Area Forecast Discussion
Issued by NWS Sterling, VA

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642 FXUS61 KLWX 031531 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1031 AM EST WED FEB 3 2016 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/...
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LIGHT RAIN OCCURRING ALONG AND WEST I-95 CORRIDOR THIS MORNING. SFC ANALYSIS SHOWING WARM FRONT EXTENDING SOUTH OVER EASTERN WV...AND SPREADING WELL SOUTH OF THE AREA WITH THE COLD FRONT STILL BACK OVER THE OH RIVER VALLEY. WEAK WIND FLOW HAS KEPT THE WARM FRONTAL PASSAGE...AND LATEST THINKING IS IT WILL OCCUR THIS AFTN WITH THE LLJ FINALLY NUDGING EAST. WITH THE LACK OF THE FRONTAL PASSAGE...TEMPS HAVE BEEN SLOW TO WARM. HAVE BACKED OFF ON HIGHS A FEW DEGREES...ESP OVER NORTHERN PORTIONS OF THE CWA. HAZARD CONCERNS...FLOODING...GUSTY WINDS...AND THUNDERSTORMS. SPARSE OBS AROUND THE POTOMAC HIGHLANDS SHOWING THAT WHILE WINDS ARE GUSTING...NOT REACHING ADVISORY LVLS ANY MORE AS THE LLJ IS PUSHING EAST. ALLOWED THE WIND ADVISORY TO EXPIRE AT 10 AM TO REFLECT THIS CURRENT TREND. NOW CONCERNING WINDS FOR THIS AFTN...GENERALLY SEEING A STABLE AIRMASS IN PLACE...RESTRICTING MUCH INCREASE IN WINDS. BETTER CHC FOR GUSTING WINDS EASTERN HALF OF THE CWA WHERE MEAGER INSTABILITY WILL BE PSBL LATER IN THE DAY IN THE WAKE OF THE WARM FRONT. HOWEVER...ANY HEAVIER RAIN SHOWER OR TSTM WILL BE CAPABLE OF MIXING DOWN THE STRONGER WINDS ALOFT...AND AS SUCH...BETWEEN 19-02Z COULD SEE BRIEF GUSTS BETWEEN 30-40 KTS. FLOOD WATCH REMAINS IN EFFECT FOR THE NORTHERN HALF OF THE CWA TO ACCOUNT FOR A COUPLE OF ISSUES...URBAN/SMALL STREAM FLOODING WITH THE HEAVIER RAIN COUPLED WITH SNOWMELT AROUND THE DC/BALT METRO AREAS...AND RIVER FLOODING BACK OVER CENTRAL MD/EASTERN WV PANHANDLE. PLEASE REFER TO THE HYDRO SECTION FOR MORE DETAILS. LASTING...FOR PCPN TIMING AND TSTM THREAT...LIGHT RAIN CONTINUING THRU MIDDAY...WITH THE HEAVIER RAIN EXPECTED THIS AFTN. LACK OF UPPER LVL FORCING SUGGESTING THEN THE BEST CHC FOR THE HEAVIER RAIN COMES WITH THE COLD FRONT PASSAGE LATER TODAY. A WEAK VORT MAX PASSING THIS EVENING COULD ENHANCE THE PCPN OVER SOUTHERN MD. MORNING HI-RES MODELS SHOWING A LINE ORGANIZING RIGHT ALONG THE FRONT LATE AFTN/EVENING TIME PERIOD WITH THE PCPN TAPERING OFF QUICKLY IN THE WAKE. AS FOR SVR...WEAK FORCING...WEAK LAPSE RATES...LACK OF SFC BASED CAPE SUGGEST NO SVR THREAT...HOWEVER WILL MAINTAIN TSTM MENTION BASED UPON NEGATIVE SHOWALTER INDICES GENERALLY DC METRO AND SOUTH THRU THIS EVENING. AS PREVIOUSLY MENTIONED...ANY HEAVIER SHOWER/TSTM COULD BRING DOWN GUSTY WINDS.
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&& .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... 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. && .LONG TERM /SATURDAY THROUGH TUESDAY/... 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. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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CONDITIONS DROPPING QUICKLY THIS MORNING WITH RAIN MVG INTO THE REGION WITH LIFR-IFR BEING REPORTED AT ALL TAF SITES. EXPECTING THE DIMINISHED CONDITIONS TO PERSIST THRU 17-19Z. WINDS LESS THAN 10 KTS AT THE SFC...WITH 45-50 KTS AT 2KFT. FOR THIS AFTN...LOW-MOD CONFIDENCE ON THE CIGS/VIS. GUIDANCE SUGGESTS IMPROVEMENT TO MVFR IF NOT VFR FOR THE AREA OUTSIDE OF THE CONVECTIVE ACTIVITY. ALONG THE COLD FRONT...A LINE OF HEAVIER SHOWERS TO ISO TSTM COULD BRING CONDITIONS DOWN TO IFR. HAVE INCLUDED IN TEMPOS IN 15Z ISSUANCE TO REFLECT TIMING. WINDS HAVE A BETTER CHC OF GUSTING KCHO/KDCA/KBWI/KMTN...WITH STRONG WINDS STILL EXPECTED AT 2 KFT THRU THE AFTN...35-45 KTS. SHOWERS WILL TAPER OFF 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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MARGINAL SCA CONDITIONS ON THE MIDDLE CHESAPEAKE BAY THIS MORNING...EXPECTING TO INCREASE THRU THE DAY. SMALL CRAFT ADVISORY REMAINS IN EFFECT 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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TEMPERATURES ARE STARTING OFF THE DAY IN THE 40S WITH RAIN OVERSPREADING THE AREA. TO THE WEST OF THE DIVIDE...TEMPERATURES ARE IN THE MID 50S...AND THAT AIRMASS WILL EVENTUALLY GET TO MOST IF NOT ALL OF THE AREA. WHILE THE WARMEST TEMPERATURES AND HIGHEST DEWPOINTS WILL BE IN THE AREA WHERE THE SNOWPACK IS ALREADY GONE... CONDITIONS WILL BE FAVORABLE TO MELT MUCH OF THE REMAINING SNOW. SMALL STREAMS HAVE HAD THE OPPORTUNITY TO RECEDE A BIT FROM THE CRESTS ON MONDAY...WHILE LARGER STREAMS CONTINUE TO STEADILY RISE. PARTIAL ICE BLOCKAGES MAY STILL BE A FACTOR...ESPECIALLY IN THE EASTERN WV PANHANDLE AND NORTHERN MARYLAND. ICE WAS ALSO REPORTED MOVING DOWN THE MIDDLE POTOMAC YESTERDAY BUT IT DOES NOT APPEAR IT IS CAUSING A SUBSTANTIAL BLOCKAGE AT THIS TIME. CONFIDENCE IS NOW HIGH FOR AT LEAST SOME FLOOD POTENTIAL DUE TO THE COMBINATION OF SNOWMELT AND RAIN OF AROUND ONE INCH IN MOST AREAS. THE HIGHEST RISK AREA IS IN THE FAR EASTERN WV PANHANDLE AND NORTHERN MD...BUT SOME URBAN FLOODING AND POTENTIALLY SIGNIFICANT PONDING OF WATER IS POSSIBLE IN THE URBAN CORRIDOR ESPECIALLY DUE TO PLOW-PILE-COVERED STORM DRAINS. RIVER FLOOD WARNINGS ARE CURRENTLY IN EFFECT FOR THE CACAPON AND OPEQUON FOR FLOODING LATER TODAY AND TOMORROW. A RIVER FLOOD WATCH WAS ISSUED FOR THE MAINSTEM SHENANDOAH YESTERDAY AND FOR THE MAINSTEM POTOMAC FROM WILLIAMSPORT TO LITTLE FALLS THIS MORNING. WATCHING THE REMAINING TRIBUTARIES AND THE UPPER TIDAL POTOMAC BUT CONFIDENCE IS NOT HIGH ENOUGH YET FOR A WATCH IN ANY OF THOSE AREAS.
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&& .TIDES/COASTAL FLOODING... 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. && .CLIMATE...
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RECORDS HIGHS FOR WED FEB 3: DCA: 65 SET IN 1927 BWI: 66 SET IN 1932 IAD: 66 SET IN 1991
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...FLOOD WATCH THROUGH LATE TONIGHT FOR DCZ001. MD...FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ013-014-503>506. FLOOD WATCH 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...FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ052>054-505-506. WV...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR WVZ051>053. MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST THURSDAY FOR ANZ530>534- 537-543. SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ535- 536-538>542.
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&& $$ SYNOPSIS...BJL/MM NEAR TERM...SEARS/MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/SEARS/MM MARINE...BJL/SEARS/MM HYDROLOGY...JE TIDES/COASTAL FLOODING...LWX CLIMATE...DFH

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