Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 041956 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 256 PM EST THU FEB 4 2016 .SYNOPSIS...A WAVE OF LOW PRESSURE WILL RIDE ALONG A STATIONARY BOUNDARY PASSING BY WELL TO OUR SOUTH AND EAST THURSDAY NIGHT INTO FRIDAY. HIGH PRESSURE WILL RETURN FOR 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 FRIDAY/...LOW PRESSURE IS DEVELOPING ACROSS THE CAROLINAS ALONG A NEARLY STATIONARY COLD FRONT. HIGHER PRESSURE IS SLOWLY MOVING INTO THE REGION FROM THE WEST TODAY HOWEVER THE PRESSURE PATTERN WILL BARELY CHANGE INTO TONIGHT. LOW PRESSURE ACROSS THE CAROLINAS WILL DEEPEN TODAY AND TONIGHT AHEAD OF A DEEP UPPER LEVEL TROUGH. COLD AIR ADVECTION WILL CONTINUE TO MOVE INTO THE MID-ATLANTIC REGION FROM THE WEST WITH THE 0 DEG 850MB ISOTHERM CURRENTLY ORIENTED N-S ALONG THE SHENANDOAH VALLEY. RAIN WILL CONTINUE TO RIDE THE STALLED FRONTAL BOUNDARY AND MOVE SOUTH TO NORTH ACROSS THE PIEDMONT AND SOUTHERN MD. DUE TO THE ORIENTATION OF THE FRONT...RAIN SHOULD STAY CONFINED TO THIS AREA THROUGH THE AFTERNOON AND EVENING. LOW PRESSURE WILL MOVE OFF THE EAST COAST AT THE OUTER BANKS AND THE ENTRANCE REGION OF THE UPPER LEVEL JET WILL BE RIGHT OVERHEAD. THIS WILL ENHANCE LIFT AND MOISTURE FROM THE ATLANTIC. CAA WILL CONTINUE OVERNIGHT AND THE REGION SHOULD BE BELOW 0 AT 850MB BY 6Z. AT THE SFC...TEMPS WILL BE DROPPING INTO THE 20S/30S OVERNIGHT. RAIN WILL BE ONGOING ACROSS THE PIEDMONT/SOUTHERN MD REGION HOWEVER AS THE LOW DEEPENS LIGHT PRECIPITATION IS EXPECTED TO MOVE FURTHER WEST WHERE IT WILL BE COLDER. LIGHT SNOW OR FLURRIES ARE POSSIBLE ACROSS THE REGION AFTER MIDNIGHT TONIGHT. FURTHER EAST...HEAVIER PRECIPITATION IS EXPECTED CLOSER TO THE COASTAL LOW AND RAIN WILL TRANSITION TO SNOW BETWEEN 6-10Z. ACCUMULATING SNOW IS EXPECTED WITH 2-3 INCHES ACROSS SOUTHERN MD TO LESS THAN AN INCH ALONG I-95. PRECIPITATION SHOULD END ACROSS THE REGION AROUND SUNRISE FRIDAY MORNING. HIGH PRESSURE WILL PUSH INTO THE REGION CAUSING WINDS TO INCREASE. NW WINDS 10-20MPH WITH GUSTS UP TO 30MPH. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...HIGH PRESSURE WILL BE IN CONTROL FRIDAY NIGHT AND INTO SATURDAY AS IT MOVES TO THE SOUTH OF THE REGION. DRY AND MOSTLY SUNNY CONDTIONS EXPECTED SATURDAY WITH TEMPS REACHING THE MID 40S. A DEEP TROUGH WILL MOVE ACROSS THE REGION SUNDAY RESULTING IN CLOUDS TO INCREASE. LOW PRESSURE IS EXPECTED TO OVER THE ATLANTIC OCEAN LEAVING THE MID- ATLANTIC DRY. TEMPS ON SUNDAY WILL BE SLIGHTLY WARMER IN THE MID TO U40S TO L50S. && .LONG TERM /MONDAY THROUGH THURSDAY/...COMPUTER MODELS HAVE SOME AGREEMENT ON A COASTAL LOW FORMING ALONG OR JUST OFFSHORE THE NORTH AND SOUTH CAROLINA COAST SUNDAY NIGHT. ONE DISAGREEMENT IS THAT THE GFS MODEL KEEPS THE COASTAL LOW AN OPEN AREA OF LOW PRESSURE AND PUSHES IT FASTER OUT TO SEA SUNDAY NIGHT AND MONDAY THAN THE EUROPEAN MODEL...WHICH CLOSES OFF THE LOW AND INTENSIFIES IT BEFORE PUSHING IT OUT TO SEA. NONETHELESS...THIS COASTAL LOW WILL JUST SPREAD ADDITIONAL CLOUDS INTO OUR REGION SUNDAY WITH NO EXPECTED PRECIPITATION. A MUCH LARGER AREA OF LOW PRESSURE IN THE UPPER LEVELS IS EXPECTED TO DROP SOUTHEASTWARD FROM THE UPPER MIDWEST AND GREAT LAKES INTO THE OHIO VALLEY AND MID-ATLANTIC REGION MONDAY. A NEW SURFACE LOW PRESSURE SYSTEM COULD FORM OVER SOUTHWEST VIRGINIA ON THE SOUTHEAST FLANK OF THIS BROAD LOW AROUND MIDDAY MONDAY AND MONDAY AFTERNOON. THIS NEWLY FORMED LOW COULD HAVE A MORE DIRECT IMPACT TO OUR REGION...BRINGING A CHANCE FOR RAIN AND SNOW SHOWERS MONDAY BEFORE BECOMING MORE OF A LIGHT TO MODERATE SNOW THREAT MONDAY NIGHT WITH COLDER AIR TO SUPPORT THE NEW LOW. ONE SIMILARITY WITH THE EUROPEAN MODEL AND THE GFS MODEL WITH THIS NEW LOW IS BOTH CLOSE OFF THE NEW LOW NEAR THE MID-ATLANTIC COAST TUESDAY BEFORE PIVOTING IT NORTHWARD TOWARD NEW ENGLAND TUESDAY NIGHT. THE DIFFERENCE IN THE POSITION OF THIS CLOSED LOW WILL DETERMINE WHETHER THE MID-ATLANTIC REGION GETS HIT HARD WITH ANOTHER SNOWSTORM OR GETS A FEW RAIN AND SNOW SHOWERS WITH LITTLE TO NO ACCUMULATION. RIGHT NOW...THE EUROPEAN MODEL CLOSES THE LOW NEAR THE MOUTH OF THE CHESAPEAKE BAY AND MAKES IT A STRONGER LOW. THE GFS MODEL CLOSES THE LOW NEAR THE MOUTH OF THE DELAWARE BAY...FARTHER NORTH...AND IS NOT AS STRONG WITH THIS SYSTEM. FOR THE TIME BEING...WE HAVE A CHANCE OF RAIN OR SNOW IN OUR REGION TUESDAY AND TUESDAY NIGHT. THE MAIN UPPER LEVEL SUPPORT BEHIND THE COASTAL LOW WILL SLOWLY PIVOT FROM THE OHIO VALLEY...ACROSS THE REGION...AND OFFSHORE WEDNESDAY AND WEDNESDAY NIGHT. SOME UPSLOPE SNOW SHOWERS MAY EXIST IN THE POTOMAC HIGHLANDS WITH COLDER AIR ALOFT PUNCHING INTO THE REGION. ELSEWHERE...COLDER AND DRIER AIR WILL FILTER INTO THE REGION AS HIGH PRESSURE BUILDS IN FROM THE WEST. HIGH PRESSURE SHOULD DOMINATE THURSDAY WITH CHILLY AND DRY AIR. ANY UPPER LEVEL DISTURBANCES MOVING OVERHEAD THURSDAY WILL BE QUICK AND MAY NOT PRODUCE ANY PRECIPITATION...JUST ADDITIONAL CLOUDS. && .AVIATION /20Z THURSDAY THROUGH TUESDAY/... VFR CONDITIONS EXPECTED TODAY AND TONIGHT. -SN IS EXPECTED ALONG AND EAST OF I-95 AFTER 6Z AND MAY RESULT IN REDUCED VSBYS HOWEVER CONFIDENCE IS LOW IN THE COVERAGE OF SNOW SHOWERS AT THIS TIME. -SN QUICKLY MOVES OUT BY 12Z FRIDAY AND VFR CONDITIONS ARE EXPECTED. NW WINDS WILL INCREASE EARLY FRIDAY MORNING. GUSTS AROUND 25KT ARE EXPECTED HOWEVER GUSTS UP TO 35KTS POSSIBLE FRIDAY MORNING. VFR CONDITIONS EXPECTED FRIDAY NIGHT THROUGH SUNDAY. VFR CONDITIONS SUNDAY NIGHT. WINDS NORTHEAST AROUND 5 KNOTS. MVFR TO IFR CONDITIONS MONDAY WITH LIGHT RAIN AND LIGHT SNOW. WINDS BECOMING SOUTHEAST 5 KNOTS GUSTS 10 TO 15 KNOTS. && .MARINE...N WINDS CONTINUE ON THE WATERS BEHIND A COLD FRONT THAT MOVED THROUGH THIS MORNING. SCA CONDITIONS WILL CONTINUE ON THE WATERS TODAY WITH GUSTS AROUND 20 KTS EXPECTED. A COASTAL LOW WILL APPROACH THE WATERS TONIGHT AND RAIN IS EXPECTED TODAY AND TONIGHT. COLDER AIR WILL MOVE INTO THE REGION AFTER MIDNIGHT AND RAIN IS MAY CHANGE TO SNOW REDUCING VSBYS. WINDS WILL INCREASE ON THE WATERS AS THE COASTAL LOW MOVES FURTHER OFF THE COAST EARLY FRIDAY MORNING. GALE CONDITIONS ARE POSSIBLE NEAR THE MOUTH OF THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC. AT THIS TIME...CONFIDENCE IS LOW AS THE STRONGEST WINDS MAY BE SOUTH OF SMITH ISLAND. HIGH PRESSURE WILL MOVE OVER THE WATERS FRIDAY AND INTO THE WEEKEND. SCA CONDITIONS WILL CONTINUE FRIDAY BEFORE WINDS DIMINISH FRIDAY NIGHT ON THE MAIN CHANNEL OF THE BAY. NO MARINE HAZARDS SUNDAY NIGHT AND MONDAY. && .HYDROLOGY...STARTING TO WIND DOWN FROM OUR SNOWMELT FLOOD...WHICH TURNED OUT TO BE NOT AS SIGNIFICANT AS FORECAST BECAUSE WE DID NOT SEE AS MUCH RAIN IN THE POTOMAC HEADWATERS AS EXPECTED...AND WE DID NOT ENTIRELY LOSE THE SNOWPACK IN SOME AREAS WHERE IT WAS EXPECTED TO HAPPEN. MINOR FLOODING IS STILL ONGOING ON THE MONOCACY...MAINSTEM SHENANDOAH...AND MAINSTEM POTOMAC BETWEEN HARPERS FERRY AND GREAT FALLS. FLOODING WILL CONTINUE ON THE MONOCACY THROUGH TONIGHT...AND ON THE SHENANDOAH AND POTOMAC THROUGH FRIDAY. THE LIGHT PRECIPITATION EXPECTED TONIGHT WILL NOT HAVE ANY EFFECT ON STREAMS. && .TIDES/COASTAL FLOODING...FRESHWATER INUNDATION OF THE POTOMAC TIDAL ZONE IN WASHINGTON DC IS OCCURRING...AND MINOR FLOODING IS LIKELY WITH THE TIDE CYCLE THIS AFTERNOON. COASTAL FLOOD ADVISORY IS IN EFFECT. COASTAL FLOOD WATCH REMAINS IN EFFECT FOR THE FOLLOWING TWO TIDE CYCLES...HOWEVER...WITH NORTHWEST WINDS...THE RIVER MAY BE ABLE TO HANDLE MORE FRESHWATER THAN USUAL. WE WILL BE MONITORING THIS TIME PERIOD CLOSELY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD WATCH FROM 10 PM EST THIS EVENING THROUGH FRIDAY EVENING FOR DCZ001. COASTAL FLOOD ADVISORY UNTIL 10 PM EST THIS EVENING FOR DCZ001. MD...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EST FRIDAY FOR MDZ017-018. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST FRIDAY FOR ANZ530>534- 537>543. SMALL CRAFT ADVISORY UNTIL 4 PM EST FRIDAY FOR ANZ535-536. && $$ SYNOPSIS...HAS NEAR TERM...HAS SHORT TERM...HAS LONG TERM...KLW AVIATION...HAS/KLW MARINE...HAS/KLW HYDROLOGY...JE TIDES/COASTAL FLOODING...JE

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