Area Forecast Discussion
Issued by NWS Sterling, VA

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042
FXUS61 KLWX 151914
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
314 PM EDT FRI MAY 15 2015

.SYNOPSIS...
HIGH PRESSURE IS CENTERED JUST OFF THE EAST COAST. A WARM FRONT
WILL SLIDE NORTHEAST ACROSS THE AREA ON SATURDAY. A BACK DOOR COLD
FRONT WILL THEN SLIDE SOUTH TOWARD THE AREA ON SUNDAY NIGHT AND
STALL ACROSS THE AREA MONDAY BEFORE A STRONGER COLD FRONT MOVES IN
FROM THE WEST ON TUESDAY. HIGH PRESSURE WILL RETURN FOR THE MIDDLE
OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
LATEST SURFACE ANALYSIS DEPICTS HIGH PRESSURE CENTERED OFF THE
DELMARVA COAST...WITH A WARM FRONT DRAPED SOUTHEAST TO NORTHWEST
ACROSS THE OHIO VALLEY AND SOUTHERN GREAT LAKES. A LOW PRESSURE
SYSTEM IS CENTERED OVER WISCONSIN...WITH A COLD FRONT EXTENDING
SOUTH AND WEST FROM THE LOW ACROSS THE CENTRAL PLAINS.

OVER THE NEXT 24 HOURS...HIGH PRESSURE WILL GRADUALLY SLIDE
FURTHER EAST INTO THE ATLANTIC...ALLOWING THE RETURN SOUTHWESTERLY
FLOW ON THE WESTERN PERIPHERY TO BRING WARMER AND MORE HUMID AIR
BACK ACROSS THE AREA. THE WARM FRONT WILL ALSO WORK NORTHEASTWARD
AS THE LOW PRESSURE IN WISCONSIN MOVES EAST TOWARDS THE SAINT
LAWRENCE VALLEY. FOR THIS EVENING...MOISTURE AND INSTABILITY
REMAIN LIMITED...AND WHILE TERRAIN INFLUENCES WILL BE ENOUGH TO
GET A FEW SHOWERS AND ISOLATED THUNDERSTORMS GOING OVER THE
MOUNTAINS...THESE SHOULD NOT HAVE ENOUGH SUPPORT TO CONTINUE
MOVING EAST INTO THE LOWER TERRAIN CLOSER TO THE I-95 CORRIDOR.
LOWS TONIGHT WILL BE CONSIDERABLY MILDER THAN RECENT NIGHTS THANKS
TO THE INFLUX OF WARMTH AND MOISTURE...WITH MANY AREAS NOT GETTING
BELOW THE 60S.

ON SATURDAY...THE WEAK END OF THE WARM FRONT WILL CROSS NORTHEAST
ACROSS THE CWA. WITHOUT SUPPORT THIS MIGHT MEAN LITTLE MORE THAN
CLOUDS...BUT AS A SHORTWAVE, ALBEIT A RATHER WEAK ONE, MOVES
ACROSS SIMULTANEOUSLY, COMBINED WITH THE CONTINUED INCREASE IN
WARMTH AND HUMIDITY...THERE WILL BE ENOUGH INSTABILITY AND UPPER
LEVEL SUPPORT FOR A GREATER COVERAGE OF SHOWERS AND THUNDERSTORMS
ON SATURDAY. MOST OF THESE WILL BE CONCENTRATED IN THE AFTERNOON
BUT SOME SHOWERS CANNOT BE RULED OUT DURING THE MORNING PRIMARILY
NORTH AND WEST OF THE I-95 CORRIDOR. SHEAR IS RELATIVELY WEAK SO
WE ARE NOT EXPECTING ANY WIDESPREAD SEVERE WEATHER...BUT CERTAINLY
SOME BRIEF HEAVY DOWNPOURS AND LIGHTNING ARE WITHIN THE REALM.
TEMPERATURES SHOULD CONTINUE WARMING WITH MOST AREAS REACHING THE
80S. THUNDERSTORMS WILL DIMINISH WITH THE PASSAGE OF THE UPPER
LEVEL DYNAMICS TOWARDS THE EAST AND THE LOSS OF DIURNAL HEATING.
LOWS WILL REMAIN RATHER MILD WITH THE MORE HUMID AIR MASS IN PLACE
LIMITING RADIATIONAL COOLING...ALONG WITH DEBRIS CLOUDS FROM THE
DAY-TIME STORMS.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
UNSETTLED WX CONTINUES THRU SUN NIGHT WITH A COUPLE OF FACTORS IN
PLAY. SFC HIGH REMAINS POSITIONED OFF THE CAROLINA COAST DURING
THE DAY AS UPPER LVL RIDGE BUILDS NORTH OVER THE EASTERN US...WITH
THE AXIS SPLITTING THE MID ATLANTIC. SWLY ON THE BACKSIDE OF THE
HIGH WILL RESULT IN INCREASING WAA AND MOISTURE
ADVECTION...KEEPING AN ALREADY WARM/MOIST AIRMASS IN PLACE. TWO
PASSING SHORTWAVES ROUNDING THE RIDGE AXIS WILL TRIGGER SCT
SHOWERS...MAINLY WEST OF THE BLUE RIDGE AND ALONG THE MASON- DIXON
LINE. BY THE AFTN...POPS INCREASE TO THE EAST WITH SFC TROUGH
DEVELOPING ACROSS THE CWA. BULK SHEAR VALUES NEAR AROUND 30
KTS...AND COMBINING WITH SBCAPE VALUES AROUND 500 J/KG...EXPECTING
THE TROUGH TO ACT AS A TRIGGER FOR SCT TSTMS. THE AFOREMENTIONED
MOISTURE ADVECTION WILL PUSH PWATS UP TO AROUND 1.7-1.8
INCHES...SO ANY TSTM THAT DOES FORM COULD PRODUCE BRIEF HEAVY
RAINFALL. NOT ANTICIPATING SVR WX FROM THE SETUP...BUT
GUSTY/STRONGER WINDS ARE NOT OUT OF THE QUESTION.

THROUGHOUT THE DAY...A NEAR STATIONARY COLD FRONT EXTENDS WEST-
EAST ALONG THE PA/NY STATE BORDERS. CLOSED LOW ALOFT WILL RIDE THE
EASTERN SIDE OF THE RIDGE THROUGH THE PERIOD...WORKING TO PUSH
THIS COLD FRONT TO THE SOUTH INTO THE DELMARVA REGION BY SUNDAY
NIGHT. AS THE FRONTAL BOUNDARY NEARS THE AREA...THIS WILL ALSO AID
IN TRIGGERING FURTHER CONVECTION AND AS SUCH HAVE KEPT CHC POPS
OVER EASTERN PORTIONS OF THE CWA FOR SUN NIGHT. THE LOSS OF
DIURNAL HEATING WILL MINIMIZE INSTABILITY OVERNIGHT...BUT CANNOT
RULE OUT AN ISO TSTM. TERRAIN CIRCULATIONS COULD KEEP PCPN ON
GOING OVER THE POTOMAC HIGHLANDS...BUT THINKING MOST OF NORTHERN
VA WILL SEE A PERIOD OF DRY WX SUN NIGHT BEFORE THE NEXT ROUND
MOVES IN FOR MONDAY.


&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
A STALLED FRONT ACROSS THE MID-ATLANTIC WILL BE THE FOCAL ZONE OF
SHOWERS AND THUNDERSTORMS MONDAY AND MONDAY NIGHT. HIGHS MONDAY
WILL BE IN THE MIDDLE TO UPPER 80S...WHILE LOWS MONDAY NIGHT WILL
DROP INTO THE MIDDLE 60S. BOTH ARE WELL ABOVE NORMAL.

THE THREAT FOR SHOWERS AND THUNDERSTORMS CONTINUE TUESDAY BEFORE
A COLD FRONT PUSHES ACROSS THE REGION. HIGHS TUESDAY WILL BE A FEW
DEGREES COOLER BUT STILL ABOVE NORMAL FOR THIS TIME IN MAY. BEHIND
THE FRONTAL PASSAGE AND THROUGH TUESDAY NIGHT...HIGH PRESSURE WILL
BUILD IN FROM THE WEST...USHERING IN COOLER AND DRIER AIR. LOWS
WILL BOTTOM OUT IN THE LOWER TO MIDDLE 50S. A GUSTY BREEZE WILL
ALSO ENSUE AS THE HIGH BUILDS EAST.

WEDNESDAY AND WEDNESDAY NIGHT WILL BE DRY WITH HIGH PRESSURE IN
CONTROL AND HIGHS IN THE LOWER TO MIDDLE 70S.

ONCE THE HIGH PRESSURE MOVES TO THE COAST THURSDAY AND THURSDAY
NIGHT...A SOUTHERLY FLOW WILL RETURN. THERE IS A SLIGHT CHANCE OF
A FEW SHOWERS OR A THUNDERSTORM AS SOME UPPER LEVEL ENERGY PUSHES
INTO THE REGION FROM THE WEST. HIGHS THURSDAY WILL BE IN THE
MIDDLE 70S.

A SECOND WAVE OF ENERGY WILL SLIDE ACROSS TO OUR NORTH AND BRING
A CHANCE OF SHOWERS ON FRIDAY.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
THUNDERSTORMS DEVELOPING OVER THE MOUNTAINS OF EASTERN WEST
VIRGINIA HAVE A CHANCE OF AFFECTING KMRB THIS EVENING SO HAVE
INCLUDED VCTS IN THE TAF THERE LATER ON. ELSEWHERE...STORMS SHOULD
DISSIPATE BEFORE REACHING THE OTHER TERMINALS WITH CIGS REMAINING
WELL ABOVE MVFR CRITERIA AND NO VISIBILITY RESTRICTIONS.

SATURDAY THE THREAT OF THUNDERSTORMS WILL INCREASE ACROSS ALL
TERMINALS AS A WEAK WARM FRONT MOVES ACROSS AND A SHORTWAVE MOVES
OVERHEAD ALOFT. NO PROBLEMS WITH CIGS OR VIS ARE EXPECTED EXCEPT
FOR A SLIGHT CHANCE OF THEM IN ANY THUNDERSTORMS.

PSBL SUB-VFR CONDITIONS WITH ANY SHOWER/TSTM SUNDAY...WITH SOME
OF THE TSTMS PRODUCING GUSTY WINDS. OUTSIDE OF PCPN...VFR
CONDITIONS PREVAIL...WITH S FLOW GENERALLY 5-10 KTS.

MVFR CONDITIONS EARLY MONDAY COULD BECOME IFR OR LIFR LATER ON
MONDAY INTO MONDAY NIGHT AS SHOWERS AND THUNDERSTORMS DEVELOP NEAR
THE TERMINALS AND ALONG A STALLED FRONT. WINDS LIGHT AND VARIABLE
EXCEPT IN ANY GUSTY THUNDERSTORMS.

ON TUESDAY...MVFR OR PERHAPS IFR CONDITIONS MAY OCCUR WITH ANY
SHOWERS AND THUNDERSTORMS AHEAD OF A COLD FRONT. WINDS WILL BE
LIGHT AND VARIABLE EXCEPT IN ANY GUSTY THUNDERSTORMS.

&&

.MARINE...
MAIN CONCERN THIS EVENING IS WITH THE CHANNELLING OF WIND ON THE
CHESAPEAKE. WINDS WILL REACH BORDERLINE SMALL CRAFT LEVELS AND
HAVE AN ADVISORY OUT THROUGH THIS EVENING. WINDS SHOULD DIMINISH
ON SATURDAY AS A WARM FRONT PASSES ACROSS THE AREA.
HOWEVER...WHILE ANY SHOWERS AND STORMS SHOULD STAY AWAY FROM THE
COASTAL WATERS TODAY...A SIGNIFICANTLY GREATER CHANCE OF THEM
REACHING THE BAY EXISTS ON SATURDAY...SO MARINERS SHOULD STAY
ALERT FOR ANY APPROACHING THUNDERSTORMS AND BE PREPARED TO TAKE
APPROPRIATE ACTION.

SUB-SCA CONDITIONS EXPECTED SUNDAY THRU TUESDAY. ANY TSTM THAT
IMPACTS THE WATERS COULD BRING A BRIEF PERIOD OF GUSTY WINDS.

&&

.TIDES/COASTAL FLOODING...
A SOUTHERLY FLOW WILL DEVELOP TODAY AND CONTINUE THROUGH THE
WEEKEND. THIS WILL LIKELY CAUSE ANOMALIES TO INCREASE A BIT...BUT
THE WIND MAY BE JUST WEST OF SOUTH...LIKELY KEEPING WATER LEVELS
BELOW MINOR FLOODING THRESHOLDS DURING THIS TIME.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT SATURDAY FOR ANZ531>534-
     537>543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...SEARS
LONG TERM...KLW
AVIATION...SEARS/RCM
MARINE...SEARS/RCM
TIDES/COASTAL FLOODING...BJL



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