Area Forecast Discussion
Issued by NWS Sterling, VA

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934 FXUS61 KLWX 022010 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 310 PM EST TUE FEB 2 2016 .SYNOPSIS... HIGH PRESSURE PUSHES EAST TONIGHT. A COLD FRONT SWINGS THROUGH THE REGION TOMORROW WITH HIGH PRESSURE BUILDING IN THE WAKE FOR THE REMAINDER OF THE WEEK INTO THIS WEEKEND. && .NEAR TERM /THROUGH WEDNESDAY/... HIGH PRESSURE EXITS THE REGION TONIGHT WITH A COLD FRONT MOVING THROUGH DURING THE DAY WEDNESDAY. MULTIPLE HAZARDS WILL BE OF A CONCERN DURING THIS TIME INCLUDING GUSTY WINDS AND FLOODING CONCERNS. A FLOOD WATCH IS IN EFFECT FOR COUNTIES ALONG THE MASON- DIXON AND EASTERN WV PANHANDLE WED AFTN-THURS AFTN. A WIND ADVISORY IS IN EFFECT FOR THE HIGHER ELEVATIONS OF THE POTOMAC HIGHLANDS AND THE BLUE RIDGE. DRY WX LATE THIS AFTN...WITH INCRSG CLOUDS AHEAD OF A WARM FRONT ASSOCIATED WITH A LARGER SYSTEM BACK OVER THE MIDWEST. THE FIRST CONCERN OF THE PERIOD IS THE STRONG WINDS TONIGHT AT THE HIGHER ELEVATIONS OVER OUR WESTERN CWA. LLJ WINDS BETWEEN 55 AND 70 KTS...THOUGH WITH AN INVERSION IN PLACE...THINKING IT WILL BE TOUGH FOR THE WINDS TO MIX DOWN TO THE VALLEYS. AS SUCH...AM HOLDING THE ADVISORY TO JUST THE WESTERN PORTIONS OF THE COUNTY. THE LLJ SHOULD AID IN PUSHING THE WARM FRONT THRU AT LEAST WESTERN PORTIONS OF THE CWA LATE TONIGHT...HANGING BACK EAST OF THE BLUE RIDGE TILL AFTR DAYBREAK. RAIN WILL SPREAD NORTH FROM THE SOUTHWEST SECOND HALF OF THE NIGHT...AND OVERSPREADING EVERYWHERE DURING THE AM HOURS WED. BRIEF BREAK IN THE PCPN PSBL WED MORNING BEFORE THE COLD FRONT BEGINS TO MOVE THRU. LATEST MODEL SOLUTIONS HINTING AT SHOWER ACTIVITY INCRSG IN COVERAGE MIDDAY...WITH PSBL LINE FORMING RIGHT AHEAD OF THE FRONT...MORE THE PM HOURS...EAST OF THE BLUE RIDGE WITH THE LLJ AXIS ALIGNING PARALLEL TO THE RIDGE. THIS LINE WILL ALSO BRING THE PERIOD OF THE HEAVIEST RAIN...19-03Z. WE HAVE BEEN DISCUSSING THE POTENTIAL FOR FLOODING WITH THE RECENT SNOW MELT...WHICH COMBINED WITH ALMOST ONE INCH...AND ISOLATED HIGHER AMTS...COULD RESULT IN FLOODING OF URBAN AND STREAMS. THE FLOOD WATCH IS IN EFFECT BEGINNING AT 18Z WED. INSTABILITY IS VERY MINIMAL AND FORCING ALOFT ON THE WEAKER END...BUT CANNOT RULE OUT AN ISO TSTM MAINLY SOUTHERN MD WITH THE LINE WED AFTN/EVENING. STRONG SHEER THROUGHOUT THE VERTICAL PROFILE SUGGESTS PSBL GUSTY WINDS...BUT THINK ANY SVR SHOULD BE SUPPRESSED SOUTH OF THE REGION. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... 12Z MODEL SUITE STILL SHOWING SOME DISCREPANCIES ON HOW QUICKLY THE COLD FRONT MOVES THROUGH THE REGION...AND THUS WHEN THE PCPN TAPERS OFF. CURRENT THINKING IS THE FRONT WILL MOVE SOUTH THE SECOND HALF OF WED NIGHT AS HIGH PRESSURE BEGINS TO BUILD BACK IN FROM THE WEST. TAPER POPS OFF WEST TO EAST...KEEP POPS ONLY EAST OF I-95 AND THE UPSLOPE REGIONS LATE WED NIGHT...TAPERING OFF DURING THE DAY THURS. OTHER THAN LIGHT UPSLOPE SNOW SHOWERS THRU THURS NIGHT...HIGH PRESSURE BUILDING IN WILL KEEP THE AREA DRY. THE COLDER AIR SLIGHTLY SLOWER TO ARRIVE...WITH A STRONGER SURGE DURING THE DAY THURSDAY. THURS NIGHT TEMPS WILL DROP BELOW FREEZING EVERYWHERE. SNOW TOTALS FOR THE UPSLOPE WILL JUST BE A FEW TENTHS...AND IS EXPECTED TO TAPER OFF BY FRI MORNING WITH A LACK OF MOISTURE IN THE SNOW GROWTH ZONE. CONCERNING FLOODING...THE URBAN FLOODING THREAT WILL DIMINISH WED NIGHT. HOWEVER...DEPENDING ON RAINFALL AMTS AND SNOW MELT...WED NIGHT THRU THURS COULD SEE RIVER FLOODING CONCERNS. SEE HYDRO SECTION FOR MORE DETAILS. && .LONG TERM /FRIDAY THROUGH TUESDAY/... A NORTHWEST WIND WILL CONTINUE BEHIND A DEPARTING FRONT THURSDAY NIGHT. THERE MAY BE A FEW LINGERING UPSLOPE SNOW SHOWERS ALONG THE ALLEGHENY FRONT. OVERALL DRY AND MOSTLY CLEAR CONDITIONS EXPECTED ELSEWHERE. HIGH PRESSURE THEN BUILDS IN OVERHEAD. MOSTLY SUNNY SKIES AND DRY WEATHER EXPECTED FOR FRIDAY AND SATURDAY. TEMPERATURES ON FRIDAY NEAR TO SLIGHTLY BELOW NORMAL...MODERATING TO SLIGHTLY ABOVE NORMAL SATURDAY. A COLD FRONT WILL MOVE OFF TO THE NORTH SUNDAY WITH LITTLE TO NO IMPACT TO THE REGION. AS A RIDGE BUILDS ON THE WEST COAST...A TROUGH WILL DEVELOP ACROSS THE EAST IN THE BEGINNING OF NEXT WEEK...WITH POTENTIAL FOR DEVELOPING COASTAL LOW. TEMPERATURES WILL START MILD ON SUNDAY...BECOMING COLDER INTO NEXT WEEK. A SECONDARY UPPER LEVEL LOW OVER THE GREAT LAKES MONDAY WILL MOVE TOWARD THE EAST. THIS SECONDARY LOW AND THE POTENTIAL DEVELOPING COASTAL LOW COULD HAVE AN IMPACT ON MONDAY`S WEATHER AND TEMPERATURES. TIMING OF THE LOW AND POSITION OF THE LOWS ARE UNCERTAIN. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... VFR CONDITIONS THRU THE FIRST HALF OF TONIGHT WITH LIGHT ELY WINDS. PCPN MOVES IN THE SECOND HALF OF TONIGHT...WHICH WILL DROP CIGS AND VIS QUICKLY...WITH IFR IN BETWEEN 08-12Z. WITH FOG DEVELOPMENT AND ANY HEAVIER RAIN...LIFR CONDITIONS WILL BE PSBL DURING THE AM HOURS AS WELL. WHILE WINDS REMAIN LIGHT AT THE SFC...STRONG LLJ WILL PRODUCE LLWS CONCERNS...WITH WINDS 40-50 KTS AT 2KFT. IFR OR LOWER CONDITIONS THRU MIDDAY...PCPN MIGHT STOP FOR A PERIOD BEFORE THE RAIN SHOWERS MOVE IN FOR THE AFTN. GENERALLY LOOKING AT MVFR CONDITIONS WITH THE RAIN. A LINE IS PSBL RIGHT ALONG THE FRONT...WHICH WILL BRING A PERIOD OF HEAVY RAIN...AND IFR OR LOWER CONDITIONS. WINDS INCREASE DURING THE DAY AS WELL PRIOR TO THE COLD FRONT...WITH GUSTS 20-25 KTS PSBL. PCPN TAPERS OFF WED EVENING...WITH A BRIEF LULL IN THE WINDS BEFORE INCRSG AGAIN FROM THE NW OVERNIGHT. VFR CONDITIONS WITH GUSTY CONDITIONS THURS THRU FRIDAY. NORTHWEST WINDS AROUND 10 KNOTS WITH GUSTS 15 TO 20 KNOTS. && .MARINE... SUB-SCA CONDITIONS ATTM...AND EXPECTED FOR A GOOD PORTION OF TONIGHT. INCRSG SLY WINDS IN THE MORNING...WITH A SCA IN EFFECT FOR ALL THE WATERS DURING THE DAY WED. HAVE LINGERING SCA ON THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC WED NIGHT. MAY NEED TO EXTEND INTO THURSDAY AS WELL WITH PERSISTENT NW FLOW. RAIN IS EXPECTED WED...WITH ISO TSTM PSBL WED AFTN/EVENING. GUSTY WINDS MAY ACCOMPANY SOME OF THE HEAVIER STORMS...WITH SMW POTENTIALLY NEEDED. PRESSURE SURGE WED EVENING COULD BRING OCNL GALES TO THE CHESAPEAKE BAY...BUT CONFIDENCE TOO LOW TO ISSUE ATTM AND WILL LET SUBSEQUENT SHIFTS DETERMINE THE NEED. SMALL CRAFT CONDITIONS POSSIBLE THURSDAY NIGHT AND FRIDAY. && .HYDROLOGY... THE WARMTH AND RAIN ON MONDAY LED TO ANOTHER HIT ON THE SNOW WATER...WHICH THIS 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. WE ARE SEEING AT LEAST SOME STREAM REACTION TO SNOW MELT IN MOST OF THE AREA NOW...THE EXCEPTION BEING SMALLER STREAMS NEAR THE PA/MD BORDER. SOME OF THIS LACK OF REACTION COULD BE DUE TO ICE. SPEAKING OF ICE...THERE WERE SEVERAL PARTIAL ICE BLOCKAGES OF STREAMS NOTED IN EASTERN WV LAST NIGHT AND THIS MORNING. ONE WAS SIGNIFICANT ENOUGH TO SEND THE CACAPON RIVER OUT OF ITS BANKS AND OVER ROADS. OTHERWISE...JUST A STEADY MELT THROUGH EARLY WEDNESDAY MORNING...AND STREAM LEVELS ON THE SMALLER STREAMS MAY ACTUALLY FALL SINCE MELT IS SLOWER THAN MONDAY. CONFIDENCE IS INCREASING IN FLOOD POTENTIAL FOR WEDNESDAY. THE MOST REMAINING SNOW PACK IS IN THE FAR EASTERN WV PANHANDLE EASTWARD ACROSS NORTHERN MARYLAND...AND WITH TEMPERATURES FORECAST TO EXCEED 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 THREE-QUARTERS OF AN INCH OF RAIN /WITH ISOLATED HIGHER AMOUNTS/ AND THAT IS A RECIPE FOR AT LEAST SOME FLOODING. A FLOOD WATCH HAS BEEN ISSUED FOR THE AREA WITH THE GREATEST REMAINING SNOW PACK FOR WEDNESDAY THROUGH THURSDAY. 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 MAINSTEAM SHENANDOAH RIVER AND THE MAINSTEAM 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 EARLY WEDNESDAY AS THE RAIN BEGINS. && .TIDES/COASTAL FLOODING... INCRSG SLY FLOW WED WILL INCREASE WATER LVLS...MAINLY NORTHERN CHESAPEAKE BAY. TIDES ARE FORECASTED TO EXCEED MINOR FLOOD THRESHOLDS AT HAVRE DE GRACE AND BOWLEYS QUARTER LATE WED. BALTIMORE AND ANNAPOLIS ARE CLOSE...BUT CURRENTLY ARE NOT FORECASTED TO GO OVER. WILL CONTINUE TO MONITOR THE TREND. WITH NW FLOW BEHIND THE FRONT...WILL SEE WATER LVLS DROP THURSDAY. && .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... DC...NONE. MD...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY AFTERNOON FOR MDZ003>006-011-507-508. VA...WIND ADVISORY FROM 1 AM TO 10 AM EST WEDNESDAY FOR VAZ503-507- 508. WV...WIND ADVISORY FROM 1 AM TO 10 AM EST WEDNESDAY FOR WVZ501-503- 505. FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY AFTERNOON FOR WVZ051>053. MARINE...SMALL CRAFT ADVISORY FROM 7 AM TO 6 PM EST WEDNESDAY FOR ANZ535-536-538>542. SMALL CRAFT ADVISORY FROM 3 AM WEDNESDAY TO 1 AM EST THURSDAY FOR ANZ533-534-543. SMALL CRAFT ADVISORY FROM 7 AM WEDNESDAY TO 1 AM EST THURSDAY FOR ANZ530>532-537. && $$ SYNOPSIS...SEARS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...KLW AVIATION...SEARS/KLW MARINE...SEARS/KLW HYDROLOGY...JE TIDES/COASTAL FLOODING...SEARS CLIMATE...LWX

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