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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