667  
FXUS61 KPHI 241106  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
606 AM EST WED JAN 24 2018  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL BUILD INTO THE EASTERN UNITED STATES THROUGH THE  
END OF THE WEEK BEFORE PROCEEDING OFFSHORE ON SATURDAY. A STRONG  
STORM SYSTEM WITH AN ACCOMPANYING COLD FRONT WILL MOVE THROUGH THE  
REGION SUNDAY AND MONDAY. HIGH PRESSURE BUILDS BACK INTO THE  
NORTHEAST BY THE MIDDLE OF NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
TODAY...MOSTLY CLOUDY THIS MORNING WITH PROBABLY SOME THINNING  
OF THE COLD AIR ADVECTION CLOUD COVER MID AFTERNOON. A FEW FLURRIES  
NEAR AND NORTH OF I-78 EARLY TODAY WITH CAA. A GUSTY NORTHWEST  
WIND OF 25 TO 30 MPH THIS MORNING- MIDDAY SHOULD DIMINISH A BIT  
BY MID AFTERNOON. STAYED CLOSE (RAISED 1F) TO THE PREV FCST MAX  
TEMPS WHICH ARE DECIDEDLY COOLER THAN THE 00Z/24 GFS MOS. STILL  
THE DAYTIME HIGH TEMP SHOULD BE WITHIN 4F OF NORMAL.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/
 
 
MID AND HIGH CLOUD INCREASES LATE, ESPECIALLY PA NJ. OTHERWISE  
A DIMINISHED WIND BUT TEMPS/WINDS WERE BASICALLY A CONTINUITY  
FORECAST FROM THE PREVIOUS 330 PM TUESDAY FORECAST. LOW TEMPS  
BASICALLY WITHIN 2F OF NORMAL. I COULD SEE THESE TEMPS RUNNING A  
FEW DEGREES WARMER IF IT BECOMES OVERCAST FOR SEVERAL HOURS.  
 

 
   
LONG TERM /THURSDAY THROUGH TUESDAY/
 
 
PROGRESSIVE PATTERN WILL CONTINUE ACROSS THE U.S. THROUGH THE  
PERIOD WITH A SURFACE LOW MOVING NEAR OR THROUGH THE AREA SUNDAY  
AND A POTENT NORTHWEST-FLOW VORT MAX MOVING THROUGH MONDAY AND  
MONDAY NIGHT THAT WILL BRING OUR NEXT CHANCE(S) FOR  
PRECIPITATION.  
 
THURSDAY AND FRIDAY WILL FEATURE A TROUGH DEPARTING THE EAST  
COAST WITH UPSTREAM RIDGING PROGRESSING INTO THE AREA. A BROAD  
SURFACE HIGH WILL ENCOMPASS THE REGION DURING THIS PERIOD, WITH  
THE NORTHERN EXTENSION OF THE HIGH ORIGINATING FROM CENTRAL  
CANADA. THIS MEANS TEMPERATURES WILL BE COLDER THAN AVERAGE,  
ESPECIALLY THURSDAY AND THURSDAY NIGHT, BEFORE THICKNESSES  
INCREASE WITH THE APPROACHING MIDLEVEL RIDGE ON FRIDAY. THE GFS  
IS SOMEWHAT MORE PROGRESSIVE THAN THE CMC/ECMWF, WITH THE  
ASSOCIATED STATISTICAL GUIDANCE CONSIDERABLY WARMER ON FRIDAY  
(10 DEGREES WARMER FOR PHL, E.G.). ENSEMBLE SIMULATIONS AND  
CONSENSUS GUIDANCE SUGGEST THAT THE GFS IS PROBABLY ON THE FAST  
SIDE, SO I KEPT TEMPERATURES MUCH BELOW MEX MOS ON FRIDAY,  
THOUGH NOT AS COOL AS ECMWF MOS WOULD SUGGEST. TEMPERATURES  
THURSDAY NIGHT ARE ALSO OF SOMEWHAT LOWER CONFIDENCE, AS THE  
COMBINATION OF LIGHT WINDS AND CLEAR SKIES WILL LIKELY ALLOW  
TEMPERATURES TO TANK IN ESPECIALLY PRONE RURAL/VALLEY LOCATIONS.  
MOS HAS BEEN WOEFULLY INACCURATE IN THESE SCENARIOS MUCH OF  
THIS WINTER, SO THE LOWS FORECAST ARE BELOW CONSENSUS AND  
POTENTIALLY STILL TOO WARM.  
 
TEMPERATURES CLIMB QUICKLY THIS WEEKEND, WITH TEMPERATURES 10 TO  
20 DEGREES ABOVE AVERAGE SATURDAY AND SUNDAY. THE FAMILIAR  
FORECAST ADJUSTMENTS WERE MADE HERE, GENERALLY INCREASING  
HIGHS/LOWS AT LEAST A DEGREE OR TWO ABOVE CONSENSUS BASED ON  
BIASES OBSERVED FOR THE PAST YEAR IN THESE PATTERNS. WITH THE  
APPROACHING SYSTEM ON SUNDAY, DID NOT GO TOO OUT OF HAND WITH  
TEMPERATURES YET, GIVEN INCREASED CLOUD COVER AND POTENTIAL  
EFFECTS OF PRECIPITATION.  
 
SATURDAY NIGHT AND SUNDAY, A MIDLEVEL VORT MAX WILL LIFT EAST-  
NORTHEAST THROUGH THE CENTRAL U.S. INTO THE NORTHEAST BY SUNDAY  
NIGHT. THERE REMAIN CONSIDERABLE DIFFERENCES IN THE SYNOPTIC-  
SCALE DETAILS OF THE ASSOCIATED TROUGH, WITH THE GFS  
FLATTER/FASTER THAN THE ECMWF (WITH THE CMC IN BETWEEN). WITH  
TUESDAY'S SYSTEM, THE GFS ENDED UP BEING TOO FAST AND THE ECMWF  
WAS A TAD TOO SLOW, SO A CONSENSUS APPROACH ON TIMING IS  
PROBABLY A GOOD IDEA, THOUGH THE FORECAST IS WEIGHTED MUCH MORE  
STRONGLY TO THE CMC/ECMWF TIMING (WHICH WORKED OUT WELL FOR THE  
SYSTEM AFFECTING THE AREA ON TUESDAY).  
 
THE GREATER UNCERTAINTY IS WITH THE POSITION/TRACK OF THE  
DEVELOPING SURFACE LOW, THOUGH THERE IS IMPROVED CONSENSUS FOR A  
TRACK FROM THE OHIO VALLEY INTO THE NORTHERN MID-ATLANTIC AND  
SOUTHERN NEW ENGLAND SUNDAY AND SUNDAY NIGHT. THIS PLACES THE  
CWA IN THE WARM SECTOR SUNDAY, SO PRECIPITATION WILL LIKELY BE  
ALL LIQUID DURING THIS PERIOD. RAIN LOOKS ESPECIALLY LIKELY  
DURING THE DAY, WITH THE BEST CONSENSUS BETWEEN 12Z SUNDAY AND  
00Z MONDAY, WHEN POPS ARE HIGHEST. QPF LOOKS FAIRLY TAME, WITH  
THE STRONGEST ASCENT GENERALLY NORTH OF THE AREA (AND THEN EAST  
AS A SOUTHERN-STREAM VORT MAX AIDS IN LARGE-SCALE LIFT AS THE  
ATTENDANT FRONT MOVES OFFSHORE). HOWEVER, GIVEN THE LARGE  
DISCREPANCIES IN SPATIAL DETAILS AND REMAINING TIMING  
UNCERTAINTY, BROADENED POPS FROM SATURDAY NIGHT THROUGH SUNDAY  
NIGHT AND CANNOT RULE OUT HIGHER QPF THAN CONSENSUS (WHICH  
CURRENTLY IS GENERALLY IN THE 0.10-0.50 INCH RANGE FOR THE  
EVENT).  
 
PERHAPS THE MOST CHALLENGING (AND INTERESTING) ASPECT OF THE  
LONG-RANGE FORECAST IS THE UPSTREAM BEHAVIOR OF THE SYSTEM, WITH  
ENSEMBLE TRENDS STRONGLY FAVORING A DEEPER TROUGH. THIS IMPLIES,  
FOR STARTERS, THAT TEMPERATURES MAY BE TOO WARM IN THE CURRENT  
OPERATIONAL SUITE, AND THERE MAY BE SUFFICIENT INSTABILITY  
UPSTREAM OF THE FRONT FOR SHOWERS MONDAY AND MONDAY NIGHT,  
ESPECIALLY AS A KICKER VORT MAX DIGS INTO THE MID-ATLANTIC  
DURING THIS PERIOD. THE 00Z ECMWF PAINTS A RATHER INTERESTING  
SCENARIO MONDAY NIGHT, WITH SOME LIGHT SNOW OCCURRING IN PARTS  
OF THE AREA AS THE VORT MAX SWINGS THROUGH. WOULD LIKE TO SEE  
BETTER CONSENSUS AMONG THE GUIDANCE BEFORE CHANGING THE FORECAST  
TOO MUCH, BUT I DID EXTEND LOW POPS THROUGH MONDAY NIGHT, WITH  
TEMPERATURES COLD ENOUGH FOR SNOW IN MOST OF THE AREA BY THE  
EVENING HOURS. FURTHER REFINEMENTS TO THE FORECAST ARE LIKELY  
HERE AS A LOT OF MODEL DIFFERENCES NEED TO BE WORKED OUT.  
 
HIGH PRESSURE BUILDS BACK IN TUESDAY AND WEDNESDAY, WHICH SPELLS  
ANOTHER COLD/DRY PERIOD FOR THE AREA.  
 

 
   
AVIATION /11Z WEDNESDAY THROUGH SUNDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
TODAY...VFR CIGS AT OR ABOVE 4,500 FEET THINNING THIS AFTERNOON  
TO SCATTERED CLOUDS TOWARD SUNSET. WEST TO NORTHWEST WINDS  
10-15 KNOTS WITH GUSTS UP TO 25 KNOTS, PERHAPS EVEN 28 KT THIS  
MORNING  
 
TONIGHT...VFR. SCT-BKN CLOUDS AOA 4000 FT, MOSTLY AOA 15000 FT.  
NORTHWEST WIND MAY GUST 15 KT.  
 
OUTLOOK...  
THURSDAY: VFR WITH NORTHWEST WINDS 10 TO 15 KTS WITH OCCASIONAL  
GUSTS TO 20 KTS OR SO. SOMEWHAT ABOVE AVERAGE CONFIDENCE.  
 
THURSDAY NIGHT AND FRIDAY: VFR WITH LIGHT/VARIABLE WINDS. HIGH  
CONFIDENCE.  
 
FRIDAY NIGHT AND SATURDAY: VFR WITH WINDS BETWEEN SOUTHEAST AND  
SOUTHWEST 5 TO 15 KTS (POTENTIALLY STRONGER NEAR THE COAST AND  
IN DELMARVA). AVERAGE CONFIDENCE.  
 
SATURDAY NIGHT: SOUTH TO SOUTHWEST WINDS 5 TO 15 KTS  
(POTENTIALLY STRONGER NEAR THE COAST) WITH INCREASING  
CLOUDINESS. INCREASING CHANCES OF RAIN, ESPECIALLY WEST OF PHL,  
WITH SUB-VFR CONDITIONS POSSIBLE. BELOW AVERAGE CONFIDENCE.  
 
SUNDAY: PERIODS OF SUB-VFR CONDITIONS LIKELY WITH A GOOD CHANCE  
OF RAIN. WINDS GENERALLY SOUTHWEST 5 TO 15 KTS. AVERAGE  
CONFIDENCE.  
 

 
   
MARINE
 
 
SCA TODAY ONLY. WATER TEMPS COOLER THAN THE OVERRIDING AIRMASS  
AND THEREFORE MOMENTUM TRANSFER IS LIMITED. NEVERTHELESS, A  
PULSE OF CAA LATER THIS MORNING SHOULD BOOST GUSTS TO 25 KT IN  
THE CW FOR A TIME. THESE WINDS ARE NOW DEVELOPING AS THIS IS  
WRITTEN. ITS POSSIBLE, IN PART DEPENDENT ON WHAT HAPPENS LATE  
THIS MORNING, THAT THE SCA MAY NEED AN EXTENSION INTO TONIGHT,  
AND EVEN TOMORROW BUT FOR NOW...A CONSERVATIVE APPROACH WAS  
APPLIED TO THE HEADLINE DUE TO OUR UNCERTAINTY. WE HAD TO LOWER  
OUR MODELED GUST SPEEDS OVER THE WATER, AND RAISE THE GUSTS OVER  
THE LANDMASS.  
 
OUTLOOK...  
 
THURSDAY: MARGINAL ADVISORY CONDITIONS POSSIBLE, ESPECIALLY IN  
THE MORNING, BUT CONFIDENCE IS NOT HIGH.  
 
THURSDAY NIGHT THROUGH FRIDAY NIGHT: NO HEADLINES ANTICIPATED.  
FAIR WEATHER.  
 
SATURDAY AND SATURDAY NIGHT: LOW-END ADVISORY (SOUTH TO  
SOUTHWEST) WINDS AND SEAS POSSIBLE, ESPECIALLY OFF THE NJ  
COAST.  
 
SUNDAY: SOUTHWEST WINDS MAY GUST AROUND 20 KTS OR SO, BUT THE  
CURRENT FORECAST IS FOR SUB-ADVISORY CONDITIONS. A GOOD CHANCE  
OF RAIN, WITH VISIBILITY RESTRICTIONS POSSIBLE.  
 

 
   
HYDROLOGY
 
 
FORECAST POINTS...MONITORING THE DELAWARE, WELL WITHIN ITS  
BANKS AND EXPECTED TO REMAIN SO. STILL THE RUNOFF AND SOME ICE  
FORCED SOME DECENT RISES VCNTY TOCKS ISLAND OVERNIGHT. THAT HAS  
JUST CHANGED WITH A SLIGHT RECESSION THERE SINCE 415 AM. NO  
ACTION ANTICIPATED, JUST MONITORING.  
 
RIVER ICE...WE CONTINUE TO RECEIVE REPORTS OF SOLID ICE COVER  
ON THE DELAWARE RIVER, BUT CONDITIONS ARE NOT AS WIDESPREAD AS  
LAST WEEK. WE KNOW OF SOLID ICE NEAR TRENTON FROM ABOUT THE  
ROUTE 1 BRIDGE SOUTH DOWN TO ABOUT BORDERNTOWN, OR NEAR THE HEAD  
OF THE TIDE. WE ALSO KNOW OF ICE FURTHER NORTH NEAR AND IN THE  
DELAWARE WATER GAP.  
 
WITH THE WARM TEMPERATURES THE LAST FEW DAYS COMBINED WITH YESTERDAY'S  
RAINS AND RISING WATER LEVELS, MELTING AND FRACTURING ICE WILL  
OCCUR. RESTRICTIONS IN FLOW OR ICE JAMS ARE POSSIBLE AS ICE  
BREAKS UP AND BEGINS TO MOVE.  
 
SINCE ICE JAMS CAN NOT BE PREDICTED WITH CERTAINTY, THE BEST APPROACH  
IS AWARENESS AND TO TAKE NOTICE OF DAY TO DAY CHANGES ON A RIVER  
OR STREAM OF CONCERN.  
 

 
   
CLIMATE
 
 
FOR WHAT ITS WORTH: ACY IS ALREADY 8" ABOVE THE ENTIRE SEASONAL  
NORMAL SNOWFALL... 24.2" VS ENTIRE SEASON 16.2.  
 
JANUARY AVERAGE TEMPS...NEGATIVE DEPARTURE WILL WARM ANOTHER  
DEGREE OR DEGREE AND ONE HALF FOR THE REST OF THE MONTH OVER THE  
ENTIRE AREA SO THAT MONTHLY NORMS WILL BE BELOW NORMAL EXCEPT  
POSSIBLY ABE AND PHL.  
 
FOR PHL: BASED ON OUR FORECAST THESE LAST 7 DAYS OF THE MONTH,  
THE MONTH WILL AVERAGE NORMAL. THAT IS ABOUT 1.2F WARMER THAN AN  
IN-HOUSE PREDICTION ON THE 18TH.  
 
SO, FOOD FOR THOUGHT. IF ONE WERE TO LOOK AT MONTHLY AVERAGES  
AS A DETERMINANT OF CLIMATE, ONE MIGHT LOOK BACK AT PHL CLIMATE  
FOR JANUARY AND NOT SEE ANYTHING UNUSUAL (PRESUMING WE END UP  
WITHIN 1F OF NORMAL). EXCEPT WE ALL KNOW BETTER.  
 
THE TWO WEEK PERIOD OF DECEMBER 24-JAN 6 WAS THE THIRD COLDEST  
IN THAT PERIOD OF TIME FOR PHL, USING CLIMATE PERSPECTIVES AND  
LOOKING BACK 146 YEARS=EQUIVALENT TO LIVING IN MILWAUKEE.  
 
WILMINGTON WAS 2ND COLDEST LOOKING BACK 125 YEARS FOR THAT  
SPECIFIC TWO WEEK PERIOD AND ALSO EQUIVALENT TO LIVING IN  
MILWAUKEE.  
 
ATLANTIC CITY WAS 3RD COLDEST.  
 
FOR ALLENTOWN LOOKING BACK 96 YEARS, THAT TWO WEEK PERIOD WAS  
THE COLDEST EVER FOR THAT TIME FRAME AND EQUIVALENT TO LIVING A  
NORMAL DAY-DAY LIFE IN ANCHORAGE.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ430-  
431-450>455.  
 

 
 

 
SYNOPSIS...CMS  
NEAR TERM...DRAG 607  
SHORT TERM...DRAG 607  
LONG TERM...CMS  
AVIATION...CMS/DRAG 607  
MARINE...CMS/DRAG 607  
HYDROLOGY...  
CLIMATE...  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab PA Page
The Nexlab NJ Page
The Nexlab DE Page
The Nexlab MD Page Main Text Page