Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 242240 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 540 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/... AREAS OF DENSE FOG HV DVLPD ACROSS CENTRAL MD SWD INTO LOUDOUN CO. AS A RESULT AN ADVSRY HAS BEEN ISSUED. WARM MOIST OVR COLD GRND W/ LGT WINDS... DEEPENING LOPRES /995 MB/ IN NW OHIO TAFTN. ISENT LIFT CONTS E OF THE APLCNS...ALTHO INTENSITY OF PCPN HAS DIMINISHED AS FCST BY GDNC. HWVR...THE MRNG PCPN HAS ONLY STEEPENED THE INVSN...AND RESULTED IN A SFC WEDGE THAT HAS PROVEN TO BE HARD TO ERODE. WINDS NIL ATTM IN LOW CLDS AND AREAS OF FOG. TEMPS IN CWFA UPR 40S-LWR 50S WHILE ORF NEAR 70F AND EKN HAS REACHED 60F. HV TAKEN TEMPS DOWN FOR THE REST OF THE AFTN...KEEPING READINGS IN THE 50S. AM HOPEFUL THAT ADVCTN AHD OF ATTENDENT CDFNT WL PUSH AT LEAST 60 DEGF AIR TO I-95 EWD... BUT THAT WUDNT OCCUR TIL THE NIGHTTIME HRS. SFC LOW WL CONT TO DEEPEN AND HEAD N TNGT AS CDFNT PUSHES E AHD OF A WELL DEFINED UPR TROF AXIS. THE ATTENDENT CDFNT WL REACH MTNS NEAR 00Z...AND SHUD BE TO THE WRN SHORE OF THE BAY INVOF 06Z. PRIND CORRIDOR OF PCPN MINIMA BTWN BEST ISENT LIFT ALONG THE BAY AND CDFNT IN THE MIDWEST WL BE TRANSITIONING OVER CWFA LT TAFTN-ELY EVNG. HV CAPTURED THIS GDNC INDICATION W/IN DATABASE...BUT DIDNT GO BELOW CHC POPS. WHILE SUPPORT ALONG FNT WL STILL BE FVRBL...W/ MSTR TRANSPORT FM 50 KT LLJ...HV OPTED TO LWR POPS DUE TO CVRG CONCERNS. WHILE AMS STILL UNSEASONABLY MOIST W/ PWAT UP TO 1.5 INCHES...RAFL THUS FAR NOT SGFNT...AND ANY ADDTL RAIN SHUD BE SPREAD OUT. GIVEN LLVL WEDGE...GDNC INDICATORS SUGGEST NOT AS MUCH INSTBY PRESENT. WL SCALE BACK RAFL INTENSITY TO LGT AND THUNDER BACK TO SCHC. THERES STILL MORE THAN ENUF DYNAMICS/SHEAR PRESENT FOR GUSTY SHOWERS TO POTENTIALLY PUNCH THRU. WL KEEP WIND ADVY IN PLACE FOR MTNS...ALTHO BASED ON CURRENT SFC PTTN...WINDOW OF OPPORTUNITY LOOKING MORE SCANT. BREEZY CONDS WL RESIDE BHD CDFNT...W/ BETTER MIXING IN PLACE. NO BIG ADJUSTMENTS FM PRVS FCSTS HERE...AS MEAN LYR SUGGESTS G25 KT OR SO. 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 /00Z 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 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... DAYTIME RAFL HAS PRODUCED A STBL LYR THAT HAS PREVENTED WINDS FM MAKING IT TO THE WATERS EDGE. FOR THE MOST PART...SCA HAS YET TO MATERIALIZE. NOT REAL CONFIDENT ON WHEN LLVL STABILITY WL ERODE... OTHER THAN IT SHUD SOMETIME THIS EVNG SINCE THE P-GRAD WL BE INCRSG. THEREFORE WL LEAVE SCA IN PLACE AS IS. LLJ JUST AHD OF CDFNT WL CONTAIN HIER WINDS...AND A FRACTION OF THAT SHUD MIX DOWN INVOF SHRA. SMW LKLY THE BEST VEHICLE TO ADDRESS THAT THREAT. AM DOUBTING IF IT WL BE WIDESPREAD. 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... WATER LVLS DEPARTURES UP TO 1.5 FT. AT THAT PACE...WL BE ECLIPSING MINOR THRESHOLDS W/ THE PM TIDE CYCLE ALONG THE WRN SHORE OF THE BAY. ADVY ALREADY IN PLACE. GDNC FOR THE UPR PTMC INDICATING NO ISSUES. 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...NONE. MD...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR MDZ501. DENSE FOG ADVISORY UNTIL 1 AM EST THURSDAY FOR MDZ004>006-011- 503>508. COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ011- 014-508. COASTAL FLOOD ADVISORY UNTIL 7 PM EST THIS EVENING FOR MDZ017- 018. VA...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR VAZ503-504. DENSE FOG ADVISORY UNTIL 1 AM EST THURSDAY FOR VAZ505-506. WV...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR WVZ501>503-505-506. MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST THURSDAY FOR ANZ535-536. SMALL CRAFT ADVISORY UNTIL 5 PM EST THURSDAY FOR ANZ530>534- 537>543. && $$ UPDATE...AS/WOODY! PRVS...HTS/GMS/KLW

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