Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 311851
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
251 PM EDT FRI JUL 31 2015

.SYNOPSIS...
A WEAKENING COLD FRONT WILL CROSS THE REGION SATURDAY. HIGH
PRESSURE WILL REBUILD ACROSS THE REGION SUNDAY. ANOTHER COLD FRONT
WILL APPROACH FROM THE NORTHWEST MONDAY AND THEN STALL IN THE
REGION TUESDAY. THE STALLED FRONT WILL LINGER IN THE AREA THROUGH
THURSDAY.

&&

.NEAR TERM /THROUGH SATURDAY/...
MUCH DRIER AIR MASS NOW IN PLACE WITH DEW POINTS DOWN INTO THE
UPPER 50S AND LOWER 60S. HIGH PRESSURE REMAINS CENTERED WELL TO
THE WEST HOWEVER...WITH A FAIRLY FAST WEST TO NORTHWEST FLOW ALOFT
OVER OUR REGION. WE SHOULD STAY MOSTLY CLEAR TONIGHT...SO
RADIATIONAL COOLING WILL PROBABLY RESULT IN SOME PATCHY FOG IN THE
MOST SHELTERED VALLEYS OF WEST-CENTRAL VIRGINIA AS TEMPS COOL TO
THE DEW POINT. OTHERWISE...PLEASANT ACROSS THE REGION THROUGH
TONIGHT.

BROAD SHORTWAVE CROSSES THE REGION ON SATURDAY ACCOMPANIED BY A
WEAKENING COLD FRONT. THIS FRONT IS BARELY IDENTIFIABLE...AND WILL
HAVE LITTLE EFFECT ON OUR WEATHER. MOISTURE WILL BE LIMITED...AND
AN INVERSION WILL CAP THE ATMOSPHERE ALOFT...WHILE THE WEAKNESS
OF THE BOUNDARY SHOULD SEAL THE DEAL FOR A DRY DAY DESPITE A FEW
PIECES OF GUIDANCE TO THE CONTRARY. WINDS MAY PICK UP A LITTLE BUT
NOTHING UNUSUAL. HIGHS WILL AGAIN BE NEAR TO SLIGHTLY ABOVE NORMAL
FOR EARLY AUGUST.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
SATURDAY NIGHT INTO SUNDAY THE FLOW ALOFT RELAXES A BIT IN THE
WAKE OF SATURDAY`S TROUGH. AT THE SURFACE HIGH PRESSURE WILL
FINALLY MOVE OVERHEAD LATER SUNDAY AND SUNDAY NIGHT. WHILE THE AIR
MASS WILL REMAIN FAIRLY DRY...ANOTHER NIGHT OF DECENT RADIATIONAL
COOLING SHOULD RESULT IN MORE PATCHY FOG ACROSS INLAND AREAS ON
SATURDAY NIGHT...POSSIBLY EXTENDING AS FAR EAST AS THE OUTSKIRTS
OF THE METRO. LOWS SATURDAY NIGHT WILL AGAIN BE COOL...WITH
ANOTHER FAIRLY WARM/LOW END HOT DAY EXPECTED SUNDAY UNDER THE
HIGH. NO PRECIPITATION IS EXPECTED.

A 500 MB SHORTWAVE WILL PIVOT ACROSS THE REGION ON MONDAY. AT THE
SAME TIME...A LEESIDE PRESSURE TROUGH WILL SHARPEN AS A COLD FRONT
APPROACHES FROM THE OHIO VALLEY. NORMALLY THIS SETUP WOULD YIELD
CONVECTION...BUT MONDAY WILL ALSO BE THE FIRST DAY OF APPRECIABLE
LOW-LEVEL MOISTURE RETURN AS HIGH PRESSURE SHIFTS OFFSHORE. WITH
THE AMOUNT OF MOISTURE IN QUESTION...INSTABILITY MAY REMAIN LOW
ENOUGH TO PRECLUDE MORE WIDESPREAD SHOWERS AND THUNDERSTORMS. FOR
NOW KEPT ISOLATED TO WIDELY-SCATTERED POPS MAINLY OVER THE
NORTHWESTERN HALF OF THE CWA COINCIDENT WITH SUPPLEMENTAL TERRAIN
FORCING.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
UPPER-LEVEL JET STRENGTHENS TUESDAY AS THE FRONT MOVES INTO THE
AREA AND STALLS. ANOTHER LEE SIDE TROUGH DEVELOPS TUESDAY
AFTERNOON...BUT AGAIN INSTABILITY IS IN QUESTION DEPENDING ON THE
POSITIONING OF THE FRONT AND CLOUD COVER. MOST GUIDANCE IS NOT
HINTING AT MUCH IN THE WAY OF SYNOPTIC LIFT EITHER ON TUESDAY SO
KEPT POPS VERY LOW /BUT STILL NON-ZERO/. TEMPERATURES WILL BE
RUNNING A FEW DEGREES ABOVE NORMAL.

MEAN TROUGHING WILL LINGER OVER THE EASTERN CONUS THROUGH THE
MIDDLE AND LATTER PORTION OF NEXT WEEK. A BOUNDARY WILL REMAIN
STALLED OVER THE AREA...AND GFS/ECMWF ARE BOTH HINTING AT A WAVE
OF LOW PRESSURE RIDING ALONG THE FRONT WEDNESDAY NIGHT-THURSDAY
WHICH WOULD ENHANCE SHOWER/THUNDERSTORM CHANCES...BUT THERE IS
STILL PLENTY OF ENSEMBLE SPREAD IN TIMING/PLACEMENT. IF THE WAVE
PASSES JUST SOUTH OF THE AREA AND/OR OVERNIGHT...SHOWERS WOULD
INCREASE BUT THUNDERSTORM CHANCES WOULD REMAIN LOW. IF THE LOW
PASSES TO THE NORTH AND DURING THE AFTERNOON...THUNDERSTORM
CHANCES WOULD BE MUCH HIGHER.

HIGH PRESSURE WILL TRY TO MAKE A COME BACK LATE NEXT WEEK
BRINGING DRIER AND SEASONABLY WARM CONDITIONS.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
VFR CIGS AND VIS OVERALL THROUGH SATURDAY NIGHT. VERY SLIGHT
CHANCE OF A SHOWER AS A VERY WEAK COLD FRONT PUSHES THROUGH
SATURDAY...BUT RISK IS BELOW 15 PERCENT. ALSO POTENTIAL FOR SOME
PATCHY FOG WITH IFR CIGS/VIS LATER TONIGHT...AND AGAIN LATER
SATURDAY NIGHT...PRIMARILY AT INLAND TERMINALS CHO AND MRB. RIGHT
NOW ODDS FAVOR SATURDAY NIGHT OVER TONIGHT SO HAVE KEPT OUT OF
TAFS. WINDS MAY GUST UP TO 20 KNOTS SATURDAY FROM THE WEST.

VFR EXPECTED SUN-WED. ANY CONVECTION SHOULD REMAIN VERY ISOLATED
AND LIKELY CONFINED TO THE AFT/EVE HRS DURING THIS TIME. NLY FLOW
AOB 10 KT BECOMES SLY AROUND 10 KT SUN...WITH GENERAL SWLY FLOW
AROUND 10 KT MON-WED. WIND DIRECTION BECOMES SOMEWHAT UNCERTAIN
TUE-WED AND DEPENDS ON POSITIONING OF THE FRONT.

&&

.MARINE...
DRY CONDITIONS EXPECTED THROUGH SATURDAY NIGHT...THOUGH THERE IS
THE SLIGHT CHANCE OF A SHOWER SATURDAY AS A VERY WEAK COLD FRONT
PASSES. OF MORE PRESSING CONCERN IS POTENTIAL FOR WINDS TO REACH
LOW END SCA SATURDAY AFTERNOON. IT LOOKS VERY BORDERLINE GIVEN
THAT HIGHS ARE EXPECTED TO BE ABOVE THE WATER TEMPS WHICH SHOULD
CREATE A LITTLE STABILITY DURING THE DAYLIGHT HOURS...SO HAVE NOT
PULLED THE TRIGGER. THE UNIDIRECTIONAL FLOW MAY OVERWHELM THE
LIMITED SURFACE STABILITY HOWEVER.

HIGH PRESSURE PASSES OVER THE WATERS SUNDAY WITH SUB-SCA
CONDITIONS EXPECTED. PRESSURE GRADIENT TIGHTENS A BIT AS A FRONT
APPROACHES THE AREA AND STALLS MON-TUE...AND COULD RESULT IN SCA
GUSTS DURING THIS TIME.

&&

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

&&

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



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