Severe Thunderstorm Warning 16, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
610 PM EDT FRI APR 19 2013

.SYNOPSIS...
A COLD FRONT WILL CONTINUE TO MOVE THROUGH THE REGION FROM WEST TO
EAST THROUGH THIS EVENING. WIDESPREAD SHOWERS AND THUNDERSTORMS
ARE EXPECTED ALONG AND AHEAD OF THE BOUNDARY. CANADIAN HIGH
PRESSURE WILL BUILD INTO THE REGION LATE TONIGHT THROUGH
SUNDAY...BRINGING DRY AND COOL CONDITIONS. HIGH PRESSURE WILL
REMAIN OVERHEAD EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
HEADLINE UPDATE...TORNADO WATCH NUMBER 131 CONTINUES FOR PORTIONS
OF THE SHENANDOAH VALLEY AND EAST...INCLUDING THE BALTIMORE-
WASHINGTON METRO AREA UNTIL 10 PM TONIGHT. COLD AIR ADVECTION
BEHIND THE LINES WILL ENABLE THE WATCH TO BE CANCELLED.

AS OF 2130Z...COLD FRONT HAS PUSHED THROUGH THE ALLEGHENY FRONT
AND IS NOW CROSSING THE SHENANDOAH VALLEY. LINES/SQUALLS OF
INTENSE SHOWERS...THUNDERSTORMS OVER THE SRN PORTION OF THE
CWA...WILL CONTINUE TO DEVELOP AND PROGRESS EAST ACROSS THE REST
OF THE AREA THROUGH THE MID TO LATE EVENING. WINDS IN EXCESS OF 50
MPH AND AN ISOLATED TORNADO THREAT PERSIST. REPORTS OF
PARTICULARLY HEAVY RAIN ARE OCCURRING. FORTUNATELY THESE LINES ARE
PROGRESSIVE...BUT PONDING ON ROAD WAYS AND VERY LIMITED VISIBILITY
IN SQUALLS.

THIN LINE OF CONVECTION IS TRYING TO DEVELOP AHEAD OF THE FRONT
OVER EASTERN WV. TSTMS ARE EXPECTED TO INCREASE IN COVERAGE THIS
AFTERNOON UNDER FAVORABLE DYNAMICS. INSTABILITY HAS BEEN THE
LIMITING FACTOR DUE TO ONGOING CLOUD COVER...BUT SOME BREAKS HAVE
DEVELOPED. MOISTURE WILL CONTINUE TO INCREASE DUE TO SOUTHERLY
FLOW. A VERY STRONG JET WILL STREAK WILL CROSS THE AREA WITH 50+KT
WINDS ABOVE 850MB AHEAD OF THE FRONT. SPC HAS ISSUED A MESOSCALE
DISCUSSION ABOUT THE UPDATED SEVERE THREAT...INCLUDING POTENTIAL
FOR A TORNADO WATCH THIS AFTERNOON.

THE COLD FRONT WILL MOVE OFF TO OUR EAST OVERNIGHT AND ANY
LEFTOVER SHOWERS WILL ALSO MOVE OUT OF OUR AREA. MIN TEMPS
OVERNIGHT WILL BE NOTICEABLY CHILLIER COMPARED TO RECENT
NIGHT...RANGING FROM THE 20S ALONG THE RIDGE TOPS IN THE POTOMAC
HIGHLANDS...TO THE MID AND UPPER 40S NEAR WASHINGTON/BALTIMORE...
TO THE LOWER 50S ACROSS SOUTHERN MARYLAND.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
HIPRES BLDS OVER THE RGN THIS WKND. WL BE IN CAA REGIME MOST OF THE
TIME...W/ NW/NLY FLOW SAT BCMG NE/ELY SUN AS CENTER OF HIGH HEADS
TWD NEW ENGLND/QUE. SHUD BE DIURNAL CU SAT...SPCLY IN THE MTNS. BY
SUN...SUBSIDENCE SHUD PREVAIL.

TEMPS WL BE BLO CLIMO SAT...AND DROP A CPL MORE BY SUN. LTST
MOS/GOING FCST IN GOOD AGREEMENT. GROWING SEASON HAS STARTED E OF
BLURDG. ALTHO IT WL BE CHILLY SAT NGT...A LGT NLY BRZ AS CURRENTLY
PROGGED WUD PRECLUDE EITHER FROST OR SUBFRZG TEMPS. RECENT TEMP BIAS
HAS BEEN TO FCST TOO COLD. WL OMIT FROM HWO ATTM AS POTL FOR
HEADLINE CONDS SLIM.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
THE STREAK OF GOOD WX WEEKENDS CONTINUES THIS WEEKEND...THOUGH DON'T
FORGET A JACKET FOR OUTDOOR PLANS. EACH DAY WILL BE COOL AND WELL
BELOW AVERAGE FOR THIS TIME OF YEAR. BREEZY ON SATURDAY...THE DAY
AFTER THE FRONTAL PASSAGE AND STILL COOL ON SUNDAY FROM THE NELY
ONSHORE FLOW. HIGHS EACH DAY WILL BARELY PEAK NEAR 60 DEG AND THE
COOLER WINDS WILL BRING THAT VALUE DOWN EVEN A FEW MORE DEG IN TERMS
OF APPARENT TEMPS. SKIES WILL CLEAR OUT ON SAT...AFTER NEARLY A WEEK
OF MOSTLY CLOUDY/CLOUDY SKIES - STAYING CLEAR INTO SUN MRNG.

A WEAK UPPER WAVE WILL QUICKLY SLIDE ACROSS THE GREAT LAKES REGION
ON SUN...PUSHING SOME UPPER LEVEL CLOUD COVER OVER THE AREA BUT THE
NEXT WX FEATURE AFFECTING THE AREA WILL COME FROM THE SOUTH. THE
FRONTAL BOUNDARY THAT WILL BE MOVING ACROSS THE AREA TONIGHT WILL
STALL WELL OFF THE COAST THIS WEEKEND - THE SOUTHERN PIECE AT LEAST.
THE TAIL END OF THE FRONT WILL DRIFT BACK TOWARD THE NORTH ONCE IT
HAS CAUGHT UP W/ THE MINOR UPPER SHORTWAVE OVER THE SRN ATLC COAST.
MOST GUIDANCE MEMBERS KEEP A BULK OF THE SYSTEM AS ITS PRECIP OFF
THE COAST AND IT TRAVELS PARALLEL TO THE NC/DELMARVA COASTLINE EARLY
NEXT WEEK. HOWEVER...THE NRN HEAD OF THE SYSTEM WILL CARRY LOW
CLOUDS FROM THE ONSHORE FLOW AND PERIODS OF VERY LIGHT RAIN AND
DRIZZLE.

THIS TYPE OF SCENARIO KEEPS THE REGION COOL AND MOIST ON MONDAY...W/
A GRADUAL WARM-UP TOWARD THE MIDDLE OF THE WEEK ONCE THE OFFSHORE
SHORTWAVE MOVES AWAY. DIRECTLY ON ITS HEELS HOWEVER IS ANOTHER
FRONTAL PASSAGE LATE WED INTO EARLY THU. AN UPPER RIDGE WILL SQUEEZE
IN BETWEEN SYSTEM ON TUE AND BRIEFLY INTO WED...KEEPING THE AREA DRY
AND PULLING OUR TEMPS BACK INTO THE M-U60S. THE FRONT WILL MOVE
THROUGH W/ THE LOW POSSIBILITY OF CONVECTION AND SOME MODERATE/HEAVY
RAIN BRIEFLY. THE FRONT WON'T TANK TEMPS LIKE THE CURRENT FRONTAL
PASSAGE...ONLY DROPPING THE DAYTIME HIGHS A FEW DEGREES HEADING INTO
THE NEXT WEEKEND - THOUGH IT WILL HELP TO DRY OUT CONDITIONS.

&&

.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
HEAVY SHOWERS/THUNDERSTORMS CROSSING THE TERMINALS THROUGH THIS
EVENING. WILL AMEND AS NECESSARY AS INFORMATION COMES IN...BUT FOR
NOW THIS ACTIVITY IS COVERED IN TEMPO GROUPS. GUSTY SOUTHERLY
WINDS WILL CONTINUE...SHIFTING TO THE W-NW THIS EVENING BEHIND THE
FRONT.

HIPRES OVR THE TERMINALS THIS WKND. NW WNDS SAT G20-25KT...BCMG NLY
AND DIMINISHING SAT NGT...AND VEERING ELY SUN.

ONSHORE FLOW DEVELOPS LATE IN THE WEEKEND AS HIPRES SHIFTS OFF THE
NEW ENGLAND COAST. THERE IS A POTENTIAL FOR AN EXTENDED PERIOD OF
LOW CLOUDS AND FOG ERY NEXT WEEK IF ONSHORE FLOW PERSISTS.

&&

.MARINE...
GALE WARNING IN EFFECT OVER ALL WATERS UNTIL 10PM. SOUTHERLY WINDS
WILL CONTINUE TO GUST IN THE 25-40KT RANGE AHEAD OF AN APPROACHING
COLD FRONT. A LINE OF HEAVY SHOWERS AND THUNDERSTORMS IS EXPECTED
ALONG AND JUST AHEAD OF THE COLD FRONT. THE BEST CHANCE FOR THE
HEAVIER PRECIPITATION OVER THE WATERS WILL BE BETWEEN ABOUT 7 PM
AND MIDNIGHT. THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY
WINDS. SPECIAL MARINE WARNINGS MAY BE NEEDED WITH THESE
THUNDERSTORMS IF WIND GUSTS REACH STORM FORCE.

THE COLD FRONT WILL MOVE OFF TO THE EAST LATE TONIGHT AND WINDS WILL
SHIFT TO THE NORTHWEST. SMALL CRAFT ADVISORIES NOW IN EFFECT
OVERNIGHT FOR ALL WATERS.

THOUGH HIGH PRES WILL BUILD IN BEHIND THE FRONT THIS WEEKEND...
BREEZY NWLY WINDS ON SAT AFTN WITH GUSTS TO AROUND 25 KT.
CONTINUED SCA THROUGH SAT NIGHT FOR MD PORTION OF BAY AND LOWER
TP. WINDS WILL SWITCH TO NELY ON SUN. A STALLED FRONTAL BOUNDARY
WILL LIFT BACK NWD LATE SUN INTO MON...PICKING WINDS BACK UP OVER
THE WATERS INTO SCA RANGE - SUBSIDING MID WEEK W/ ANOTHER
APPEARANCE OF HIGH PRESSURE.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES CONTINUE TO INCREASE TO 1.25 FT...AND WILL
PROBABLY REACH 1.5 FT ON THE BAY AS HIGH TIDE OCCURS. WENT AHEAD
WITH A COASTAL FLOOD ADVISORY FOR CALVERT AND ANNE ARUNDEL BASED
ON TIMING OF FRONT /FRONT WILL BE WELL THROUGH BALTIMORE AND
HARFORD BY THE TIME THEY HIT HIGH TIDE SAT MRNG/. HEAVY RAINFALL
MAY COMPLICATE COASTAL FLOODING CONCERNS IN SENSITIVE AREAS LIKE
IN ANNAPOLIS.

DEPARTURES SHOULD BE LOWER FOR THE AM CYCLE SAT...BUT BLOWOUT
CONDS MAY NOT BE REALIZED TIL LATE SAT-SAT NGT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 AM EDT
     SUNDAY FOR ANZ530>534-537-539>541-543.
     GALE WARNING UNTIL 10 PM EDT THIS EVENING FOR ANZ530>543.
     SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 6 PM EDT
     SATURDAY FOR ANZ535-536-538-542.

&&

SYNOPSIS...BAJ/KS
NEAR TERM...BAJ/KS
SHORT TERM...KS
LONG TERM...GMS
AVIATION...BAJ/GMS
MARINE...BAJ/GMS/KS
TIDES/COASTAL FLOODING...BAJ

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
645 PM EDT FRI APR 19 2013

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0607 PM     TSTM WND DMG     1 E ORANGE              38.25N  78.09W
04/19/2013                   ORANGE             VA   LAW ENFORCEMENT

            TREE DOWN ON VA STATE HWY 20 APPROXIMATELY ONE HALF
            MILE EAST OF ORANGE VA.

&&

EVENT NUMBER LWX1300075

KCS

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