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/...
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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.
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&& .SHORT TERM /WEDNESDAY/...
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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.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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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.
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&& .AVIATION /14Z TUESDAY THROUGH SATURDAY/...
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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.
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&& .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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