Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 301409 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1009 AM EDT THU APR 30 2015

.SYNOPSIS...
LOW PRESSURE WILL IMPACT THE AREA TODAY THROUGH TONIGHT BEFORE
MOVING OFFSHORE FRIDAY. HIGH PRESSURE WILL BUILD OVERHEAD DURING
THE WEEKEND BEFORE SHIFTING TO THE SOUTH EARLY NEXT WEEK. A COLD
FRONT MAY IMPACT THE AREA DURING THE MIDDLE PORTION OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
LARGE UPPER CUTOFF LOW OVER LAKE MICHIGAN WILL MOVE SLOWLY ACROSS
THE OHIO VALLEY EARLY TODAY AND ACROSS THE MID SOUTH TONIGHT.
ENERGY TRANSFER FROM THE UPPER LOW TO THE COAST WILL ALLOW A
SURFACE LOW TO GRADUALLY INTENSIFY OFF THE CAROLINA COAST. BOTH
SYSTEMS WILL BRING SOME IMPACT TO THE MIDDLE ATLANTIC REGION OVER
THE NEXT 24 HOURS.

THROUGH TODAY...SHOWERS WILL PERSIST MAINLY WEST OF THE BLUE RIDGE
FOR THE FIRST PART OF TODAY. HAVE INCREASED POPS TO CATEGORICAL
VALUES ESPECIALLY OVER THE HIGHLANDS. WILL CONTINUE HIGHER POPS
FOR THESE AREAS GIVEN UPSLOPE COMPONENT OVER THE HIGHER TERRAIN
ADDING CONVERGENCE AND PRECIP ENHANCEMENT. THREAT FOR ANY FLOODING
APPEARS MINIMAL BASED ON LOWER PWATS AND SOILS BEING ABLE TO
HANDLE RAINFALL.

COLD CORE DYNAMICS ASSOCIATED WITH THE UPPER LOW WILL POSE A
THREAT FOR SMALL HAIL WITHIN ANY THUNDERSTORM THAT DEVELOPS THIS
AFTERNOON AND EARLY EVENING. NAM BUFKIT SOUNDING PROFILE AT KIAD
SHOWS AN INVERTED-V SUBCLOUD LAYER WITH WBZ AOA 800MB AND SKINNY
CAPE ALOFT. IF ENOUGH SOLAR INSOLATION CAN BE REALIZED PRIOR TO
OVERCAST CONDITIONS...WILL SEE SMALL HAIL THREAT DEVELOP.
INSTABILITY IS MARGINAL AT BEST AND THUS SEVERE THREAT IS VERY
LOW.

OUR BEST CHANCE FOR RAIN IS TONIGHT. OVERALL RAIN SHOULD REMAIN
FAIRLY LIGHT...AND PWATS DO NOT GET ALL THAT HIGH...BUT UPSLOPE
FLOW AT H9/H8...NEAR THE SURFACE AT HIGHER ELEVATIONS...WILL AID
IN POTENTIALLY HEAVIER PRECIPITATION IN THESE FAVORED REGIONS. NOT
CONSIDERING A FLOOD WATCH AT THIS TIME...BUT LOCALIZED UPSLOPE
HEAVY RAIN IS POSSIBLE. OVERNIGHT LOW TEMPERATURES WILL DIP BACK
INTO THE 40S IN MOST LOCATIONS...EXCEPT 50S IN THE METRO CENTERS.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
FRIDAY...THE UPPER LOW PUSHES OFFSHORE... WITH WINDS BECOMING
UNIDIRECTIONALLY NORTH. THIS WILL LIMIT MOISTURE AND POPS WERE
TRENDED SIMILARLY...HIGHEST SOUTH AND LOWEST NORTH. TEMPS WILL BE
A BIT COOLER WITH HIGHS ONLY 55 TO 65. FRIDAY NIGHT LOOKS DRY. THE
HIGHLANDS COULD DROP INTO THE UPPER 30S AS WINDS DECOUPLE.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AN UPPER-LEVEL TROUGH WILL REMAIN OVERHEAD SATURDAY WHILE SURFACE
HIGH PRESSURE APPROACHES FROM THE WEST. MAX TEMPS WILL BE CLOSER
TO CLIMO DUE TO MORE SUNSHINE. HOWEVER...WITH THE COOLER AIR ALOFT
STILL IN PLACE...THE SUNSHINE WILL LEAD TO LIMITED INSTABILITY
DURING THE AFTERNOON AND EVENING HOURS. THIS WILL CAUSE A BKN CU
DECK TO DEVELOP AND THERE MAY BE ENOUGH INSTABILITY FOR A FEW
SHOWERS ACROSS THE AREA. MOISTURE WILL BE LIMITED AND FORCING
WILL BE WEAK SO MOST OF THE TIME WILL BE DRY AND COVERAGE OF
SHOWERS WOULD BE SCATTERED AT BEST.

THE HIGH WILL BUILD OVERHEAD SATURDAY NIGHT. LIGHT WINDS AND
CLEARING SKIES MAY RESULT IN CHILLY CONDITIONS SATURDAY NIGHT WITH
MIN TEMPS IN THE 40S ACROSS MANY LOCATIONS AND EVEN 30S IN
PORTIONS OF THE POTOMAC HIGHLANDS. MIN TEMPS WILL HOLD IN THE 50S
FOR DOWNTOWN WASHINGTON AND BALTIMORE.

THE UPPER-LEVEL TROUGH WILL BEGIN TO SLIDE TO THE EAST SUNDAY AND
HIGH PRESSURE OVERHEAD WILL BEGIN TO SLIDE TO THE SOUTH. A RETURN
FLOW AROUND THE HIGH ALONG WITH SUNSHINE AND RISING HEIGHTS WILL
ALLOW FOR WARMER CONDITIONS DURING THE AFTERNOON. THE WARMING
TREND WILL CONTINUE FOR MONDAY AND TUESDAY DUE TO A SOUTHWEST FLOW
AROUND HIGH PRESSURE CENTERED TO OUR SOUTH. MAX TEMPS IN THE 80S
ARE LIKELY FOR MANY LOCATIONS. A COLD FRONT WILL DROP SOUTH
TOWARD THE REGION LATE TUESDAY AND IT WILL STALL OUT NEARBY FOR
THE MIDDLE PORTION OF NEXT WEEK. UNSETTLED CONDITIONS ARE POSSIBLE
DURING THIS TIME.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
A LOT OF THE MOISTURE TODAY IS ALOFT /5 KFT AND HIGHER/ SO EVEN
THOUGH SHRA AND A FEW TSRA ARE EXPECTED...LOW CIGS ARE NOT
PARTICULARLY LIKELY DURING THE DAY TODAY. LOW LEVEL MOISTURE DOES
INCREASE TONIGHT...AND THUS CIGS SHOULD LOWER TO AT LEAST MVFR AFTER
MIDNIGHT. IFR CIGS ARE POSSIBLE AROUND SUNRISE BUT DID NOT INCLUDE
THEM IN THE TAF YET. VSBY RESTRICTIONS IN SHRA SHOULD BE MVFR AT
WORST. CONDITIONS VFR BY SHORTLY AFTER DAYBREAK FRIDAY AS LOW LEVELS
DRY. WINDS WILL GENERALLY BE LESS THAN 10 KT TODAY...INCREASING TO
10 TO 15 KT THROUGH THE REST OF THE TAF PERIOD...BECOMING LIGHT
FRIDAY NIGHT.

VFR CONDITIONS ARE EXPECTED MOST OF THE TIME SATURDAY THROUGH
MONDAY. A FEW SHOWERS ARE POSSIBLE SATURDAY AFTERNOON AND
EVENING...BUT MOST OF THE TIME WILL BE DRY.

&&

.MARINE...
SCA IN EFFECT STARTING THIS EVENING AS LOW PRESSURE STRENGTHENS
OFFSHORE. GUSTS TO 20 KTS LOOK LIKELY TONIGHT INTO EARLY FRIDAY
BEFORE WINDS GRADUALLY DECREASE. SCA WAS EXTENDED TO NOON FRIDAY
IN THE UPPER BAY/UPPER POTOMAC...AND THROUGH 6 PM FRIDAY
ELSEWHERE. THE SOUTHERN BAY COULD CONTINUE TO GUST FRIDAY
EVENING...SO THE SCA MAY HAVE TO BE FURTHER EXTENDED BY FUTURE
SHIFTS.

HIGH PRESSURE WILL BUILD TOWARD THE WATERS SATURDAY BEFORE
SETTLING OVERHEAD SATURDAY NIGHT. A NORTHERLY FLOW SATURDAY WILL
BECOME LIGHT AND VARIABLE SATURDAY NIGHT. HIGH PRESSURE WILL BUILD
TO THE SOUTH FOR SUNDAY THROUGH EARLY NEXT WEEK. SOUTHERLY WINDS
ARE EXPECTED DURING THIS TIME. WIND GUSTS MAY APPROACH SCA
CRITERIA FOR PORTIONS OF THE WATERS MONDAY NIGHT AND TUESDAY.

&&

.TIDES/COASTAL FLOODING...
A NORTHEAST WIND WILL INCREASE TONIGHT...THIS WILL KEEP WATER
LEVELS ELEVATED BUT THE NORTHERLY COMPONENT WILL LIKELY KEEP
ANOMALIES LOW ENOUGH SO WATER LEVELS REMAIN BELOW MINOR FLOODING
THRESHOLDS WITH THE HIGH TIDE CYCLE LATE TONIGHT INTO FRIDAY
MORNING.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO NOON EDT FRIDAY
     FOR ANZ530-531-535-538-539.
     SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 6 PM EDT FRIDAY
     FOR ANZ532>534-536-537-540>543.

&&

$$
SYNOPSIS...KRW
NEAR TERM...KRW
SHORT TERM...JCE
LONG TERM...BJL
AVIATION...BJL/KRW
MARINE...BJL/KRW
TIDES/COASTAL FLOODING...JCE/KRW



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