National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS61 KPHI 200625
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
225 AM EDT MON MAY 20 2013

.SYNOPSIS...
A FRONTAL BOUNDARY TO OUR SOUTH IS EXPECTED TO WEAKEN AND DISSIPATE
AS IT REMAINS NEARLY STATIONARY THROUGH MONDAY. HIGH PRESSURE
CENTERED EAST OF NEW JERSEY WILL SINK SOUTH AND EAST SLOWLY THROUGH
MID-WEEK. ANOTHER HIGH WILL BUILD TOWARD US FROM EASTERN CANADA. AN
ASSOCIATED FRONTAL BOUNDARY FROM THE NORTH IS FORECAST TO MOVE INTO
OR NEAR OUR AREA LATE ON TUESDAY AND THEN LIFT BACK TO THE NORTH
ON WEDNESDAY AND THURSDAY. A COLD FRONT FROM THE WEST IS EXPECTED
TO ARRIVE ON THURSDAY NIGHT OR EARLY FRIDAY, FOLLOWED BY HIGH
PRESSURE FOR SATURDAY.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
A QUICK UPDATE TO ISSUE A DENSE FOG ADVISORY FOR A GOOD PORTION OF
THE AREA. THE FRONTAL BOUNDARY IS DRAPED ACROSS THE CENTRAL
DELMARVA AND SOUTHERN NEW JERSEY EARLY THIS MORNING. AREAS NORTH
OF THE BOUNDARY HAVE DEVELOPED DENSE FOG WITH WIDESPREAD 1/4-1/2
MILE VISIBILITIES REPORTED. WE WILL RUN IT THROUGH 8 AM AND SEE
HOW THE VISIBILITIES DO OVER THE NEXT FEW HOURS AS THE FRONT TRIES
TO SLOWLY MOVE NORTHWARD.

OTHERWISE, THE ONSHORE FLOW IN FRONT OF THE APPROACHING WARM
FRONT WILL OVERNIGHT. LOW CLOUDS AND DRIZZLE ALONG WITH  FOG WILL
PRECEDE THE FRONT AND A FEW SHOWERS ARE POSSIBLE BEHIND IT. POPS
OVERALL WILL SLOWLY DECREASE THROUGH THE NIGHT...ARRIVING AT SLGT
CHC/LOW CHC BY MORNING. WINDS WILL MOSTLY BE ERLY/SERLY THIS
EVENING AND THEN VEER TO SWRLY BY MON MORNING. LOWS WILL NOT BE
TOO LOW TONIGHT...WITH LOWER 60S ACROSS THE SRN AREAS AND UPPER
50S ACROSS THE NORTH.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
THERE WILL BE SOME IMPROVEMENT IN THE WEATHER MONDAY. UPPER HEIGHTS
BEHIND THE DEPARTING WARM FRONT WILL BE RISING A LITTLE AND WINDS
THROUGH THE LOWEST LAYERS WILL VEER TO A MORE WRLY DIRECTION. THESE
FACTORS SHOULD ALLOW SOME DRIER AIR TO WORK ITS WAY INTO THE AREA.
THERE WILL STILL BE SOME HIGHER DEW POINTS DURING THE MORNING...AND
ANY SUNSHINE WILL PROBABLY CREATE SOME INSTABILITY SHOWERS DURING
THE AFTERNOON. POPS WILL BE SLGT CHC IN THE MORNING...RISING TO CHC
BY AFTERNOON. CAPE VALUES POINT TO THE POSSIBILITY FOR A FEW
TSTMS...SO THEY WERE LEFT IN THERE FROM BEFORE. WINDS WILL BE MOSTLY
SWRLY AT AROUND 10 MPH.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
THERE IS BETTER MODEL AGREEMENT THROUGH MUCH OF THE LONG TERM.
WHETHER THAT CONTINUES IS A QUESTION, BUT FOR THE TIME BEING THE
MODELS AGREE AT MID LEVELS THAT THE REMNANTS OF A MID LEVEL LOW THAT
HAS BEEN MOVING SLOWLY EAST WILL MOVE TO NEAR THE MID-ATLANTIC COAST
ON TUESDAY AND THEN WEAKEN AS AN EASTERN U.S./WESTERN ATLANTIC RIDGE
BEGINS TO BUILD. WE CARRY CHANCE TO SLIGHT CHANCE POPS WITH THIS.

THE RIDGE THEN BUILDS AND ESTABLISHES A CONFLUENT ZONE OFF NEW
ENGLAND, AND THAT WILL CARRY AN ASSOCIATED BACK DOOR COLD FRONT AS
SURFACE HIGH PRESSURE RIDGES DOWN FROM EASTERN CANADA. WHETHER THE
FRONT MAKES IT INTO OUR AREA IS ANOTHER QUESTION. NEITHER THE LATEST
RUN OF THE GFS NOR THE LAST THREE RUNS OF THE ECMWF ARE BRINGING IT
THIS FAR SOUTH, BUT IT MAY GET CLOSE ENOUGH TO TRIGGER SOME ACTIVITY
IN THE TUESDAY TO TUESDAY NIGHT TIME FRAME. WE CARRY CHANCE TO
SLIGHT CHANCE POPS THAT ARE HIGHEST NORTH.

BY WEDNESDAY, THE BUILDING MID LEVEL RIDGE AXIS WILL BE TO OUR EAST,
AND THAT OPENS US UP TO ANY ENERGY THAT MIGHT BE KICKING OUT AN
ADVANCING AND WEAKENING MID LEVEL LOW. THAT LOW WILL BE PART OF A
REX BLOCK OVER THE NORTHERN PLAINS AND CANADA INTO EARLY WEDNESDAY,
BUT THE MODELS AGREE TO OPEN IT AND MOVE IT INTO THE WESTERN GREAT
LAKES BY LATE WEDNESDAY. HPC IS HITTING WEDNESDAY POPS PRETTY HARD;
WE`RE NOT QUITE SO SURE ABOUT WHEN ENERGY FROM THE OPENING LOW MAKES
IT HERE AND SO WE CARRY MORE CHANCE POPS THAT ARE BETTER NORTHWEST
AND FOCUSED AROUND WEDNESDAY INTO WEDNESDAY NIGHT.

THROUGH THE ABOVE TIME PERIOD, THERE ALWAYS IS A LOT OF MOISTURE
AVAILABLE AND INSTABILITY GENERALLY WAXES DURING THE AFTERNOON
HOURS. THAT INCREASINGLY BECOMES DUE TO A SOUTH TO SOUTHWEST FLOW
AROUND SURFACE HIGH PRESSURE THAT IS ASSOCIATED WITH THE MID LEVEL
RIDGE AND THAT RESEMBLES A BERMUDA HIGH, AND IT MEANS THAT WHAT THE
PREVIOUS FORECASTER NOTED STILL APPLIES: THERE IS THE POTENTIAL FOR
LOCALIZED DOWNPOURS.

THE LOW FROM THE WEST WEAKENS INTO A NEUTRAL TROUGH ROTATING AROUND
AN EASTERN CANADIAN VORTEX AS IT APPROACHES OUR AREA ON THURSDAY. BY
THE END OF THE DAY, THERE IS AN UPPER JET THAT HAS US IN THE RIGHT
EXIT REGION, AND WITHOUT GOING INTO THE SPECIFICS OF THE FORCING AND
THE WIND FIELDS THIS FAR OUT, AT LEAST SOME OF THAT COME TOGETHER
WITH STILL-COPIOUS MOISTURE OVER THE FORECAST AREA IN A TIME PERIOD
CENTERED AROUND THURSDAY EVENING OR THURSDAY NIGHT. OF COURSE, THE
AMOUNT OF INSTABILITY AVAILABLE IS TO SOME DEGREE DEPENDENT ON WHEN
THE FRONT ARRIVES. THIS SYSTEM SEEMS TO BE THE BEST OPPORTUNITY FOR
ORGANIZED CONVECTION WITH HEAVY DOWNPOURS AND STRONG WINDS, BUT WE
HAVE LOTS OF TIME AND LOTS OF MODEL RUNS TO ASSESS THAT.

WE NOTE THAT THE TIMING OF THIS HAS SPED UP FROM PREVIOUS RUNS
DESPITE THERE BEING A REX BLOCK UPSTREAM EARLIER IN THE PERIOD, BUT
THIS FORECASTER BIT THE BAIT THANKS TO MODEL AGREEMENT. WE PRESENTLY
CARRY LINGERING CHANCE POPS FOR THE FIRST PART OF FRIDAY AND THEN GO
DRY FOR THE REST OF THE FORECAST PERIOD. THE LATEST ECMWF PUSHES
ENERGY MOVING AROUND THE EASTERN CANADIAN VORTEX LATE IN THE WEEKEND
FURTHER SOUTH. THE GFS IS SLOWER WITH SAID ENERGY. THE MID LEVEL
FLOW LOOKS FAIRLY MERIDIONAL, SO EITHER SOLUTION IS A PLAUSIBLE
EXCUSE TO GO OPTIMISTIC.

UNTIL THAT LATE WEEK FRONT ARRIVES, NIGHTTIME MINS WILL BE WELL
ABOVE NORMAL. DAYTIME MAXES ALSO WILL BE ABOVE NORMAL, BUT SUBJECT
TO ANY CONVECTION. IT ALSO WILL BE HUMID UNTIL THE FRONT ARRIVES.
TEMPERATURES WILL RETURN TO NORMAL OR A BIT BELOW NORMAL AFTER THE
FRONT.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.

A CONTINUATION OF THE MOSTLY IFR CONDITIONS IS EXPECTED AT THE
TERMINALS TONIGHT INTO MONDAY MORNING. THE SFC/LOW-LEVEL FLOW WILL
REMAIN MOSTLY ONSHORE UNTIL THE SFC WARM FRONT CROSSES THE AREA.
ONCE THIS HAPPENS...LOW LEVEL WINDS WILL BEGIN TO VEER TO S THEN
SW MONDAY. THIS SHOULD ALLOW DRIER AIR TO ARRIVE AND AN EVENTUAL
SCOURING OUT OF THE LOWEST CLOUDS. THE MAV/MET GUIDANCE SHOWS THE
TREND TOMORROW, THE EXACT TIMING MAY BE A FEW HOURS OFF.

MON...SW WINDS WILL INCREASE TO AROUND 10 KNOTS BY AFTERNOON AND
CIGS WILL IMPROVE BACK TO VFR AROUND THE NOON HOUR. THE VFR
CONDITIONS SHOULD LAST INTO THE AFTERNOON...BUT THERE MAY BE A FEW
SCT SHOWERS WITH TEMPORARILY LOWER CONDITIONS LATER MON AFTERNOON.

OUTLOOK...
MONDAY NIGHT THROUGH THURSDAY...MVFR AND IFR CONDITIONS ARE POSSIBLE
FROM LATE AT NIGHT TO EARLY IN THE MORNING THROUGH THIS PERIOD.
MAINLY VFR CONDITIONS ARE EXPECTED OTHERWISE, ALTHOUGH THEY
WOULD DETERIORATE IN ANY CONVECTION. CONFIDENCE IS MODERATE.

THURSDAY NIGHT...POSSIBLE CONVECTION WITH ASSOCIATED MVFR OR IFR
CONDITIONS. CONFIDENCE IS LOW ESPECIALLY ON THE TIMING.

FRIDAY...VFR IF CONVECTION CLEARS THE AREA BY THEN. WORSE IF NOT.
CONFIDENCE IS LOW.

&&

.MARINE...
A QUICK UPDATE TO THE FORECAST TO ISSUE A DENSE FOG ADVISORY.
DENSE FOG IS PRETTY WIDESPREAD ON THE LAND, AND WITH DEWPOINTS
NEAR OR HIGHER THAN THE WATER TEMPERATURES, DENSE FOG IS LIKELY
OCCURRING ACROSS A PORTION OF OUR COASTAL WATERS.

WINDS AND SEAS CONTINUE TO SLOWLY BUILD ACROSS THE OCEAN WATERS
AND OVER DEL BAY. THE SCA CONDITIONS THAT HAVE BEEN ON THE
SOUTHERN WATERS ALREADY APPEAR TO BE HEADING NORTH...SO THE
ONGOING FLAG WILL CONTINUE ACROSS THE OCEAN WATERS. GUIDANCE
SUGGESTS THAT THE CONDITIONS WILL CONTINUE INTO MONDAY...SO WE
WILL EXTEND THE FLAG FOR NOW...ALTHOUGH IT WILL BE A LOW-END
ADVISORY AT BEST. OCNL SHOWERS AND FOG ON THE WATERS TONIGHT AND
SCAT SHOWERS OR A TSTM MONDAY. WINDS WILL VEER TO SRLY LATE
TONIGHT AND THEN BECOME SWRLY ON MONDAY AS THE WARM FRONT CROSSES
THE REGION.

OUTLOOK...
WIND SPEEDS ARE FORECAST TO REMAIN SUB-ADVISORY INTO WEDNESDAY
NIGHT, THEN BEGIN TO INCREASE SOME IN ADVANCE OF THE LATE WEEK COLD
FRONT. WAVE HEIGHTS ARE FORECAST TO BE SUB-ADVISORY OVER THE BAY
THROUGH FRIDAY, BUT THEY ARE FORECAST TO START AT ADVISORY LEVELS,
SUBSIDE TO SUB-ADVISORY LEVELS ON TUESDAY BUT THEN RISE AGAIN IN
ADVANCE OF THE COLD FRONT.

&&

.EQUIPMENT...
NWR LEWES DE HAS RETURNED TO SERVICE..

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...DENSE FOG ADVISORY UNTIL 8 AM EDT THIS MORNING FOR PAZ054-055-
     060>062-070-071-101>106.
NJ...DENSE FOG ADVISORY UNTIL 8 AM EDT THIS MORNING FOR NJZ001-
     007>010-012>020-026-027.
DE...DENSE FOG ADVISORY UNTIL 8 AM EDT THIS MORNING FOR DEZ001.
MD...DENSE FOG ADVISORY UNTIL 8 AM EDT THIS MORNING FOR MDZ008.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR
     ANZ450>455.
     DENSE FOG ADVISORY UNTIL 8 AM EDT THIS MORNING FOR ANZ450-451.

&&

$$
SYNOPSIS...DELISI
NEAR TERM...KLINE/ROBERTSON/O`HARA
SHORT TERM...O`HARA
LONG TERM...DELISI
AVIATION...DELISI/O`HARA
MARINE...DELISI/ROBERTSON/O`HARA
EQUIPMENT...