Area Forecast Discussion
Issued by NWS Sterling, VA

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421 FXUS61 KLWX 051120 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 620 AM EST FRI FEB 5 2016 .SYNOPSIS... LOW PRESSURE WILL PASS BY TO OUR EAST THIS MORNING. HIGH PRESSURE WILL BUILD OVERHEAD LATER TODAY THROUGH SATURDAY. COASTAL LOW PRESSURE WILL PASS BY WELL TO THE SOUTH AND EAST SUNDAY. ANOTHER LOW PRESSURE SYSTEM MAY IMPACT THE AREA MONDAY INTO TUESDAY. THE LOW WILL MOVE AWAY FROM THE AREA DURING THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AS OF 615 AM...BACK EDGE OF PRECIPITATION SHIELD NOW MOVING THROUGH THE REGION. HAVE TRIMMED BACK THE ADVISORY ON THE WESTERN/NORTHERN SIDES AS SNOW COMES TO AN END...AND WEBCAMS INDICATE WET ROADWAYS. WILL LET ADVISORY CONTINUE FOR EASTERN/SOUTHERN MARYLAND WHERE HEAVIEST SNOW RATES REMAIN AND WEBCAMS INDICATING SOME LIGHT ACCUMULATION. HIGHEST TOTALS EXPECTED IN ST MARYS AND CALVERT COUNTIES. PREVIOUS DISCUSSION FROM 320 AM... LOW PRESSURE CONTINUING TO ORGANIZE AND STRENGTHEN OFF THE OUTER BANKS OF NORTH CAROLINA WILL QUICKLY TRACK FROM NEAR CAPE HATTERAS EARLY THIS MORNING TO A POSITION SOUTH OF CAPE COD BY 18Z TODAY. PRECIP HAS BLOSSOMED NICELY EARLY THIS MORNING WITH A WIDESPREAD MIX OF LIGHT RAIN AND SNOW (AS WELL AS SOME BRIEF SLEET) BEING OBSERVED FROM ABOUT A CHARLOTTESVILLE-LEESBURG- FREDERICK LINE AND EAST. TEMPERATURES REMAIN ABOVE FREEZING AT ALL SITES AS OF 3 AM...WITH LITTLE TO NO ACCUMULATION SO FAR. OVER THE NEXT COUPLE OF HOURS AS BOUNDARY LAYER COOLS...SHOULD SEE JUST ABOUT EVERYONE TRANSITION OVER TO SNOW. PRECIP WILL THEN SHUT OFF QUICKLY BETWEEN 6 AM AND 9 AM FROM WEST TO EAST AS LOW PULLS AWAY. HEAVIEST PRECIP RATES WILL AFFECT EASTERN AND SOUTHERN MARYLAND...FROM THE BALTIMORE METRO AREA AND DOWN THROUGH CALVERT AND SAINT MARYS COUNTIES. FURTHER NORTH AND WEST...NORTHWEST WINDS CONTINUE TO DRY OUT THE LOW LEVELS...INHIBITING BETTER SNOW RATES. WITH SURFACE TEMPERATURES...AS WELL AS ROAD TEMPERATURES...STILL ABOVE FREEZING...THE ACCUMULATING SNOW WILL REMAIN PRIMARILY ON GRASSY SURFACES...HOWEVER CANT RULE OUT A LIGHT SLUSHY ACCUMULATION ON UNTREATED SURFACES. EXCEPTIONS WILL BE ACROSS SOUTHERN AND EASTERN MARYLAND WHERE SNOW RATES WILL BE HIGHER. WILL LEAVE WINTER WEATHER ADVISORIES AS IS...WITH TOTAL SNOWFALL ACCUMULATIONS FROM 1-2" LOCALLY 3" IN THE ADVISORY...WITH A COATING TO A FEW TENTHS ELSEWHERE. SKIES BEGIN TO CLEAR SHORTLY AFTER PRECIP ENDS. NORTHWEST WINDS WILL ALSO INCREASE THROUGH THE DAY WITH GUSTS 20-30 MPH. TEMPERATURES WONT GO VERY FAR...WITH HIGHS IN THE UPPER 30S TO MID 40S. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... HIGH PRESSURE BUILDS IN AND WILL BE IN CONTROL THROUGH THE WEEKEND. DEVELOPING LOW OFF THE SOUTHEAST COAST ON SATURDAY WILL STAY WELL SOUTH AND EAST OF THE REGION. HIGHS EXPECTED IN THE 40S ON SATURDAY AND 40S TO LOW 50S SUNDAY. LOWS IN THE 20S TO LOW 30S...COLDEST TONIGHT. && .LONG TERM /MONDAY THROUGH THURSDAY/... CONFIDENCE REMAINS HIGH FOR A HIGH AMPLITUDE PATTERN WITH A POTENT UPPER-LEVEL TROUGH DIGGING OVER THE MIDWEST MONDAY AND SHIFTING EASTWARD INTO THE EASTERN CONUS TUESDAY. GIVEN THE HIGH AMPLITUDE PATTERN...THE UPPER-LEVEL TROUGH IS EXPECTED TO DIG QUITE FAR TO THE SOUTH AND A CLOSED UPPER-LEVEL LOW IS LIKELY TO DEVELOP. THE CLOSED UPPER-LEVEL LOW WILL TRACK OVER OUR AREA LATER MONDAY INTO TUESDAY. COASTAL LOW PRESSURE IS EXPECTED TO DEVELOP ALONG THE MID-ATLANTIC COAST AS THE UPPER-LEVEL LOW INTERACTS WITH THE BAROCLINIC ZONE ALONG THE COAST. HOWEVER...THE UNCERTAINTY STILL REMAINS AS TO HOW STRONG THE LOW WILL GET BEFORE MOVING OFF TO OUR NORTH AND EAST. IF THE UPPER-LEVEL LOW DIGS FARTHER SOUTH AND THE COASTAL LOW INTENSIFIES BEFORE MOVING OFF TO OUR NORTH AND EAST...THEN A SIGNIFICANT WINTER STORM IS POSSIBLE ACROSS THE MID- ATLANTIC. HOWEVER...IF THE LOW MOVES OFF TO OUR NORTH AND EAST BEFORE RAPIDLY INTENSIFYING...THEN LIGHTER QPF AMOUNTS ARE EXPECTED WITH A RAIN/SNOW MIX. BOTH SCENARIOS ARE STILL POSSIBLE AT THIS TIME. THE LOW WILL MOVE AWAY FROM THE WEDNESDAY AND THURSDAY...BUT THE UPPER-LEVEL TROUGH WILL REMAIN OVERHEAD. COLD CONDITIONS ARE EXPECTED AND A FEW SNOW SHOWERS ARE POSSIBLE DUE TO THE UPPER-LEVEL TROUGH. && .AVIATION /11Z FRIDAY THROUGH TUESDAY/... WIDESPREAD LIGHT RAIN/SNOW AND ASSOCIATED MVFR EARLY THIS MORNING WILL QUICKLY COME TO AN END...BY 13Z FOR MOST SITES...WITH IMPROVEMENT TO VFR SHORTLY AFTER. OTHERWISE...GUSTY NORTHWEST WINDS UP TO 25 KNOTS WILL DEVELOP AND CONTINUE THROUGH THE DAY. AFTERWARD...WINDS WEAKEN TONIGHT AND VFR CONDITIONS ARE EXPECTED THROUGH SUNDAY. AN UPPER-LEVEL LOW WILL LIKELY BRING SOME RAIN OR SNOW SHOWERS TO THE AREA LATER MONDAY INTO TUESDAY ALONG WITH SUBVFR CONDITIONS. UNCERTAINTY REMAINS ON HOW MUCH A COASTAL LOW MAY IMPACT THE AREA. IF THE COASTAL LOW INTENSIFIES BEFORE MOVING AWAY...THEN HEAVIER SNOW IS POSSIBLE. THE LOW WILL MOVE AWAY FROM THE AREA WEDNESDAY. GUSTY NORTHWEST WINDS ARE EXPECTED BEHIND IT. && .MARINE... GUSTY NORTHWEST WINDS WILL INCREASE IN INTENSITY THIS MORNING BEHIND DEPARTING COASTAL LOW. WINDS WILL GUST UP TO AROUND 35 KNOTS FOR A TIME THIS MORNING SO HAVE UPGRADED THE LOWER CHESAPEAKE AND LOWER POTOMAC TO GALE WARNINGS. SMALL CRAFT ADVISORIES WILL CONTINUE ELSEWHERE. AFTER 17Z (12 NOON)...WINDS WILL GRADUALLY WEAKEN BACK TO SCA CRITERIA OVER ALL WATERS. HIGH PRESSURE WILL THEN MOVE OVER THE WATERS TONIGHT AND INTO THE WEEKEND WITH SCA CONDITIONS ENDING LATE THIS EVENING. NO MARINE HAZARDS EXPECTED SATURDAY THROUGH MONDAY. LOW PRESSURE WILL LIKELY IMPACT THE WATERS MONDAY INTO TUESDAY. DETAILS ON HOW STRONG THE LOW WILL BE ARE UNCERTAIN AT THIS TIME...BUT A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS. THE LOW WILL MOVE AWAY FROM THE WATERS WEDNESDAY...BUT GUSTY NORTHWEST WINDS ARE LIKELY BEHIND THE DEPARTING LOW. && .HYDROLOGY... MINOR FLOODING IS STILL ONGOING ON THE MONOCACY...THE MAINSTEM SHENANDOAH AT MILLVILLE...AND THE MAINSTEM POTOMAC BETWEEN PORT OF ROCKS AND GREAT FALLS. THE LIGHT PRECIPITATION LAST NIGHT WILLL NOT HAVE ANY EFFECT ON STREAMS. && .TIDES/COASTAL FLOODING... WATER LEVELS AROUND WASHINGTON DC REMAIN 2+ FEET ABOVE ASTRO NORMS OVERNIGHT. NW WINDS SHOULD PUSH A BIT OF THE TIDAL INFLUENCE AWAY FROM THE AREA...WHICH WILL OPEN UP MORE ROOM FOR FRESHWATER WHEN IT DOES ARRIVE...WHICH WILL BE TODAY. FORECASTS OF THE WATER COMING DOWN THE POTOMAC HAVE FLUCTUATED UPWARD SLIGHTLY ONCE AGAIN. BASED ON THIS ALONE GEORGETOWN WOULD EASILY REACH MINOR AGAIN THIS MORNING. BASED ON EXPERIENCE...THE EXCESS FRESHWATER FANS OUT SUBSTANTIALLY BEFORE REACHING SW DC. AFTER MONITORING THE UPSTREAM RIVER FORECASTS AND THE DIFFERENCE BETWEEN THE TIDAL ANOMALIES AT DC VS THE REST OF OUR WATERS...HAVE ACHIEVED ENOUGH CONFIDENCE TO ISSUE COASTAL FLOOD ADVISORY FOR DC. I/M NOT SURE IT WILL BE THAT SIMPLE THOUGH. FOR ONE THING...IT APPEARS AS THOUGH THE FRESHWATER CONTRIBUTION WILL BE CHASING THE HIGH TIDE DOWN RIVER. THAT IS...THE TIDE WILL BE REPLACED BY THE FRESHWATER CREST. HAVE LENGTHENED THE TIME FRAME FROM THE TYPICAL SCENARIO TO ACCOMMADATE FOR THIS. BASED ON THE LITTLE FALLS FORECAST...ITS POSSIBLE THAT A MARGINAL WARNING WOULD BE NECESSARY. THAT WOULD NEED TO BE A GAME TIME CHANGE. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 11 AM EST THIS MORNING FOR DCZ001. MD...WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR MDZ011-013-014-016>018-508. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ530>532-538>540. SMALL CRAFT ADVISORY FROM NOON TODAY TO 10 PM EST THIS EVENING FOR ANZ533-534-537-541>543. GALE WARNING UNTIL NOON EST TODAY FOR ANZ533-534-537-541>543. SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR ANZ535- 536. && $$ SYNOPSIS...BJL/MM NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM HYDROLOGY...JE/BJL/MM TIDES/COASTAL FLOODING...BJL

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