Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 011358
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
958 AM EDT MON SEP 1 2014

.SYNOPSIS...
A BERMUDA HIGH WILL PERSIST THROUGH TUESDAY. A TROUGH WILL
PERSIST OVER THE AREA THIS AFTERNOON. A WEAK COLD FRONT WILL CROSS
THE AREA TUESDAY NIGHT...FOLLOWED BY HIGH PRESSURE INTO THE
WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
12Z KIAD SOUNDING WAS JUICY...PW VALUE OVER 2 INCHES. WATER VAPOR
LOOP INDICATES SOME RELATIVELY DRIER AIR PUNCHING INTO THE
HIGHLANDS LIKELY TO EXPAND EAST TOWARD THE INTERSTATE 95 CORRIDOR
THROUGH THE AFTERNOON. THIS WOULD EXPLAIN WHY RUC/NAM/GFS FORECAST
SOUNDINGS AT VARIOUS POINTS SHOW THE PW VALUE DECREASING A BIT BY
AFTERNOON. BUT EVEN 1.75" ISN/T BAD FOR THIS TIME OF THE YEAR.

MUCH OF THE AREA WILL LIKELY BE DRY THROUGH THE REST OF THE
MORNING...SAVE FOR A FEW SHOWERS ACROSS LOWER SOUTHERN AND
NORTHEAST MD. A FEW SHOWERS MAY ALSO AFFECT THE HIGHLANDS BY
MIDDAY. AM UNCERTAIN ON COVERAGE OF CONVECTION BY THIS AFTERNOON.
SHORTWAVE RIDGING AND MID LEVEL DRYING MAY HELP TO INHIBIT
COVERAGE...BUT ONE WOULD THINK THAT LOW LEVEL
MOISTURE/INSTABILITY AND PRESENCE OF A SURFACE TROUGH/CONVERGENT
BOUNDARY SHOULD ALLOW FOR AT LEAST ISOLATED THUNDERSTORMS /MAYBE
LOW END SCATTERED/ TO FORM BY MID-AFTERNOON. POPS/WX REFLECT THIS.

GIVEN HIGH MOISTURE CONTENT...ANY STORMS THAT FORM MAY PRODUCE
HEAVY RAINFALL ALTHOUGH STORM MOTION SHOULD BE SUFFICIENT ENOUGH
TO MOVE CONVECTION AND THUS LIMIT FLASH FLOODING POTENTIAL.
INSTABILITY MAY ALSO SUPPORT SOME GUSTY WINDS BUT IF SHEAR REMAINS
RELATIVELY WEAK THIS SHOULD LIMIT DAMAGING WIND POTENTIAL AS WELL.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
WEAK SFC RIDGING CROSSES THE CENTRAL MID-ATLANTIC TONIGHT INTO
TUESDAY...MAKING FOR AN OVERNIGHT/MOST OF TUESDAY REPRIEVE FROM
THUNDERSTORMS. WITH THE BERMUDA HIGH IN PLACE...EXPECT TUESDAY TO
HAVE THE HIGHEST TEMPERATURE DAY SINCE JULY. MAX TEMPS LOW TO MID
90S ACROSS LOWER ELEVATIONS. TEMPERATURES MAY BE LOWER OUT WEST
WHERE ACTIVITY WILL FIRE FIRST AHEAD OF AN APPROACHING WEAK COLD
FRONT.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
BEHIND A SHARP AND POTENT UPPER TROUGH AXIS WILL BE LARGE ZONAL FLOW
PATTERN ABOVE THE NRN HALF OF THE CONUS DURING THE MIDDLE OF THE
CURRENT WEEK. THIS UPPER-LEVEL HIGHWAY OF FAST-MOVING FLOW WILL NOT
ONLY TAKE THE TUE TROUGH PASSAGE QUICKLY AWAY FROM THE AREA AND OFF
TOWARD NEW ENGLAND...BUT BRING ANOTHER TOWARD THE AREA JUST A COUPLE
OF DAYS LATER - ALL THE WAY FROM THE NRN ROCKIES. THE UPPER RIDGE
LAID OUT ACROSS THE SRN HALF OF THE CONUS HOWEVER...WILL KEEP THESE
LOW PRES SYSTEM PASSES FROM MAKING A RUN TOO FAR SOUTH. THE FRONTAL
PASSAGE OF THE TUE/EARLY WED SYSTEM AND THE LATE WEEK ONE WILL
LARGELY SKIM THE REGION W/ THE JUST THE RESIDUAL/LEFTOVER EFFECTS OF
THE MORE POTENT SYSTEM FURTHER TO THE NORTH.

EVEN W/ THE COLD FRONT EXPECTED TO MOVE ACROSS THE AREA LATE TUE W/
MORE SHOWER/TSTM ACTIVITY...THE UPPER DYNAMICS BEHIND THE STRENGTH
OF THE FRONT WILL TAKE OFF TO THE NE. THE LEFTOVER BOUNDARY WILL
STALL-OUT TO OUR SOUTH AND ALLOW FOR WEAK HIGH PRES TO BUILD IN
ACROSS THE MID-ATLC STATES WED INTO THU. ONLY A SLIGHT AIRMASS
CHANGE BEHIND THE FRONT WILL PREVENT TEMPS FROM REACHING THE HIGHER
LEVELS EXPECTED ON TUE - THAT OF L-M90S. INSTEAD...MUCH OF THE AREA
WILL TOP OUT IN THE M80S...W/ U80S DOTTING THE I-95 CORRIDOR AREA
AND EAST. SKIES WILL CLEAR OUT AND A LIGHT WNW WIND WILL DOWNSLOPE
AND HELP BUMP UP TEMPS A COUPLE MORE DEG.

WITH THE STALLED BOUNDARY TO OUR SOUTH TO CLOSE OUT THE WEEK...DAILY
DIURNAL SHOWERS/TSTMS WILL BE DEVELOPING ALONG IT - ACROSS THE
CAROLINAS AND POSSIBLY UP INTO CNTRL VA...BUT LIKELY JUST SHY OF THE
SRN PERIPHERY OF THE CWA. THE NEXT UPPER LEVEL DISTURBANCE WILL BE
THE FAST-MOVING SYSTEM COMING OUT OF THE NRN PLAINS AND OVER THE
GREAT LAKES REGION TO CLOSE OUT THE WEEK. THE SFC HIGH WILL ROLL OFF
THE COAST AND START UP AN ONSHORE FLOW AS THE COLD FRONT APPROACHES.
THIS WILL HELP TO START OUR COOL-DOWN FROM THE ABNORMALLY HOT/HUMID
CONDITIONS OF THE PAST FEW DAYS. PRECIP CHANCES WILL INCREASE W/ THE
FRONTAL PASSAGE ON FRI INTO SAT.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
PATCHY LOW CLOUDS SHOULD DISSIPATE BY 14Z AT THE HUBS.
OTHERWISE...MUCH OF THE TIME THROUGH MIDDAY SHOULD BE DRY WITH
JUST A PASSING SHOWER. CURRENT FORECAST CALLS FOR SCATTERED
COVERAGE OF THUNDERSTORMS BY 18-19Z...THUS THE VCTS. THIS MAY BE
TOO EARLY...AND AM SOMEWHAT UNCERTAIN ON HOW MUCH COVERAGE WILL
BE APPARENT THIS AFTERNOON AS WELL. WILL EVALUATE 12Z GUIDANCE AND
LATEST RUNS OF THE HRRR/WRF-ARW AND AMEND AS NECESSARY.

COLD FRONT APPROACHES TUESDAY WITH LEADING THUNDERSTORM ENTERING
FROM THE WEST LATE IN THE DAY. SKIES WILL CLEAR OUT ON WED...W/
WINDS SHIFTING TOWARD NWLY AND HIGH PRES BUILDING IN FROM THE
NORTH. THE HIGH WILL KEEP CONDITIONS QUIET INTO FRI...AS A COLD
FRONT APPROACHES FROM THE UPPER MIDWEST. THE FRONT IS EXPECTED TO
BRING MORE PRECIP FROM FRI INTO SAT...SAGGING JUST S OF THE AREA
FOR THE COMING WEEKEND.

&&

.MARINE...
MAIN CONCERN OVER THE WATERS WILL BE POTENTIAL FOR A FEW
THUNDERSTORMS LATE THIS AFTERNOON AND EVENING...WITH LOW VIS IN
HEAVY RAIN AND GUSTY WINDS/WIND SHIFTS. THUNDERSTORMS ALSO
POSSIBLE TUESDAY EVENING WITH A COLD FRONT.

HIGH PRESSURE WILL BUILD BEHIND A COLD FRONT LATE TUE EVE. THE FRONT
WILL DRIFT JUST SOUTH OF THE AREA...TOWARD THE CAROLINAS. THE SFC
HIGH WILL LARGELY KEEP WINDS LIGHT INTO THE LATTER HALF OF THE
WEEK...MOVING OFF THE COAST BY EARLY FRI - AHEAD OF ANOTHER COLD
FRONT. SCA CONDITIONS NOT ANTICIPATED FOR THE MED/LONG RANGES OF THE
FORECAST.

&&

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

&&

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






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