIS MORNING...BUT WITH INCREASING SOUTHERLY FLOW...WILL CONTINUE WITH SMALL CRAFT ADVISORY THROUGH TODAY AND INTO THIS EVENING WITH GUSTS UP TO 25-27 KNOTS. HAVE ALSO KEPT LINGERING SCA ON THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC FOR TONIGHT. RAIN IS ALSO EXPECTED TODAY...WITH THE POSSIBILITY FOR ISOLATED THUNDERSTORMS THIS AFTERNOON/EVENING. LOCALLY HIGHER GUSTS MAY ACCOMPANY SOME OF THE HEAVIER STORMS...WITH SMW POTENTIALLY NEEDED. WINDS WILL SLACKEN ON THURSDAY MORNING...BUT AN ADDITIONAL SCA MAY BE NEEDED THURSDAY NIGHT INTO FRIDAY WITH DEVELOPING NORTHWEST FLOW. HIGH PRESSURE WILL BUILD OVER THE WATERS LATER FRIDAY AND SATURDAY. LOW PRESSURE WILL LIKELY STAY WELL SOUTH AND EAST OF THE WATERS SUNDAY THROUGH SUNDAY NIGHT. THE GRADIENT MAY BE ENOUGH FOR WIND GUSTS TO APPROACH SCA CRITERIA THOUGH. ANOTHER COASTAL LOW MAY IMPACT THE WATERS EARLY NEXT WEEK. TIMING AND DETAILS REMAIN UNCERTAIN THIS FAR OUT.
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&& .HYDROLOGY...
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THE WARMTH AND RAIN ON MONDAY LED TO ANOTHER HIT ON THE SNOW WATER...WHICH TUESDAY MORNING WAS DOWN TO JUST NINE TENTHS OF AN INCH. THE BULK OF THE SNOW IS GONE AT THIS POINT...ACTUALLY COMPLETELY GONE IN MUCH OF THE SOUTH FORK SHENANDOAH... RAPIDAN...RIVANNA...AND JAMES BASINS...AND IN SOUTHERN MARYLAND. HAVE SEEN SOME STREAM REACTION TO SNOW MELT IN MOST OF THE AREA YESTERDAY AND OVERNIGHT...AS WELL AS SOME ICE MOVEMENT. THERE WERE SEVERAL PARTIAL ICE BLOCKAGES OF STREAMS NOTED IN EASTERN WV ON TUESDAY. ONE WAS SIGNIFICANT ENOUGH TO SEND THE CACAPON RIVER OUT OF ITS BANKS AND OVER ROADS. CONFIDENCE CONTINUES TO INCREASE FOR FLOOD POTENTIAL TODAY THROUGH THURSDAY. THE MOST REMAINING SNOW PACK IS IN THE FAR EASTERN WV PANHANDLE EASTWARD ACROSS NORTHERN MARYLAND...AND WITH TEMPERATURES FORECAST TO REACH THE 50S TO NEAR 60 IN MOST OF THAT AREA...AND DEWPOINTS IN THE 50S EAST OF THE BLUE RIDGE...MUCH OF WHAT IS LEFT WILL NOT LAST PAST WEDNESDAY. COMBINE THAT MELT WITH AN EXPECTED HALF TO ONE INCH OF RAIN /WITH ISOLATED HIGHER AMOUNTS/ AND THAT IS A RECIPE FOR AT LEAST SOME FLOODING. A FLOOD WATCH CONTINUES FOR MUCH OF MARYLAND...AND HAVE ADDED IN PARTS OF NORTHERN VIRGINIA AND DC. THEN ALL THE RAIN AND SNOW MELT FUNNELS INTO LARGER STREAMS. SIGNIFICANT WITHIN-BANK RISES ARE EXPECTED AREAWIDE. CURRENTLY FLOODING IS FORECAST ON OPEQUON CREEK /NEAR THE SNOW WATER BULLSEYE/...AS WELL AS THE MAINSTEM SHENANDOAH RIVER AND THE MAINSTEM POTOMAC BELOW WILLIAMSPORT. A FLOOD WARNING HAS BEEN ISSUED FOR THE OPEQUON...AND A WATCH FOR THE SHENANDOAH. FLOODING ON THE MAINSTEM POTOMAC WOULD NOT START BEFORE THURSDAY EVENING AND IS MORE UNCERTAIN SINCE IT IS DEPENDENT ON BOTH RAIN AND SNOW MELT. FOR THAT REASON...NOT ENOUGH CONFIDENCE EXISTS YET FOR A WATCH OR WARNING ON THE MAINSTEM POTOMAC. WILL REASSESS THIS LATER THIS MORNING AS THE RAIN BEGINS.
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&& .TIDES/COASTAL FLOODING...
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SOUTHERLY FLOW WILL INCREASE TODAY WHICH WILL CAUSE TIDAL ANOMALIES TO INCREASE. GUIDANCE CONTINUES TO SHOW MINOR FLOODING LATER THIS AFTERNOON AND EVENING ACROSS THE NORTHERN PORTION OF THE CHESAPEAKE BAY NEAR BOWLEYS QUARTERS AND HAVRE DE GRACE. BALTIMORE AND ANNAPOLIS ARE CLOSE...BUT GUIDANCE CONTINUES TO SHOW WATER LEVELS JUST BELOW MINOR FLOODING THRESHOLDS. A NORTHWEST FLOW WILL DEVELOP LATE TONIGHT INTO THURSDAY. TIDAL ANOMALIES WILL DROP DURING THIS TIME.
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&& .CLIMATE... RECORDS HIGHS FOR WED FEB 3: DCA: 65 SET IN 1927 BWI: 66 SET IN 1932 IAD: 66 SET IN 1991 RECORD MAX MINS FOR WED FEB 3: DCA: 44 SET IN 2006 BWI: 43 SET IN 2006 IAD: 42 SET IN 2006 AND 1990 && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...FLOOD WATCH FROM NOON EST TODAY THROUGH LATE TONIGHT FOR DCZ001. MD...FLOOD WATCH FROM NOON EST TODAY THROUGH LATE TONIGHT FOR MDZ013-014-503>506. FLOOD WATCH FROM NOON EST TODAY THROUGH THURSDAY AFTERNOON FOR MDZ003>006-011-507-508. COASTAL FLOOD ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM EST THIS EVENING FOR MDZ011-508. VA...WIND ADVISORY UNTIL 10 AM EST THIS MORNING FOR VAZ503-507-508. FLOOD WATCH FROM NOON EST TODAY THROUGH LATE TONIGHT FOR VAZ052>054-505-506. WV...WIND ADVISORY UNTIL 10 AM EST THIS MORNING FOR WVZ501-503-505. FLOOD WATCH FROM NOON EST TODAY THROUGH THURSDAY AFTERNOON FOR WVZ051>053. MARINE...SMALL CRAFT ADVISORY FROM 7 AM THIS MORNING TO 1 AM EST THURSDAY FOR ANZ530>532-537. SMALL CRAFT ADVISORY FROM 7 AM THIS MORNING TO 6 PM EST THIS EVENING FOR ANZ535-536-538>542. SMALL CRAFT ADVISORY UNTIL 1 AM EST THURSDAY FOR ANZ533-534- 543.
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&& $$ SYNOPSIS...BJL/MJM NEAR TERM...MJM SHORT TERM...MJM LONG TERM...BJL AVIATION...BJL/MJM MARINE...BJL/MJM HYDROLOGY...JCE/MJM/BJL TIDES/COASTAL FLOODING...BJL CLIMATE...WFO LWX

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