Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 011903
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
303 PM EDT TUE SEP 1 2015

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN CENTERED TO THE WEST THROUGH TONIGHT.
AN UPPER-LEVEL DISTURBANCE ALONG WITH ITS ASSOCIATED SURFACE
TROUGH WILL PASS THROUGH THE REGION WEDNESDAY. WEAK HIGH PRESSURE
WILL BUILD OVERHEAD THURSDAY BEFORE A BACKDOOR COLD FRONT MOVES
INTO THE AREA LATE FRIDAY INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
SFC HIGH PRESSURE IS CENTERED OVER THE OH/TN VALLEYS THIS
AFTERNOON WITH A WEAK LOW OFF CAPE HATTERAS. ALOFT...RIDGING IS
CENTERED ALONG THE EASTERN SEABOARD WITH A CUTOFF LOW OVER INDIANA.
CONVECTION HAS FORMED WITH THE HELP OF LOCAL FEATURES...NAMELY THE
HIGHER TERRAIN OF THE ALLEGHENYS AND BLUE RIDGE. HOWEVER A COUPLE
SHOWERS HAVE ALSO FORMED IN CHARLES COUNTY WHERE THE ONSHORE
BREEZES FROM THE BAY AND THE POTOMAC CONVERGED. LITTLE TO NO
LIGHTNING HAS BEEN OBSERVED WITH POOR MID LEVEL LAPSE RATES...SO
FOR THE MOST PART THESE WILL JUST PRODUCE BRIEF DOWNPOURS. WHILE
THE INITIAL ACTIVITY HAS PULSED DOWN...THESE AREAS WILL BE FAVORED
FOR ISOLATED ADDITIONAL DEVELOPMENT UNTIL THE SUN STARTS TO SET.
ELSEWHERE IT IS JUST HOT AS HEAT INDICES ARE REACHING THE MID 90S.

LIGHT TO CALM WINDS AND ELEVATED DEW POINTS WILL RESULT IN ANOTHER
NIGHT WHERE FOG IS POSSIBLE. THE UNCERTAINTY FACTOR TONIGHT WILL
BE THE APPROACH OF CLOUDS FROM THE WEST. AS A RESULT...THE VA
PIEDMONT MAY ONCE AGAIN BE THE FAVORED LOCATION. LOWS ONLY FALL TO
THE MID 60S TO LOWER 70S.

THE CLOSED LOW IS FORECAST TO OPEN AND DIVE SOUTHEAST WEDNESDAY AS
RIDGING BUILDS OVER THE PLAINS. THE TRACK ISN/T MUCH DIFFERENT
THAN THE OVERNIGHT FORECAST BUT IS STILL FARTHER SOUTH THAN
PREVIOUS DAYS. WHILE THE UPPER LEVEL TROUGH AND WEAK SFC
REFLECTION WILL BE A SOURCE OF LIFT...APPEARS THE MAIN VORT MAX
WILL JUST CLIP THE SOUTHWESTERN CWA. THEREFORE HAVE FOCUSED
HIGHEST POPS THERE. IT IS QUITE POSSIBLE THAT DC...AND ESPECIALLY
BALTIMORE...SEE LITTLE TO NO ACTIVITY. MAY SEE SHOWERS DEVELOP
BEFORE TYPICAL DIURNAL TIMING DEPENDING ON TIMING OF FORCING.
INSTBY AND SHEAR ARE NOT VERY IMPRESSIVE...SO DO NOT HAVE MUCH OF
A SEVERE CONCERN. HIGHS MAY BE DEPENDENT ON CLOUD COVER...BUT
UPPER 80S TO LOWER 90S ARE STILL SUPPORTED ACROSS MUCH OF THE
AREA.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
THE TROUGH ALOFT WILL BE EAST OF THE AREA BY AROUND 06Z...SO HAVE
THE LINGERING POPS IN THE SOUTHEAST CWA ENDING BY THEN. THERE
SHOULD BE SOME CLEARING...ESPECIALLY IN NORTHERN AREAS. HOWEVER
WITH LITTLE CHANGE TO THE LOW LEVEL AIR MASS...IT WILL AGAIN BE
MUGGY WITH LOWS IN THE MID 60S TO LOWER 70S.

THU...WEAKENING UPPER LEVEL SHORT WAVE WILL BE SOUTH AND EAST OF CWA
LEAVING US IN REGION OF HEIGHT RISES AND SUBSIDENCE. ANOTHER IN A
STRING OF DAYS WITH TEMPERATURES 5-10 DEGREES ABOVE NORMAL...WITH
HIGHS IN U80S/L90S. MODERATE HUMIDITY WITH DEWPOINTS IN M60S...BUT
LITTLE CHANCE OF MEANINGFUL PRECIP...AS LAPSE RATES REMAIN POOR AND
THERE IS LITTLE FORCING FOR ASCENT. AS SUCH...EXPECT ONLY ISOLATED
AFTERNOON ACTIVITY ALONG/WEST OF BLUE RIDGE...WITH MOST AREAS
REMAINING DRY MOST OF THE TIME.

FRI...AFTER SEVERAL DAYS OF TEMPERATURES IN THE U80S/L90S...THERE
COULD BE A LITTLE RELIEF BY FRIDAY...AS WEAK BACK DOOR COLD FRONT
NUDGES INTO THE AREA. CURRENT FRONTAL AND THUNDERSTORM TIMING OCCURS
EARLY ENOUGH THAT DAYTIME HIGHS MIGHT BE A FEW DEGREES LOWER THAN
PREVIOUS DAYS...GENERALLY IN M/U80S...THOUGH STILL ABOVE NORMAL.
HEAT AND HUMIDITY REMAIN IN PLACE AHEAD OF THE FRONT AND MID-LEVEL
TEMPS COOL SLIGHTLY...WHICH WILL LEAD TO AT LEAST LOW-END SHOWER AND
THUNDERSTORM CHANCES ACROSS THE ENTIRE AREA AS LAPSE RATES STEEPEN
EVER SO SLIGHTLY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
UPR LEVEL DISTURBANCE IN ADDITION TO A  WILL BRING THE CHANCE FOR
SCATTERED SHOWERS AND TSTMS FRI NIGHT INTO SAT... MAINLY WEST OF
THE BLUE RIDGE AND IN THE SOUTHERN PART OF OUR CWA. AFTER A
BACKDOOR COLD FRONT SLIPS DOWN THE MID-ATLANTIC COAST...HIGH
PRESS BUILDS IN ON SAT THROUGH TUE BRINGING DRIER CONDITIONS.
APPROACHING COLD FRONT MAY BRING SHOWERS AND TSTMS ON TUE AFTN.
TEMPS WILL BE NEAR NORMAL DURING THE WKND...BECOMING ABOVE NORMAL
MON AND TUE.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
ISOLATED SHOWERS FORMING ALONG BLUE RIDGE COULD PASS NEAR CHO THIS
AFTERNOON. ELSEWHERE SCT CU AROUND 5 KFT. MAINTAINED FORECAST
CONSISTENCY IN REGARDS TO FOG TONIGHT. CLOUD COVER IS THE MAIN
UNCERTAINTY AND POTENTIAL LIMITING FACTOR. HAVE NOT INCLUDED BR AT
IAD FOR NOW...BUT GROUND FOG IS A POSSIBILITY. TROUGH OF LOW
PRESSURE PASSES THROUGH REGION WEDNESDAY...BRINGING A LITTLE
BETTER PROB OF STORMS...ESPECIALLY IN THE AFTERNOON. CHO WILL BE
THE MAIN TARGET...WITH MUCH MORE UNCERTAINTY IN COVERAGE WITH NE
EXTENT (ESPECIALLY BALTIMORE AREA). ANY IMPACTS SHOULD BE SHORT-
LIVED. MAY BE SOME FOG AGAIN IN PRONE LOCATIONS WEDNESDAY NIGHT.
AFTER LIGHT/VRB WINDS THROUGH TONIGHT...A MORE NW COMPONENT SHOULD
BE OBTAINED WED.

VFR CONDITIONS EXPECTED THURSDAY UNDER HIGH PRESSURE. AFTERNOON AND
EVENING SHOWER/THUNDERSTORM CHANCES RETURN FRIDAY WITH BRIEF PERIODS
OF SUB-VFR POSSIBLE NEAR ANY ACTIVITY.

VFR CONDITIONS EXPECTED FRI NIGHT AND SAT. SUB VFR CONDITIONS
PSBL DUE TO SCATTERED SHOWERS AND TSTMS.

&&

.MARINE...
ONSHORE COMPONENT TO WINDS THIS AFTERNOON...PERHAPS BECOMING SW
TONIGHT. WINDS BECOME W TO NW WED. SPEEDS REMAIN UNDER 10 KT MOST
OF THE TIME THROUGH WED NIGHT. ISOLATED TO SCATTERED STORMS A
LITTLE BETTER POSSIBILITY ON WEDNESDAY...MORE SO OVER THE
SOUTHERN WATERS.

WINDS EXPECTED TO REMAIN SUB-SCA THURSDAY AND FRIDAY. THUNDERSTORM
CHANCES INCREASE ALONG THE WATERS FRIDAY AS FRONT MOVES INTO THE
REGION.

SUB-SCA CONDITIONS EXPECTED FOR FRI NIGHT INTO SAT. SOME SHOWERS
AND TSTMS PSBL OVER THE WATERS.

&&

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

&&

$$
SYNOPSIS...ADS
NEAR TERM...ADS
SHORT TERM...ADS/MSE
LONG TERM...IMR
AVIATION...ADS/IMR/MSE
MARINE...ADS/IMR/MSE


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