NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Apr 16, 4:05 PM EST, 2 hours 31 minutes earlier.
Area forecast discussion, Apr 16, 4:05 PM EST, 2 hours 31 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
505 PM EDT SAT APR 16 2011
.SYNOPSIS...
LOW PRESSURE, LOCATED OVER NORTHERN LOWER MICHIGAN LATE THIS
AFTERNOON, WILL CONTINUE TO PROGRESS TO THE NORTHEAST. THE SYSTEM
IS EXPECTED TO PULL A COLD FRONT THROUGH OUR REGION TONIGHT. THE
LOW IS FORECAST TO MOVE ACROSS CENTRAL QUEBEC ON SUNDAY AND INTO
NEWFOUNDLAND ON MONDAY. IT SHOULD PULL ANOTHER COLD FRONT INTO OUR
REGION ON MONDAY NIGHT AND THE BOUNDARY MAY STALL HERE ON TUESDAY.
ANOTHER LOW IS ANTICIPATED TO MOVE ACROSS THE GREAT LAKES ON
TUESDAY NIGHT AND WEDNESDAY PULLING YET ANOTHER COLD FRONT THROUGH
OUR REGION ON WEDNESDAY NIGHT. HIGH PRESSURE SHOULD FOLLOW FOR
THURSDAY AND FRIDAY.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
A MID LEVEL LOW, LOCATED OVER LOWER LAKE MICHIGAN LATE THIS
AFTERNOON, WAS DRIFTING TO THE NORTHEAST. IT IS EXPECTED TO GET
ABSORBED INTO ANOTHER MID LEVEL LOW FROM THE NORTHWEST THAT WAS
DROPPING TOWARD LAKE SUPERIOR THIS AFTERNOON.
AT THE SURFACE, LOW PRESSURE WAS LOCATED OVER NORTHERN LOWER
MICHIGAN AT 500 PM. A COLD FRONT EXTENDED SOUTHEAST TO THE UPPER
OHIO RIVER VALLEY, THEN SOUTH TO THE CAROLINAS. THE LOW WILL
PROGRESS TO THE NORTHEAST, PULLING THE FRONT EASTWARD. THE COLD
FRONT IS EXPECTED TO REACH CENTRAL PENNSYLVANIA, CENTRAL MARYLAND
AND EASTERN VIRGINIA AROUND 800 PM. THE BOUNDARY SHOULD REACH OUR
WESTERN COUNTIES AROUND 1000 PM AND IT IS EXPECTED TO PASS OFF THE
NORTHERN PART OF THE NEW JERSEY COAST AROUND 200 AM.
THE BEST LIFT AND THE HEAVIEST RAIN ARE ANTICIPATED ALONG AND
JUST AHEAD OF THE FRONTAL BOUNDARY. PRECIPITABLE WATER VALUES ARE
EXPECTED TO APPROACH 1.5 INCHES THIS EVENING.
THE 1200 UTC NAM IS GIVING US ABOUT AN INCH OF RAIN NEAR THE
COAST AND CLOSE TO 2.5 INCHES IN THE LEHIGH VALLEY, THE POCONOS
AND NORTHWESTERN NEW JERSEY. THE 1200 UTC GFS IS ABOUT A QUARTER
INCH LOWER THAN THE 1200 UTC NAM. THE 1200 UTC ECMWF FAVORS THE
GFS NEAR THE COAST BUT IS ONLY NEAR 1.5 INCHES IN OUR NORTHERN
COUNTIES. BASED ON A MODEL CONSENSUS AND GUIDANCE FROM HPC, WE
WILL CONTINUE TO FORECAST RAINFALL AMOUNTS OF 1 TO 2 INCHES IN OUR
REGION, FOLLOWING A RAINFALL PATTERN SIMILAR TO THAT OF THE 1200
UTC GFS. AS A RESULT, THE FLOOD WATCH WILL BE LEFT IN PLACE FOR
NORTHERN DELAWARE, EASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY.
IN REGARD TO THE WIND, WE WILL ALSO LEAVE THE WIND ADVISORY IN
PLACE. WINDS AT 925 HPA ARE EXPECTED TO BE IN EXCESS OF 60 KNOTS
THIS EVENING. THE MODERATE TO HEAVY RAIN SHOULD WORK TO MIX DOWN
SOME WIND GUSTS. IT SEEMS AS THOUGH THE MOST LIKELY AREAS TO
RECEIVE STRONG WIND GUSTS WILL BE OUR SOUTHERN COUNTIES AND THE
HIGHER ELEVATIONS UP NORTH.
AT 440 PM, A TORNADO WATCH WAS ISSUED FOR SOME OF OUR WESTERN AND
SOUTHERN COUNTIES. WHILE THE BOUNDARY LAYER REMAINS QUITE STABLE,
THERE IS A CHANCE THAT THE STABLE LAYER MAY ERODE ENOUGH TO ALLOW
FOR AN ISOLATED STRONG THUNDERSTORM TO DEVELOP OR MOVE INTO OUR
AREA. IF A STRONG THUNDERSTORM DOES DEVELOP, THERE IS ENOUGH
DIRECTIONAL AND SPEED SHEAR TO RESULT IN AN ISOLATED TORNADO. THE
TORNADO WATCH IS IN EFFECT UNTIL 1100 PM.
TEMPERATURES SHOULD CONTINUE TO RISE SLOWLY INTO THIS EVENING
UNTIL THE FRONT PASSES.
A MID LEVEL SHORT WAVE IS FORECAST TO LIFT UP OVER OUR REGION
FROM THE SOUTHWEST, BRINGING AND END TO THE RAIN.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
THE MID LEVEL LOW IS EXPECTED TO PASS ACROSS THE GREAT LAKES
TONIGHT AND SUNDAY MORNING, THEN DOWN THE SAINT LAWRENCE RIVER
VALLEY ON SUNDAY AFTERNOON AND SUNDAY EVENING. A MID LEVEL SHORT
WAVE SHOULD PASS OVER OUR REGION ON SUNDAY EVENING, WITH THE
PATTERN BECOMING ZONAL IN ITS WAKE FOR SUNDAY NIGHT AND MONDAY. A
TROUGH SHOULD DIG OVER THE GREAT PLAINS ON TUESDAY.
WE WILL INDICATE A SLIGHT CHANCE OF SHOWERS IN OUR NORTHERN
COUNTIES FOR LATE SUNDAY IN ASSOCIATION WITH THE SHORT WAVE. THE
1200 UTC NAM WAS ACTUALLY INDICTING LIFTED INDEX VALUES A BIT
BELOW ZERO AT THAT TIME AND CAPE VALUES UP AROUND 400 J/KG. THE
GFS IS LESS UNSTABLE. FOR NOW, WE WILL NOT MENTION ANY THUNDER AND
WE WILL SEE WHAT SUBSEQUENT MODEL GUIDANCE SUGGESTS.
A FRONTAL BOUNDARY FROM THE NORTHWEST IS EXPECTED TO DROP INTO
OUR REGION ON MONDAY AND MONDAY NIGHT. WITHOUT MUCH OF A PUSH
BEHIND IT, THE FRONT SHOULD STALL ON TUESDAY. AS IS COMMON WITH
SUCH FRONTS AT THIS TIME OF THE YEAR, FORECAST CONFIDENCE
REGARDING ITS TIMING AND SOUTHWARD PROGRESS IS RATHER LOW. WE WILL
MENTION A CHANCE OF RAIN, ESPECIALLY FOR OUR NORTHERN AND CENTRAL
COUNTIES.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
THIS TIME FRAME APPEARS TO BE UNSETTLED BUT WILL ALSO FEATURE A
WARM UP AROUND WEDNESDAY. AS THE RIDGING NEAR THE WEST COAST
BREAKS DOWN, 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 THROUGH THURSDAY, THEN
BLENDED IN AN INCREASING PERCENTAGE OF THE ECMWF ENSEMBLE MEAN.
THIS IS TO PARTIALLY CORRECT FOR THE GENERAL FAST BIAS OF THE GFS
AND ITS ENSEMBLE MEMBERS. WE INITIALIZED THE DATABASE WITH HPC
GUIDANCE THAN MADE SOME TWEAKS BASED ON ADDITIONAL COLLABORATION.
BASED ON THE ABOVE, A WARM FRONT IS FORECAST TO BE SITTING MOSTLY
ACROSS OUR SOUTHERN ZONES TUESDAY NIGHT WHICH THEN LIFTS NORTHWARD
WEDNESDAY. THIS WILL PLACE MOST OF THE CWA IN THE WARM SECTOR WITH
A RATHER WARM SOUTHWEST FLOW OCCURRING FOR A TIME WEDNESDAY. THERE
IS SOME UNCERTAINTY WITH THE DEGREE OF SHOWERS OR A PERIOD OF RAIN
BECOMING STRETCHED WEST TO EAST NORTH OF THE WARM FRONT. FOR NOW,
WE KEPT POPS IN THE CHC TO SLIGHT CHC RANGE WITH THE HIGHEST
VALUES ACROSS THE FAR NORTH TUESDAY NIGHT INTO WEDNESDAY, WITH THE
POPS THEN ERODING FROM SOUTH TO NORTH WEDNESDAY MORNING. THIS
PRECIPITATION MAY BE TIED TO ANY CONVECTIVE ACTIVITY WELL TO OUR
WEST AS IT ROLES EASTWARD, SO FOR NOW WE WILL GO WITH SHOWERS
INSTEAD OF RAIN. IN THE WARM SECTOR WEDNESDAY, STRONG WAA IS
FORECAST TO BOOST 850 MB TEMPERATURES TO NEAR +18C. THIS ALONG
WITH AT LEAST SOME SUNSHINE AND INCREASED MIXING SHOULD ALLOW
HIGHS TO NEAR 80 DEGREES SOUTH OF THE WARM FRONT ESPECIALLY FROM
THE I-95 CORRIDOR ON EASTWARD /COOLER ALONG THE COAST THOUGH AS
THE SURFACE WINDS MAY BE TO SOUTHERLY FOR AWHILE/.
AS LOW PRESSURE TRACKS ACROSS SOUTHEASTERN CANADA WEDNESDAY NIGHT
INTO THURSDAY, ITS COLD FRONT SWEEPS THROUGH OUR AREA. GIVEN THE
WARM AIRMASS AHEAD OF THIS BOUNDARY ALONG WITH THE MOISTURE
RETURN, WE WILL CONTINUE TO INCLUDE A CHC OF THUNDER WEDNESDAY
AFTERNOON AND EVENING. AS A STRONG SURFACE HIGH THEN SLIDES ACROSS
SOUTHERN CANADA, IT SHOULD TEND TO BUILD DOWN INTO THE MID
ATLANTIC STATES ALLOWING THE AFOREMENTIONED COLD FRONT TO BE
PUSHED WELL TO OUR SOUTH. A COOLER AIRMASS WILL ACCOMPANY THIS
SURFACE HIGH AND ULTIMATELY WE MAY HAVE A LIGHT ONSHORE FLOW
OCCURRING LATE 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 /OVERRUNNING RAIN?/. WE STARTED
TO INCREASE THE POPS FRIDAY AND CONTINUED THAT SATURDAY. THERE
HOWEVER IS SOME UNCERTAINTY ON THE TIMING ESPECIALLY WITH THE
MOSTLY ZONAL FLOW REGIME, THEREFORE KEPT POPS IN THE LOW CHC
RANGE. AS FOR TEMPERATURES, WE GENERALLY FOLLOWED HPC WITH MAINLY
MINOR TWEAKS.
&&
.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
RAIN MOVED IN FROM THE WEST-SOUTHWEST EARLY THIS AFTERNOON ACROSS
OUR TAF SITES, WITH ASSOCIATED CEILINGS OF AROUND 1000 FEET AND
VSBYS IN THE 2 TO 5 SM RANGE. THESE CONDITIONS WERE EXPECTED TO
PERSIST THROUGH THE MID AFTERNOON HOURS, THEN IMPROVE SLIGHTLY FOR
A COUPLE OF HOUR BEFORE THE NEXT ROUND OF HEAVIER SHOWERS AND
PERHAPS A FEW THUNDERSTORMS MOVE IN WITH THE FRONT DURING THE LATE
AFTERNOON AND EVENING HOURS. HAVE ALSO INCLUDED A WIND SHEAR
ELEMENT IN THE TAFS THROUGH THE EVENING HOURS. HAVE INCLUDED CB
WITH THE TEMPO CLOUD GROUPING IN THE TAFS BUT ANY THUNDERSTORMS
THAT DO DEVELOP SHOULD BE WIDELY SCATTERED. AFTER THE FRONT MOVES
THROUGH LATE THIS EVENING, WINDS WILL TURN OVER TO THE WEST AND
VFR CONDITIONS WILL RETURN. WINDS ARE EXPECTED TO PICK UP AGAIN ON
SUNDAY, BUT WITH HIGH PRESSURE MOVING BACK IN...VFR CONDITIONS
WILL CONTINUE. BOTTOM LINE...FLYING CONDITIONS WILL BE POOR
THROUGH THE EVENING HOURS...THEN THEY WILL GET BETTER.
OUTLOOK...
LATER MONDAY INTO WEDNESDAY, A FRONTAL BOUNDARY IS FORECAST TO
STALL NEAR OR CLOSE TO THE TERMINAL AREA. THIS SHOULD BRING SOME
MVFR CONDITIONS AT TIMES IN ANY PRECIPITATION.
&&
.MARINE...
GALE WARNINGS WILL CONTINUE INTO THE OVERNIGHT HOURS FOR ALL OF
OUR MARINE AREAS. GALE FORCE GUSTS IN THE 40 TO 45 KT RANGE SHOULD
PEAK THIS EVENING AND THEN SLOWLY DECREASE LATER TONIGHT. SMALL
CRAFT ADVISORY WINDS SHOULD THEN CONTINUE IN THE WESTERLY FLOW ALL
AREAS INTO SUNDAY BEFORE FALLING BELOW CRITERIA SUNDAY NIGHT.
SMALL CRAFT ADVISORY CONDITIONS DUE TO SEAS MIGHT PERSIST INTO
SUNDAY NIGHT ON THE OCEAN WATERS.
A FRONTAL BOUNDARY IS THEN FORECAST TO SETTLE OVER OR NEAR OUR
AREA WATERS LATER MONDAY INTO WEDNESDAY. RIGHT NOW IT LOOKS AS
THOUGH WINDS SHOULD REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA,
ALTHOUGH SOUTHERLY SWELLS OF SMALL CRAFT ADVISORY CRITERIA
GENERATED SOUTH OF THIS BOUNDARY MIGHT EFFECT OUR OCEAN WATERS
TUESDAY INTO WEDNESDAY.
&&
.HYDROLOGY...
THE BEST LIFT AND THE HEAVIEST RAIN ARE ANTICIPATED ALONG AND
JUST AHEAD OF THE FRONTAL BOUNDARY. PRECIPITABLE WATER VALUES ARE
EXPECTED TO APPROACH 1.5 INCHES THIS EVENING.
THE 1200 UTC NAM IS GIVING US ABOUT AN INCH OF RAIN NEAR THE
COAST AND CLOSE TO 2.5 INCHES IN THE LEHIGH VALLEY, THE POCONOS
AND NORTHWESTERN NEW JERSEY. THE 1200 UTC GFS IS ABOUT A QUARTER
INCH LOWER THAN THE 1200 UTC NAM. THE 1200 UTC ECMWF FAVORS THE
GFS NEAR THE COAST BUT IS ONLY NEAR 1.5 INCHES IN OUR NORTHERN
COUNTIES. BASED ON A MODEL CONSENSUS AND GUIDANCE FROM HPC, WE
WILL CONTINUE TO FORECAST RAINFALL AMOUNTS OF 1 TO 2 INCHES IN OUR
REGION, FOLLOWING A RAINFALL PATTERN SIMILAR TO THAT OF THE 1200
UTC GFS. AS A RESULT, THE FLOOD WATCH WILL BE LEFT IN PLACE FOR
NORTHERN DELAWARE, EASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY.
THE MAIN STEM RIVERS SHOULD EASILY BE ABLE TO HANDLE THE EXPECTED
RAINFALL AMOUNTS, AS SHOULD MOST OF THE LARGER STREAMS AND CREEKS.
IT SEEMS AS THOUGH THE MOST LIKELY SPOTS THAT MAY FLOOD IN THIS
EVENT ARE SMALL STREAMS AND AREAS OF POOR DRAINAGE. ROADWAY FLOODING
IS ALSO ANTICIPATED AS SOME STORM DRAINS MAY NOT BE ABLE TO
HANDLE THE VOLUME OF RAINWATER IN THE HEAVY DOWNPOURS.
&&
.TIDES/COASTAL FLOODING...
WITH A STRONG SOUTHEASTERLY WIND, WE/RE CONCERNED THAT MINOR
TIDAL FLOODING MAY OCCUR IN THE UPPER REACHES OF THE CHESAPEAKE
BAY WITH THE HIGH TIDE LATE THIS AFTERNOON AND EARLY THIS EVENING.
HIGH TIDE HAS ALREADY OCCURRED AT CAMBRIDGE, BUT DOESN/T OCCUR
UNTIL AROUND 6 PM AT TOLCHESTER BEACH AND A LITTLE LATER FURTHER
NORTH. ANY FLOODING THAT DOES OCCUR IN THE NORTHERN AREAS OF THE
CHESAPEAKE BAY THIS EVENING WILL BE MINOR, BUT IT STILL NEEDS TO
BE MENTIONED. A COASTAL FLOOD ADVISORY HAS THEREFORE BEEN ISSUED
FOR THIS AREA. RENEWED MINOR FLOODING IS POSSIBLE ON THE
CHESAPEAKE BAY FOR THE NEXT HIGH TIDE LATE TONIGHT AND SUNDAY
MORNING. IF THE WIND DIRECTION CHANGES A LITTLE FASTER THAN
EXPECTED, MAYBE FLOODING WON/T BE A PROBLEM, BUT JUST TOO SOON TO
TELL SO THE ADVISORIES WILL BE LEFT AS IS UNTIL WE GET A BETTER
HANDLE ON THE METEOROLOGY.
THE COASTAL FLOOD WARNING CONTINUES FOR THIS EVENINGS/NIGHTTIME
HIGH TIDE CYCLE FOR THE ATLANTIC COAST, OUR PART OF RARITAN BAY,
DELAWARE BAY AND TIDAL SECTIONS OF THE DELAWARE RIVER. THIS SYSTEM
HAS SIMILARITIES IN STRENGTH AND STRUCTURE TO THE DECEMBER 1, 2010
EVENT IN WHICH THE HIGH TIDE DEPARTURES AVERAGED AROUND 2 FEET,
SLIGHTLY HIGHER IN THE DELAWARE RIVER. THE HIGH ASTRONOMICAL TIDES
ASSOCIATED WITH THE UPCOMING FULL MOON AND THE POORLY TIMED
COINCIDENTAL HIGHER OF THE TWO DAILY ASTRONOMICAL TIDES HAVE
INCREASED THE RISK. THE EASTERLY FLOW VEERING TO THE SOUTHEAST
WOULD PLACE THE GREATEST RISK FOR MODERATE TIDAL FLOODING IN
DELAWARE BAY AND TIDAL SECTIONS OF THE DELAWARE RIVER. IF THE
WINDS VEER TO THE SOUTHEAST SOONER, THE LEAST CHANCE WOULD BE
TOWARD NYC IN RARITAN BAY AND NORTH COASTAL NEW JERSEY. OUR LOCAL
STUDY PROCEDURE IS FORECASTING TIDAL DEPARTURES CLOSE TO 2.0 FEET
ABOVE NORMAL WHICH FOR MOST PLACES IS BORDERLINE BETWEEN MINOR AND
MODERATE TIDAL FLOODING THRESHOLDS. THE EXCEPTION IS UPPER
DELAWARE BAY WHERE WE WOULD CLEARLY BE IN THE MODERATE TIDAL
FLOODING CATEGORY AND LIKELY ALSO THE DELAWARE RIVER.
THIS WILL BE A ONE TIDE CYCLE EVENT AS WINDS WILL SHIFT TO THE
WEST BY THE TIME OF THE NEXT HIGH TIDE CYCLE. THE WINDS WILL COME
CLOSE TO SHIFTING IN THE DELAWARE RIVER AS THE HIGH TIDE CYCLE IS
OCCURRING TONIGHT WHICH CERTAINLY WOULD HELP. |
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FLOOD WATCH THROUGH LATE TONIGHT FOR PAZ054-055-060>062-
067>071.
WIND ADVISORY UNTIL 11 PM EDT THIS EVENING FOR PAZ054-055-
060>062.
WIND ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR PAZ067>071.
COASTAL FLOOD WARNING FROM 10 PM THIS EVENING TO 3 AM EDT
SUNDAY FOR PAZ070-071.
NJ...FLOOD WATCH THROUGH LATE TONIGHT FOR NJZ001-007>010-012-015.
WIND ADVISORY UNTIL 11 PM EDT THIS EVENING FOR NJZ001-007-008.
WIND ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR NJZ009-010-
012>027.
COASTAL FLOOD WARNING UNTIL MIDNIGHT EDT TONIGHT FOR
NJZ012>014-020>027.
COASTAL FLOOD WARNING FROM 10 PM THIS EVENING TO 3 AM EDT
SUNDAY FOR NJZ016>019.
DE...FLOOD WATCH THROUGH LATE TONIGHT FOR DEZ001.
WIND ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR DEZ001>004.
COASTAL FLOOD WARNING UNTIL MIDNIGHT EDT TONIGHT FOR
DEZ002>004.
COASTAL FLOOD WARNING FROM 10 PM THIS EVENING TO 3 AM EDT
SUNDAY FOR DEZ001.
MD...WIND ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR MDZ008-012-015-
019-020.
COASTAL FLOOD ADVISORY UNTIL 10 PM EDT THIS EVENING FOR MDZ008-
012-015-019-020.
COASTAL FLOOD ADVISORY FROM 2 AM TO 10 AM EDT SUNDAY FOR
MDZ008-012-015-019-020.
MARINE...GALE WARNING UNTIL 6 AM EDT SUNDAY FOR ANZ450>455.
GALE WARNING UNTIL 2 AM EDT SUNDAY FOR ANZ430-431.
&&
SYNOPSIS...IOVINO
NEAR TERM...IOVINO
SHORT TERM...IOVINO
LONG TERM...GORSE
AVIATION...MIKETTA
MARINE...MIKETTA
HYDROLOGY...IOVINO
TIDES/COASTAL FLOODING...MIKETTA