096
FXUS61 KPHI 230516
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1216 AM EST SAT FEB 23 2019
SYNOPSIS
HIGH PRESSURE SHIFTS TO OFF THE NEW ENGLAND COAST DURING SATURDAY
INTO SATURDAY NIGHT. MEANWHILE, LOW PRESSURE FORMS OVER THE CENTRAL
PLAINS AND DEEPENS RAPIDLY AS IT MOVES NORTHEASTWARD INTO THE GREAT
LAKES BY SUNDAY MORNING. THIS INTENSE LOW WILL CONTINUE ACROSS
SOUTHEAST CANADA SUNDAY AND SUNDAY NIGHT, WITH AN ATTENDANT COLD
FRONT CROSSING THE MID-ATLANTIC REGION SUNDAY AFTERNOON. HIGH
PRESSURE WILL BUILD IN BEHIND THE LOW LATE MONDAY AND TUESDAY. A
WEAK LOW PRESSURE SYSTEM MAY AFFECT THE AREA AROUND WEDNESDAY, THEN
HIGH PRESSURE SHOULD RETURN BY FRIDAY.
NEAR TERM /UNTIL 6 AM THIS MORNING/
FORECAST GENERALLY REMAINS ON TRACK, SO WILL MAKE SOME
ADJUSTMENTS BASED ON HOURLY GRIDS, BUT NO SIGNIFICANT CHANGES
OVERALL. LOW TEMPERATURES WERE ADJUSTED DOWN SOME FOR SEVERAL
AREAS AS A RESULT. NO OTHER SIGNIFICANT CHANGES WERE NEEDED AT
THIS TIME. LOWER DEW POINTS REMAIN ACROSS MUCH OF THE AREA AND
THIS TREND MAY CONTINUE OVERNIGHT AS THE STRONG SURFACE HIGH
STARTS TO BECOME MORE CENTERED TO OUR NORTH-NORTHEAST. A WEALTH
OF HIGH LEVEL CLOUDINESS CONTINUES TO MOVE ACROSS THE REGION
ASSOCIATED WITH AN UPPER-LEVEL JET. SOME SPRINKLES AND LIGHT
RAIN SOUTH AND SOUTHWEST OF SOUTHERN DELAWARE IS ANTICIPATED TO
REMAIN THERE DUE TO DRIER AIR NORTHWARD.
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/
BIGGEST CHANGE IN THIS PERIOD WAS TO DELAY THE ONSET OF RAIN
THROUGH THE DAY TIME HOURS. MOST OF THE REGION, WITH THE
EXCEPTION OF DELMARVA AND FAR SOUTH JERSEY, WILL LIKELY NOT SEE
ANY RAIN DURING THE DAY TIME HOURS. THIS SLOWER ARRIVAL OF RAIN
MAKES SENSE GIVEN HOW SLOW THE SURFACE HIGH WILL BE TO SHIFT OFF
SHORE AWAY FROM OUR REGION. HIGHS LOOK TO BE MOSTLY IN THE 40S
ACROSS THE REGION.
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
MOST OF THE ACTION IN THE LONG TERM IS IN THE FIRST COUPLE OF
DAYS, I.E., SATURDAY NIGHT THROUGH MONDAY. AN UPPER LEVEL SHORTWAVE
RIDGE AND SURFACE HIGH PRESSURE OFF THE NEW ENGLAND COAST WILL
GIVE WAY TO A STRONG SHORTWAVE TROF AND ASSOCD DEEPENING LOW
PRESSURE, MOVING INTO THE GREAT LAKES BY SUNDAY MORNING. PRECIP
WILL OVERSPREAD THE AREA FROM SW TO NE DURING SATURDAY EVENING
AND MAY BECOME MODERATE TO HEAVY AT TIMES OVERNIGHT.
TEMPERATURES SHOULD SLOWLY RISE OVERNIGHT, HOWEVER THEY MAY
HOVER AROUND FREEZING FOR A FEW EVENING HOURS IN THE POCONOS.
THUS A BIT OF FREEZING IS POSSIBLE, BUT CONFIDENCE IS NOT HIGH,
AND DURATION WOULD BE RATHER BRIEF.
OTHERWISE, THE HEAVIEST RAIN SHOULD OCCUR IN A 6- TO 12-HOUR
WINDOW CENTERED AROUND 12Z SUNDAY. EXPECTED TOTAL RAINFALL IS
AROUND AN INCH AND NO SIGNIFICANT FLOODING IS EXPECTED. SEE THE
HYDRO SECTION BELOW FOR MORE INFO. RAIN WILL END WITH A SHARP
COLD FRONT PASSAGE SUNDAY AFTERNOON. FORECAST INSTABILITY IS
VERY LIMITED, BUT SHOWERS WITH THE FRONT COULD CONTAIN SOME
ISOLATED THUNDER. HIGH TEMPS SUNDAY MAY REACH MID 50S TO MID
60S, ESPECIALLY AFTER RAIN ENDS AND WINDS WITH THE FRONTAL
PASSAGE MIX THE PBL.
BEHIND THE FRONT, THE MAIN ISSUE BECOMES THE WIND. CONTINUED
DEEP LOW PRESSURE OVER SOUTHEAST CANADA WITH RESULT IN A STRONG
PRESSURE GRADIENT AND GUSTY WNW WINDS. WINDS A FEW THOUSAND FEET
ALOFT ARE FORECAST TO REACH 50-60KT, BUT DOWNWARD MIXING OF
MOMENTUM WILL BE LIMITED AS THE SURFACE COOLS AFTER SUNSET. A
WIND ADVISORY COULD EVENTUALLY BE NEEDED LATE SUNDAY INTO SUNDAY
NIGHT.
A POST-FRONTAL TROF IS FORECAST TO MOVE THROUGH AROUND 12Z
MONDAY WITH AN APPARENT SECONDARY SURGE OF WINDS. ALSO DAYTIME
HEATING WILL PROMOTE MIXING AND ENHANCED DOWNWARD MOM XFER. THUS
THE STRONGEST WINDS ARE EXPECTED MONDAY MORNING, WHEN GUSTS
COULD REACH 50KT REQUIRING A HIGH WIND WARNING.
BY TUESDAY THE LOW FINALLY PULLS AWAY INTO THE GULF OF ST.
LAWRENCE AND HIGH PRESSURE BUILDS IN OVER THE MID-ATLANTIC FROM
THE WEST. THIS WILL IN FAIR AND RELATIVELY CALM CONDITIONS.
THE FORECAST GRIDS BEYOND NEXT TUESDAY WERE NOT CHANGED FOR THIS
PACKAGE. THERE IS CONSIDERABLE UNCERTAINTY AND VARIATION BETWEEN
THE GFS AND THE ECMWF REGARDING TEMPS AND POSSIBLE LIGHT PRECIP,
BUT AS OF NOW NO SIGNIFICANT WEATHER IS EXPECTED AT LEAST
THROUGH MID-WEEK.
AVIATION /05Z SATURDAY THROUGH WEDNESDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
OVERNIGHT...VFR WITH HIGH LEVEL CLOUDINESS. NORTHERLY WINDS
AROUND 5 KNOTS, BECOMING LIGHT AND VARIABLE TO LOCALLY CALM.
SATURDAY...VFR OVERALL, HOWEVER CEILINGS WILL GRADUALLY LOWER
AS SOME LIGHT RAIN STARTS TO ARRIVE FROM THE SOUTHWEST LATE IN
THE DAY. FOR THE PHL AREA NORTHWARD, ANY LIGHT RAIN SHOULD HOLD
OFF UNTIL SATURDAY EVENING. LIGHT AND VARIABLE WINDS, BECOMING
NORTHEAST TO EAST AROUND 5 KNOTS, THEN SOUTHEAST 4-7 KNOTS IN
THE AFTERNOON.
OUTLOOK...
SATURDAY NIGHT...CIG/VSBY RESTRICTIONS EXPECTED IN RAIN AND
FOG. WINDS E/SE 3-8 KNOTS. HIGH CONFIDENCE.
SUNDAY...AM RESTRICTIONS IN RAIN AND LOW CLOUDS, BUT WITH PM
IMPROVEMENT. W/SW WINDS INCREASING TO 15 TO 25 KNOTS WITH GUSTS
OF 30 TO 35 KNOTS BY LATE DAY CONTINUING INTO THE EVENING.
MODERATE CONFIDENCE.
MONDAY...VFR BUT WITH STRONG W/NW WINDS EXPECTED AT 20-25
POTENTIALLY GUSTING 40 TO 50 KNOTS. MODERATE CONFIDENCE.
TUESDAY...VFR WITH NW WINDS 5-10 KNOTS. MODERATE CONFIDENCE.
WEDNESDAY...MAINLY VFR BUT WITH OCCASIONAL REDUCED CIGS/VSBYS
POSSIBLE IN SCATTERED RAIN OR SNOW SHOWERS. MODERATE CONFIDENCE.
MARINE
WINDS AND WAVES ARE EXPECTED TO REMAIN BELOW SMALL CRAFT
ADVISORY CONDITIONS THROUGH SATURDAY.
OUTLOOK...
SATURDAY NIGHT THRU SUNDAY...WINDS/SEAS INCREASING WITH SCA
CONDITIONS POSSIBLE BY LATE SATURDAY NIGHT INTO EARLY SUNDAY AND
GALE CONDITIONS POSSIBLE BY LATE DAY SUNDAY.
SUNDAY NIGHT THRU MONDAY NIGHT...W/NW GALES EXPECTED. STORM
FORCE WINDS POSSIBLE MONDAY.
TUESDAY AND WEDNESDAY...WINDS/SEAS DIMINISH TO BELOW SCA
LEVELS ON TUESDAY AND REMAIN SO ON WEDNESDAY.
HYDROLOGY
THERE ARE A COUPLE CHANGES TO NOTE WITH THE 12Z GFS/NAM
SOLUTIONS. ONE, THE ONSET OF THE PRECIPITATION IS SLOWER. TWO,
QPF HAS COME UP A LITTLE BIT. SO OTHER THAN THE DELMARVA, THE
RAINS MAY NOW HOLD OFF UNTIL SATURDAY EVENING FOR MUCH OF THE
FORECAST AREA. THE MAJORITY OF THE RAIN WILL FALL SATURDAY
EVENING THROUGH MIDDAY SUNDAY. THE MARFC IS USING BETWEEN 1.00
TO 1.50 INCHES OF RAIN TO DRIVE THEIR HYDROLOGIC MODELS TODAY.
BEFORE DISCUSSING STREAM/RIVER RESPONSE, I WANTED TO MENTION THAT
MUCH OF THE SNOW WE RECEIVED A COUPLE DAYS AGO HAS MELTED. OTHER
THAN FAR NW NJ AND THE SOUTHERN POCONOS, THERE ISN'T MUCH LEFT ON
THE GROUND. IT DOESN'T EVEN LOOK LIKE IT SNOWED HERE IN BURLINGTON
COUNTY. THIS WILL HELP AS MUCH OF THE MELTED SNOW IS MOVING THROUGH
THE RIVER SYSTEMS NOW VS. THIS WEEKEND AS IT'S RAINING. THE ONLY
REAL SWE TO MENTION IS UP ACROSS CARBON AND MONROE COUNTIES WHERE UP
TO 0.25" REMAINS. ELSEWHERE, THE SWE IS PRETTY MUCH HYDROLOGICALLY
INSIGNIFICANT.
USING THE 1.00 TO 1.50 OF QPF, WE ARE SEEING RESPONSES AT OUR
FORECAST POINTS. NO FLOODING IS CURRENTLY FORECAST, BUT MODELS DO
PUT SOME CRESTS NEAR BANKFUL. OVER THE WEEKEND, KEEP AN EYE THESE
FORECAST POINTS...THE NORTH BRANCH RANCOCAS AT PEMBERTON, THE
MILLSTONE RIVER AT BLACKWELLS MILLS, THE PASSAIC RIVER AT MILLINGTON
AND PINE BROOK, AND THE ROCKAWAY RIVER AT BOONTON. OUTSIDE OF THE
PASSAIC RIVER, FLOODING POTENTIAL IS LOW ON OUR OTHER MAINSTEM
RIVERS.
SO AS THE EVENT UNFOLDS SATURDAY NIGHT, LOOK FOR MINOR FLOODING
ACROSS AREAS OF POOR DRAINAGE AND IN LOW-LYING AREAS. SOME SMALLER
CREEKS THAT HAVE BEEN PRONE TO HIGH WATER THE LAST SIX MONTHS WILL
BE PRONE ONCE AGAIN THIS WEEKEND. THIS WATER WILL RUNOFF/MAKE IT
INTO THE ABOVE MENTIONED LARGER CREEKS AND STREAMS ON SATURDAY
NIGHT. RISES CAN BE EXPECTED LATE SATURDAY NIGHT, SUNDAY, SUNDAY
NIGHT, AND MAYBE INTO MONDAY. IF FLOODING OCCURS AT ANY OF OUR
FORECAST POINTS, IT APPEARS THE FLOODING WOULDN'T INITIATE UNTIL
SUNDAY NIGHT.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.
SYNOPSIS...AMC/GORSE
NEAR TERM...GORSE/MPS
SHORT TERM...JOHNSON
LONG TERM...AMC/FITZSIMMONS
AVIATION...AMC/GORSE/MPS
MARINE...AMC/JOHNSON/MPS
HYDROLOGY...
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