Area Forecast Discussion
Issued by NWS Sterling, VA

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882 FXUS61 KLWX 050257 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1057 PM EDT WED MAY 4 2016 .SYNOPSIS... A SURFACE TROUGH WILL REMAIN ACROSS THE REGION THROUGH THURSDAY. UPPER LEVEL LOW PRESSURE IS EXPECTED TO IMPACT THE AREA THURSDAY AND FRIDAY BEFORE HIGH PRESSURE RETURNS SATURDAY EVENING. A WEAK COLD FRONT IS EXPECTED TO PUSH THROUGH THE REGION SUNDAY. && .NEAR TERM /THROUGH THURSDAY/... UPPER LEVEL LOW PRESSURE IS DIVING INTO OH VALLEY TONIGHT AND REACHES THE CAROLINAS BY THU AFTERNOON. AS HEIGHTS CONTINUE TO FALL THIS EVENING AND SFC CONVERGENCE INCREASES...RAIN WILL BECOME MORE PERSISTENT AND ORGANIZED ESPECIALLY OVER AND WEST OF THE BLUE RIDGE MTNS. STILL A FEW LIGHTNING STRIKES NEAR CHO AND CBE...AND THUNDER WILL REMAIN POSSIBLE IN WESTERN SECTIONS THROUGH AT LEAST MIDNIGHT. FROM THE GREATER DC AREA TO THE NORTHEAST...HIGH PRESSURE IS WEDGING IN...AND MARINE FLOW IS RESULTING IN DZ. EXPECT THIS TO BE PRIMARY PRECIP OVERNIGHT...ALTHOUGH A FEW LIGHT SHOWERS MAY ALSO DEVELOP. GUIDANCE IS NOT TOO PESSIMISTIC ON VSBY...BUT SOME LIGHT FOG IS CERTAINLY POSSIBLE...WORSE AT HIGHER ELEVATIONS DUE TO LOW CLOUDS. MIN TEMPS MAY NEED TO BE LOWERED SLIGHTLY IN THE N/E GIVEN READINGS ALREADY IN THE LOWER-MID 50S. THE LATEST GFS SHOWS A SFC CONVERGENCE ZONE ESTABLISHING FROM PETERSBURG WV SOUTHEAST TO CHARLOTTESVILLE TONIGHT AND REMAINING STATIONARY THROUGH ALL DAY THURSDAY. ON AVERAGE...GUIDANCE SUGGESTS 1-3 INCHES OF RAIN APPEAR POSSIBLE IN THAT AREA. SINCE THIS APPEARS TO BE A PROLONGED AND SLOW EVENT...FLASH FLOODING IS NOT A THREAT BUT RISES ON SOME AREA STREAMS AND RIVERS CAN BE EXPECTED. N/E SECTIONS OF THE CWA MAY REMAIN IN A MORE DRIZZLY ENVIRONMENT FOR MUCH OF THE DAY WITH A FEW LIGHT SHOWERS. HAVE LOWERED MAX TEMPS...ESPECIALLY SW (MDT RAIN) AND NE (CLOUDS/NE FLOW). && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... UPPER LOW SHIFTS SOUTHWARD THU NIGHT WITH GUIDANCE INDICATING SFC CONVERGENCE ZONE SHIFTING MORE EASTWARD TOWARD DC/BALT METRO AREAS FOCUSING SHOWERS MORE IN THAT AREA. EXPECT DIURNAL RANGE OF TEMPS TO REMAIN MINIMIZED DUE TO CLOUDS AND PRECIP. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... UPR LEVEL LOW WILL LINGER AROUND THROUGH THE DAY SAT... KEEPING TEMPS BELOW NORMAL AND PARTLY CLOUDY... MAINLY IN THE EASTERN PART OF THE CWA. SOME CLEARING PSBL AS UPR LOW MOVES AWAY... BUT CLOUDS QUICKLY RETURN SAT NIGHT INTO EARLY SUN AS COLD FRONT MOVES ACROSS OUR REGION. FRONTAL BOUNDARY LINGERS TO OUR SOUTH AS A WEAK HIGH PRESS BUILDS NEAR OUR REGION SUN INTO LATE MON. FRONTAL BOUNDARY SLOWLY LIFTS NORTH AS A WARM FRONT TUE INTO WED BRINGING BACK SHOWERS TO OUR REGION. HIGH TEMPS WILL BE GRADUALLY INCREASING FROM THE LOW 70S INTO THE UPR 70S DURING THIS PERIOD... LOW TEMPS WILL BE MAINLY IN THE 50S... 40S SUN NIGHT. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... TSRA NEAR CHO AT 01Z...BUT OTHERWISE PRECIP IS LIGHT AND SPOTTY. MARINE LAYER INVADING NORTHERN TERMINALS AND MAY MAKE DZ THE MORE PREDOMINANT PTYPE OVERNIGHT. SHRA DEVELOPMENT MAY STILL OCCUR AT MRB/CHO OVERNIGHT. MVFR TO IFR CIGS OVERSPREADING THE AREA...AND WILL EVENTUALLY REACH CHO. THESE MAY LIFT SOME DURING THE DAY ON THURSDAY ONLY TO FALL AGAIN THURSDAY NIGHT. MODELS NOT TOO PESSIMISTIC ON VSBY OVERNIGHT...BUT ALREADY SEEING SOME VERIFY LOWER IN DZ AND BR. MDT RAIN LIKELY AT CHO ON THURSDAY FROM LATE MORNING THROUGH AFTERNOON WITH IFR OR LOWER RESTRICTIONS LIKELY. LIGHTER SHRA OR DZ ELSEWHERE. EXPECT MORE WIDESPREAD PRECIP THURSDAY NIGHT INTO FRIDAY AS LOW PRESSURE PIVOTS TO OUR S/E. SUB-VFR CONDITIONS POSSIBLE SAT INTO EARLY SUN AS UPR LEVEL LOW AND COLD FRONT BRING SHOWERS INTO OUR REGION. VFR CONDITIONS EXPECTED LATER ON SUN AND INTO MON AS HIGH PRESS BUILDS IN. && .MARINE... ONSHORE TO NORTHERLY FLOW WILL CONTINUE THROUGH FRIDAY. FOR THE MOST PART WINDS WILL BE 5-10 KT. WINDS ALOFT WILL BE SLIGHTLY STRONGER THURSDAY AND FRIDAY MORNINGS...BUT ATTM APPEARS THIS MAY ONLY RESULT IN 15 KT GUSTS AND PRECLUDE AN SCA. SUB-SCA CONDITIONS EXPECTED SAT AND MON AS WINDS WILL BE BELOW THE SCA CRITERIA. SCA CONDITIONS PSBL ON SUN WITH WIND GUSTS UP TO 20 KTS. && .TIDES/COASTAL FLOODING...
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ONSHORE FLOW HAS RESULTED ON ELEVATED WATER LEVELS AROUND ONE FOOT ABOVE NORMAL. THE LEVELS HAVE SEEMINGLY LEVELED OFF FOR THE TIME BEING...BUT PERSISTENT ONSHORE FLOW NEXT FEW DAYS WILL RESULT IN WATER LEVELS RISING FURTHER. MINOR COASTAL FLOODING LIKELY AT MANY COASTAL LOCATIONS ALONG THE CHESAPEAKE BAY AND POTOMAC RIVER. MODERATE FLOODING IS POSSIBLE AT STRAITS POINT AND ANNAPOLIS IF THE HIGHER ESTOFS SURGE VERIFIES. HAVE ISSUED A COASTAL FLOOD ADVISORY FOR THE MORE CERTAIN LOCATIONS FROM ANNAPOLIS SOUTHWARD. HAVE EXPANDED ADVISORY TO DC/ALEXANDRIA AND BALTIMORE WILL HAVE TO BE MONITORED. WILL LET LATER SHIFTS DETERMINE IF WATER LEVELS WARRANT A CONTINUATION OF THE ADVISORY OR IF THE INTERMEDIARY HIGH TIDE CYCLE WILL FALL JUST SHORT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...COASTAL FLOOD ADVISORY FROM 5 AM TO 9 AM EDT THURSDAY FOR DCZ001. MD...COASTAL FLOOD ADVISORY UNTIL 4 AM EDT THURSDAY FOR MDZ017-018. COASTAL FLOOD ADVISORY UNTIL 7 AM EDT THURSDAY FOR MDZ014. VA...COASTAL FLOOD ADVISORY FROM 5 AM TO 9 AM EDT THURSDAY FOR VAZ054. WV...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...LFR NEAR TERM...ADS/LFR SHORT TERM...LFR LONG TERM...IMR AVIATION...ADS/IMR MARINE...ADS/IMR TIDES/COASTAL FLOODING...ADS/LFR

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