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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