Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 161754
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
154 PM EDT THU APR 16 2015

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST THROUGH TONIGHT.
A WEAK COLD FRONT WILL PASS THROUGH THE REGION FRIDAY AND HIGH
PRESSURE WILL RETURN FOR SATURDAY. THE HIGH WILL MOVE OFF THE
COAST SUNDAY AND A WARM FRONT WILL MOVE INTO THE AREA SUNDAY NIGHT
INTO MONDAY. A COLD FRONT WILL PASS THROUGH LATE MONDAY INTO
MONDAY NIGHT BEFORE HIGH PRESSURE RETURNS FOR THE MIDDLE PORTION
OF NEXT WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
ANALYSIS THIS AFTERNOON SHOWS HIGH PRESSURE ALONG THE NEW ENGLAND
COAST AND A SURFACE RIDGE AXIS EXTENDING FROM THIS HIGH INTO THE
MID-ATLANTIC. AN UPPER-LEVEL RIDGE IS ALSO LOCATED ACROSS NEW
ENGLAND SOUTH TOWARD THE MID-ATLANTIC COAST. SURFACE LOW PRESSURE
REMAINS OFF THE SOUTHEAST COAST AND AN UPPER-LEVEL DISTURBANCE IS
MOVING THROUGH THE OHIO VALLEY.

THE RETURN FLOW AROUND THE HIGH HAS COMBINED WITH THE UPPER-LEVEL
DISTURBANCE TO BRING PLENTY OF CLOUDS AND EVEN SOME SHOWERS TO
CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS. HOWEVER...THESE
CLOUDS HAVE BEEN DISSIPATING AS THEY RUN INTO THE RIDGE AXIS
TOWARD THE METROPOLITAN AREAS NORTH AND EAST. THE UPPER-LEVEL
RIDGE WILL CONTINUE TO MOVE OFF TO OUR EAST THROUGH THIS EVENING
AND THE SURFACE HIGH WILL ALSO SHIFT OFF THE NEW ENGLAND COAST.
THIS WILL CAUSE HIGH AND MID-LEVEL CLOUDS TO SHIFT EAST ACROSS THE
REST OF THE AREA. HOWEVER...PRECIPITATION WILL LIKELY REMAIN
ACROSS CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS...WHERE
MOISTURE IS DEEPER. HAVE LEFT THE FORECAST DRY FOR THE REST OF THE
AREA THIS AFTERNOON AND EVENING...BUT A FEW SPRINKLES CANNOT BE
RULED OUT AS THE UPPER-LEVEL DISTURBANCE SWINGS THROUGH. THERE IS
A TIGHT GRADIENT IN TEMPERATURES THIS AFTERNOON DUE CLOUDS AND
PRECIP VS. SUNSHINE. MAX TEMPS IN THE LOWER TO MIDDLE 70S ARE
EXPECTED ACROSS THE METROPOLITAN AREAS INTO NORTHERN
MARYLAND...BUT MAX TEMPS IN THE 50S ARE EXPECTED ACROSS THE
CENTRAL SHENANDOAH VALLEY INTO THE POTOMAC HIGHLANDS WHERE MORE
CLOUDS AND PRECIP ARE.

THE UPPER-LEVEL DISTURBANCE WILL MOVE OFF TO OUR EAST LATER THIS
EVENING...BUT A SOUTHERLY FLOW WILL CONTINUE TO INCREASE MOISTURE
ACROSS OUR AREA...RESULTING IN PLENTY OF CLOUDS. MOST LOCATIONS
MAY END UP DRY DUE TO A LACK OF FORCING...BUT THERE MAY BE A FEW
SHOWERS ACROSS CENTRAL VIRGINIA INTO THE ALLEGHENY AND POTOMAC
HIGHLANDS WHERE MOISTURE IS DEEPEST.

A COLD FRONT WILL APPROACH FROM THE WEST LATE TONIGHT. WITH PLENTY
OF MOISTURE IN PLACE THERE WILL BE SOME SHOWERS THAT BREAK OUT
AHEAD OF THE FRONT...ESPECIALLY ACROSS NORTHERN AND WESTERN
PORTIONS OF THE CWA CLOSER TO THE BOUNDARY. LIFT WITH THIS SYSTEM
WILL BE WEAK SO PRECIPITATION AMOUNTS WILL BE LIGHT. MILD
CONDITIONS ARE EXPECTED AHEAD OF THE FRONT. LEANED TOWARD THE
WARMER GUIDANCE DUE TO THE SOUTHERLY FLOW AND INCREASED CLOUD
COVER.

THE COLD FRONT WILL MOVE INTO THE REGION FRIDAY. THE TEMPERATURE
GRADIENT WILL BE WEAK ALONG THE FRONT...SO WARM CONDITIONS ARE
EXPECTED EVERYWHERE. LEANED TOWARD THE WARMER GUIDANCE...WITH THE
THINKING THAT SOME SUNSHINE WILL BREAK OUT AS DRIER AIR ALOFT
CLEARS OUT ANY HIGH AND MID-LEVEL CLOUDS LEAVING JUST A SCT TO BKN
CU DECK. MAX TEMPS WILL RANGE FROM THE 60S IN THE MOUNTAINS TO THE
MID AND UPPER 70S NEAR WASHINGTON AND BALTIMORE INTO CENTRAL
VIRGINIA. THE WARM AND RELATIVELY MOIST CONDITIONS WILL CAUSE
SOME INSTABILITY TO DEVELOP. THIS MAY BE ENOUGH FOR A FEW SHOWERS
AND POSSIBLY EVEN A THUNDERSTORM...ESPECIALLY LATER IN THE
AFTERNOON EAST OF THE BOUNDARY FOR LOCATIONS NEAR AND EAST OF THE
BLUE RIDGE MOUNTAINS. THE THREAT FOR SEVERE WEATHER IS LOW DUE TO
LIMITED INSTABILITY...WEAK SHEAR PROFILES AND A LACK OF A
SIGNIFICANT LIFTING MECHANISM SINCE FORCING ON THE FRONT WILL BE
WEAK.


&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
THE FRONT WILL MOVE OFF TO THE EAST FRIDAY EVENING. ANY LEFTOVER
SHOWERS FRIDAY EVENING NEAR AND EAST OF INTERSTATE 95 WILL
DISSIPATE OVERNIGHT AS DRIER AIR MOVES IN FROM THE NORTHWEST.
LEANED TOWARD THE WARMER GUIDANCE DUE TO A NORTHWEST WIND
INCREASING MIXING BEHIND THE FRONT...PREVENTING RADIATIONAL
COOLING.

HIGH PRESSURE WILL CONTINUE TO BUILD OVERHEAD SATURDAY THROUGH
SATURDAY NIGHT. DRY AND SEASONABLE CONDITIONS ARE EXPECTED.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
A LARGE AND SLOW-MOVING UPPER-LEVEL TROUGH WILL APPROACH THE
REGION FROM THE UPPER MIDWEST DURING THE SECOND HALF OF THE
WEEKEND. RAIN CHANCES WILL INCREASE FROM SOUTHWEST TO NORTHEAST
AHEAD OF A WARM FRONT DURING THE DAY SUNDAY. AN INCREASING LOW-
LEVEL JET WILL USHER PLENTIFUL MOISTURE INTO THE REGION...IN
TANDEM WITH UPPER-LEVEL DIVERGENCE FROM THE RIGHT ENTRANCE REGION
OF AN 250 MB JET. THIS SHOULD SET THE STAGE FOR A WIDESPREAD
SOAKING RAIN SUNDAY NIGHT...SOME OF WHICH MAY BE HEAVY. NOT ENOUGH
CONFIDENCE AT THIS TIME TO INCLUDE ANY FLOODING MENTION IN THE HWO
BUT AT LEAST SPOTTY NUISANCE FLOODING COULD BE POSSIBLE DURING
THIS TIME.

PARTS OF THE AREA MAY WARM SECTOR MONDAY...BUT THAT DEPENDS ON HOW
FAR NORTH THE WARM FRONT CAN GET GIVEN RAIN-COOLED AIR AND CLOUD
DEBRIS. AT LEAST ISOLATED ELEVATED THUNDER IS POSSIBLE LATE SUNDAY
NIGHT INTO MONDAY EVENING THOUGH.

RAIN CHANCES SLOWLY DIMINISH AS A COLD FRONT/TROUGH AXIS PIVOT
THROUGH THE AREA LATER MONDAY NIGHT. HIGH PRESSURE BRIEFLY RETURNS
LATE TUESDAY INTO WEDNESDAY...BEFORE ANOTHER SYSTEM APPROACHES FROM
THE WEST BY LATE NEXT WEEK.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
VFR CONDITIONS ARE EXPECTED THROUGH THIS EVENING. A FEW SHOWERS
MAY IMPACT KCHO DURING THIS TIME. HIGH AND MID-LEVEL CLOUDS WILL
INCREASE ELSEWHERE. SOUTH TO SOUTHEAST WINDS WILL GUST AROUND 15
TO 20 KNOTS THIS AFTERNOON BEFORE DIMINISHING TOWARD SUNSET.

A FEW SHOWERS ARE POSSIBLE LATE TONIGHT INTO FRIDAY
MORNING...ESPECIALLY ACROSS THE NORTHERN TERMINALS. CIGS/VSBYS MAY
APPROACH MVFR LEVELS AT THIS TIME. THE BEST CHANCE FOR MVFR LEVELS
WILL BE AT KCHO DUE TO DEEPER MOISTURE. A COLD FRONT WILL PASS
THROUGH THE TERMINALS LATER FRIDAY INTO FRIDAY EVENING. A FEW
SHOWERS AND PERHAPS A THUNDERSTORM ARE POSSIBLE. VFR CONDITIONS
ARE EXPECTED BEHIND THE FRONT FRIDAY NIGHT.

VFR W/ NLY FLOW 10 KT SAT-SAT NIGHT. FLOW BECOMES ELY 10-
15 KT SUN-SUN NIGHT W/ LWR CIGS/RA LEADING TO SUB-VFR. FLOW BECOMES
SLY INTO MON AND INCREASES 10-20 KT. SUB-VFR CONDS MAY BECOME MORE
SCTD DURING THIS TIME.

&&

.MARINE...
HIGH PRESSURE WILL CONTINUE TO MOVE OFF THE COAST TODAY. A DEEPER
MIXING LAYER HAS CAUSED WINDS TO INCREASE AWAY FROM THE WATERS
THIS AFTERNOON. HOWEVER...THE MIXING LAYER IS NOT AS DEEP OVERHEAD
DUE TO THE RELATIVELY COOLER WATERS. THE MIXING LAYER MAY INCREASE
SOME LATE THIS AFTERNOON BEFORE WINDS DECREASE THIS EVENING. WILL
CONTINUE WITH THE SMALL CRAFT ADVISORY FOR THIS REASON...BUT
CONFIDENCE IS HIGHER ACROSS THE EDGES OF THE WATERS WHERE TEMPS
ARE BIT WARMER.

SOUTHERLY WINDS WILL CONTINUE TONIGHT...BUT THE GRADIENT WILL BE
WEAK ENOUGH FOR SUBSCA CONDITIONS. A COLD FRONT WILL PASS THROUGH
THE WATERS LATE FRIDAY INTO FRIDAY EVENING. SOUTH TO SOUTHWEST
WINDS AHEAD OF THE FRONT WILL SHIFT TO THE NORTHWEST BEHIND THE
FRONT. WINDS SHOULD REMAIN BELOW SCA CRITERIA. THERE MAY BE A FEW
SHOWERS AND EVEN A COUPLE THUNDERSTORMS AHEAD OF THE FRONT FRIDAY
AFTERNOON. SHOULD THUNDERSTORMS DEVELOP...THEY WILL BE CAPABLE OF
PRODUCING LOCALLY GUSTY WINDS.

MARGINAL SCA GUSTS POSSIBLE SAT-SAT NIGHT IN NLY CHANNELING...THEN
ELY FLOW AS HIGH PRESSURE ESTABLISHES ITSELF TO THE NORTH AND A
WARM FRONT DEVELOPS TO THE SOUTH...INCREASING THE GRADIENT. SCA
LIKELY SUN-MON...W/ OUTSIDE CHANCE OF GALE BUT NOT ENOUGH
CONFIDENCE FOR HWO MENTION JUST YET GIVEN HIGHEST LLJ OVERNIGHT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR
     ANZ530>543.

&&

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



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