Severe Thunderstorm Warning 3, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
348 PM EST WED JAN 30 2013

.SYNOPSIS...
A STRONG COLD FRONT WILL PASS THROUGH THE AREA TONIGHT. HIGH
PRESSURE WILL BRIEFLY BUILD OVERHEAD THURSDAY...BUT ANOTHER COLD
FRONT WILL PASS THROUGH THURSDAY NIGHT. HIGH PRESSURE WILL RETURN
FRIDAY...BUT WEAK LOW PRESSURE MAY IMPACT THE REGION SATURDAY
THROUGH SATURDAY NIGHT. HIGH PRESSURE WILL RETURN FOR SUNDAY.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
INITIAL CONVECTIVE LINE /WITHOUT LIGHTNING/ CONTINUES TO TREK TO THE
EAST ACROSS CENTRAL MARYLAND EARLY THIS AFTERNOON...WITH AN AREA OF
MODERATE RAIN BEHIND IT. THIS LINE HAS PRODUCED SOME 40 TO 45 KT
WIND GUSTS. ANOTHER ORGANIZED LINE MAY BE SHOWING ITSELF ACROSS
SOUTHWEST VIRGINIA EARLY THIS AFTERNOON...WHICH CAN TRACK NORTHEAST
AND AFFECT THE CWA THIS EVENING.

THE TRUE COLD FRONT IS STILL LOCATED ACROSS INDIANA EARLY THIS
AFTERNOON. STRONG SOUTHERLY FLOW AHEAD OF THE FRONT HAS BROUGHT A
WARM AND MOIST ATMOSPHERE ACROSS THE CWA. TIGHTENING GRADIENT AND
STRONG WIND FIELDS ALOFT HAVE LEAD TO 30 TO 40 KT WINDS AT THE
SURFACE EVEN OUTSIDE OF ANY SHOWERS. THIS IS LIKELY TO CONTINUE OR
EVEN INTENSIFY INTO THIS EVENING...AND WIND ADVISORY HAS BEEN
EXPANDED.

STILL THINK THERE IS THE RISK OF SEVERE WEATHER THIS EVENING WITH A
NEWLY ORGANIZED LINE MOVING IN FROM THE SOUTHWEST. INSTABILITY FROM
18Z KIAD RAOB IS WEAK...BUT NOT ZERO. BUT EVEN WITH WEAK
INSTABILITY...WIND FIELDS/SHEAR ARE STRONG ENOUGH TO RAISE THE
CONCERN FOR DAMAGING WIND GUSTS ACROSS THE CWA WITH ORGANIZED
CONVECTION. CONVECTION MAY NOT HAVE LIGHTNING AND THUNDER...BUT
MOMENTUM TRANSFER MAY BE SUFFICIENT ENOUGH FOR DAMAGING WIND GUSTS.

IN ADDITION...HEAVY RAINFALL REMAINS A RISK THIS EVENING AND FLASH
FLOOD WATCH HEADLINE REMAINS AS IS...FOCUSING ON THE GREATEST
THREATS IN THE MOUNTAINS AND URBAN CORRIDOR.

AFTER ANY ORGANIZED LINE OF CONVECTION...THERE IS LIKELY TO BE A
SEVERAL HOUR PERIOD OF MODERATE RAINFALL BEFORE PRECIPITATION ENDS
AS THE COLD FRONT MOVES THROUGH OVERNIGHT. COLDER AIR WILL START TO
MOVE IN TO THE HIGHLANDS AND RAIN SHOWERS MAY CHANGE TO SNOW
SHOWERS.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
LOW PRESSURE WILL TRACK THROUGH EASTERN CANADA WHILE THE COLD FRONT
MOVES OUT TO SEA THURSDAY. A TIGHT PRESSURE GRADIENT BETWEEN LOW
PRESSURE OVER EASTERN CANADA AND HIGH PRESSURE OVER THE NORTHERN
CONUS WILL CAUSE WINDY CONDITIONS. WESTERLY WINDS WILL GUST
FREQUENTLY AROUND 30 TO 40 MPH. STRONG COLD ADVECTION BEHIND THE
FRONT WILL MAKE IT FEEL MORE LIKE JANUARY. MAX TEMPS WILL RANGE FROM
THE 20S IN THE ALLEGHENY HIGHLANDS TO MID AND UPPER 40S ACROSS LOWER
SOUTHERN MARYLAND.

A REINFORCING COLD FRONT WILL PASS THROUGH THE REGION THURSDAY
NIGHT. DESPITE LITTLE MOISTURE...THERE MAY BE SOME SNOW SHOWERS
OVERNIGHT THURSDAY. LIGHT SNOWFALL ACCUMULATIONS ARE POSSIBLE.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
BLUSTERY AND COLD CONDITIONS ARE EXPECTED BEHIND THE COLD FRONT
FRIDAY. HIGH PRESSURE WILL BUILD OVERHEAD FRIDAY NIGHT. A CLIPPER
TYPE SYSTEM WILL PASS THROUGH THE REGION LATE SATURDAY AND SATURDAY
NIGHT...BRINGING A CHANCE FOR SNOW SHOWERS TO THE AREA. LIGHT
SNOWFALL ACCUMULATIONS ARE POSSIBLE.

HIGH PRESSURE WILL BUILD OVERHEAD SUNDAY BEFORE ANOTHER COLD FRONT
MOVES THROUGH LATE MONDAY INTO TUESDAY. HIGH PRESSURE MAY RETURN FOR
THE MIDDLE PORTION OF NEXT WEEK.

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
FIRST LINE OF CONVECTION IS FORECAST TO BRUSH BY MTN/BWI THROUGH
22Z...WITH SHOWERS MOVING ACROSS THE REST OF THE TERMINALS. ANOTHER
LINE OF CONVECTION MAY DEVELOP ACROSS SOUTHWEST VIRGINIA AND MOVE
NORTHEAST AFFECTING MOST TERMINALS EXCEPT POSSIBLY MRB THIS EVENING.
HEAVY RAINFALL AND STRONG GUSTY WINDS MAY ACCOMPANY THIS LINE. MVFR
CONDITIONS ARE LIKELY...WITH THE POTENTIAL FOR BRIEF IFR CONDITIONS.
COLD FRONT/WIND SHIFT MOVE THROUGH FROM THE WEST OVERNIGHT.

GUSTY WESTERLY WINDS AROUND 30 TO 35 KNOTS ARE EXPECTED BEHIND
THE COLD FRONT THURSDAY.

ANOTHER REINFORCING COLD FRONT WILL PASS THROUGH LATE THURSDAY NIGHT
INTO FRIDAY...BRINGING A CHANCE FOR SNOW SHOWERS. GUSTY NORTHWEST
WINDS ARE EXPECTED BEHIND THE FRONT FRIDAY.

WEAK LOW PRESSURE MAY IMPACT THE TERMINALS LATER SATURDAY AND
SATURDAY NIGHT BEFORE HIGH PRESSURE RETURNS SUNDAY.

&&

.MARINE...
GALES ARE IN EFFECT THROUGH TONIGHT WITH STRONG SOUTHERLY WINDS
AHEAD OF A COLD FRONT. ANY CONVECTIVE LINE MAY PRODUCE STRONGER
WINDS. COLD FRONT MOVES THROUGH LATE TONIGHT...GALES AND SMALL CRAFT
ADVISORIES CONTINUE ON THURSDAY.

GUSTY WESTERLY WINDS ARE EXPECTED BEHIND THE COLD FRONT THURSDAY. A
GALE WARNING IS IN EFFECT FOR THE LOWER TIDAL POTOMAC RIVER AND
MIDDLE PORTIONS OF THE BAY. A SMALL CRAFT ADVISORY IS IN EFFECT
ELSEWHERE.

A COLD FRONT WILL PASS THROUGH THE WATERS THURSDAY NIGHT. A SMALL
CRAFT ADVISORY WILL LIKELY BE NEEDED. GUSTY NORTHWEST WINDS ARE
EXPECTED BEHIND THE COLD FRONT FRIDAY. HIGH PRESSURE WILL BUILD
TOWARD THE WATERS FRIDAY NIGHT INTO SATURDAY BEFORE WEAK LOW
PRESSURE POSSIBLY IMPACTS THE AREA SATURDAY NIGHT.

&&

.HYDROLOGY...
RAINFALL PROJECTIONS HAVE INCREASED SINCE YESTERDAY...LEADING TO
HIGHER CONFIDENCE IN FLOOD POTENTIAL. CURRENT FORECAST INDICATES
OVER TWO INCHES OF RAIN IN THE POTOMAC HIGHLANDS...AND OVER AN INCH
AND A HALF NEAR AND WEST OF THE BLUE RIDGE. A RIVER FLOOD WATCH IS
IN EFFECT FOR THE POTOMAC RIVER AT POINT OF ROCKS AND THE SOUTH
BRANCH POTOMAC RIVER NEAR SPRINGFIELD. MANY POINTS ALONG THE
POTOMAC ARE LIKELY TO RISE ABOVE ACTION STAGE...SO WE WILL BE
KEEPING AN EYE ON ALL THE FORECAST POINTS...WITH ADDITIONAL
WATCHES OR WARNINGS POSSIBLE.

FLASH FLOOD WATCH IS IN EFFECT FOR LOCATIONS WEST OF THE BLUE
RIDGE AND ALSO THE WASHINGTON/BALTIMORE METROPOLITAN AREAS.

&&

.TIDES/COASTAL FLOODING...
A COASTAL FLOOD ADVISORY REMAINS IN EFFECT FOR THE WESTERN SHORE OF
THE MARYLAND CHESAPEAKE BAY AND UPPER TIDAL POTOMAC RIVER TONIGHT.
STRONG SOUTHERLY WINDS WILL CAUSE TIDAL ANOMALIES TO INCREASE TO
NEAR 2 FEET ABOVE NORMAL. MINOR FLOODING IS EXPECTED NEAR TIMES OF
HIGH TIDE THROUGH TONIGHT. WILL CONTINUE TO WATCH TIDAL ANOMALIES
WITH THE STRONG SOUTHERLY FLOW...MODERATE FLOODING IN SENSITIVE
AREAS CANNOT BE RULED OUT. A STRONG OFFSHORE FLOW WILL ALLOW FOR
TIDAL ANOMALIES TO DECREASE THROUGHOUT THE DAY THURSDAY.

HOWEVER...FRESHWATER RIVER LEVELS MAY RISE ENOUGH TO CAUSE A
COASTAL FLOOD THREAT NEAR WASHINGTON DC LATER FRIDAY INTO
SATURDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR DCZ001.
     FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR DCZ001.
     COASTAL FLOOD ADVISORY FROM 7 PM THIS EVENING TO 3 AM EST
     THURSDAY FOR DCZ001.
MD...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR MDZ003>007-009>011-
     013-014-016>018-501-502.
     FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ003>007-009>011-
     013-014-501-502.
     COASTAL FLOOD ADVISORY UNTIL 4 AM EST THURSDAY FOR MDZ007-011-
     014.
     COASTAL FLOOD ADVISORY UNTIL 4 AM EST THURSDAY FOR MDZ017-018.
VA...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR VAZ025>031-036>040-
     042-050>057-501>504.
     FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ025>031-042-053-
     054-503-504.
     COASTAL FLOOD ADVISORY FROM 7 PM THIS EVENING TO 3 AM EST
     THURSDAY FOR VAZ054.
WV...WIND ADVISORY UNTIL 6 AM EST THURSDAY FOR WVZ050>053-055-
     501>506.
     FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR WVZ050>053-055-
     501>506.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 6 PM EST THURSDAY FOR
     ANZ530>532-535-536-538>540.
     GALE WARNING UNTIL 6 AM EST THURSDAY FOR ANZ530>532-535-536-
     538>540.
     GALE WARNING UNTIL 6 PM EST THURSDAY FOR ANZ533-534-537-
     541>543.

&&

SYNOPSIS...BJL
NEAR TERM...BPP
SHORT TERM...BJL
LONG TERM...BJL
AVIATION...BJL/BPP
MARINE...BJL/BPP
HYDROLOGY...JE/BJL
TIDES/COASTAL FLOODING...BJL

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
525 PM EST WED JAN 30 2013

MDZ004-009-VAZ030-031-042-501-WVZ053-302345-
FREDERICK MD-MONTGOMERY MD-WARREN VA-CLARKE VA-JEFFERSON WV-
NORTHERN FAUQUIER VA-LOUDOUN VA-
525 PM EST WED JAN 30 2013

...SHOWERS WITH HEAVY RAIN TO CONTINUE ALONG THE BLUE RIDGE IN
FREDERICK...MONTGOMERY...WARREN...CLARKE...JEFFERSON...NORTHERN
FAUQUIER AND LOUDOUN COUNTIES...

AT 522 PM EST...SHOWERS PRODUCING HEAVY RAIN WERE LOCATED NEAR THE
BLUE RIDGE ALONG A LINE EXTENDING FROM FRONT ROYAL TO POINT OF
ROCKS. THESE SHOWERS WERE MOVING OVER THE SAME AREAS.

LOCATIONS IMPACTED INCLUDE NEERSVILLE...PURCELLVILLE...ROUND HILL AND
BLUEMONT.

NWS DOPPLER RADAR AND RAINFALL REPORTS SHOW RAINFALL AMOUNTS UP TO
ONE AND HALF INCHES OF RAIN HAS ALREADY FALLEN...WHICH WILL CAUSE
PONDING OF WATERS ON ROADWAYS.

ADDITIONAL HEAVY RAIN IN EXCESS OF ONE INCH IS POSSIBLE WITH THIS
ACTIVITY THROUGH THIS EVENING...AND A FLOOD WARNING MAY BE NEEDED.

&&

LAT...LON 3925 7737 3878 7791 3892 7818 3938 7761
TIME...MOT...LOC 2215Z 062DEG 7KT 3917 7763 3884 7816

JRK

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
541 PM EST WED JAN 30 2013

VAZ025-026-029-036>039-050-302330-
ORANGE VA-NELSON VA-GREENE VA-MADISON VA-PAGE VA-ROCKINGHAM VA-
ALBEMARLE VA-AUGUSTA VA-
541 PM EST WED JAN 30 2013

...SHOWERS WITH HEAVY RAIN TO AFFECT ORANGE...NELSON...GREENE...
MADISON...PAGE...ROCKINGHAM...ALBEMARLE AND AUGUSTA COUNTIES...

AT 539 PM EST...SHOWERS WITH GUSTY WINDS AND HEAVY RAIN WERE LOCATED
ALONG A LINE EXTENDING FROM NEAR STAUNTON AIRPORT TO STUARTS DRAFT
TO 8 MILES WEST OF MASSIES MILL...MOVING NORTHEAST AT 55 MPH.

LOCATIONS IMPACTED INCLUDE
MCGAHEYSVILLE...WINGINA...SHIPMAN...LOVINGSTON...CHARLOTTESVILLE...
NELLYSFORD...WINTERGREEN...ROCKFISH...ELMA...FABER AND SCHUYLER.

HEAVY RAIN WITH THESE SHOWERS WILL REDUCE VISIBILITIES TO BELOW ONE
MILE AND MAY CAUSE PONDING OF WATER ON ROADWAYS.

WIND GUSTS OF 40 TO 50 MPH CAN BE EXPECTED WITH THESE SHOWERS. WINDS
THIS STRONG CAN BRING DOWN LARGE TREE BRANCHES. TAKE SHELTER UNTIL
THE SHOWERS HAVE PASSED.

&&

LAT...LON 3754 7890 3769 7899 3770 7905 3777 7908
      3781 7917 3830 7891 3872 7853 3875 7845
      3839 7812 3822 7814 3794 7836 3776 7855
      3774 7863 3768 7864 3767 7866 3769 7869
      3763 7872 3764 7880 3753 7883
TIME...MOT...LOC 2239Z 233DEG 48KT 3829 7884 3805 7895
          3782 7909

SMZ

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