Special Weather Statement, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
327 PM EDT SUN AUG 26 2012

.SYNOPSIS...

LOW PRESSURE WILL REMAIN WEAKEN OVER THE REGION TODAY BEFORE MOVING
OFF TO THE EAST TONIGHT. A COLD FRONT WILL APPROACH FROM THE
NORTHWEST LATE MONDAY BEFORE PASSING THROUGH TUESDAY. THE BOUNDARY
WILL STALL OUT TO OUR SOUTH DURING THE MIDDLE PORTION OF THE WEEK.
LOW PRESSURE - THE REMNANTS OF ISAAC...MAY AFFECT THE MID ATLANTIC
REGION NEXT WEEKEND.

&&

.NEAR TERM /TONIGHT/...

THE SFC LOW NOW MEANDERING INTO N CNTRL VA...BUT ON A SLOW DECLINE
IN TERMS OF INTENSITY. HOWEVER...THE WARM SECTOR REGION OF THE LOW
STILL GOING STRONG. SEVERAL BANDS OF TROPICAL-TYPE CONVECTION
STREAMING NWD ACROSS THE AREA AND TOWARD THE AREA FROM THE VA
TIDEWATER REGION. THE MAIN THREAT FOR A LARGE-SCALE REGION OVER THE
NEXT FEW HRS WILL BE LOCALIZED FLOODING.

A FLASH FLOOD WATCH IS NOW IN EFFECT FOR MUCH OF THE ERN HALF OF THE
CWA. THE AREAS HIGHLIGHTED ARE THE DC/BALT METRO AREAS...SRN MD AND
BACK TOWARD THE ERN WV PANHANDLE. THOUGH THE AXIS OF THESE HEAVY
RAIN BANDS WILL PIVOT SLOWLY TOWARD THE EAST AND NORTH...SEVERAL
STRIPES OF OUR AREA ARE RECEIVING HIGH RAIN RATES AND IN SHORT TIME
WINDOW. LOCALIZED HEAVY RAIN DROPPING A QUICK COUPLE OF INCHES WILL
LIKELY LEAD TO FLASH FLOODING IN AREAS THAT HAVE ALREADY SEEN RAIN
EARLIER THIS MRNG...AND PERIODICALLY THRU THE DAY.

KEEP THIS IN MIND W/ ANY OUTDOOR PLANS INTO THE EVE HRS - EVEN
WEAKER CONVECTION WILL PRODUCE LIGHTNING...HEAVY DOWNPOURS AND
GUSTY WINDS. VERY LOCALIZED AND RELATIVELY SMALL SHOWERS W/ DROP A
QUICK BURST OF HEAVY RAIN...LASTING FOR ONLY A FEW MINUTES...THEN
ANOTHER ROUND MAY BEGIN SHORTLY THEREAFTER.

AS THE LOW GRADUALLY WEAKENS IT WL MEANDER FURTHER INLAND AND
AWAY FROM THE WARMER COASTAL WATERS...THE TRAINING WAVES OF
SHOWERS WILL PIVOT AROUND AND CHANGE ORIENTATION. THIS WILL ALLOW
FOR PLACES LIKE DC PROPER AND N CNTRL MD TO POTENTIALLY RECEIVE
SOME RAIN SHOWERS INTO TONIGHT. CLOSER TO THE CENTER OF THE LOW
WHICH IS OVER THE LOWER SHEN VLY...CONDITIONS WILL BE COOL BUT
MAINLY DRY.

THE LOW WILL AGAIN TRANSITION OVERNIGHT...WEAKENING TO WHERE THE
SHOWER ACTIVITY WILL BE LESS WIDESPREAD AND LESS INTENSE. CLOUDY
SKIES WILL KEEP TEMPS MODERATED INTO THE 60S-L70S OVERNIGHT.

&&

.SHORT TERM /MONDAY/...

MONDAY WILL BE THE RECOVERY DAY FROM THE WEEKEND LOW...AS PRECIP
DISSIPATES FROM WEST-TO-EAST OVERNIGHT. BY SUNRISE...ANY LINGERING
SHOWER ACTIVITY IS EXPECTED TO BE CENTERED OVER THE MD BAY AND
DISSIPATING OVER THE I-95 CORRIDOR. CLOUDS WILL ALSO BEGIN TO CLEAR
UP ACROSS THE WEST AND PARTLY CLOUDY/MOSTLY SUNNY SKIES WILL TAKE
OVER TOWARD THE AFTN HRS.

THIS LULL PERIOD WILL BE RELATIVELY SHORT AS A COLD FRONT MAKES ITS
WAY TOWARD THE AREA LATER IN THE DAY. THE FRONT WILL BE ON THE
DOORSTEP OF THE NW QUADRANT OF THE AREA BY EVE. GUIDANCE CARRIES
ONLY A PERCENTAGE OF THE OHIO VLY PRECIP ACROSS THE MTNS...LARGELY
WASHING OUT AS IT NEARS THE AREA. A FEW SHOWERS AND ISOLATED TSTMS
WILL BE POSSIBLE HEADING INTO THE EVE/OVERNIGHT HRS...WHILE THE
FRONT SLOWS DOWN AND CROSSES THE AREA INTO TUE.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...

IN THE DSCN SAT AFTN I WROTE THIS: "SUSPECT THE MID-LATE WK..THE
MAIN PLAYERS ARE 1) THE AFOREMENTIONED CD FNT 2) HIGH PRES MOVG
INTO THE NE BEHIND THE FNT AND 3) THE REMNANTS OF ISAAC."

NOTHING HAS CHGD REGARDING THESE 3 THINGS. THE GOOD NEWS IS THAT
FOR THE 2ND HALF OF THE WORKWEEK HIGH PRES LOOKS TO BE THE MAIN
PLAYER FOR THE MID ATLC WHILE ALL EYES ARE ON THE GULF STATES.

SCT TSTMS ARE PSBL MON NGT AS THE CD FNT/TROF APRCH FM THE NW. IT
SHOULD BE A FAIRLY WARM NGT W/ LOWS IN THE MU60S W OF I-95...L70S
IN THE CITIES AND E OF THE HWY.

TUE THE FNT WL PUSH THRU...MOSTL LKLY DURG THE 1ST PART OF THE DAY
WHEN CNVCTN WL NOT BE AS MUCH OF A CONCERN. BRKS OF SUN IN THE
AFTN WL HELP TEMPS GET INTO THE MU80S.

AND AFTR THAT THE MAIN PLAYER WL BE HIGH PRES COMING DOWN FM THE
UPR MIDWEST. XPCT WED AND THU WL BE FAIRLY COMFORTABLE W/ HIGHS IN
THE M80S...DWPTS IN THE U50S/L60S. AS OF NOW IT LOOKS LK THE CD
FNT WL SINK FAR ENOUGH S THAT THE MID ALTC CLDS WOULD BE OF THE
MID/HIGH VARIETY.

GFS KEEPS AREA UNDER HIGH PRES UNTIL AT LEAST SAT. THE ECM...00Z
EDITION...DRAWS REMNANTS OF ISAAC INTO TN BY FRI AFTN WHILE GFS
TAKES IT INTO E TX. OBVIOUSLY IT'S HARD TO MAKE A FCST FOR NEXT
WKND WHEN THERE IS SO MUCH DISPARITY IN THE LONG RNG MDLS. FOR NOW
WL MAKE FCST USING GFS SOLN WHICH WOULD CAUSE REMNANT LOW TO TURN
INTO THE OH VLLY NEXT SUN...WHICH BRINGS ABT NEED FOR CHC POPS
IN THE MID ATLC. THIS FCST IS CERTAIN TO HV SOME ADJUSTMENTS IN THE
COMING DAYS.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...

OUTSIDE OF THE CURRENT SHOWER/TSTM ACTIVITY...THE LOWEST CIG HEIGHTS
HAVE MIXED-OUT TO THE HIGH-END MVFR RANGE W/ SOME LOW-END VFR AS
WELL. THIS WILL CONTINUE THRU LATER TONIGHT BEFORE CIGS DROP AGAIN
BACK TOWARD SOLID MVFR. BRIEF IFR POSSIBLE BY THE PREDAWN HRS ACROSS
THE VA/MD PIEDMONT BUT WILL MIX OUT INTO THE MID MRNG MON.
CONDITIONS WILL IMPROVE AND SKIES WILL CLEAR OUT TOWARD LATE MRNG
MON.

HIGH PRES XPCTD TO BUILD INTO THE RGN TUE-FRI. MAIN PROBLEM WOULD
BE PTNL FOR FOG DVLPMNT LATE NGT/ERLY MRNG...AT CHO/MRB/IAD.

&&

.MARINE...

MARGINAL SCA GUSTS FROM THE AMBIENT WIND CONDITIONS...BUT THE HIGHER
GUSTS ARE APPEARING FROM AREA SHOWER AND TSTM ACTIVITY. THE SCA
LASTS THRU 8 PM FOR ALL AREAS BUT THE DC TP ZONE. SPEC MARINE WRNGS
WILL CONTINUE TO BE ISSUED FOR THE STRONGER TSTMS INTO LATE TONIGHT.
THIS ACTIVITY IS EXPECTED TO DISSIPATE LATE TONIGHT...W/ MAINLY A
NUMBER OF SHOWERS CONTINUING INTO THE EARLY MRNG MON. A GENERAL
10-15KT BREEZE OUT OF THE SOUTH IS EXPECTED ON MON AFTN.

HIGH PRES XPCTD TO BUILD INTO THE AREA TUE. SCA WINDS PSBL DURG THE
DAY. THE HIGH SHOULD CENTER OVR THE AREA DURG MIDWEEK.

&&

.TIDES/COASTAL FLOODING...

TIDAL ANOMALIES NOW AROUND A FOOT ACROSS THE MD BAY AND TP RVR...BUT
HEADING INTO - AND OUT OF - THE AFTN H.T. CYCLE...AREAS ARE BELOW
MINOR FLOODING. IF THESE LEVELS STAY THEIR COURSE...THE NEXT HIGH
TIDE CYCLE WILL CLOSER TO MINOR FL LEVELS IN SELECT LOCATIONS. WIND
DIRECTION AND RELATIVE SPEED WILL ALSO BE A FACTOR...AND WILL
CONTINUE TO MONITOR OVER THE NEXT FEW HRS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLASH FLOOD WATCH UNTIL 10 PM EDT THIS EVENING FOR DCZ001.
MD...FLASH FLOOD WATCH UNTIL 10 PM EDT THIS EVENING FOR MDZ003>007-
     009>011-013-014-016>018.
VA...FLASH FLOOD WATCH UNTIL 10 PM EDT THIS EVENING FOR VAZ042-
     052>055-057.
WV...FLASH FLOOD WATCH UNTIL 10 PM EDT THIS EVENING FOR WVZ051>053.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR
     ANZ530>534-536>543.

&&

PRODUCTS...GMS/WOODY!

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