Severe Thunderstorm Warning 344, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
327 PM EDT TUE SEP 18 2012

.SYNOPSIS...
A STRONG COLD FRONT WILL MOVE EAST OF THE AREA TONIGHT.
HIGH PRESSURE WILL BUILD IN DURING THE MID TO LATE PORTION OF THE
WEEK. ANOTHER SYSTEM COULD BRING INCLEMENT WEATHER OVER THE
WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
AS OF 3PM THIS AFTN...A LINE OF SEVERAL SVR BOWING SEGMENTS HAS
BISECTED THE CWA AND IS MOVING TOWARD THE I-95 CORRIDOR. ISOLATED
STRONG/SVR GUSTS ASSOCIATED W/ THIS ACTIVITY AS THE WHOLE LINE GETS
PUSHED EWD AHEAD OF A STRONG COLD FRONT. THE FRONT IS PUSHING ACROSS
THE NRN SHENANDOAH VLY...MAKING A PUSH TOWARD THE BLUE RIDGE. BEHIND
THE FRONT CONDITIONS ARE STILL WET BUT THE BIGGEST HAZARDS REMAIN
ASSOCIATED W/ THE LINE OF CONVECTION. THE LINE WILL AFFECT ANY ONE
LOCATION FOR 10-20 W/ NEAR ZERO VISIBILITIES AND WIND GUSTS 40-50MPH
OR HIGHER.

A STRONG LOW LEVEL JET IS THE DRIVING FORCE FOR THIS ACTIVITY MOVING
UP THE I-95 CORRIDOR OF THE ERN SEABOARD. THIS FEATURE WILL PUSH OFF
THE COAST OF THE MID-ATLC WITHIN THE NEXT FEW HRS. A GENERAL 2-3
INCHES OF RAIN HAVE FALLEN OVER MUCH OF THE SHENANDOAH VLY AND INTO
N CNTRL MD SINCE EARLY THIS MRNG...W/ LOCALLY HIGHER AMOUNTS. A
FLASH FLOOD WATCH IS IN EFFECT FOR MUCH OF THE REGION BECAUSE OF
THIS...AND FOR THE POTENTIAL FOR URBAN FLOODING AS THE STORMS MOVE
ACROSS THE POPULATED AREAS.

TRAILING STRATIFORM - LIGHTER - PRECIP WILL CONTINUE FOR MUCH OF THE
EVE HRS...W/ A GRADUAL END TOWARD LATE TONIGHT. THE TORNADO WATCH
REMAINS IN EFFECT THRU 7PM...THE FLASH FLOOD WATCH THRU 8 PM.

SKIES WILL BEGIN TO CLEAR OVERNIGHT BEHIND THE COLD FRONT AND WINDS
WILL SHIFT TOWARD NWLY. DEWPOINTS WILL DROP AND SO WILL TEMPS...W/ A
COOL NIGHT AND BREEZY NIGHT IN STORE FOR THE REGION.

&&

.SHORT TERM /WEDNESDAY AND THURSDAY/...
UPPER LEVEL LOW PRESSURE REMAINS ANCHORED OVER SOUTHERN CANADA AND
THE OHIO VALLEY BUT SURFACE HIGH PRESSURE BUILDS OVER THE MID
ATLANTIC IN THE WAKE OF THE COLD FRONT. A NORTHERLY SURFACE FLOW
WEDNESDAY WILL KEEP TEMPERATURES IN THE LOWER 70S IN THE METRO
AREAS...TO THE 60S IN THE WESTERN MOUNTAINS.

DRY AND CHILLY CONDITIONS ARE EXPECTED WEDNESDAY NIGHT AS HIGH
PRESSURE BUILDS IN STRONGER. CLEAR SKIES AND LIGHT WINDS WILL
CONTRIBUTE TO EXCELLENT RADIATIONAL COOLING. OVERNIGHT LOWS WILL DROP
INTO THE LOWER 50S IN THE METRO AREAS...AND EVEN INTO THE UPPER
40S IN SOME AREAS. THE WESTERN MOUNTAINS WILL LIKELY DROP INTO THE
UPPER 30S...A TRUE TASTE OF FALL.

HIGH PRESSURE WILL WEAKEN OVER THE AREA THURSDAY AND A RETURN
FLOW OFF THE OCEAN WILL DEVELOP...ALLOWING FOR MILDER
TEMPERATURES. DRY WEATHER WILL CONTINUE.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
THE UPPER LOW OVER SOUTHERN CANADA RELOADS AND LIFTS SLOWLY TOWARD
THE HUDSON BAY DURING THE PERIOD. THE GFS IS SLOWER NOW WITH
ANOTHER...BUT WEAKER COLD FRONT SATURDAY NIGHT AND SUNDAY. IT IS
ALSO WEAKER THAN THE ECMWF WITH THE FRONT. IN EITHER EVENT WE WOULD
EXPECT NEAR NORMAL TEMPERATURES AND HIGHER HUMIDITY FRIDAY AND
SATURDAY...WITH INCREASING CHANCES OF RAIN LATE SATURDAY INTO
SUNDAY. SOME TIMING UNCERTAINTIES CONTINUE TO EXIST IN THE
MODELS. IT APPEARS HIGH PRESSURE WILL REDEVELOP EARLY NEXT WEEK.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
THE DC/BALT AND OTHER I-95 AIRPORTS ON ALERT THRU 5-6PM AS A LINE OF
TSTMS MOVES OVER THE AREA...AS WELL AS A STRONG LOW LEVEL JET. SFC
WINDS OF 40-50KT POSSIBLE W/ THE LINE OF TSTMS AND THE JET REGION
WILL HAVE EMBEDDED WINDS OF 60-70KT IN THE 2-5KFT LAYER. A STRONG
COLD FRONT WILL SWEEP MUCH OF THIS ACTIVITY OFF THE COAST TOWARD
LATE THIS EVE. BEHIND THE FRONT WILL BE CLEARING SKIES...THOUGH
WINDS WILL SHIFT TO NWLY...STEADY IN THE 10-15KT RANGE FOR THE NEXT
DAY OR SO.

HIGH PRESSURE WILL BRING VFR CONDITIONS MOST OF THE TIME
WEDNESDAY THROUGH FRIDAY. PATCHY BR/FOG MAY REDUCE VSBYS DURING
THE EARLY MORNING HOURS EACH DAY. A COLD FRONT WILL PASS THROUGH
THE TERMINALS LATE SATURDAY AND SUNDAY...BRINGING THE CHANCE FOR
SHOWERS.

&&

.MARINE...
GALE WINDS CONTINUE TO PUSH ACROSS THE BAY/TP AHEAD OF A LINE OF
STRONG/SVR TSTMS. THE LINE WILL MOVE OVER THE WATERS FROM 4-7PM AND
WINDS WILL DISSIPATE ONCE THE COLD FRONT MOVES OVER THE AREA SHORTLY
AFTERWARD. WINDS WILL STAY IN SCA RANGE OVERNIGHT AND INTO WED...OUT
OF THE NW.

A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS WEDNESDAY
BEHIND THE COLD FRONT. HIGH PRESSURE WILL BUILD OVER THE WATERS
WEDNESDAY NIGHT INTO THURSDAY ALLOWING FOR WINDS TO DIMINISH. HIGH
PRESSURE WILL MOVE OFF THE COAST FRIDAY AND A COLD FRONT WILL
IMPACT THE WATERS DURING THE WEEKEND.

&&

.TIDES/COASTAL FLOODING...
STRONG SLY WINDS GUSTING WELL INTO THE GALE RANGES FOR THE LAST
SEVERAL HRS HAVE DRAMATICALLY BROUGHT UP POSITIVE TIDAL ANOMALIES TO
AROUND THE 2-2.5FT RANGE FOR THE NRN-MIDDLE MD BAY. FURTHER SOUTH
ALONG THE BAY AND TP RVR INLET...LESSER ANOMALIES BUT STILL THE
POTENTIAL FOR BRIEF MINOR FLOODING AT HIGH TIDE TONIGHT. THE DC/ALEX
PORTION OF THE POTOMAC RVR HAS ABOUT THE SAME EFFECTS AS THE
NRN/MIDDLE BAY....W/ NEAR 2FT ANOMALIES. CONDITIONS ARE EXPECTED TO
SLIDE BACK TOWARD NORMAL INTO WED MRNG...BEHIND A COLD FRONT THAT
WILL TURN WINDS BACK TO NW AND PUSH THE EXCESS WATER BACK DOWN THE
BAY/RVR.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR DCZ001.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR DCZ001.
MD...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR MDZ003>007-
     009>011-013-014-016>018.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR MDZ013.
     COASTAL FLOOD WARNING FROM 6 PM THIS EVENING TO 2 AM EDT
     WEDNESDAY FOR MDZ007-011-014.
     COASTAL FLOOD ADVISORY UNTIL 6 PM EDT THIS EVENING FOR MDZ007-
     011-014.
     COASTAL FLOOD ADVISORY UNTIL 10 PM EDT THIS EVENING FOR MDZ017-
     018.
VA...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR VAZ025>031-
     036>040-042-050>057-501-502.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR VAZ053-
     054.
WV...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR WVZ051>053.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 5 PM EDT
     WEDNESDAY FOR ANZ530>532-535-536-538>540.
     GALE WARNING UNTIL 6 PM EDT THIS EVENING FOR ANZ530>532-535-
     536-538>540.
     SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 5 PM EDT
     WEDNESDAY FOR ANZ533-534-537-541>543.
     GALE WARNING UNTIL MIDNIGHT EDT TONIGHT FOR ANZ533-534-537-
     541>543.

&&

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

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