AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
354 AM EDT MON APR 18 2011

.SYNOPSIS...
A COLD FRONT WILL MOVE INTO THE AREA, STALLING ACROSS OUR REGION
TONIGHT AND THEN REMAINING IN THE VICINITY THROUGH TUESDAY. A LOW
PRESSURE SYSTEM MOVING ACROSS THE GREAT LAKES ON WEDNESDAY WILL
DRAG THE BOUNDARY NORTHWARD AS A WARM FRONT AND THEN DRAG A COLD
FRONT THROUGH EARLY THURSDAY, HIGH PRESSURE WILL THEN BUILD IN
FROM THE WEST FOR THE REST OF THE WEEK. ANOTHER LOW PRESSURE
SYSTEM IS FORECAST TO MOVE ACROSS THE GREAT LAKES ON FRIDAY NIGHT
INTO SATURDAY, PULLING A COLD FRONT THROUGH OUR REGION EARLY
SUNDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A WEAK BACK DOOR FRONT WILL MOVE INTO THE AREA THIS MORNING BUT
SHOULD START TO LIFT NORTHWARD THROUGH THE COURSE OF THE DAY.

OVERALL, TODAY WILL BE AN INBETWEEN KIND OF DAY. SKIES WILL BE
CLEAR, MAINLY HIGH CLOUDS AROUND THE REGION, BEFORE STARTING TO
FILL IN AGAIN IN ADVANCE OF THE APPROACHING COLD FRONT. AREAS TO
THE SOUTH OF I-95 MAY SEE A BIT MORE SUN AND THUS WILL BE ABLE TO
WARM UP A BIT MORE DURING THE DAY. WINDS WILL ALSO BE LESS GUSTY
TODAY THAN THEY WERE OVER THE WEEKEND.

TEMPERATURES TODAY SHOULD REACH INTO THE 60S THROUGH MOST OF THE
AREA, WITH 50S ACROSS THE HIGHER TERRAIN. SOUTHERN AREAS MAY
REACH AROUND 70 OR A BIT HIGHER.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/...
A COLD FRONT WILL MOVE INTO THE REGION TONIGHT. SHOWERS WILL
ACCOMPANY THE FRONT AND SPREAD FROM NORTHWEST TO SOUTHEAST THIS
EVENING. THE FRONT FAILS TO CLEAR THE REGION AND INSTEAD MEANDERS
THROUGH TUESDAY, WHICH MAKE THE FORECAST MORE DIFFICULT. THE
MODELS ARE STILL IN DISAGREEMENT OVER EXACTLY WHERE THE FRONT WILL
STALL AND THIS WILL INDEED PLAY A ROLE IN WHAT TEMPERATURES AND
CLOUD COVER MAY BE EXPECTED OVER THE AREA. FOR NOW, WE HAVE TRIED
TO STAY CLOSE TO CONTINUITY AND HOPE THAT THE GUIDANCE REACHES A
BETTER CONSENSUS IN LATER MODEL RUNS. HOWEVER, THE SYSTEM
DEVELOPING TO OUR WEST AND CROSSING THE GREAT LAKES REGION WILL
HELP TO DRAG THE BOUNDARY NORTHWARD AS A WARM FRONT LATE TUESDAY
OR EARLY WEDNESDAY. WEDNESDAY LOOKS TO BE THE JACKPOT FOR WARM
DAYS THIS WEEK AS TEMPERATURES MAY APPROACH OR EVEN REACH INTO THE
80S IN SOME PLACES.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
THIS TIME FRAME APPEARS TO BE UNSETTLED AT TIMES. AS THE RIDGING
NEAR THE WEST COAST BREAKS DOWN EARLY ON, THE FLOW IS FORECAST TO
BECOME GENERALLY ZONAL ACROSS THE U.S. THIS MAY THEN TRY TO
AMPLIFY SOME TOWARD THE END OF THE PERIOD AS TROUGHING MAY DIG
ACROSS THE WEST AND ALSO THE MIDWEST. HPC UTILIZED AN EVEN BLEND
OF THE GFS/ECMWF ENSEMBLE MEAN. WE INITIALIZED THE DATABASE WITH
HPC GUIDANCE THAN MADE SOME TWEAKS BASED ON ADDITIONAL
COLLABORATION.

BASED ON THE ABOVE, A WARM FRONT SHOULD HAVE CLEARED THE AREA AT
THE START OF THIS TIME FRAME AS LOW PRESSURE TRACKS ACROSS
SOUTHEASTERN CANADA. THIS WILL SWEEP A COLD FRONT THROUGH OUR AREA
WEDNESDAY NIGHT INTO EARLY THURSDAY MORNING. GIVEN THE WARM
AIRMASS AHEAD OF THIS BOUNDARY ALONG WITH THE MOISTURE RETURN, WE
WILL CONTINUE TO INCLUDE A CHC OF THUNDER WEDNESDAY EVENING BEFORE
TAPERING POPS DOWN FROM WEST TO EAST FROM ABOUT 04Z ONWARD.

AS A STRONG SURFACE HIGH THEN SLIDES ACROSS THE GREAT LAKES TO
THE NORTHEAST, IT SHOULD TEND TO BUILD DOWN INTO THE MID ATLANTIC
STATES ALLOWING THE AFOREMENTIONED COLD FRONT TO BE PUSHED WELL TO
OUR SOUTH AND POSSIBLY DISSIPATE. A COOLER AIRMASS WILL ACCOMPANY
THIS SURFACE HIGH AND ULTIMATELY WE MAY HAVE A LIGHT ONSHORE FLOW
OCCURRING LATER THURSDAY AND FRIDAY. AS THE SURFACE HIGH SLIDES
OFF THE NEW ENGLAND COAST FRIDAY NIGHT AND SATURDAY, LOW PRESSURE
SHOULD BE QUICKLY MOVING ACROSS THE GREAT LAKES REGION. ITS
ASSOCIATED WARM FRONT WILL BE MAKING ITS WAY INTO OUR AREA
SATURDAY WITH THE CHC OF SHOWERS AND POSSIBLY A PERIOD OF
OVERRUNNING RAIN. WE STARTED TO INCREASE THE POPS LATER FRIDAY AND
CONTINUED THAT SATURDAY INTO SUNDAY. THE COLD FRONT ATTM IS
SCHEDULED TO BE MOVING THROUGH OUR AREA EARLY SUNDAY. THERE IS
HOWEVER SOME UNCERTAINTY ON THE TIMING ESPECIALLY WITH THE MOSTLY
ZONAL FLOW REGIME, THEREFORE KEPT POPS IN THE LOWER CHC RANGE. DID
TRY TO PORTRAY THE WARM FRONTAL OVERRUNNING POTENTIAL FROM SOUTH
TO NORTH SWITCHING FROM RAIN TO SHOWERS. THERE LOOKS TO BE ENOUGH
OF A WARM SECTOR ACROSS ESPECIALLY OUR DELMARVA ZONES FOR THUNDER,
THEREFORE ADDED A CHC IN FOR SATURDAY AFTERNOON AND EARLY EVENING.
AS FOR TEMPERATURES, WE GENERALLY FOLLOWED HPC WITH MAINLY MINOR
TWEAKS.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

VFR CONDITIONS ARE EXPECTED AT THE TAF SITES TODAY AND TONIGHT. A
DRY FRONT IS CROSSING THE AREA EARLY THIS MORNING WITH SCT-BKN AC
CLOUDS ASSOCIATED WITH IT. WINDS WILL VEER TO W OR NW BEHIND THE
FRONT BY DAWN. THE FRONT WILL STALL TO THE SOUTH TODAY AND THEN
TRAVEL BACK NORTH ACROSS THE AREA TONIGHT AS A WAVE OF LOW PRESSURE
MOVES ALONG IT. THIS PATTERN WILL CONTINUE INTO TUE BEFORE ANOTHER
STRONG WAVE TO THE WEST PUSHES THE FRONT BACK ACROSS THE WHOLE AREA
TUE NIGHT. ONLY SCT-BKN AC AND CI CLOUDS WILL BE AROUND TODAY AND
TONIGHT WITH WINDS SHIFTING TO S LATE TODAY AND REMAINING S OR SW
TONIGHT.

.OUTLOOK...MOST OF THE TIME VFR TUE AND WED. BKN TO OVC CLOUD COVER
WILL BE COMMON TUE AND WED WITH SOME SHOWERS AND SCAT TSTMS. LOWER
CONDITIONS MAY DEVELOP WITH THE RAINS TUE AFTERNOON (NORTH) AND TO
ALL AREAS WED AFTERNOON AND EVENING. VFR EXPECTED THU AND FRI.

&&

.MARINE...
WE WILL KEEP THE PRESENT SCA FLAG FOR THE OCEAN UNTIL 600 AM AND
THEN LET IT GO AS WINDS AND SEAS CONTINUE TO DECREASE. MUCH OF TODAY
WILL HAVE SUB-SCA CONDITIONS WITH WEAK HIGH PRESSURE BUILDING IN.
THE FRONT CROSSES BACK NORTH TONIGHT. WINDS AND SEAS INCREASE AGAIN
TO NEAR SCA CRITERIA FOR A FEW HOURS DURING THE EVENING. THE MODEL
SOUNDINGS SHOW THAT IT DOES NOT LAST TOO LONG BEFORE DECREASING
AGAIN. WE WILL LET THE DAY SHIFT EVALUATE THE NEED FOR A SCA
TONIGHT. DRY WEATHER EXPECTED TODAY. A SMALL CHC FOR SHOWERS OVER
THE NRN WATERS TONIGHT. CHC FOR SHOWERS INCREASE TUE AND REMAIN INTO
WED WITH ANOTHER FRONT AND WAVE CROSSING THE AREA.

&&

.HYDROLOGY...
RIVER STAGES CONTINUE TO FALL AND WE HAVE BEEN ABLE TO DROP A
COUPLE OF WARNINGS OVERNIGHT. HOWEVER, FLOODING IS OCCURRING AND
FORECAST TO CONTINUE AT SEVERAL OF OUR NORTHERN NEW JERSEY
FORECAST POINTS.

THE NORTH BRANCH OF THE RANCOCAS CREEK IS FORECAST TO CREST AND
THEN REMAIN AROUND FLOOD STAGE INTO TUESDAY, WHICH MAY RESULT IN
SOME MINOR FLOODING.

IN ADDITION, THE SUSQUEHANNA BELOW CONOWINGO DAM IS FORECAST TO
RISE ABOVE FLOOD STAGE AND THEN CREST THIS EVENING.

PLEASE CHECK OUR WEBPAGE FOR THE MOST CURRENT WARNINGS ISSUED.

&&

.TIDES/COASTAL FLOODING...
THE SUN OVERNIGHT AND EARLY MON TIDE CYCLE REACHED MINOR TIDAL
LEVELS ALONG THE SHORE AND ACROSS DEL BAY AND TIDAL DEL RIVER. A
COASTAL FLOOD STATEMENT ISSUED EARLIER WILL BE REMOVED WITH THE
EARLY MORNING PACKAGE. THE NEXT HIGH TIDE LOOKS LOWER BY ABOUT 1/2
FOOT...SO HOPEFULLY NO MORE TIDAL ISSUED WILL OCCUR TONIGHT. WE WILL
MONITOR IT HOWEVER.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR
     ANZ450>455.

&&

$$
SYNOPSIS...MEOLA