Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250240 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 940 PM EST WED DEC 24 2014 .SYNOPSIS... STRENGTHENING LOW PRESSURE WILL LIFT INTO THE GREAT LAKES TONIGHT...BRINGING A COLD FRONT ACROSS THE REGION. MILD SOUTHERN HIGH PRESSURE WILL MOVE IN FOR THE END OF THE WEEK. A WEAK COLD FRONT WILL PUSH IN FROM THE NORTHWEST SUNDAY. THEN...LOW PRESSURE FROM THE DEEP SOUTH WILL RIDE UP ALONG THAT FRONT AND OVER THE REGION EARLY NEXT WEEK. COLDER HIGH PRESSURE WILL FOLLOW FOR MID WEEK. && .NEAR TERM /THROUGH THURSDAY/... 02Z WATER VAPOR IMAGERY INDICATING CENTER OF SFC LOW PIVOTING THROUGH GREAT LAKES REGION...WITH ASSOCIATED COLD FRONT EXTENDING SOUTH OVER WESTERN PA/CENTRAL WV. WARM FRONT SITUATED TO THE EAST NOW...TAKING THE LIGHT RAIN WITH IT. MOIST AIRMASS IN PLACE HAS RESULTED IN WIDESPREAD FOG WITH AREAS OF DENSE FOG MAINLY EAST OF BLUE RIDGE. CONTINUING DENSE FOG ADV HERE TO ACCOUNT FOR VIS BEING REDUCED TO 1/4 MILE OR LESS. AS THE PCPN MOVES IN...ENOUGH MIXING SHOULD OCCUR TO IMPROVE VIS TO AT LEAST A MILE OR MORE. A LINE OF SHOWERS WITH EMBEDDED HEAVIER SHOWERS NOTED RIGHT ALONG THE COLD FRONT. ISO SVR TSTMS HAD BEEN OBSERVED IN THE LINE EARLIER THIS EVENING...BUT WITH LOSS OF ANY INSTABILITY...WHICH WAS MINIMAL TO BEGIN...NOT ANTICIPATING ANY THUNDER TO EXTEND INTO OUR CWA. MATCHING WITH LATEST HRRR RUN AND TIMING OF THE RADAR...STEP THE PCPN ACROSS DURING THE OVERNIGHT HOURS. HRRR ALSO SUGGESTIVE OF A BIG WAVE OF PCPN COMING UP FROM THE SOUTH AHEAD OF THIS LINE. WITH THE MOISTURE IN PLACE AND DECENT FORCING ALOFT NOT QUESTIONING THE FORMATION OF THESE SHOWERS...JUST THE INTENSITY/COVERAGE. AS SUCH...KEPT LIGHT SHOWER MENTION...WITH THE PCPN TAPERING OFF FROM THE WEST THROUGH THE DAYLIGHT HOURS. EXPECTING ALL PCPN TO HAVE CLEARED THE AREA BY 12Z. ANOTHER CONCERN FOR THE NIGHT IS A WIND ADVISORY IN PLACE FOR THE POTOMAC HIGHLANDS. STRONG LLJ EXPECTED TO MOVE WITH WINDS AT 850MB 45-55 KTS. WITH THE HIGHER ELEVATIONS...COULD SEE SOME OF THESE STRONGER WINDS IMPACT THE AREA. WOULD ALSO LIKE TO NOTE THE HEAVIER SHOWERS MOVING THROUGH WITH THE COLD FRONT COULD BRING DOWN HEAVIER GUSTS. RIGHT NOW THE ADVISORY GOES THROUGH 11Z...BUT COULD VERY WELL SEE IT END SOONER WITH THE STRONGEST LLJ WINDS LOOKING TO MOVE THROUGH THAT AREA BY 08Z. BREEZY CONDS WL RESIDE BHD CDFNT...W/ BETTER MIXING IN PLACE. SOURCE RGN OF AMS NOT THAT COLD...AND WL HV DOWNSLOPING WNDS. THEREFORE...MAXT TMRW SHUD BE SIMLR TO TDA...OR PERHAPS A PINCH WARMER. MRNG CLDS FM PVA WL QUICKLY ERODE. MOSUN FOR THE REST OF THE DAY. UPSLOPE CONDS GOOD FOR CONTD CLDCVR ALONG THE WRN SLOPES...BUT LACK OF MSTR NOT FVRBL FOR PRODUCING PCPN. MTN POPS THU STILL CAPPED AT CHC...AND HV PTYPE MIX RA/SN. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... AFTER THE MULTI-DAY PERIOD OF INFLUENCE FROM ANOTHER MONSTROUSLY LARGE LOW PRESSURE SYSTEM...BY THURS NIGHT - WE WILL BE ON THE CUSP OF A MULTI-DAY REPRIEVE...AT LEAST A COUPLE OF DAYS. IN THE WAKE OF THE EXITING LOW...SFC HIGH PRESSURE WILL BUILD IN TO OUR SOUTH... WHICH IS AN IMPORTANT KEY BECAUSE IT WILL SPREAD WARMER TEMPS UP THE ERN SEABOARD INTO THE WEEKEND. FRIDAY WILL BE CLEAR AND QUIET. AFTER A BREEZY/WINDY THURSDAY...WINDS WILL DROP OFF TO A LIGHT SLY FLOW. ALTHOUGH NOT AN INCREDIBLY WARM DAY...MAX TEMPS ON FRI SHOULD REACH 5-10F ABOVE AVG FOR LATE DEC. WHILE THE HIGH ROLLS OFF THE CAROLINA COAST INTO SATURDAY...SLY FLOW WILL AGAIN BRING IN SLIGHTLY WARMER AIR W/ MAX TEMPS A BIT HIGHER THAN FRIDAY...TOPPING OUT IN THE M-U50S. ANOTHER LOW PRESSURE WAVE WILL SET UP OVER THE SRN PLAINS/LOWER MS VLY. GULF COAST MOISTURE WILL AGAIN BE TAPPED FOR THE EARLY STAGES OF THIS NEXT SYSTEM...BUT IN TERMS OF NORTHWARD EXTENT - IT WILL HAVE TROUBLE W/ SECONDARY WAVES COMING IN FROM THE NW. 12Z RUNS OF THE GFS/EURO ARE IN THE CLOSEST ALIGNMENT W/ EACH OTHER IN THE PAST FEW DAYS AS TO THE INTERACTIONS/PROGRESSIONS OF THESE FEATURES. A STRONG ENOUGH UPPER JET WILL TRANSPORT THE SHEARED EDGE OF THE GULF MOISTURE UP ACROSS THE UPPER MIDWEST LATE SAT NIGHT. HOWEVER...A POTENT UPPER LOW SLIDING JUST SOUTH OF HUDSON BAY WILL TAKE THIS NRN MOISTURE UP AND OVER THE REGION BEFORE THE SRN SYSTEM CAN GET FULLY ORGANIZED. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... HIGH PRESSURE ALONG THE MID ATLANTIC COAST WILL HANG ON INTO SATURDAY NIGHT. DRY CONDITIONS WILL LINGER. THERE IS A CHANCE FOR A FEW UPSLOPE SNOW SHOWERS IN THE HIGHER PARTS OF THE POTOMAC HIGHLANDS. JUST TWENTY FOUR HOURS AGO...THE EURO AND GFS MODELS WERE BOTH HINTING OF A COLD FRONTAL PASSAGE SATURDAY INTO SATURDAY NIGHT. SINCE THEN...BOTH MODELS HAVE BACKED OFF ON THIS IDEA. THE COLD FRONT SHOULD PUSH ACROSS THE AREA SUNDAY BEFORE SLIDING TO THE SOUTH AND STALLING ACROSS THE CAROLINAS BY SUNDAY NIGHT. SOME LIGHT STRATIFORM RAIN WILL ACCOMPANY THE FRONT SUNDAY AND INTO MONDAY WITH THE FRONT JUST TO OUR SOUTH. THE 00Z EURO MODEL STILLS WANTS TO HANG ONTO THE IDEA OF A LOW DEVELOPING ALONG THE STALLED FRONT BUT NOW THE GFS JUST WANTS TO PUSH ELONGATED STRANDS OF ENERGY ALONG THE SURFACE FRONT AND OUT TO SEA. CONSIDER THIS...HIGH UNCERTAINTY ON WHETHER WE SEE ADDITIONAL PERIODS OF LIGHT RAIN OR PERHAPS LIGHT SNOW IN OUR CWA BY MONDAY NIGHT. THERE IS A SLIGHT CHANCE OF SOME DEPARTING RAIN OR SNOW SHOWERS TUESDAY...SHOULD A LOW DEVELOP ALONG THE FRONT. OTHERWISE...DRY CONDITIONS WILL BE BROUGHT ABOUT WITH HIGH PRESSURE BUILDING LATER TUESDAY THROUGH WEDNESDAY. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... IFR OR LOWER CONDITIONS THIS EVENING AHEAD OF APPROACHING FRONT. LIFR CIGS ACROSS THE AREA THRU AT LEAST 05Z. CURRENTLY HAVE CIGS IMPROVING TO IFR OR MVFR AS THE FRONT/SHOWERS MOVE THRU. HOWEVER...IMPROVEMENT TIME COULD BE 2-3 HOURS LATER THAN IN TAF. NOT EXPECTING VFR TILL LATE TONIGHT. LOW CONFIDENCE ON TIMING OF CIGS. VIS VARYING FROM LESS THAN 1 MILE TO 3 MILES ACROSS THE TAF SITES. WILL KEEP VIS DOWN THROUGH THE NIGHT TILL FROPA...IMPROVING TO P6SM LATE TONIGHT. THE 1 MILE OR LESS COULD CONTINUE 1-2 HOURS LATER THAN IN TAF. HIGHEST CONFIDENCE IN FORECAST IS WINDS...SLY FLOW THIS EVENING...BCMG SW THEN W OVERNIGHT WITH FROPA. PSBL OCNL GUSTS WITH W FLOW LATE TONIGHT...THEN MORE PERSISTENT GUSTS 20-25 KTS DURING THE DAY TOMORROW. VFR CONDITIONS AS WELL THRU THE DAY WITH SCT CU. HIGH PRESSURE BUILDS IN AS THE POTENT LOW PRESSURE SYSTEM MOVES OFF THE COAST LATE THU. THE HIGH WILL KEEP CONDITIONS QUIET/SOLID VFR INTO THE WEEKEND. && .MARINE... WINDS SLOW TO INCREASE THIS EVENING ON THE WATERS WITH QUITE A STABLE AIRMASS IN PLACE. OCNL GUSTS TO 17-18 KTS MAINLY OVER THE SOUTHERN WATERS...BUT OTHERWISE...NOT QUITE AT SCA YET. HOWEVER...EXPECTING A STRONG LLJ TO MOVE OVER THE WATERS THROUGH THE OVERNIGHT...WHICH COULD SEE ENOUGH ENERGY MIX DOWN TO RESULT IN GUSTS TO 20 KTS. HIGHER CONFIDENCE OF SCA EXISTS THOUGH IN THE WAKE OF THE COLD FRONT THURS. CDFNT E OF WATERS BY THU. WHILE GLW CONDS NOT OUT OF THE QSTN...IT WUD TAKE IDEAL MIXING. STICKING W/ MEAN MIXED LYR...AND CARRYING SCA THRU THE DAY. LIGHT WINDS TO CLOSE OUT THE WEEK AS A LARGE SFC HIGH DEVELOPS TO OUR SOUTH AND CALMS DOWN THE AREA WIND FIELD. SLY CHANNELING POSSIBLE INTO LATE SAT W/ THE HIGH MOVING OFF THE COAST AND ANOTHER LOW PRESSURE SYSTEM APPROACHING FROM THE WEST. && .TIDES/COASTAL FLOODING... TIME OF HIGH TIDE HAS PASSED FOR LOWER CHESAPEAKER BAY WITH WATER LEVELS SLOWLY COMING DOWN NOW. AS OF 7 PM...LEVELS BELOW ANY FLOODING THRESHOLDS SO ALLOWED THE ADV TO EXPIRE THERE. CONTINUING NORTHERN CHESAPEAKE BAY WESTERN SHORE AS ANNAPOLIS CURRENTLY SHOWING IN SOLID MINOR LVLS...AND THE REMAINING AREAS EXPECTING TO REACH MINOR LVLS WITH 1.5 FT ANOM PSBL. A COLD FRONT CROSSES THE WATER TONIGHT. DIRECTION NOT ALL THAT GREAT FOR BLOWOUT CONDITIONS. WE WILL NEED TO SEE HOW MUCH WATER IS TRULY PUSHED OUT. MAY NEED AN ADVISORY FOR ANOTHR CYCLE...ESPECIALLY MID BAY. ON THE FLIP SIDE...THE AM CYCLE IS THE LOWER OF THE TWO ASTRONOMICALLY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...DENSE FOG ADVISORY UNTIL 1 AM EST THURSDAY FOR DCZ001. MD...DENSE FOG ADVISORY UNTIL 1 AM EST THURSDAY FOR MDZ004>006-011- 013-014-016>018-503>508. WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR MDZ501. COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ011- 014-508. VA...DENSE FOG ADVISORY UNTIL 1 AM EST THURSDAY FOR VAZ052>057-505- 506. WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR VAZ503-504. WV...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR WVZ501>503-505-506. MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST THURSDAY FOR ANZ530>543. && $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE... TIDES/COASTAL FLOODING...

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