Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 020759
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
359 AM EDT TUE SEP 2 2014

.SYNOPSIS...
BERMUDA HIGH PRESSURE WILL PERSIST TODAY AHEAD OF A WEAK COLD
FRONT THAT WILL CROSS THE AREA TONIGHT. HIGH PRESSURE WILL THEN
BUILD FROM THE MIDWEST THROUGH WEDNESDAY THEN PERSIST OFFSHORE
THURSDAY INTO THE WEEKEND. A COLD FRONT WILL ENTER THE REGION IN
THE SATURDAY NIGHT TIME FRAME.

&&

.NEAR TERM /THROUGH TONIGHT/...
ANOTHER MUGGY OVERNIGHT W/ MUCH OF THE REGIONAL OBS SHOWING
DEWPOINTS IN THE L70S - PLENTY HUMID FOR AN EARLY SEPT NIGHT.
SMALLER SCALE RIPPLES IN THE LOWER ATMOS CAUSED SOME SCATTERED
SHOWERS/TSTMS OVER THE NERN QUADRANT OF THE CWA EARLIER IN THE
OVERNIGHT WHICH HAVE SINCE DISSIPATED...BUT EVIDENCE OF THE
INSTABILITY THAT CAN BE TAPPED EVEN OVERNIGHT. THE 00Z KIAD SNDG
FROM LAST NIGHT SHOWS OVER 2K J/KG SFC CAPE...THOUGH THE TYPICAL
NIGHTTIME DECOUPLING TOOK AWAY MUCH OF THE LL CONVERGENCE.

LITTLE AIRMASS CHANGE OVER THE NEXT 12-18HRS WILL BASICALLY KEEP
THE OVERHEAD ATMOS IN MAINTENANCE MODE - ALLOWING ISOLATED
SHOWERS/TSTMS TO DEVELOP W/ EVEN WEAK/DISORGANIZED FORCING. A
HANDFUL OF SHOWERS NOW REACHING THE SPINE OF THE APLCNS. THOUGH
THIS ACTIVITY WILL LIKELY LOOK MUCH DIFFERENT OVER THE NEXT FEW
HRS...THE ARM OF LOW LEVEL ENERGY CAUSING THEM MAY DEVELOP MORE
ACTIVITY FURTHER EAST INTO THE MIDDAY. NEAR TERM WRF DERIVATIVES
LARGELY POINT TOWARD A LATE AFTN COLLECTION OF TSTMS DEVELOPING
NEAR THE BLUE RIDGE AND SLIDING E THRU THE REMAINDER OF THE EVE. A
COLD FRONT WILL BE A FEW HRS BEHIND THIS ACTIVITY...SO THE
AFTN/EVE TSTMS WILL LIKELY BE FORCED BY A PRE-FRONTAL TROUGH/
DIFFERENTIAL HEATING BOUNDARY.

IT HAS BEEN A HOT/HUMID PAST FEW DAYS...AND TODAY WILL LIKELY BE
THE APEX OF THE CURRENT STRETCH. WINDS WILL BE MAINLY WSW...BUT W/
SOME DOWNSLOPING LATER COMPONENT TO THE WINDS. THESE WINDS MAY
ALSO DO WELL IN PREVENTING CONVECTION FOR A LARGE PART OF THE DAY.
DRY/UNIDIRECTIONAL FLOW IS TYPICALLY NOT GOOD FOR CONVERGENCE...
SO A LOW LEVEL BOUNDARY WOULD BE NECESSARY FOR EFFECTIVE
INITIATION. HEATING WON`T BE AN ISSUE HOWEVER...W/ TEMPS QUICKLY
RISING RIGHT BACK INTO THE 80S THRU THE MRNG HRS AND L-M90S BY THE
PEAK HEATING OF THE MID AFTN. AN INFLUX OF DENSE LOW-MID CLOUD
DECKS FROM THE WEST DURING THE MID AFTN MAY HELP TO CUT DOWN ON
THE HIGHER TEMPS...AND SO WOULD ANY ONGOING SHOWERS/TSTMS.
DEWPOINTS IN THE U60S/L70S WILL ALSO CREATE ANOTHER HOT/HUMID
ENVIRONMENT W/ HEAT INDICES WELL INTO THE U90S W/ A FEW LOCALES
POTENTIALLY POKING JUST ABOVE THE 100F DEG MARK IN THE URBAN
AREAS.

AFTER THE SHOWERS/TSTMS HAVE ROLLED THRU LATER THIS EVE...THE
FRONT WILL BEGIN TO CLEAR OUT THE AREA FROM THE WEST. SKIES WILL
START TO CLEAR AND WINDS WILL TURN NWLY. THIS PASSAGE THOUGH WON`T
BE PARTICULARLY STRONG...W/ WINDS ONLY IN THE 5-10KT RANGE AT BEST
AND ONLY ABOUT A 5F DEG DEWPOINT DROP OVERALL...SO THE HUMIDITY
WILL REMAIN ELEVATED AS WE HEAD INTO WED.

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
DRY AND STABLE ON WED. NO POPS IN THE FORECAST. ANOTHER WARM AND
RELATIVELY HUMID DAY...AS HIGHS WILL AGAIN APPROACH THE 90F DEG
MARK ACROSS MUCH OF THE AREA. DEWPOINTS WILL STILL BE IN THE
L-M60S...CREATING HEAT INDICES RIGHT AROUND THE AMBIENT TEMP
LEVELS/SLIGHTLY HIGHER.

WEDNESDAY NIGHT...HIGH PRESSURE CENTER OVER THE AREA SHIFTS
OFFSHORE WITH A RETURN FLOW DEVELOPING IN THE OVERNIGHT HOURS.
DEWPOINTS QUICKLY RAISE BACK TO NEAR 70F...MIGHT AS WELL GET AREAS
OF FOG WORDING IN THE GRIDS. WITH THE HIGH PERSISTING
OFFSHORE...AN UNSTABLE GULF AIRMASS BRINGS THE MID-ATLANTIC RIGHT
BACK INTO AN ACTIVE PATTERN BY THURSDAY. CHANCES FOR DIURNAL
DRIVEN SCATTERED THUNDERSTORMS. SHOULD LOW LEVEL FLOW BE MORE SELY
THAN SLY...TERRAIN ENHANCEMENT WOULD ALSO BE A FACTOR IN
THUNDERSTORM DEVELOPMENT. SIMILAR PATTERN FOR FRIDAY WITH THE NEXT
COLD FRONT.

MAX TEMPS THURSDAY AND FRIDAY AROUND 90F THOUGH CLOUD COVER WILL
BE A FACTOR.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
ANOTHER WEAK COLD FRONT APPROACHES FRIDAY NIGHT. LIKELY POPS FOR
THUNDERSTORMS WEST FROM THE BLUE RIDGE SATURDAY AS THERE IS GOOD
CONSENSUS BETWEEN THE 00Z GFS AND 00Z ECMWF. QUESTION IS HOW
QUICKLY THE FRONT PUSHES THROUGH THE AREA. THE ECMWF LINGERS THE
COLD FRONT OVER SERN ZONES THROUGH SUNDAY.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
AFTER SOME EARLIER SHOWER/TSTMS PASSED NEAR THE DC/BALT METRO
AREAS A FEW HRS AGO...SKIES HAVE GENERALLY CLEARED OUT. MORE
CLOUDS ON THE WAY FROM THE WEST...AS WELL AS A FEW SHOWERS THAT
WILL LIKELY DISSIPATE TOWARD DAWN. A WSW WIND DURING THE DAYTIME
HRS...W/ SCTD SHOWERS AND TSTMS EXPECTED TO DEVELOP LATE TODAY -
SURROUNDING THE 00Z TIME PERIOD - W/IN A COUPLE HRS EITHER SIDE.
SOME EARLIER ACTIVITY POSSIBLE...AFTER 18Z BUT TIMING/PLACEMENT
CONFIDENCE IS LOW ATTM. A COLD FRONT WILL PUSH THIS ACTIVITY OFF
THE COAST LATE TONIGHT AND CLEAR OUT THE AREA FOR WED.

FOG WEDNESDAY NIGHT UNDER HIGH PRESSURE. LIGHT SLY RETURN FLOW
THURSDAY AND FRIDAY WITH MAINLY AFTERNOON CHANCES FOR
THUNDERSTORMS. COLD FRONT ENTERS THE AREA LATE SATURDAY WITH
THUNDERSTORMS AHEAD OF IT.

&&

.MARINE...
A RELATIVELY LIGHT SWLY FLOW OVER THE WATERS TONIGHT...THE HIGHER
GUSTS NEAR 15KT OVER THE LOWER BAY ZONES. THIS WILL CONTINUE INTO
THE DAYTIME HRS...THOUGH MORE OF A WLY DIRECTION TO THE FLOW THRU-
OUT THE DAY. SCTD TSTMS POSSIBLE LATE THIS AFTN/EVE...SO ANOTHER
POTENTIAL FOR CONVECTIVE MARINE HAZARDS. A COLD FRONT WILL WEAKLY
PASS THRU THE REGION OVERNIGHT...TURNING WINDS TO NWLY BUT STILL
LOWER THAN SCA CRIT. WED WILL SEE HIGH PRES BUILD INTO THE REGION
AND DROP WIND SPEEDS DOWN EVEN FURTHER.

LIGHT AND VARIABLE FLOW WEDNESDAY EVENING GIVES WAY TO SLY FLOW AS
HIGH PRESSURE MOVES OFFSHORE. WILL HAVE TO WATCH FOR CHANNELING
AGAIN (PROBABLY THURSDAY EVENING) BUT AS OF NOW THERE ARE NO SCA
HEADLINES EXPECTED. COLD FRONT APPROACHES THE WATERS SATURDAY WITH
GOOD CHANCES FOR THUNDERSTORMS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...BAJ
NEAR TERM...GMS
SHORT TERM...GMS
LONG TERM...BAJ
AVIATION...GMS/BAJ
MARINE...GMS/BAJ






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