468  
FXUS61 KPHI 222121  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
421 PM EST FRI FEB 22 2019  
   
SYNOPSIS
 
 
HIGH PRESSURE CENTERED OVER THE NORTHERN MID- ATLANTIC REGION  
TONIGHT WILL SHIFT EAST AND OFF THE COAST OF NEW ENGLAND ON  
SATURDAY INTO SATURDAY NIGHT. MEANWHILE LOW PRESSURE WILL FORM  
OVER THE CENTRAL GREAT PLAINS AND DEEPEN RAPIDLY AS IT MOVES  
NORTHEAST INTO THE GREAT LAKES BY SUNDAY MORNING. THIS DEEP LOW  
WILL CONTINUE EAST ACROSS SOUTHEAST CANADA ON SUNDAY AND SUNDAY  
NIGHT, WITH AN ATTENDANT COLD FRONT CROSSING THE MID- ATLANTIC  
REGION SUNDAY AFTERNOON. HIGH PRESSURE WILL BUILD IN BEHIND THE  
LOW ON MONDAY AND TUESDAY. A WEAK LOW- PRESSURE DISTURBANCE MAY  
AFFECT THE AREA AROUND WEDNESDAY, BUT HIGH PRESSURE SHOULD  
RETURN FOR THE LATTER PART OF NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
 
 
LARGE SURFACE HIGH SHIFTS EAST OVER THE REGION TONIGHT. EXPECT  
DRY CONDITIONS AND LIGHT WINDS. INCREASED SKY COVER OVERNIGHT.  
SATELLITE SHOWS AN EXTENSIVE DECK OF CIRROSTRATUS ASSOCIATED  
WITH THE UPPER LEVEL JET, AND THIS IS EXPECTED TO CONTINUE INTO  
TOMORROW. IT SHOULD BE ALL HIGH CLOUDS THOUGH, SO SHOULD HAVE  
MINIMAL IMPACT ON TEMPERATURES OVERNIGHT. HOWEVER, RADIATIONAL  
COOLING WILL BE LIMITED BY DEW POINTS WHICH ARE ALREADY IN THE  
20S AND SHOULD INCREASE AS WINDS SHIFT SLIGHTLY ONSHORE  
OVERNIGHT. THEREFORE, LOWS ARE EXPECTED TO BE FROM THE MID 20S  
ACROSS THE SOUTHERN POCONOS AND NW NJ UP TO THE MID 30S FOR  
COASTAL LOCATIONS AND DELMARVA.  
 

 
   
SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/
 
 
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 /SATURDAY 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 PRESSUE OFF THE NEW ENGLAND COAST WILL  
GIVE WAY TO A STRONG SHORWAVE 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 FORECAT 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 /20Z FRIDAY THROUGH WEDNESDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT: VFR CONDITIONS EXPECTED WITH ONLY HIGH CIRRUS CLOUDS ACROSS  
THE REGION. NORTHWESTERLY WINDS WILL BECOME LIGHT AND VARIABLE  
OVERNIGHT. HIGH CONFIDENCE.  
 
SATURDAY: VFR CONDITIONS ARE EXPECTED FOR MOST OF THE DAY. CEILINGS  
AND VISIBILITY WILL GRADUALLY LOWER AS PRECIPITATION MOVES IN LATE  
IN THE DAY. HOWEVER, FOR MOST TAF SITES, THIS DOESN'T LOOK LIKELY TO  
OCCUR DURING THE DAY TIME ON SATURDAY. LIGHT WINDS (LESS THAN 10 KT)  
WILL BE SHIFTING FROM NORTHEASTERLY TO SOUTHEASTERLY THROUGH THE  
DAY. MODERATE CONFIDENCE; MAIN SOURCE OF UNCERTAINTY IS WITH THE  
TIMING OF HOW QUICKLY THE RAIN MOVES IN.  
 
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 OCCASSIONAL 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 TONIGHT AND 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.  
 
WEDNESDAY...  
 

 
   
HYDROLOGY
 
 
THERE ARE A COUPLE CHANGES TO NOTE WITH THIS MORNING'S 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  
NEAR TERM...JOHNSON  
SHORT TERM...JOHNSON  
LONG TERM...AMC  
AVIATION...AMC/JOHNSON  
MARINE...AMC/JOHNSON  
HYDROLOGY...KRUZDLO  
 
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