Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 020800
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
400 AM EDT THU JUL 2 2015

.SYNOPSIS...
A STATIONARY FRONT WILL REMAIN OVER CENTRAL VIRGINIA AND SOUTHERN
MARYLAND THROUGH TODAY...AND LINGER OVER THE AREA THROUGH THE
WEEKEND. WITH SEVERAL WAVES OF LOW PRESSURE WILL MOVE EAST ALONG
THE FRONT AS AN ACTIVE PATTERN CONTINUES. HIGH PRESSURE WILL
RETURN FOR THE FIRST HALF OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
LATEST SURFACE ANALYSIS SHOWS A COLD FRONT STRETCHING ACROSS
CENTRAL/SOUTHERN VIRGINIA WITH HIGH PRESSURE OVER THE GREAT LAKES
AND A WAVE OF LOW PRESSURE IN THE CENTRAL PLAINS. DEW POINTS HAVE
LOWERED A BIT AS THE CANADIAN AIR HAS GRADUALLY PUSHED INTO THE
REGION. OF NOTE IS THAT MUCH OF THE REDUCED VISIBILITY (REDUCED AS
IN BELOW 10 MILES) BEING REPORTED ACROSS THE REGION IS PROBABLY
DUE TO SOME CANADIAN WILDFIRE SMOKE WHICH HAS WORKED ITS WAY
SOUTHWARD BEHIND THE FRONT.

MOST GUIDANCE SHOWS THE FRONT STALLING OUT IN SOUTHERN VIRGINIA
TODAY. ONE OR MORE WAVES OF WEAK LOW PRESSURE ARE ALSO PROGGED TO
MOVE EASTWARD ALONG THE BOUNDARY LATER TODAY AND TONIGHT AS A
COUPLE OF WEAK VORTICITY MAXIMA MOVE EAST ACROSS THE AREA IN THE
FAST FLOW ALOFT. THE EXACT AMOUNT OF NORTHWARD MOTION WITH THE
PRECIPITATION ASSOCIATED WITH EACH WAVE IS IN QUESTION...WITH THE
MORE MESO-SCALE NAM AND RGEM KEEPING MOST OF THE PRECIPITATION
SOUTH OF DC/BALTIMORE METRO CLOSER TO THE STALLED FRONTAL
BOUNDARY THROUGH TONIGHT...WHILE THE GFS AND ECMWF ARE MORE
GENEROUS AND BRING SOME SHOWERS INTO THE METRO. GIVEN
UNCERTAINTY...KEPT POPS IN THE METRO AREAS BELOW 50 PERCENT. THERE
IS SOME INSTABILITY...SO A FEW THUNDERSTORMS CAN`T BE RULED OUT
ESPECIALLY THIS AFTERNOON AND EVENING...BUT WITH OUR REGION BEING
ON THE NORTH SIDE OF THE FRONT THINK THEY SHOULD BE PRETTY
ISOLATED WITH MOST ACTIVITY BEING OF THE NON- THUNDERY TYPE. HIGHS
WILL BE SEVERAL DEGREES LOWER THAN YESTERDAY AND DEW POINTS WILL
ALSO BE LOWER...BUT CLOUDS SHOULD BE MORE COMMON. LOWS TONIGHT
WILL GENERALLY BE SIMILAR TO THIS MORNING`S.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
RIGHT NOW...THE BEST CHANCE OF PRECIPITAITON ACROSS THE AREA WOULD
APPEAR TO BE FRIDAY...AS A DECENT SHORTWAVE AND VORT MAX MOVES
ACROSS THE AREA SUPPORTING A MORE NOTABLE LOW PRESSURE WAVE AT
THE SURFACE ALONG THE STALLED FRONT. UNCERTAINTY REMAINS AS TO HOW
LONG IT LINGERS FRIDAY NIGHT...WITH SOME GUIDANCE ALLOWING IT TO
PULL AWAY FAST ENOUGH SO THAT THE REGION DRIES OUT...WHILE OTHER
MODELS KEEP THE SHOWERS OVER THE AREA. FOR NOW KEPT HIGHEST POPS
DURING THE DAY...BUT THE POSSIBILITY OF DECENT PRECIPITATION
DURING FRIDAY NIGHT IS DEFINITELY OF NOTE AND IF THERE IS BETTER
CONSENSUS IN THE FUTURE...POPS MAY CERTAINLY END UP SIGNIFICANTLY
HIGHER. TEMPERATURES WILL BE COOL FRIDAY WITH MANY AREAS FAILING
TO REACH 80...WHILE LOWS WILL REMAIN SIMILAR TO RECENT DAYS.

FOURTH OF JULY...STATIONARY FRONT LINGERING OVER THE AREA (WITH
SHORTWAVES RIDING ALONG IT) MAKES FOR A COMPLICATED FORECAST.
CONSENSUS AMONG 00Z GFS/ECMWF/NAM IS FOR A MORNING LOW TO CROSS
SRN MD/WATERS WITH A SECONDARY SHORTWAVE TO CROSS THE POTOMAC
HIGHLANDS LATE IN THE AFTERNOON. BOTH OF THESE FEATURES WILL SHIFT
THE FRONTAL SYSTEM...TO AN UNCERTAIN EXTENT. FELT THE LIKELY POPS
FOR THE SRN HALF OF THE CWA WAS A BIT HIGH...SO WENT CHANCE MOST
PLACES IN THE AFTERNOON. WITH SHORTWAVE ENTERING THE WEST IN THE
PEAK HEATING...WENT LIKELIES FOR THE POTOMAC/ALLEGHENY HIGHLANDS.
MAX TEMPS LIMITED BY STRATO-CU AND ANY PRECIP...GENERALLY LOW 80S
(WITH DEWPOINTS IN THE MID 60S...EXPECT A BIT OF A HEAT INDEX TO
THE MID 80S).

SATURDAY NIGHT...KEY FOR EVENING POP IS PROGRESSION OF WEAK SHORT
WAVE FROM THE CENTRAL APPALACHIANS AND REMAINING INSTABILITY. THOSE
DETAILS WILL BECOME MORE APPARENT WITH FUTURE MODEL RUNS...BUT
CURRENT BEST GUESS IS TO HAVE SCATTERED THUNDERSTORM ACTIVITY
CONTINUE.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
FRONTAL BOUNDARY SOUTH OF THE AREA DRIFTS FARTHER SOUTH SUNDAY
AND MONDAY AS UPR RIDGE BUILDS EAST OVER THE MIDWEST. ANY ISOLATED
TO POSSIBLY SCATTERED THUNDERSTORMS BOTH DAY LOOK TO BE DIURNALLY
DRIVEN.

QUIET WX TUES UNDER HIGH PRESSURE AND NEAR NORMAL TEMPS.

NEXT COLD FRONT APPROACHES REGION FROM THE MIDWEST WEDNESDAY AND
SLOWS WITH MORE ACTIVE WEATHER INTO LATE NEXT WEEK.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
FAIRLY LIGHT WINDS FROM THE NORTH THIS MORNING SHIFTING EASTERLY
BY TONIGHT. VFR CIGS AND VIS OUTSIDE OF ANY SHOWERS...POSSIBLY
MVFR IN SHOWERS OR EVEN VERY BRIEF IFR IN A HEAVIER SHOWER OR
THUNDERSTORM...BUT THESE SHOULD BE ISOLATED. NOTE THAT SOME
DIFFUSE WILDFIRE SMOKE FROM CANADA IS LIKELY TO BE THE PRIMARY
CAUSE OF THE SUB-10 MILE VISIBILITY REPORTS WE ARE SEEING AT MANY
TERMINALS THIS MORNING.

LOW PRESSURE MAY BRING SOME STEADIER RAIN TO THE REGION BY
FRIDAY POSSIBLY INTO FRIDAY NIGHT...WITH POTENTIAL FOR A MORE
SUSTAINED PERIOD OF MVFR OR EVEN IFR CIGS/VIS. TIMING AND
NORTHWARD EXTENT OF THIS IS STILL IN QUESTION AND SO CONFIDENCE IS
NOT HIGH.

STATIONARY FRONT LINGERS JUST SOUTH OF DC METROS
SATURDAY...BEFORE DRIFTING FARTHER SOUTH SUNDAY AND MONDAY.
SCATTERED THUNDERSTORMS THROUGH SATURDAY INTO THE EVENING ACROSS
THE TERMINALS. MORNING NELY FLOW 10 TO 15 KT AS LOW PASSES SRN MD.
DIURNALLY ISOLATED SUN/MON. QUIET WX TUES.

&&

.MARINE...
WINDS SHOULD STAY BELOW SCA LEVELS TODAY...WITH NORTHERLY WINDS
BELOW 10 KNOTS GRADUALLY SHIFTING TO EASTERLY. A FEW HEAVIER
SHOWERS OR EVEN AN ISOLATED THUNDERSTORM ARE POSSIBLE
TODAY...WHICH COULD PRODUCE GUSTIER WINDS...BUT THINK THESE SHOULD
BE UNCOMMON.

WINDS MIGHT INCREASE TO SCA LEVELS LATER FRIDAY AND FRIDAY NIGHT
AS A LOW PRESSURE WAVE PASSES BY TO THE SOUTH AND SOUTHEAST WITH
MORE WIDESPREAD RAIN SHOWERS. CONFIDENCE IS NOT HIGH SO DID NOT
ISSUE AN SCA JUST YET...BUT IT MAY BE NEEDED.

WILL NEED TO WATCH A WEAK LOW PASS SRN MD SATURDAY MORNING FOR
NELY GUSTS AROUND 20 KT. SCATTERED THUNDERSTORMS POSSIBLE ALL
DAY/EVENING. LIGHT ONSHORE FLOW THEN SUNDAY AND MONDAY AS FRONT
DIPS FARTHER SOUTH OF THE AREA. QUIET TUESDAY.

&&

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

&&

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



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