Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 270755
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
355 AM EDT WED MAY 27 2015

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OFFSHORE THIS WEEK. A SOUTHERLY FLOW
WILL BRING WARM HUMID CONDITIONS TO THE MID ATLANTIC THROUGH
SATURDAY. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE EACH
AFTERNOON AND EVENING. A WEAK COLD FRONT WILL APPROACH THE REGION
THURSDAY BUT WASH OUT BEFORE IT MAKES IT THROUGH. A STRONGER COLD
FRONT WILL ARRIVE SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
MAIN STORY TODAY WILL BE THE INCRSG LIKELIHOOD OF SHOWERS AND
TSTMS BY THIS AFTN/EVENING...WITH THE POTENTIAL FOR SVR
STORMS...MAINLY EAST OF A HAGERSTOWN TO DC TO SOUTHERN MD LINE.

REGION REMAINS PLACED UNDER PERSISTING UPPER LVL RIDGE TODAY WHILE
AN UPPER LVL TROUGH SWINGS THROUGH THE MIDWEST AND APPROACHES THE
AREA BY TONIGHT. AT THE SFC...HIGH PRESSURE REMAINS ANCHORED
OFFSHORE...THOUGH WILL WEAKEN ITS HOLD ON THE AREA THIS AFTN WITH
THE FORMATION OF A LEE TROUGH EXPECTED BY THIS AFTN. WEAK SHORTWAVE
RIDING THE RIDGE THIS MORNING IS RESULTING IN ON GOING CONVECTION
OVER THE EASTERN OH RIVER VALLEY AS NOTED ON 07Z WATER VAPOR.
EXPECTING THIS PCPN TO REACH THE FAR WESTERN AREAS NEAR DAYBREAK
THIS MORNING. MAINLY SHOWERS THOUGH CANNOT RULE OUT AN ISO TSTM
INITIALLY.

INCRSG COVERAGE IN THE CONVECTION BY MIDDAY. THE QUESTION THE PAST
FEW DAYS HAD BEEN HOW UNSTABLE THE ATMO WOULD BECOME THIS AFTN...AND
AS A RESULT WHAT WOULD BE THE POTENTIAL FOR STRONGER TO SVR TSTMS.
WHILE SHEAR HAS STRENGTHEN SLIGHTLY ON THE LATEST MODEL
RUNS...GENERALLY AROUND 20-25 KTS...INSTABILITY REMAINS THE BIGGER
PLAYER IN THE DEVELOPMENT OF THE STRONGER STORMS FOR TODAY. AXIS OF
HIGHEST INSTABILITY ALIGNS ALONG THE LEE SFC TROUGH THIS AFTN...WITH
THE THINKING THAT A THINNER LAYER OF CLOUDS WILL SET UP OVER THE
EASTERN AREAS...LEADING TO BETTER DIURNAL HEATING. THE NAM...WITH
THE TYPICAL HIGHER DEW PTS...HAS THE MUCH HIGHER SBCAPE VALUES...ABV
2000 J/KG FOR INSTANCE AT DCA. BUT EVEN THE GFS IS SHOWING AROUND
1000 J/KG...SO EVEN BEING CONSERVATIVE THERE IS A GOOD AMT
INSTABILITY. GENERALLY THINKING THAT WITH THE NEAR UNIDIRECTIONAL
WIND FLOW...WILL SEE DEVELOPMENT OF A LINE OF STORMS OVER CENTRAL MD
MIDDAY UNDER THE RIGHT ENTRANCE REGION. AS THE LINE PUSHES
EAST...EXPECTING IT TO HIT THE LEE TROUGH ALIGNED JUST EAST OF THE
BLUE RIDGE...AND THOUGH LACKING ON THE SHEAR...THE INSTABILITY WILL
BE ENOUGH TO TRIGGER STRONGER TO POSSIBLY EMBEDDED SVR STORMS. WITH
THE LACK OF SHEAR...EXPECTING GUSTY TO DAMAGING WINDS TO BE THE MAIN
THREAT WITH THESE STORMS.

BY THIS EVENING...WITH LOSS OF SFC BOUNDARY AND INSTABILITY...
EXPECTING THE PCPN TO TAPER OFF...WITH AREAS WEST OF THE BLUE
RIDGE BCMG DRY DURING THE FIRST HALF OF THE NIGHT...AND EVERYWHERE
ELSE BY THE SECOND HALF OF THE NIGHT. ANOTHER MILD NIGHT CAN BE
EXPECTED WITH TEMPS IN THE 60S TO NEAR 70 IN THE MAIN METRO AREAS.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...

ANOTHER DAY WITH SHOWERS AND TSTMS AS SFC LOW CURRENTLY OVER THE
GREAT LAKES LIFTS TO THE NORTH AND EAST...DRAGGING ITS ASSOCIATED
COLD FRONT INTO THE REGION BY THURS MORNING. HOWEVER...THE SFC
HIGH AND UPPER LVL RIDGE WILL WORK TO STALL THE PROGRESSION OF THE
FRONT...WITH IT BCMG NEARLY STATIONARY FOR MOST OF THURS ACROSS
THE NORTHERN HALF OF THE CWA...EVENTUALLY WEAKENING BY THURS
NIGHT. THIS SFC BOUNDARY WILL BE THE TRIGGER MECHANISM FOR
ACTIVITY DURING THE DAY AS THE ATMO BECOMES DECENTLY UNSTABLE YET
AGAIN WITH TEMPS PUSHING WELL INTO THE 80S AND DEW PTS PERSISTING
IN THE 60S. WHILE THE INSTABILITY WONT BE NEAR THE LVLS AS
TODAY...EXPECTING A BUT MORE SHEAR OVER THE AREA TO AID IN TSTM
DEVELOPMENT. OVERALL SVR PARAMETERS ON THE WEAKER SIDE...AND WITH
A LACKING OF UPPER LVL SUPPORT AS THE BETTER FORCING REMAINS NORTH
OF THE AREA...NOT ANTICIPATING SVR OR EVEN STRONGER TSTM
DEVELOPMENT.

AS THE FRONTAL BOUNDARY DISSIPATES THURS NIGHT...ALONG WITH ANY
DAYTIME RESULTING INSTABILITY...PCPN IS EXPECTED TO TAPER OFF FROM
NORTH TO SOUTH. HAVE MAINTAINED AT LEAST SLIGHT CHC POPS THRU THE
NIGHT EVERYWHERE...BUT THESE COULD VERY WELL BE OVERDONE...WITH THE
PCPN TAPERING OFF SOONER. SLIGHTLY COOLER TEMPS THURS NIGHT BEHIND
THE FRONT...STILL IN THE 60S THOUGH.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
SFC TROFFING WILL BE SOUTH OF THE AREA BY FRI MRNG. ANY THERMAL
DISCONTINUITY WUD HV WASHED OUT BY THEN...AND MID LVL HGTS START TO
RISE ONCE AGN. THE BERMUDA HIGH TYPE SYNOP PTTN WL BE RETURNING IN
RELATIVELY WK SFC FLOW. WL ONCE AGN HV THE RISK FOR DIURNALLY DRIVEN
SHRA/TSTMS...BUT SUPPORT FOR NMRS OR MATURE STORMS SEEMS TO BE
LACKING. HV POPS NO HIER THAN CHC...INITIATING IN THE HIER TRRN BY
MID AFTN AND MIGRATING TWD THE COAST. HWVR...THE LOSS OF SUNSHINE
SHUD SPELL THEIR DEMISE...AND POPS ALONG THE WRN SHORE OF THE BAY WL
END UP LWR THAN INLAND AREAS. MAXT WL BE A CPL DEGF LWR THAN THU. WL
BE KEEPING MIN-T IN THE MID-UPR 60S DUE TO DEBRIS CLDS. THAT CUD
POTENTIALLY END UP BEING A PINCH TOO WARM BASED ON PROJECTED DEWPTS.

A STRONGER CDFNT WL SLOWLY MARCH TWD THE AREA THIS WKND. WL BE IN
THE SW FLOW AHD OF FNT SAT...W/ GREATER INSTABILITY BEING PULLED NWD
AHD OF BNDRY. THE INSTBY AXIS WL REMAIN W OF THE MTNS...WHICH IS
WHERE THE HIEST POPS WL BE PLACED /AIDED BY OROGRAPHIC LIFT/. IN
ADDITION...SAT HAS THE BEST CHC AT REACHING 90F. FOR NOW WL BE
HOLDING MAXT JUST SHY OF THAT.

THE FNT WL BE DRAGGED ACRS AREA ON SUNDAY...W/ NRN STREAM LOPRES
HEADING TWD THE CNDN MARITIMES. THAT WL MAKE THE ORIENTATION OF THE
FNT MORE PERPENDICULAR TO UPR FLOW. EXACT TIMING STILL A BIT UP IN
THE AIR...BUT RAFL RATES WL BE A CONCERN SINCE PWAT WL BE NEAR 2
INCHES. HV LKLY POPS AND SLGTLY LWR TEMPS.

IN A PTTN SUCH AS THIS...ITS ALWAYS QSTNBL HOW FAR S FNT WL MAKE IT
BEFORE STALLING/WASHING OUT. HV COOLER AIR IN FCST FOR MON-TUE...BUT
AM NOT SURE WHETHER FOCUS FOR STORMS WL COMPLETELY PUSH THROUGH.
THEREFORE...HV CHC POPS THRU XTNDD FCST.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
GENERALLY VFR CONDITIONS FOR THE TAF PERIOD. PSBL MVFR CIGS
AROUND 12Z THIS MORNING WITH CIGS AROUND 2KFT CURRENTLY NOTED JUST
TO THE SOUTH AND WEST. ANY MVFR CIGS EXPECTED TO SCATTER OUT BY
14/15Z...WITH SCT CU AND BKN-OVC MID LVL DECK THEN EXPECTED.

MOD CONFIDENCE ON THE PCPN TIMING...COULD SEE +/- 1-2 HRS. WHILE
CURRENTLY HAVE VFR CONDITIONS WITH THE VCTS MENTION...CANNOT RULE
OUT MVFR OR LOWER CONDITIONS WITH ANY STRONGER TSTM...ESP
DC/BALTIMORE METRO TAF SITES. SOME STORMS MAY ALSO PRODUCE
GUSTY-STRONG WINDS AND HEAVY RAINS BRIEFLY.

PCPN TAPERS OFF THIS EVENING...WITH DRY WX THEN TONIGHT. ANOTHER
ROUND OF PCPN WILL BE PSBL ON THURS...BRINGING YET ANOTHER CHC FOR
SUB-VFR CONDITIONS.

WINDS GENERALLY SLY TODAY 8-10 KTS...BCMG LESS THAN 5 KTS TONIGHT.
WINDS SHIFT TO THE NW TOMORROW...THOUGH STILL REMAINING LESS THAN 5
KTS.

CHC OF SHOWERS/STORMS EXIST EACH DAY IN THE OUTLOOK...SPCLY
DURING THE AFTN/EVE HRS. BEST CHC FOR STORMS WL BE ON SUNDAY. LCL
FLGT RESTRICTIONS TO IFR OR LWR EXIST INVOF STORMS.

&&

.MARINE...

SCA REMAINS IN EFFECT TODAY FOR ALL ZONES EXCEPT THE UPPER TIDAL
POTOMAC. HAVE ADDED THE UPPER ZONE OF THE CHESAPEAKE BAY FOR THIS
AFTN TO ACCOUNT FOR SLY CHANNELING. FOR THE LATTER HALF OF
TONIGHT...ONLY KEEPING THE SOUTHERN CHESAPEAKE BAY ZONE...WITH
SUB- SCA CONDITIONS THEN EXPECTED ON ALL WATERS BY THURS
MORNING...LASTING THRU THURS NIGHT.

TSTMS EXPECTED THIS AFTN COULD BRING PERIOD OF GUSTY TO STRONG
WINDS.

WINDS WL BE ON THE LIGHT SIDE ELY FRI...BUT S/SWLY FLOW WL REASSERT
ITSELF BY AFTN-EVNG...CONTG THRU SAT. CHANNELING WL COME CLOSE TO
SCA BY FRI EVNG...BUT THINK THAT SAT AFTN-EVE HAS A BETTER SCA RISK.
CDFNT WL SAG ACRS AREA SUNDAY...MAKING FOR NMRS TSRA.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ531>533-
     537>542.
     SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ534-543.
     SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 PM EDT THIS EVENING
     FOR ANZ530.

&&

$$
SYNOPSIS...HTS
NEAR TERM...SEARS
SHORT TERM...SEARS
LONG TERM...HTS
AVIATION...SEARS/HTS
MARINE...SEARS/HTS


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