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000
FXUS61 KPHI 151417
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1017 AM EDT WED MAY 15 2013

.SYNOPSIS...
LOW PRESSURE TRACKING ACROSS SOUTHEASTERN CANADA TODAY WILL PULL A
WARM FRONT ACROSS OUR AREA, THEN A COLD FRONT SLIDES THROUGH OUR
REGION TONIGHT. THIS FRONT WILL STALL TO OUR SOUTH THURSDAY THROUGH
THE WEEKEND AND INTO MONDAY AS HIGH PRESSURE BUILDS ACROSS NEW
ENGLAND. THE BOUNDARY SHOULD THEN LIFT NORTH OF OUR AREA AS A WARM
FRONT LATE MONDAY INTO TUESDAY, AS LOW PRESSURE TRACKS ACROSS THE
GREAT LAKES REGION.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HIGH PRESSURE WILL REMAIN TO THE SOUTHEAST OF THE AREA TODAY AND
GRADUALLY MOVE OFFSHORE. AS IT DOES, LOW PRESSURE OVER SERN
CANADA WILL ADVANCE EWD BRINGING A STRONG WARM FRONT THROUGH THE
REGION THIS AFTERNOON. THERE WILL BE SOME RAIN WITH THE FRONT, BUT
THERE IS CONSIDERABLE DISAGREEMENT WITHIN THE MDLS AS TO HOW MUCH.
MDL SOLUTIONS AT THIS CLOSE TIME SCALE VARY FROM VIRTUALLY DRY TO
ALMOST 0.10 IN SPOTS. REGARDLESS, IT LOOKS TO BE FAIRLY CLOUDY AS
COMPARED TO THE LAST COUPLE OF DAYS BUT MUCH WARMER, WITH HIGH
TEMPERATURES REBOUNDING TO NEAR OR EVEN SLIGHTLY ABOVE NRML. BY
AFTN, THE WIND WILL INCREASE FROM THE S AS THE FRONT APPROACHES.

THERE COULD BE SOME THUNDER AS WELL THIS AFTN DUE TO THE WARM
FRONT, AND MOISTURE WILL BE INCREASING AS DEW POINTS RECOVER INTO
THE 50S AND PUSH 60. OF SOME CONCERN ARE THE FORECAST STEEP MID
LEVEL LAPSE RATES, THE CONSIDERABLE SHEAR AND THE LOW LEVEL JET.
REGARDING THE JET, SOUNDINGS FROM DTX TO ILN TO OHX CAME IN WITH
H925 WINDS AROUND 45 KT THIS MORNING. THE NAM AND GFS EACH WERE
CLOSER TO THE TRUTH ON THESE THAN THE ECMWF, BUT THE NEW NAM IS
TEMPERING THOSE WINDS SOME FOR THIS AFTERNOON AND LOOKS MORE LIKE
THE ECMWF THAN THE GFS. AS NOTED PREVIOUSLY, THE DEW POINTS WILL
TAKE SOME TIME TO RISE, AND WE PRESENTLY DON`T EXPECT THEM TO
REACH LEVELS SUFFICIENT TO ELIMINATE THE SURFACE BASED CIN THAT
THE AMERICAN MODELS SHOW. WE THEREFORE ARE NOT READY TO START
TALKING ABOUT SEVERE CONVECTION.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
A CDFNT WILL CROSS THE REGION TONIGHT AND PRECIP SHOULD COME TO
AN END. HOWEVER, A WEAK BNDRY WILL REMAIN JUST TO THE S OVERNIGHT.
THE WIND WILL TURN MORE WLY OR NWLY BEHIND THE CFP.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
THE OVERALL SYNOPTIC SETUP IS COMPRISED OF A TROUGH IN EASTERN
CANADA THAT AMPLIFIES SOME ACROSS THE NORTHEAST FRIDAY AND INTO THE
WEEKEND. THE UPPER-LEVEL FLOW MAY THEN UNDERGO ADDITIONAL
AMPLIFICATION LATE IN THE WEEKEND AND DURING THE FIRST HALF OF NEXT
WEEK, AS A TROUGH EJECTS OUT INTO THE PLAINS WITH TIME ALLOWING
DOWNSTREAM RIDGING TO TAKE PLACE. THIS GENERALLY ALLOWS WARMING TO
CONTINUE TO OCCUR INTO THE EAST, HOWEVER A POTENTIAL FLY IN THE
OINTMENT IS SURFACE HIGH PRESSURE THAT BUILDS DOWN INTO NEW ENGLAND
OVER THE WEEKEND. THIS COULD ALLOW AN ONSHORE FLOW TO OCCUR ACROSS
OUR AREA, RESULTING IN COOLER TEMPERATURES. WE USED A MODEL BLEND
APPROACH THURSDAY THROUGH FRIDAY, THEN BLENDED IN NEW WPC GUIDANCE
INTO CONTINUITY.

FOR THURSDAY AND FRIDAY...AN UPPER-LEVEL TROUGH ACROSS EASTERN
CANADA AMPLIFIES SOUTHWARD SOME IN THE NORTHEAST THURSDAY. SINCE
THIS TROUGH IS NOT FORECAST TO DIG ALL THAT FAR SOUTH, A FRONTAL
BOUNDARY WILL BE STALLING IN A WEST TO EAST FASHION TO OUR SOUTH.
SOME SHORT WAVE ENERGY ON THE SOUTHERN SIDE OF THE TROUGH COMBINED
WITH A TIGHTENING THERMAL GRADIENT COULD RESULT IN SOME SHOWERS OR
THUNDERSTORMS ACROSS THE DELMARVA THURSDAY AFTERNOON. THESE SHOULD
WANE THURSDAY NIGHT AS THEY MOSTLY THRIVE OFF OF THE DAYTIME
HEATING. A SIMILAR SETUP FOR FRIDAY, HOWEVER HIGH PRESSURE IS
FORECAST TO START BUILDING SOUTHWARD WHICH SHOULD PUSH THE SURFACE
FRONT A BIT FURTHER SOUTH. IF THIS IS THE CASE, ANY CONVECTION
SHOULD THEN REMAIN TO OUR SOUTH DURING FRIDAY. WE MAINTAINED SOME
LOW CHC POPS ACROSS THE DELMARVA ON THURSDAY GIVEN THE PROXIMITY TO
THE STALLING FRONT, THEN SLIGHT CHC POPS FRIDAY AFTERNOON. THURSDAY
LOOKS TO BE WARM WITH A WESTERLY FLOW OCCURRING.

FOR SATURDAY AND SUNDAY...HIGH PRESSURE CENTERED WELL TO OUR NORTH
SATURDAY IS FORECAST TO SETTLE SOUTHWARD SUNDAY. THIS IS IN RESPONSE
TO A TROUGH MOVING INTO THE PLAINS WHICH DRIVES A RIDGE EASTWARD. A
TROUGH IN THE ATLANTIC MAY THEN PROVIDE A BLOCK FOR A TIME, ALLOWING
SURFACE HIGH PRESSURE TO MOVE SOUTH FIRST BEFORE SHIFTING EASTWARD.
THE TIMING AND POSITIONING OF THIS SURFACE HIGH WILL HAVE AN IMPACT ON
THE RETURN FLOW THAT EVENTUALLY WILL SETUP. A WAA PATTERN SHOULD BE
ONGOING UP THE OHIO VALLEY DURING THIS TIME, WHICH HELPS TO TURN THE
STALLED BOUNDARY INTO A WARM FRONT. SOME GUIDANCE WANTS TO TOSS SOME
CONVECTION ACROSS THE DELMARVA AT TIMES, HOWEVER THE SURFACE FRONT
BEING FARTHER SOUTH MAY END UP PREVENTING THIS. WE SHOULD ALSO HAVE
AN ONSHORE FLOW OCCURRING DURING THE WEEKEND, RESULTING IN COOLER
TEMPERATURES /PERHAPS MORE CLOUDS/ ESPECIALLY CLOSER TO THE COAST.
AS OF NOW, THE ONSHORE FLOW DOES NOT LOOK TERRIBLY ROBUST.

FOR MONDAY AND TUESDAY...WE GENERALLY FOLLOWED CLOSER TO WPC
GUIDANCE WHICH SLOWED THE WARM FRONT A BIT ON ITS NORTHWARD MOTION.
THIS IS MOSTLY DUE TO THE SURFACE LOW ACROSS THE MIDWEST SLOWING
PERHAPS SOME AS SURFACE HIGH PRESSURE GRADUALLY EASES OFF THE NEW
ENGLAND COAST. THE WARM FRONT SHOULD BE LIFTING NORTH OF OUR AREA
LATER MONDAY AND TUESDAY. THERE MAY NOT BE MUCH WITH THE WARM FRONT,
AS WE THEN AWAIT FOR THE COLD FRONT TO ARRIVE LATE TUESDAY. GIVEN
LOWER CONFIDENCE WITH THE TIMING AND CONVECTIVE EVOLUTION, WE
MAINTAINED LOW CHC POPS ACROSS THE AREA.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

A LOW CONFIDENCE FCST FOR LATER TODAY. CONDS WILL START OUT VFR
AND EVEN IF THERE IS SOME LIGHT RAIN, IT SHOULD BE FALLING OUT OF
MID LEVEL CLOUDS AND BE OPERATIONALLY INSIGNIFICANT.

THEN, HIGH PRESSURE TO THE SE WILL CONTINUE TO MOVE OFFSHORE. A
STRONG WARM FRONT WILL CROSS THE REGION THIS AFTERNOON AND SOME
MDLS INDICATE THAT BY EVENING THERE COULD BE MVFR AND EVEN LWR
CONDS. NOT BUYING THIS COMPLETELY JUST YET BUT THE POTENTIAL IS
THERE ANYTIME YOU ARE INVOF A WMFNT. THERE COULD BE SOME TSRA THIS
AFTN AND EVENING BUT CHCS ARE TOO LOW AT AN INDIVIDUAL SITE TO
MENTION ATTM. THEN LATE TONIGHT A CDFNT WILL CROSS THE REGION AND
THINGS SHOULD IMPROVE BEHIND THAT CFP.

WE ARE A LITTLE CONCERNED ABOUT 40 KT OR GREATER WINDS OCCURRING AT
ABOUT 2000 FT OFF THE SURFACE LATER THIS AFTERNOON. THERE WOULD BE
ABOUT 40 DEGREES AND 25 KNOTS OF SHEAR IN THE LAYER. THE LATEST
MODELS SEEM TO BE CONFINING THAT TO ALONG THE COAST.

SURFACE WINDS WERE COMING AROUND TO S AND WERE BEGINNING TO PICK
UP THIS MORNING. THEY COULD GUST TO OR A BIT ABOVE 20 KT LATER
TODAY. THEY WILL BECOME MORE WLY TONIGHT AND EVENTUALLY NWLY
BEHIND THE CFP.

OUTLOOK...
THURSDAY THROUGH FRIDAY...MOSTLY VFR. A SHOWER OR THUNDERSTORM
POSSIBLE SOUTH OF KPHL THURSDAY AFTERNOON. WEST-NORTHWEST WINDS
AROUND 10 KNOTS, HOWEVER POSSIBLY TURNING SOUTHEAST FRIDAY AFTERNOON
AT KMIV AND KACY.

SATURDAY THROUGH SUNDAY...MOSTLY VFR, ALTHOUGH AN ONSHORE FLOW MAY
BRING IN SOME LOWER CLOUDS OFF THE OCEAN /LOWER CONFIDENCE/. A
SHOWER OR THUNDERSTORM POSSIBLE MAINLY EACH AFTERNOON WITH PERHAPS
LOCAL MVFR. LIGHT WINDS EARLY SATURDAY BECOMING SOUTHEAST NEAR 10
KNOTS.

&&

.MARINE...
WILL LEAVE THE SCA IN EFFECT UNCHANGED AS INCREASING SLY FLOW AHEAD
OF A WARM FRONT WILL CAUSE AN INCREASE IN SEAS. THE WIND IS ALSO
FORECAST TO PICK UP LATER TODAY. A CFP WILL OCCUR LATER TONIGHT
AND THE WIND WILL BECOME MORE WLY THEN NWLY BEHIND IT.

OUTLOOK...
A COLD FRONT IS FORECAST TO SETTLE TO OUR SOUTH THURSDAY AND THEN
STALL. MEANWHILE, HIGH PRESSURE OVER EASTERN CANADA WILL GRADUALLY
BUILD SOUTHWARD FRIDAY AND OVER THE WEEKEND. THE WINDS ARE
ANTICIPATED TO BE LIGHTER WITH SEAS SUBSIDING DURING THURSDAY INTO
FRIDAY. THE SEAS ON THE OCEAN COULD BE RIGHT NEAR 5 FEET FOR AWHILE
THURSDAY, HOWEVER THEY SHOULD BE LOWERING THEREFORE WE OPTED TO NOT
EXTEND THE SMALL CRAFT ADVISORY ATTM BEYOND 12Z. OVER THE WEEKEND,
AN EAST OR SOUTHEAST FLOW IS FORECAST TO OCCUR. THIS FLOW DOES NOT
APPEAR TO BE ALL THAT ROBUST, ALTHOUGH SOME LOCAL ENHANCEMENT COULD
OCCUR ESPECIALLY NEARSHORE AND UP DELAWARE BAY. AS OF NOW, WE KEPT
THE CONDITIONS BELOW SMALL CRAFT ADVISORY CRITERIA.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EDT THURSDAY FOR ANZ450>455.
     SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ431.

&&

$$
SYNOPSIS...GORSE
NEAR TERM...NIERENBERG/DELISI
SHORT TERM...NIERENBERG
LONG TERM...GORSE
AVIATION...GORSE/NIERENBERG/DELISI
MARINE...GORSE/NIERENBERG