Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 250007
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
707 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.

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 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...
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...
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...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.
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 ANZ530>543.

&&

$$





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