NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Apr 1, 2:46 PM EST, 2 hours 22 minutes earlier.
Area forecast discussion, Apr 1, 2:46 PM EST, 2 hours 22 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
346 PM EDT FRI APR 1 2016
.SYNOPSIS...
A COLD FRONT WILL MOVE ACROSS OUR AREA THROUGH THIS EVENING. THIS
FRONT WILL STALL TO OUR SOUTH, WITH AN AREA OF LOW PRESSURE
DEVELOPING ALONG THE BOUNDARY AND PASSING TO OUR EAST. AN AREA OF
LOW PRESSURE WILL MOVE OUT OF THE GREAT LAKES REGION TONIGHT AND
INTO EASTERN CANADA SATURDAY, PULLING A COLD FRONT INTO OUR AREA
DURING THE DAY. ANOTHER LOW WILL OUT OF THE MID WEST AND INTO OUR
AREA SATURDAY NIGHT, PULLING A STRONGER COLD FRONT ACROSS THE
AREA. THESE LOWS WILL STRENGTHEN AS THEY MOVE TO THE NORTHEAST.
HIGH PRESSURE BRIEFLY AFFECTS THE AREA SUNDAY NIGHT, BEFORE AN
AREA OF LOW PRESSURE APPROACHES FROM THE WEST MONDAY INTO MONDAY
NIGHT. HIGH PRESSURE RETURNS FOR TUESDAY NIGHT INTO EARLY
WEDNESDAY, BEFORE ANOTHER STORM SYSTEM APPROACHES FROM THE WEST
AROUND THURSDAY AND THURSDAY NIGHT.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
AT 3 PM...VISIBLE SATELLITE IMAGERY SHOWS MOSTLY SUNNY SKIES
ACROSS MOST OF THE AREA ALTHOUGH THERE ARE MORE CLOUDS MOVING INTO
OUR FAR WESTERN ZONES IN PA. CURRENT SURFACE OBSERVATIONS AND SPC
MESOANALYSIS OVER THE AREA INDICATE STEEPENING LOW-LEVEL LAPSE
RATES AND 500-1000 J/KG OF SBCAPE ACROSS THE FORECAST AREA IN
RESPONSE TO THE AFTERNOON HEATING.
SCATTERED SHOWERS AND THUNDERSTORMS WERE FOCUSED ALONG A LINE
JUST AHEAD OF THE COLD FRONT TO OUR WEST. WE STILL THINK THERE
WILL BE AN UPTICK IN CONVECTION ALONG THIS LINE LATE THIS
AFTERNOON/EARLY EVENING AS THE ACTIVITY ALONG THE COLD FRONT MOVES
INTO THE DELAWARE VALLEY WHERE A MORE UNSTABLE AIRMASS RESIDES. WE
ARE STILL UNDER A MARGINAL RISK FOR SEVERE STORMS WITH THE LATEST
D1 OUTLOOK FROM SPC. THE PRIMARY THREAT WILL BE LOCALLY DAMAGING
WINDS. IN THE SETUP, WITH STRONG 50-60 KT OF EFFECTIVE BULK SHEAR,
THE STRONGER CONVECTION COULD POTENTIALLY GROW UPSCALE AND
ORGANIZE INTO A LINE.
THE GUIDANCE CONTINUES TO TREND SLOWER WITH THE FRONT, SO THESE
SHOWERS AND STORMS MAY NOT REACH THE DELAWARE VALLEY UNTIL AFTER 4
PM AND THEN MOVE OFF THE DELMARVA/S NJ COAST SOMETIME BETWEEN 9
AND 11 PM.
THE STEERING FLOW ALOFT WILL ACTUALLY BACK MORE OUT OF THE
SOUTHWEST TONIGHT AS A RESULT OF UPSTREAM TROUGH AMPLIFICATION
OCCURRING OVER THE MIDWEST AND PERSISTENT DOWNSTREAM RIDGE
BLOCKING OVER THE WESTERN ATLANTIC. THE RESULTANT PATTERN WILL
CAUSE THE COLD FRONT TO SLOW DOWN AS IT MOVES THRU THE COASTAL
PLAIN THIS EVENING AND OFF THE NJ/DE COAST OVERNIGHT. MEANWHILE,
SYNOPTIC LIFT WILL INCREASE OVER THE MID-ATLANTIC COAST OVERNIGHT
WHEN A MID-LEVEL SHORTWAVE TROUGH APPROACHES FROM THE SOUTHWEST
AND THE REGION BECOMES POSITIONED IN THE RIGHT-ENTRANCE REGION OF
A 175 KT UPPER-LEVEL JET STREAK.
THE ABOVE SETUP WILL LIKELY RESULT IN A NORTHWARD EXPANSION OF
ANAFRONTAL PRECIP TOWARD THE DELMARVA OVERNIGHT. THERE IS STILL
SOME MODEL SPREAD AND FORECAST UNCERTAINTY REGARDING HOW FAR
INLAND THE RAIN GETS TO. THE GFS/ECMWF KEEP THE PRECIP CLOSE TO
THE COAST BEFORE DAYBREAK TOMORROW WHILE MOST OF THE OTHER
GUIDANCE BRINGS IT IN FARTHER WEST. FAVORED THE MORE WESTERN
SCENARIOS GIVEN THE STRENGTH OF THE DOWNSTREAM BLOCKING OFF THE
COAST AND TREND FOR THIS FRONT TO MOVE SLOWER THAN GUIDANCE HAD
INDICATED.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
A WEAK WAVE OF LOW PRESSURE IS FORECAST TO DEVELOP ALONG THE COLD
FRONT THAT IS FORECAST TO BE LOCATED ABOUT 75-100 MILES OFFSHORE
12Z SATURDAY. WE EXPECT A PERIOD OF STEADY RAIN DURING THE MORNING
ALONG THE COASTAL PLAIN. POPS DECREASE FARTHER INLAND AND ARE ONLY
IN CHANCE CATEGORY NORTH AND WEST OF I-95 WHERE THE WESTERN EDGE
OF THE PRECIP SHIELD IS LIKELY TO SETUP NEARBY.
A SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST DURING THE
MORNING SHOULD MOVE INTO NORTHEASTERN PA IN THE AFTERNOON. THIS
KICKER SYSTEM WILL AID IN STEERING THE OFFSHORE LOW AND COLD FRONT
FARTHER OUT TO SEA. EXPECT BREAKS IN THE CLOUD COVER TO DEVELOP
FROM WEST TO EAST DURING THE AFTERNOON. FORECAST MAX TEMPS ARE IN
THE MID 50S TO LOWER 60S.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
AN ACTIVE PATTERN FOR THE EXTENDED, WITH VERY STRONG WIND
POTENTIAL AND EVEN SNOWFALL POTENTIAL FOR SOME OF THE AREA.
ON SATURDAY NIGHT, AN AREA OF LOW PRESSURE WILL OUT OF THE MID
WEST AND INTO OUR AREA, PULLING A STRONG COLD FRONT ACROSS THE
AREA. A STRONG SHORT WAVE WILL BE MOVING ACROSS THE AREA AT THE
SAME TIME, SO THERE WILL BE THE POTENTIAL FOR SCATTERED SHOWERS TO
AFFECT THE AREA. IT IS POSSIBLE THAT TEMPERATURES MAY BE COLD
ENOUGH FOR SOME PRECIPITATION TO FALL AS SNOW ACROSS THE NORTHERN
PARTS OF THE AREA FOR A BRIEF PERIOD OF TIME SATURDAY NIGHT. WE
HAVE ONE TO TWO INCHES ACROSS THE FAR NORTHERN AREAS. WITH THE
STRONG WIND POTENTIAL, IF SNOW SHOWERS/SQUALLS DO DEVELOP, IT
COULD CAUSE A PERIOD OF DANGEROUS DRIVING CONDITIONS.
THE MAIN CONCERN DURING THE SATURDAY NIGHT THROUGH SUNDAY PERIOD
IS THE POTENTIAL FOR STRONG WINDS. WINDS COULD GUSTS OF 50 TO 60
MPH ARE EXPECTED LATE SATURDAY INTO SATURDAY NIGHT AS STRONG
PRESSURE GRADIENT WILL BE ACROSS THE AREA ALONG WITH STRONG WINDS
ALOFT THAT ARE EXPECTED TO MIX DOWN TO THE SURFACE. WE WILL
MAINTAIN THE HIGH WIND WATCH, AND UPGRADE TO A HIGH WIND WARNING
OR WIND ADVISORY WITH WITH LATER FORECASTS AS NEEDED.
WE HAVE ALSO ISSUED A FREEZE WATCH FOR UPPER MONTGOMERY, CHESTER,
AND CECIL COUNTIES AS THE GROWING SEASON HAS STARTED HERE AND
TEMPERATURES ARE FORECAST TO DROP TO NEAR 30 DEGREES. ADDITIONAL
FREEZE WATCHES MAY BE NEEDED EACH NIGHT THROUGH TUESDAY NIGHT FOR
THOSE AREAS WHERE THE GROWING SEASON HAS STARTED.
THE LOW WILL LIFT AWAY FROM THE AREA LATER SUNDAY INTO SUNDAY
NIGHT, AS HIGH PRESSURE BUILDS ACROSS THE AREA SUNDAY NIGHT. WINDS
WILL SLOWLY DIMINISH LATE SUNDAY AND INTO SUNDAY NIGHT. A DRYING
OUT PERIOD SHOULD OCCUR SUNDAY INTO SUNDAY NIGHT, ALTHOUGH SOME
LAKE EFFECT SHOWERS OR FLURRIES CANNOT BE RULED OUT IN THE
NORTHWEST FLOW SUNDAY.
MODELS CONTINUE TO INDICATE A CLIPPER SYSTEM AFFECTING THE AREA
NEXT MONDAY INTO MONDAY NIGHT. THE QUESTION BECOMES PRECIPITATION
TYPE ACROSS SOME OF THE AREA. PRECIPITATION WILL LIKELY BEGIN AS
AS SNOW IF IT STARTS EARLY ENOUGH MONDAY MORNING, THEN BECOME RAIN
FOR MOST AREAS DURING THE DAY. BUT AS THICKNESSES LOWER ACROSS THE
AREA LATER INTO THE EVENING, THERE IS THE POTENTIAL THAT WE COULD
HAVE A PERIOD OF SNOW ON THE BACKSIDE OF THE LOW BEFORE THE
PRECIPITATION ENDS. A LIGHT ACCUMULATION IS POSSIBLE, MAINLY FOR
NORTHERN AREAS.
HIGH PRESSURE RETURNS FOR LATE TUESDAY INTO EARLY WEDNESDAY WHICH
WILL ALLOW FOR DRY WEATHER TO RETURN. HOWEVER, THIS MAY BE SHORT
LIVED AS ANOTHER LOW PRESSURE SYSTEM AND ASSOCIATED FRONTAL
BOUNDARY IS FORECAST TO MOVE TOWARD THE AREA THURSDAY INTO FRIDAY.
MODELS INITIALLY BRING AN AREA OF LOW PRESSURE INTO THE GREAT
LAKES REGION WEDNESDAY NIGHT INTO THURSDAY, BRINGING A COLD FRONT
TOWARD OUR AREA. AS THE FRONT APPROACHES, A TRIPLE POINT LOW FORMS
NEAR OUR AREA, WHICH WILL SLOW THE PROGRESS OF THIS SYSTEM.
PRECIPITATION CHANCES START LATE WEDNESDAY INTO THURSDAY, BUT
CONTINUE INTO THURSDAY NIGHT AND FRIDAY AS THE TRIPLE POINT LOW
SLOWLY MOVES EASTWARD. IT LOOKS LIKE PRECIPITATION SHOULD BE ALL
RAIN, EXCEPT AT THE VERY BEGINNING IF IT STARTS EARLY ENOUGH, AND
AT THE END IF IT HOLDS ON LONG ENOUGH.
&&
.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
VFR CONDITIONS ACROSS MOST OF THE REGION THIS AFTERNOON. KACY AND
KMIV HAVE BEEN ON THE BACK EDGE OF A LOWER CLOUD DECK WHICH HAS
LED TO VARIABILITY WITH CEILINGS EARLY THIS AFTERNOON. MORE
CONSISTENT VFR CONDITIONS ARE EXPECTED AT THESE SITES BY LATE THIS
AFTERNOON.
OCCASIONAL WIND GUSTS AROUND 25 KNOTS ARE LIKELY THROUGH THE
AFTERNOON AT ALL TAF SITES AS WELL. A COLD FRONT WILL APPROACH THE
REGION TONIGHT. A NARROW BAND OF SHOWERS AND THUNDERSTORMS IS
OCCURRING AHEAD OF THE FRONT AND LOOKS TO ROUGHLY TIME FROM 20Z AT
KRDG, 21Z AT ABE, 22Z AT PHL AND 23Z FOR ACY. HOWEVER, SOME
UNCERTAINTY IN BOTH TIMING AND COVERAGE IS PRESENT LATE THIS
AFTERNOON AND EARLY EVENING, TEMPO GROUPS ATTM IN TAFS FOR LOWER
CEILINGS AND VSBYS DUE TO CONVECTION CHANCE.
VFR CONDITIONS TONIGHT AS WELL WITH WINDS DECREASING. CLOUDS WILL
INCREASE AND LOWER TOWARD SUNRISE SATURDAY WITH A PERIOD OF
SHOWERS IN THE MORNING AND EARLY AFTERNOON HOURS. MVFR CEILINGS
AND VSBYS POSSIBLE IN SPOTS. WESTERLY WIND GUSTS INCREASING
SATURDAY AFTERNOON TO AROUND 20 KNOTS.
OUTLOOK...
SATURDAY NIGHT-SUNDAY...GENERALLY VFR EXPECTED. A CHANCE OF SHOWERS
SATURDAY NIGHT WHICH MAY LOWER CONDITIONS. STRONG WEST TO NORTHWEST
WINDS OVERNIGHT SATURDAY AND SUNDAY. WIND GUSTS COULD REACH 40-50
KNOTS LATE SATURDAY INTO SUNDAY.
SUNDAY NIGHT...GENERALLY VFR. WINDS DIMINISH SUNDAY NIGHT, THEN
INCREASE OUT OF THE SOUTHWEST MONDAY WITH GUSTS 20-30 KNOTS POSSIBLE.
MONDAY-MONDAY NIGHT...VFR EARLY, LOWERING CONDITIONS LATER IN THE
DAY AND INTO THE NIGHT WITH RAIN DEVELOPING. SNOW POSSIBLE LATE AS
PRECIPITATION ENDS. GUSTY SOUTHWEST WINDS AHEAD OF A FRONT, THEN
NORTHWEST BEHIND THE FRONT. GUSTS AT LEAST 25-30 KNOTS.
TUESDAY-TUESDAY NIGHT...VFR. GUSTY NORTH-NORTHWEST WINDS 25-30 KNOTS.
WEDNESDAY...VFR AND LIGHT WINDS EXPECTED.
&&
.MARINE...
CURRENT SCA IN EFFECT FOR THE WATERS HAS BEEN VERIFYING MOST OF
THE DAY WITH WIND GUSTS IN THE BAY...AND WITH WIND GUSTS AND SEAS
IN THE COASTAL ATLANTIC. THE ONLY CHANGES TO THE SCA WITH THE
AFTERNOON UPDATE WAS TO EXTEND THE SCA FOR THE DE BAY A FEW HOURS
LATER TO COVER THE FIRST HALF OF THE EVENING SINCE THE POTENTIAL
FOR GUSTY SW WINDS WILL LINGER UNTIL A COLD FRONT MOVES THRU
AROUND OR JUST AFTER SUNSET.
THE SCA CONTINUES THRU TONIGHT FOR THE COASTAL ATLANTIC WATERS.
THE WINDS WILL WEAKEN LATER THIS EVENING AND BECOME LIGHT LATE
TONIGHT AS THE FRONT MOVES OFF THE COAST. HOWEVER, IT WILL TAKE
TIME FOR THE SEAS TO SUBSIDE AFTER THE WIND FIELD DOES FIRST.
THERE IS A CHANCE THAT SEAS AT OUR OFFSHORE BUOYS TAKE A BIT
LONGER TO FALL BELOW 5 FT. IF THIS HAPPENS, THE SCA MAY NEED TO BE
EXTENDED INTO SATURDAY MORNING.
OUTLOOK...
SATURDAY NIGHT-SUNDAY...STORM WATCH REMAINS IN EFFECT. GALE FORCE
CONDITIONS EXPECTED, WITH STORM FORCE LIKELY OVERNIGHT SATURDAY INTO
SUNDAY, BEHIND A COLD FRONTAL PASSAGE MOVING ACROSS THE AREA LATE
SATURDAY.
SUNDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS POSSIBLE EARLY,
DIMINISHING OVERNIGHT.
MONDAY-TUESDAY NIGHT...INCREASING WINDS THROUGH THE DAY MONDAY,
WITH A RETURN TO SMALL CRAFT ADVISORY LEVEL WINDS LIKELY, POSSIBLY
NEAR GALE FORCE, ESPECIALLY BEHIND A COLD FRONTAL PASSAGE. A BRIEF
LULL POSSIBLE EARLY MONDAY NIGHT, BEFORE INCREASING AGAIN TO SMALL
CRAFT LEVELS, POSSIBLY GALE OVERNIGHT MONDAY INTO TUESDAY NIGHT.
WEDNESDAY...CONDITIONS LOWER BELOW ADVISORY LEVELS.
&&
.FIRE WEATHER...
FOR SUNDAY...VERY WINDY CONDITIONS WITH RELATIVE HUMIDITY LEVELS
DROPPING INTO 25-30 PERCENT RANGE FOR A TIME IN THE AFTERNOON.
THIS COULD LEAD TO FIRE WEATHER CONCERNS, ALTHOUGH THE EXTENT WILL
DEPEND ON HOW MUCH DRYING OF THE FUELS TAKES PLACE LEADING UP TO
SUNDAY.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
MORNING FOR PAZ054-055-060>062-070-071-101>106.
NJ...HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
MORNING FOR NJZ001-007>010-012>027.
DE...HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
MORNING FOR DEZ001>004.
MD...HIGH WIND WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY
MORNING FOR MDZ008-012-015-019-020.
MARINE...STORM WATCH FROM LATE SATURDAY NIGHT THROUGH SUNDAY MORNING
FOR ANZ430-431-450>455.
SMALL CRAFT ADVISORY UNTIL 7 AM EDT SATURDAY FOR ANZ450>455.
SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ430-
431.
&&
SYNOPSIS...ROBERTSON
NEAR TERM...KLEIN
SHORT TERM...KLEIN
LONG TERM...ROBERTSON
AVIATION...KLEIN/ROBERTSON
MARINE...KLEIN/ROBERTSON
FIRE WEATHER...