Dense Fog Advisory 6, NWS Philadelphia/Mount Holly

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
338 PM EDT SUN MAY 10 2015

.SYNOPSIS...
HIGH PRESSURE LOCATED OVER THE WESTERN ATLANTIC WILL LOSE ITS
INFLUENCE OVER OUR WEATHER GRADUALLY TONIGHT AND MONDAY. THE
REMNANTS OF TROPICAL DEPRESSION ANA ARE FORECAST TO TRACK OFF THE
DELAWARE AND NEW JERSEY COASTS MONDAY NIGHT. A COLD FRONT WILL
APPROACH FROM THE NORTHWEST ON TUESDAY AND MOVE THROUGH THE AREA
TUESDAY EVENING. CANADIAN HIGH PRESSURE BUILDS INTO THE REGION FOR
THE SECOND HALF OF THE UPCOMING WORK WEEK. THE CENTER OF THE HIGH IS
EXPECTED TO SHIFT OFFSHORE BY THE START OF THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
HI PRES TO THE NE WILL KEEP A GENL S TO SE FLOW OVER THE AREA.
LOW LEVEL MOISTURE AND THE SELY FLOW WILL BEING IN ABUNDANT LOW
CLOUDS AND FOG, AS WE ARE IN A PERSISTENT WX PATN. WE WILL, ONCE
AGAIN ISSUE A DENSE FOG ADVY FOR THE COASTAL STRIP AND NEXT ROW OF
COUNTIES INLAND FROM TO MIDNIGHT UNTIL 10 AM. THE ADVY MAY NEED TO
BE EXPANDED WWD, BUT WE CAN SEE HOW THINGS DEVELOP DURG THE EVENING
AND OVERNIGHT.

OTHERWISE, WILL CARRY SOME LOW POPS, MAINLY FOR SRN AREAS THRU THE
EVE AS SOME SHWRS ARE EVIDENT ON RADAR FROM MOISTURE AHEAD OF TD ANA.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
THE REMNANTS OF TS ANA WILL MOVE NEWD ON MON AND SOME OF ITS
MOISTURE WILL IMPACT MAINLY SRN AND ERN PORTIONS OF THE AREA.

WILL CARRY HIGHEST POPS ACRS THESE LOCATIONS. WITH NO OTHER SIG
TRIGGERS, WILL CARRY SOME LOW POPS ACRS THE REST OF THE AREA FOR
SOME DIURNAL SHRA/TSRA.

ASSUMING WE BREAK OUT EARLY ENOUGH, WE CAN BE QUITE WARM AGAIN ON
MON, WITH TEMPS WELL INTO THE 80S, BUT IT MAY BE SLOW TO WARM UP
AGAIN THRU THE MRNG.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
THE MID-ATLANTIC REGION WILL BE POSITIONED ON THE WESTERN PERIPHERY
OF AN UPPER RIDGE AND DOWNSTREAM OF A MID-LATITUDE TROUGH OVER THE
UPPER MIDWEST MONDAY NIGHT. A DEEP SOUTHERLY FETCH IN BETWEEN THESE
TWO SYSTEMS WILL CONTINUE TO PUMP A WARM AND MOIST, TROPICAL-LIKE
AIRMASS INTO OUR AREA. THE OFFICIAL FORECAST TRACK FROM THE NHC HAS
THE REMNANTS OF TROPICAL DEPRESSION ANA ACCELERATING NORTHEASTWARD
ALONG OR JUST OFF THE DELMARVA AND NJ COAST MONDAY NIGHT. DOWNSTREAM
IMPLICATIONS OF THE APPROACHING TROUGH TO OUR WEST INCLUDE THE RIDGE
BREAKING DOWN OVER THE EASTERN SEABOARD. THE STRONGER DEEP-LAYER
SHEAR THAT ANA WILL ENCOUNTER WILL CAUSE IT TO SUBSEQUENTLY WEAKEN
AND TRANSITION TO POST TROPICAL. MODELS SHOW ANA OBTAINING AN
INCREASINGLY ASYMMETRICAL STRUCTURE WITH THE CORE OF HEAVY PRECIP
AND STRONGER WINDS SEPARATING FARTHER TO THE SOUTHEAST OF THE
REMNANT CIRCULATION. ACCORDINGLY, ANA SHOULD BRING MINIMAL
IMPACTS TO OUR CWA. THE PRESENCE OF TROPICAL MOISTURE AND A BRIEF
SOUTHEASTERLY WIND SURGE AHEAD OF THE LOW WOULD BOOST THE
LIKELIHOOD FOR ANOTHER EPISODE OF LOW CLOUDS AND FOG ON MONDAY
NIGHT.

A COLD FRONT WILL APPROACH FROM THE GREAT LAKES/OHIO VALLEY TUESDAY.
ALTHOUGH THE FRONT ITSELF IS NOT EXPECTED MOVE THRU UNTIL THE
EVENING, A WIND SHIFT WILL OCCUR DURING THE AFTERNOON IN ASSOCIATION
WITH A PRE-FRONTAL TROUGH THAT IS FORECAST TO SHARPEN ALONG THE
COAST DURING THE AFTERNOON. DOWNSLOPING WESTERLY FLOW TO THE WEST OF
THE SURFACE TROUGH WILL HELP DRY OUT THE BOUNDARY LAYER WHILE THE
MID AND UPPER LEVELS DRY IN CONCERT WITH ARRIVAL OF A WELL-DEFINED
DRY SLOT AHEAD THE GREAT LAKES TROUGH. MAJORITY OF AVAILABLE MODEL
GUIDANCE DEPICTS A CONVECTIVE POTENTIAL THAT DIMINISHES THROUGHOUT
THE DAY. ADDITIONALLY, THE SYNOPTIC LIFT ASSOCIATED WITH THE UPPER
JET STREAK AND MID-LEVEL SHORTWAVE TROUGH IS EXPECTED TO TRACK TO
OUR NORTH SO THERE WILL LIKELY BE LITTLE IF ANY PRECIP WITH THE
FROPA. GFS/NAM FORECAST SOUNDINGS ON BUFKIT SHOW AN INVERTED V
BECOMING MORE PRONOUNCED. HOWEVER, THE ATMOSPHERE MAY BECOME
CONDUCIVE FOR DRY DOWNBURSTS BY LATE IN THE DAY AS MODELS SHOW A
PRONOUNCED INVERTED V SIGNAL IN THE BOUNDARY LAYER AND STRENGTHENING
WESTERLY WINDS AT THE TOP OF A DEEP MIXED LAYER. LOOKING BACK ONLY A
FEW WEEKS TO APRIL 22ND, WHEN A DRY DOWNBURST FROM A SHOWER PRODUCED
A 71 MPH WIND GUST AT PHL AIRPORT, THE OBSERVED TEMP-DEWPT
DEPRESSION OF ABOUT 35 DEGREES ON APRIL 22ND IS SIMILAR TO WHAT IS
EXPECTED AT 21Z TUESDAY. HOWEVER, THE WINDS AT THE TOP OF THE
BOUNDARY LAYER WERE A BIT STRONGER ALOFT ON APRIL 22ND (50-60 KT)
THAN WHAT IS FORECAST AT 21Z TUESDAY (40-45 KT).

A SECONDARY COLD FRONT WILL MOVE THROUGH ON WEDNESDAY AND PROVIDE A
REINFORCING SHOT OF COOL CANADIAN AIR WITH HIGHS NEAR NORMAL. NW
WINDS WILL BE BREEZY, GUSTING 20-30 MPH.

A QUIET WX PATTERN IS IN STORE FOR LATE IN THE WEEK AS CANADIAN HIGH
PRESSURE BUILDS IN TO THE REGION. TEMPS MAY BE A FEW DEGREES BELOW
NORMAL THURSDAY-THURSDAY NIGHT AND RIGHT AT CLIMO FOR FRIDAY.

THE CENTER OF THE HIGH IS EXPECTED TO MOVE OFFSHORE LATE IN THE DAY
FRIDAY. RETURN FLOW AROUND THE HIGH WILL DRAW WARMER AND MORE HUMID
AIR UP THE EASTERN SEABOARD RIGHT INTO NEXT WEEKEND. MODELS CONTINUE
TO SHOW PRECIP OVERSPREADING THE AREA FRIDAY NIGHT WHEN A WARM
FRONT ARRIVES. A SERIES OF WEAK UPPER SHORTWAVE TROUGHS MAY TRACK
AROUND THE NORTHERN PERIPHERY OF THE UPPER RIDGE, LEADING TO
PERIODIC CHANCES FOR SHOWERS SATURDAY AND SUNDAY.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.

SAME SONG, DIFFERENT VERSE. PERSISTENT S TO SELY FLOW HAS KEPT
LOW LVL MOISTURE OVER THE AREA. THIS HAS RESULTED IN FOG AND
STRATUS EACH NIGHT THRU THE MRNG HOURS AND ONCE AGAIN WE ARE IN
FOR A REPEAT. ALL SITES HAVE BECOME VFR AND SHOULD REMAIN THAT WAY
THROUGH THE EVENING, A RETURN TO MVFR, IFR AND LIFR IS EXPECTED
OVERNIGHT. AFTER DAYBREAK A SLOW RETURN TO VFR IS ANTICIPATED.

OUTLOOK...

MONDAY NIGHT...LOW CLOUDS AND FOG LIKELY TO REDEVELOP NEAR THE COAST
DURING THE EVENING AND PROPAGATE INLAND OVERNIGHT. THE COVERAGE
OF THE LOW CLOUDS AND COVERAGE/INTENSITY OF THE FOG STILL
UNCERTAIN WITH HIGHER CLOUDS MOVING IN AHEAD OF A COLD FRONT.

TUESDAY AND TUESDAY NIGHT...MAINLY VFR. WIND SHIFT FROM S TO W
EXPECTED DURING THE DAY AND NW DURING THE EVE. WINDS WILL BE GUSTY
DURING THE AFTERNOON AND EVENING.

WEDNESDAY THROUGH FRIDAY...VFR.

&&

.MARINE...
THE MARINE DENSE FOG ADVY HAS BEEN EXTENDED THRU NOON MON. ALSO,
WITH THE PERSISTENT SELY FLOW, SEAS WILL INCREASE SLOWLY AND BY
THE END OF THE PD, WITH THE APPROACH OF THE REMNANTS OF TS ANA
SEAS COULD REACH SCA CRITERIA OF THE SRN WATERS SO A SCA WILL BE
ISSUED FOR THE SRN WATERS.

OUTLOOK...

MONDAY NIGHT AND TUESDAY...A SCA FOR HAZARDOUS SEAS WAS ISSUED FOR
THE COASTAL MARINE ZONES WITH WAVE HEIGHTS FORECAST TO BUILD TO 4-6
FT AS THE REMNANTS OF TROPICAL DEPRESSION ANA PASS THRU OR JUST TO
THE EAST OF OUR WATERS. WINDS WILL LIKELY NOT REACH SCA LEVELS SINCE
THE STRONGEST WINDS SHOULD STAY TO THE SE OF THE CIRCULATION. FOG
LIKELY TO PERSIST THROUGH TUESDAY MORNING, RESULTING IN POOR VSBYS
AT TIME.

TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...A SCA MAY BE NEEDED WITH NW
WINDS GUSTING TO 25 KT OR POTENTIALLY HIGHER.

THURSDAY THROUGH FRIDAY...NO MARINE HAZARDS EXPECTED.

&&

.FIRE WEATHER...
BOTH TUESDAY (PARTICULARLY LATE IN THE DAY) AND WEDNESDAY THIS WEEK
MAY CONTAIN AN ENHANCED FIRE RISK DUE TO THE DRY CONDITIONS AND
GUSTY WINDS. THE LIMITING FACTOR FOR RED FLAG CONDITIONS MAY BE RH
WITH MIN RH BOTH DAYS CURRENTLY FORECAST IN THE MID TO UPPER 30S.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...DENSE FOG ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT MONDAY
     FOR NJZ013-014-020>024-027.
DE...DENSE FOG ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT MONDAY
     FOR DEZ002>004.
MD...NONE.
MARINE...DENSE FOG ADVISORY UNTIL NOON EDT MONDAY FOR ANZ430-431-
     450>455.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 8 PM MONDAY TO 6
    PM EDT TUESDAY FOR ANZ450>452.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 PM MONDAY TO 6
    PM EDT TUESDAY FOR ANZ453>455.

&&

SYNOPSIS...KLEIN
NEAR TERM...NIERENBERG
SHORT TERM...NIERENBERG
LONG TERM...KLEIN
AVIATION...KLEIN/NIERENBERG
MARINE...KLEIN/NIERENBERG
FIRE WEATHER...KLEIN

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