000
FXUS61 KLWX 170741
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
341 AM EDT FRI MAY 17 2013

.SYNOPSIS...
A FRONTAL BOUNDARY WILL STALL OUT TO THE SOUTH THROUGH THIS
WEEKEND...AS HIGH PRESSURE ANCHORS ITSELF ACROSS THE NORTH
ATLANTIC. THE FRONTAL BOUNDARY WILL RETURN TO THE NORTH AS A WARM
FRONT EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
A WEAK PSEUDO-STATIONARY FRONTAL BOUNDARY HAS FINALLY DRIFTED SOUTH
OF THE MASON-DIXON LINE AND IS HELPING TO CLEAR OUT THE AREA
OVERNIGHT. THIS BOUNDARY CONTINUES TO STRETCH FROM THE ATLC
COAST...DIRECTLY WEST TO THE PLAINS. NOW W/ THE BOUNDARY SET-UP OVER
THE REGION AND NO DISCERNIBLE SYSTEMS COMING DOWN THE PIKE IN THE
NEXT COUPLE OF DAYS...IT WILL RESIDE JUST SOUTH OF THE AREA AND BE
THE FOCUS FOR DAILY WEAKLY-FORCED CONVECTION DEPENDING ON WHERE IT
IS LOCATED.

PRECIP ALONG THIS BOUNDARY AS ALL BUT ENDED OVER THE PAST FEW HRS
AND CONDITIONS WILL BE STABLE UNTIL DAWN. LOCALIZED HRRR CONTINUES
TO DEVELOP TERRAIN CONVECTION LATER TODAY. ISOLATED SHOWERS AND
TSTMS WILL LIKELY DEVELOP THIS AFTN/EVE FROM A LIGHT ESE FLOW
BANKING INTO THE ERN SIDES OF THE HIGHEST TERRAIN OF THE CENTRAL
APPALACHIANS...TAPERING OFF TOWARD THE SHEN VLY. STEERING FLOW WILL
BE INCREDIBLY LIGHT...A MEAN 10-15KT FLOW ALL THE WAY UP TO THE
UPPER LEVELS...WON`T TAKE MUCH OF THIS ACTIVITY EWD. WEAK OUTFLOW
BOUNDARIES WILL HAVE TO DO THAT IN ORDER TO SPREAD POPS MUCH FURTHER
EAST.

CUT BACK ON POPS OVERNIGHT FOR THE ERN HALF OF THE REGION.
DEPICTIONS FROM THE NAM/GFS FOR A LOCALIZED BATCH OF PRECIP
STREAMING ACROSS A BULK OF THE CWA DURING THE PREDAWN HRS SAT STILL
A BIT SUSPECT. PLACEMENT OF SUCH A SMALL-SCALE UPPER WAVE CAUGHT IN
THE FLOW STILL A BIT TOO FAR OUT TO PLACE IN THE CURRENT FORECAST.

TEMPS TODAY WILL BE EVEN MORE MODERATED TODAY FROM YESTERDAY W/
DRIER AIR AND A LIGHT BUT STEADY NE BREEZE COMING DOWN THE I-95
CORRIDOR FOR MUCH OF THE DAY. MOST AREAS WILL PEAK IN THE U70S...W/
A FEW LOCALES HITTING 80 LATE THIS AFTN. OVERNIGHT LOWS WILL BE
SIMILAR TO THE CURRENT OVERNIGHT PERIOD...TEMPS DROPPING INTO THE
U50S/L60S.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
FRONTAL BOUNDARY WILL REMAIN STALLED OUT TO THE SOUTH THIS
WEEKEND...AS HIGH PRESSURE ANCHORS ITSELF OFF THE NORTHEAST
COAST AND NORTH ATLANTIC.

RESULT WILL BE AN EAST OR SOUTHEAST FLOW IN THE LOW LEVELS WHICH
WILL PROMOTE CLOUDY SKIES MUCH OF THE TIME AND ALSO TEMPER WARMING.
THE DEGREE TO WHICH WARMING IS TEMPERED DIFFERS BETWEEN THE NAM AND
GFS DERIVED MOS GUIDANCE...WITH THE GFS BEING LOWER BY 10 DEGREES
IN SOME CASES FOR MAXIMA. DIFFERENCES ARE LIKELY EXPLAINED BY THE
PRESENCE OF PRECIPITATION OR LACK THEREOF.

THE GFS IS MUCH MORE AGGRESSIVE BRINGING MEASURABLE RAINFALL ACROSS
THE CWA WHILE THE NAM IS MORE CONSERVATIVE. SREFS FORMS A NICE
COMPROMISE...FOCUSING SHOWERS /AND PERHAPS A FEW THUNDERSTORMS/
ACROSS THE SOUTHWEST PORTION OF THE CWA SATURDAY AND THEN
SPREADING CHANCES /OR LIKELIHOODS/ FOR RAINFALL NORTHEAST INTO
SUNDAY. MOISTURE IS CERTAINLY THERE...WHETHER ISENTROPIC LIFT
WORKS THIS FAR NORTH AND WHETHER THERE ARE SHORTWAVES IN 500 MB
FLOW IS SOMEWHAT IN QUESTION.

FOR TEMPERATURES...HAVE TAKEN A BLEND OF BIAS CORRECTED MAV/MET AND
ALSO ECMWF WHICH FAVORS LOWER 70S ACROSS MUCH OF THE AREA FOR
MAXIMA. NO MATTER HOW ONE SLICES IT...MAXIMA OVER THE WEEKEND WILL
LIKELY BE BELOW NORMAL WITH NEAR TO SLIGHTLY ABOVE NORMAL MINIMA.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
FRONTAL BOUNDARY WILL LIFT BACK TO THE NORTH AS WARM FRONT EARLY
NEXT WEEK...MOST LIKELY LATE MONDAY INTO EARLY TUESDAY AND PLACING
THE CWA IN A WARM SECTOR DURING THE MIDDLE OF THE WEEK. THIS SHOULD
BRING LOW LEVEL SOUTH-SOUTHWEST FLOW WHICH WILL KEEP MOISTURE ACROSS
THE AREA AND SOME SURFACE-BASED INSTABILITY. THEREFORE FORECAST
REFLECTS A CHANCE OF MAINLY DIURNAL CONVECTION EACH DAY. FRONTAL
BOUNDARY MAY APPROACH ON THURSDAY.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
A WEAK FRONTAL BOUNDARY SINKING SWD THRU THE AREA THIS MORNING.
THIS FEATURE WILL STABILIZE MUCH OF THE AREA...W/ DRIER AIR
SPREADING ACROSS THE REGION AND CLOUDS DISSIPATING ACROSS THE
AREA. THE SWRN QUADRANT OF THE CWA...AREAS TO THE SOUTH AND WEST
OF KCHO WILL REMAIN THE TARGET FOR ISOLATED SHOWERS...ANY FOG AND
MID CLOUDS TODAY. OUTSIDE OF THIS AREA...ONLY A FEW BATCHES OF
MID/UPPER CLOUD DECKS TODAY...SO SOLID VFR CONDITIONS THRU THE TAF
PERIOD. A LIGHT NELY FLOW THIS MRNG WILL EVENTUALLY SWITCH SELY
LATER TONIGHT.

EAST-SOUTHEAST FLOW DEVELOPS THIS WEEKEND. IT IS BECOMING MORE
LIKELY THAT A PERIOD OF MVFR/IFR CIGS WILL DEVELOP SATURDAY NIGHT
INTO EARLY SUNDAY AND AGAIN SUNDAY NIGHT INTO EARLY MONDAY BEFORE A
STALLED FRONTAL BOUNDARY WORKS BACK TO THE NORTH AS A WARM FRONT
EARLY NEXT WEEK. PRECIPITATION WOULD LIKELY BE SHOWERS OVER THE
WEEKEND...THEN THUNDERSTORMS WILL BE POSSIBLE EARLY TO MID NEXT WEEK
IN THE WARM SECTOR.

&&

.MARINE...
LIGHT WINDS TODAY AND TONIGHT...AS A WEAK FRONTAL BOUNDARY SLIDES
SOUTHWARD. BEHIND THE FRONT...WINDS WILL COME DOWN FROM THE NE FOR
THE MRNG HAS AND EVENTUALLY TURN SELY LATER TODAY AS THE BOUNDARY
DROPS SOUTH OF THE TP/CHES BAY CONFLUENCE REGION.

FRONTAL BOUNDARY WILL REMAIN SOUTH OF THE WATERS THROUGH THE WEEKEND
BEFORE LIFTING BACK TO THE NORTH EARLY NEXT WEEK. EAST-SOUTHEAST
FLOW IS EXPECTED BUT WITH A RELATIVELY WEAK GRADIENT WINDS ARE
GENERALLY EXPECT TO REMAIN BELOW SCA CRITERIA. WINDS TURN TO THE
SOUTH EARLY NEXT WEEK.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...GMS/BPP
NEAR TERM...GMS
SHORT TERM...BPP
LONG TERM...BPP
AVIATION...GMS/BPP
MARINE...GMS/BPP