Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 301423 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1023 AM EDT TUE SEP 30 2014

.SYNOPSIS...
LOW PRESSURE OVER LAKE ERIE WILL TRACK ACROSS THE NORTHEASTERN
U.S. THIS AFTERNOON AND THIS EVENING BRINGING RAIN CHANCES TO THE
MID ATLANTIC REGION. HIGH PRESSURE WILL RETURN TO THE EAST COAST
WEDNESDAY AND REMAIN IN PLACE UNTIL A COLD FRONT APPROACHES THE
AREA FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
LOW LEVEL MOISTURE REMAINED SOCKED IN EAST OF THE BLUE RIDGE THIS
MORNING. WEAK HIGH PRESSURE CENTERED OVER NORTHERN NEW ENGLAND
EXTENDS SOUTH INTO THE MIDDLE ATLANTIC REGION PROVIDING A BIT OF A
CAD WEDGE OVER THE REGION. 12Z IAD SOUNDING ALSO SHOWING A STOUT
INVERSION AT 850MB WITH WEAK STEERING FLOW AT THE LOWEST LEVELS.
LOW CLOUDS SHOULD HOLD IN PLACE AT LEAST INTO MIDDAY...AWAITING
ENERGY ASSOCIATED WITH A CUTOFF UPPER LOW TRACKING ACROSS THE
GREAT LAKES. DRIER AIR WILL EVENTUALLY MOVE IN AND MIX OUT THE
CLOUD COVER BUT A BIT LATER THAN PREVIOUSLY FORECAST...EAST OF THE
BLUE RIDGE. WILL LOWER DAYTIME MAX TEMPS A FEW DEGREES FOR THESE
LOCATIONS. PATCHY DENSE FOG WILL ALSO CONTINUE TO GRADUALLY BURN
OFF.

WEST OF THE BLUE RIDGE...SOME PATCHY FOG REMAINS IN VALLEY
LOCATIONS BUT CLOUD COVER HAS FOR THE MOST PART ERODED OUT. ENERGY
ASSOCIATED WITH THE UPPER LOW WILL HELP DESTABILIZE THE MID LEVELS
TODAY AND SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL BE
POSSIBLE THIS AFTERNOON INTO THE EARLY EVENING MAINLY WEST OF THE
BLUE RIDGE. COOLING ALOFT WILL LEAD TO SOME STEEPENING LAPSE RATES
WITH SMALL HAIL POSSIBLE BUT ANY SEVERE THREAT IS EXPECTED TO BE
NORTH OF THE FORECAST AREA.

PATCHY FOG...SOME LOCALLY DENSE MAY DEVELOP AGAIN OVERNIGHT. LOWS
WILL DROP BACK INTO THE 50S IN MOST LOCATIONS...EXCEPT 60S IN THE
METRO AREAS.

&&

.SHORT TERM /WEDNESDAY/...
UPPER CUTOFF LOW WILL GRADUALLY MOVE EAST OFF THE COAST DURING
WEDNESDAY. PATCHY MORNING FOG WILL BE POSSIBLE. HIGH
PRESSURE WILL BUILD INTO THE MIDDLE ATLANTIC REGION FROM THE WEST
BRINGING A BIT MORE SUNSHINE AND A RETURN TO TEMPERATURES IN THE
MIDDLE 70S.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
BEHIND THE EXITING UPPER LOW WED NIGHT...LOW-LEVEL MOISTURE WILL BE
TRAPPED OVER THE MID-ATLC REGION TO CLOSE OUT THE WORK WEEK. THU
WILL BE MAINLY DRY...BUT WAVERING BETWEEN CLOUDY AND MOSTLY CLOUDY.
THESE SKY CONDITIONS WILL MODERATE TEMPS...AS THEY DID ON MON. EVEN
W/ A HIGH PRESSURE RIDGE SLIDING OVERHEAD...THE BOUNDARY LAYER WILL
REMAIN MOIST. A HANDFUL OF LIGHT SHOWERS MAY DEVELOP ACROSS THE MTNS
BUT BARELY ENOUGH TO WARRENT POPS ACROSS THESE AREAS. THE SKY COVER
WILL BE A FAIRLY SHALLOW LOW STRATUS DECK THAT WILL BEGIN TO MIX OUT
DURING THE LATE AFTN HRS - W/ SOME POKES OF SUN BEFORE EVE.

A MODERATED OVERNIGHT TEMP PROFILE THU NIGHT. EVEN THOUGH A STRONG
COLD FRONT WILL BE FAST-APPROACHING FROM THE UPPER MIDWEST/TENN
VLY...OUR AREA WILL BE WELL E OF THIS FEATURE OVERNIGHT AND HAVE
ANOTHER RELATIVELY WARM NIGHT SET-UP FOR THE REGION/.

SMALLER UPPER WAVES OF MID-LEVEL ENERGY WILL MAKE THEIR WAY ACROSS
THE CNTRL APLCNS AND BEGIN TO COMBINE OR AT LEAST INTERACT AS THEY
REACH THE MS VLY REGION. WHAT STARTED AS A MORE COMPACT LOW PRESSURE
SYSTEM OVER THE PLAINS ON THU WILL BE A MORE POTENT AND EXTENSIVE
SYSTEM STRETCHING FROM THE GULF COAST TO NORTH OF THE GREAT LAKES
EARLY FRI. THE MAIN RESULTANT VORT MAX WILL START TO DISSIPATE AS IT
CROSSES THE SRN APLCNS AND MOVES TOWARD THE VA TIDEWATER REGION.

SLIGHTLY LAGGING BEHIND BUT NOT LACKING ANY PUNCH WILL BE YET
ANOTHER UPPER WAVE - THIS ONE PACKING THE CANADIAN AIR - WILL SWING
IN FROM THE BEHIND LATER IN THE DAY. A WAVE OF PRE-FRONTAL RAINS
WILL SLIDE ACROSS THE EAST COAST...INCLUDING OUR REGION...BUT IT
DEPENDS ON THIS SECONDARY INCOMING CANADIAN AIRMASS. THE STRENGTH
AND TIMING OF THIS FEATURE COMING IN ON THE BACKSIDE OF THE EAST
COAST SYSTEM WILL DETERMINE IF MUCH OF PRECIP DISSIPATES AND PULLS
UP NORTH OF US LATE FRI NIGHT. THE GFS IS LESS-SHARP W/ THE INCOMING
TROUGH AXIS THAN THE RUN AT THIS TIME LAST NIGHT. A COMPLEX COUPLE
OF UPPER VORT LOBES WILL BE SWINGING AROUND THE BOTTOM OF THE UPPER
TROUGH AS IT NEARS THE AREA. EACH ONE COULD INDIVIDUALLY HAVE AN
INFLUENCE...LIKE DIGGING THE SYSTEM FURTHER SOUTH OR FORCING A BRIEF
AREA OF STRONG LIFT ACROSS THE WARM SECTOR. HOWEVER...THE DYNAMICS
OF THE SYSTEM SHOULD LARGELY EXIT OFF TO THE NORTH INTO EARLY
SAT...LIMITING NOT ONLY THE CONVECTIVE POTENTIAL BUT RAIN POTENTIAL
ACROSS THE REGION. NOT MUCH QPF BEING PRINTED-OUT BY LONG TERM
GUIDANCE AS MODELS LARGELY BYPASS OUR AREA FOR RAINFALL. SEEMS
REASONABLE W/ WHERE THE DYNAMICS OF THE SYSTEM WILL BE AND THE
RELATIVE MOVEMENT AWAY FROM THE AREA.

HIGHS ON FRI WILL LIKELY REACH THE M-U70S AND THE COLD FRONT WILL
MOVE THRU OVERNIGHT...LOWS WILL STILL ONLY DROP INTO THE 50S FOR
MUCH OF THE AREA. THE MTNS WILL START TO SEE 40S OVERNIGHT W/ THE
COLDER LOW LEVEL AIR COMING IN...BUT THE FRONT WON`T ARRIVE QUICK
ENOUGH TO REALLY COOL OFF THE AREA - THAT WILL BE THE NEXT NIGHT.
THE TROUGH AXIS WILL BE APPROACHING ON SAT...SO CONDITIONS WILL BE
PLEASANT W/ HIGHS IN THE L70S AND A DRIER AIRMASS...BUT W/ THE
TROUGH AXIS SLIDING OVER THE AREA LATE IN THE DAY - SWEEPING IN THE
COLDER AND MUCH DRIER AIRMASS...OVERNIGHT LOWS SAT NIGHT WILL DROP
BACK INTO THE U40S AND L50S. ANOTHER ONE-DAY REPRIEVE BEFORE ANOTHER
CLIPPER SHORTWAVE LACKING PRECIP WILL SWING DOWN FROM THE GREAT
LAKES...REINFORCING THE COOLER/DRIER AIRMASS.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
LOW CLOUDS AND SOME PATCHY FOG WILL PERSIST EAST OF THE BLUE RIDGE
FOR A COUPLE MORE HOURS. FOG WILL LIKELY BURN OFF FIRST BUT CLOUDS
WILL HOLD IN LONGER. WILL KEEP SUB VFR CONDITIONS THROUGH LATE
MORNING/MIDDAY THEN RISING. SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS POSSIBLE GENERALLY WEST OF THE BLUE RIDGE THIS
AFTERNOON INTO THE EVENING. LOW CONFIDENCE IN SHOWERS/STORMS
IMPACTING THE TERMINALS THUS WILL LEAVE OUT MENTION. ADDITIONAL
PATCHY FOG POSSIBLE OVERNIGHT INTO WEDNESDAY MORNING.

TRAPPED LOW LEVEL MOISTURE ACROSS THE REGION OVER THE NEXT FEW DAYS
WILL KEEP THE CLOUDS IN PLACE. PERIODIC LIFTING OF THE STRATUS DECK
HEIGHT POSSIBLE...ESPC DURING THE AFTN HRS EACH DAY UNTIL FRI.
SHOULD REMAIN DRY AND CLOUDY/MOSTLY CLOUDY UNTIL A FRONTAL PASSAGE
LATE FRI NIGHT. HIGH PRESSURE INTO THE WEEKEND...BUT COOLER AND
DRIER CANADIAN AIRMASS.

&&

.MARINE...
WINDS BLO SCA VALUES TDA THRU WED.

AN UPPER LOW MOVING OFF THE NY/NEW ENGLAND COAST WILL KEEP AN ARM OF
LOW LEVEL MOISTURE STRETCHED ACROSS THE REGION ON THU. ALTHOUGH
WE`LL BE DRY THAT DAY...SLY WINDS WILL PICK UP AHEAD OF A COLD FRONT
APPROACHING FROM THE WEST. THE FRONT WILL ARRIVE LATE FRI...BRINGING
NW WINDS BEHIND IT THAT WILL LAST INTO THE WEEKEND.

&&

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

&&

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






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