NWS Sterling Area Forecast Discussion

000
FXUS61 KLWX 111940
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
240 PM EST THU MAR 11 2010

.SYNOPSIS...

LOW PRESSURE OVER IOWA WILL SLOWLY APPROACH THE AREA THROUGH FRIDAY
NIGHT. A SECOND AREA OF LOW PRESSURE WILL FORM ALONG THE VIRGINIA
COAST FRIDAY NIGHT INTO SATURDAY...BRINGING A ROUND OF HEAVY RAIN
TO THE AREA. LOW PRESSURE WILL REMAIN IN THE MID ATLANTIC REGION
INTO THE EARLY PART OF NEXT WEEK BEFORE HIGH PRESSURE BUILDS IN
DURING THE MIDDLE PART OF THE WEEK.

&&

.NEAR TERM /TONIGHT/...

WARM FRONTAL PCPN NOW MOVG INTO INTO SW VA WL BE PUSHING INTO
HIGHLAND/NELSON IN THE NEXT FEW HRS. ENTIRE AREA TO BECOME OVC BY
EVE W/ AT LEAST A CHC OF RA BY LATE EVE...BUT OUR EYES WL BE ON THE
COUNTIES WHERE THE N BRANCH OF THE PTMC FLOWS. FLD WTCH HAS BEEN
IN EFFECT FOR SOME TIME...AND WE WL BE WATCHING THE COMBINATION OF
RAINFALL AND SNOWMELT AND THEIR IMPACT ON THE RIVER. A RLTVLY WARM
NGT - W/ LOWS RANGING FM THE M40S IN THE MTNS TO L50S IN DC AND S
DOWN I-95.

&&

.SHORT TERM /FRIDAY/...

BY SUNRISE FRI...WIDESPREAD RAIN WILL BE PUSHING ACROSS THE
SHENANDOAH VLY - INTO THE METRO AREAS AS A WEAK COASTAL LOW MOVES
NWD AND PARALLEL TO THE MID ATLC COAST. THE FIRST SFC LOW WILL BE
CARRYING MAINLY LOCALIZED AREAS OF WEAK-MODERATE LIFT. THIS COASTAL
LOW WILL BEGIN TO DISSIPATE AFTER MOVING CAPE MAY FRI
AFTN...DECREASING THE ONSHORE FLOW MOISTURE FETCH AND WEAKENING
THE LOW LEVEL LIFT. AS THE BULK OF THE PRECIP DOES MOVE THRU THE
REGION EARLY FRI...THE ELY FLOW WILL BE FAVORABLE TO OROGRAPHICALLY
ENHANCED PRECIP ACROSS PORTIONS OF THE VA BLUE RIDGE/CNTRL APLCNS
AND ADJACENT RIDGELINES. THE RAINFALL ACTIVITY WILL BEGIN TO
DISSIPATE FRI AFTN-EVENING BUT ONLY A BRIEF LULL BEFORE THE NEXT
ROUND OF PRECIP.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...

THIS FAR-REACHING AND COMPLEX SYSTEM WILL HAVE A SERIES OF SFC
LOWS DOTTING THE SOUTHEAST AND SRN ATLC COAST. THE MAIN UPPER LOW
BACK ACROSS THE WRN OHIO VLY /THE DRIVING FORCE BEHIND THE
ACTIVITY MOVING UP THE ERN SEABOARD/ WILL BASICALLY PIVOT AROUND
ITSELF FROM LATE FRI INTO SAT. BY LATE FRI NIGHT...A STRONGER
COASTAL LOW WILL BE DEVELOPING OFF THE CAROLINA COAST. MUCH LIKE
OTHER SITUATIONS W/ A CUT-OFF UPPER LOW AND COASTAL SFC LOWS
...TIMING-STRENGTH-TRACK OF THESE FEATURES STILL A BIT UNCERTAIN
ESPECIALLY W/ SUCH A LARGE SYSTEM THAT BASICALLY WILL ENCOMPASS
THE ERN HALF OF THE CONUS AND OFFSHORE ATLC AREAS.

WHAT GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON IS THAT LATE FRI INTO
SAT...A STEADY AND INCREASINGLY STRONG FETCH OF ATLC MOISTURE WILL
BE PUSHING ONSHORE INTO MUCH OF THE CWA. A STRONG 50-70KT 850MB JET
WILL BE POSITIONED WEST-TO-EAST FROM THE CNTRL APLCNS TO THE ATLC
COAST - MOVING NWD OVERNIGHT FRI INTO EARLY SAT. UNDERNEATH THE JET
MAX WILL BE ENHANCED RAIN-RATES...ESPECIALLY W/ UPSLOPE MTN AREAS
/THE ERN SIDES OF THE APLCNS-BLUE RIDGE/. CERTAINLY...QPF VALUES FOR
ANY LOCATION WILL HAVE DECENT VARIABILITY OVER THE COURSE OF THE
EVENT - W/ AT LEAST A COUPLE OF INCHES OF STORM-TOTAL PRECIP
POSSIBLE ACROSS THE MID ATLC. AS MENTIONED...AREAS LIKE RIDGELINES
AND LEE SIDES OF THESE LOCATIONS MAY BE OF CONCERN FOR LOCALIZED
HEAVIER RAINFALL IN A SHORTER AMOUNT OF TIME.

SNOW-MELT ACROSS THE WRN ZONES AND MUCH OF THE CNTRL APLCNS IS THE
OTHER CONCERN. EVEN LIGHT AND INTERMITTENT RAIN OVER THE COURSE OF
THE NEXT COUPLE OF DAYS WILL AIDE IN ENHANCED SNOW MELT AND A
SUBSEQUENT RISE IN NEARLY ALL AREA CREEKS-STREAMS AND EVENTUALLY THE
MAIN STEM RIVERS - THAT MAY LAST INTO THE EARLY PART OF NEXT WEEK.

THE UPPER LOW WILL EVENTUALLY ROTATE BACK AROUND AND MOVE BACK
TOWARD THE EAST...MAKING A TREK ACROSS THE CNTRL/SRN APLCNS LATE SAT
INTO SUN - AND THEN OFF THE MID ATLC COAST BY EARLY MON. AFTER THE
HEAVIEST PRECIP HAS ENDED ACROSS THE REGION BY EARLY SUN
MORNING...MAINLY AN INTERMITTENT DRIZZLE/SCATTERED LIGHT REGIME WILL
BE OVER THE REGION FOR THE REST OF SUNDAY AND INTO EARLY MON. VERY
LITTLE ADDITIONAL RAINFALL EXPECTED. JUST A FAIRLY STEADY SWATCH OF
LIGHT PRECIP COVERING THE MID ATLC STATES...ASSOCIATED W/ THE
BACK-END OF THE EXITING UPPER LOW.

AFTER THIS SYSTEM HAS MOVED OFF THE ATLC COAST...ANOTHER SERIES OF
UPPER DISTURBANCES WILL GLIDE DOWN ACROSS THE GREAT LAKES REGION AND
MIDDLE-UPPER MISSISSIPPI VLY REGIONS. FOR THE MID ATLC THO...LITTLE
IF ANY OF THIS ACTIVITY WILL AFFECT THE REGION OTHER THAN KEEPING
TEMPS DOWN INTO SEASONAL AND SLIGHTLY LOWER THAN AVG TEMPS FOR THE
EARLY-MIDDLE PARTS OF NEXT WEEK.

&&

.AVIATION /TONIGHT THROUGH TUESDAY/...

CIGS WL DEGREADE TO MVFR AT ALL STATIONS DURG THE EVE HRS...W/
VSBYS DROPPING TO IFR IN LGT RAIN/FG AFTR MDNGT. CIGS WL DESCEND
FURTHER DURG FRI MRNG.

AVIATION CONDS LOOK TO BE RLTVLY POOR FOR MUCH OF THE WKND. STRONG
LO LVL ERLY WINDS FRI NGT/SAT WL BRING RAIN TO IAD/BWI/DCA ALONG
W/ LO CIGS AS WELL AS LO LVL WIND SHEAR. CONDS LOOK TO REMAIN POOR
INTO THE BEGINNING OF THE NEW WK B4 FAINLLY SEEING IMRVMNT TUE.

&&

.MARINE...

SCA WL GO INTO EFFECT FOR THE BAY/LOWER PTMC ON FRI..AND THEN THE
UPPER PTMC FRI NGT. THIS WL LKLY THEN RMN IN EFFECT FOR THE RMNDR
OF THE WKND.

&&

.HYDROLOGY...

FLD WTCH CURRENTLY IN EFFECT FOR THE N BRANCH OF PTMC
TNGT...XTENDING INTO THE MAIN PTMC E OF CUMBERLAND FRI MRNG.

FOR THE TIME BEING WE HAVE DECIDED TO HOLD ON XPANDING THE FFA
AREA FURTHER E...BUT THE PTNL FOR FURTHER XPANSION DOES EXIST
WHICH WOULD PRBLY BE DONE ON THE MID SHIFT FOR FRI NGT/SAT. MD/ERN
PANHANDLE WOULD BE MAIN THREAT AREA. THIS WOULD BE FOR THE SMALLER
RIVERS. 12 HR FLD GDNC IN ALLEGANY CO. IS ONLY 1"..HOWARD CO. ONLY
1.4" IN 12 HRS.

PITPOT FCSTG MDT/MAJ FLDG ALONG THE PTMC BTWN SAT AND MON. AS WE
ARE 3-4 DAYS OUT IT IS STILL TOO EARLY TO FCST CREST HGTS.

&&

.TIDES/COASTAL FLOODING...

THERE IS A POTENTIAL FOR COASTAL FLOODING AS LOPRES TRACKS ACROSS
THE MID-ATLANTIC REGION THIS WEEKEND. AS DISCUSSED IN PREVIOUS
DISCUSSIONS...THERE ARE MULTIPLE FACTORS INVOLVED - 1) FRESHWATER
FROM POTENTIALLY HEAVY RAINS FRI NGT AND SAT FLOWING DOWNSTREAM IN
THE PTMC 2) INCREASING ASTRONOMICAL/LUNAR INFLUENCE AS WE APPROACH
THE NEW MOON ON MONDAY AND 3) LOW LVL SERLY FLOW FRI-SAT WILL HINDER
DRAINAGE IN THE PTMC/CHES BAY. WITH ALL THESE FACTORS...AT LEAST MINOR
COASTAL FLOODING APPEARS INCREASINGLY LIKELY SAT AND SUN.

&&

.EQUIPMENT...

WE HAVE JUST RECEIVED THE PART THAT WL (HOPEFULLY) GET THE 88D
BACK UP AND RUNNING.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...FLOOD WATCH FROM 7 PM EST THIS EVENING THROUGH SATURDAY
     EVENING FOR MDZ501-502.
     FLOOD WATCH FROM FRIDAY MORNING THROUGH SATURDAY EVENING FOR
     MDZ003.
VA...FLOOD WATCH FROM 7 PM EST THIS EVENING THROUGH SATURDAY
     EVENING FOR VAZ021.
WV...FLOOD WATCH FROM 7 PM EST THIS EVENING THROUGH SATURDAY
     EVENING FOR WVZ054-501>504.
     FLOOD WATCH FROM FRIDAY MORNING THROUGH SATURDAY EVENING FOR
     WVZ050>053-055.
MARINE...SMALL CRAFT ADVISORY FROM 8 AM FRIDAY TO 6 AM EST SATURDAY FOR
     ANZ530>534-537>543.
     SMALL CRAFT ADVISORY FROM 7 PM FRIDAY TO 6 AM EST SATURDAY FOR
     ANZ535-536.

&&

$$

PRODUCTS...WOODY!/GMS

NWS LWX Office Area Forecast Discussion