248  
FXUS61 KPHI 050214  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
914 PM EST WED MAR 4 2015  
   
SYNOPSIS
 
 
SEVERAL WAVES OF LOW PRESSURE WILL TRACK NORTHEASTWARD ALONG A COLD  
FRONTAL BOUNDARY TONIGHT AND THURSDAY. THIS COLD FRONTAL BOUNDARY  
WILL MOVE OFFSHORE THURSDAY NIGHT AND WILL GIVE WAY TO AN AREA OF  
HIGH PRESSURE MOVING INTO THE REGION ON FRIDAY. FOR THE WEEKEND  
AND EARLY NEXT WEEK, WE WILL ALTERNATE BETWEEN AREAS OF HIGH  
PRESSURE AND COLD FRONTS MOVING THROUGH THE REGION.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
915 PM: CHECKING THE NEW 00Z/5 NAM. I THINK WE'RE CLOSE TO WHAT  
WILL OCCUR. AMOUNTS WITH AN INCH OR 2 VARIATION ON OUR NEW SNOW  
MAP. WE'LL CONTINUE THE DENSE FOG ADVISORY BUT ITS MARGINAL AND  
SOON SHOULD BLOW AWAY AS COLD AIR ADVECTION DEVELOPS.  
 
835 PM: EARLY ESTF UPDATED FOR THE DENSE FOG ADVISORY AND ALSO  
HAVE UPDATED DELAYED TIMING OF RAIN CHANGING TO SNOW PER REALITY  
AND THE HRRR. SNOW AMOUNTS DECREASED IN THE 00Z-06Z/5 TIME FRAME  
AND ALSO DECREASED ON THE SOUTHERN EDGE NEAR PHILADELPHIA IN THE  
06Z- 12Z/5 TIME FRAME. INCREASED THE SNOWFALL IN THE 12Z-18Z TIME  
FRAME TO COMPENSATE AND BALANCE AMOUNTS CLOSE TO OUR 330 PM FCST.  
WILL UPDATE THE SNOW MAP AROUND 945 PM PENDING A QUICK CHECK OF  
THE NAM. TEMPERATURES WERE INCREASED THROUGH 14Z AS WERE DEWPOINTS  
AND POPS TOO. REWORKED THE WX GRIDS WITH DELAYED CHANGE TO SNOW  
AND ADDED HEAVY SNOW TO THE WORDING FOR THURSDAY MORNING THOUGH  
ITS NOT A CLEAR CUT HEAVY. SNOW WATER RATIOS WILL PROBABLY BE  
CLOSER TO 8 TO 1 FOR THE FIRST FEW HOURS. SO THE BASIC MESSAGE IS  
THE SAME AND THE MORNING RUSH HOUR IS DESTINED TO BECOME HAZARDOUS  
AND DIFFICULT, ESPECIALLY PHILADELPHIA NORTHWARD WITH MANY DELAYS  
ANTICIPATED, IF NOT CANCELLATIONS.  
 
800PM UPDATE...A DENSE FOG ADVISORY HAS BEEN ISSUED FOR SOUTHERN  
NEW JERSEY...PARTS OF SOUTHEAST PENNSYLVANIA AND NORTHERN DELMARVA  
INCLUDING ALL OF DELAWARE. NUMEROUS STATIONS ARE REPORTING  
VISIBILITY OF 1/4 MILE OR LESS IN FOG. APPARENTLY MELTING SNOW  
EVAPORATED INTO THE LOWER ATMOS TODAY AND THEN SLIGHT COOLING  
AROUND SUNDOWN ENABLED THE FOG TO FORM. NOT SURE HOW LONG FOG WILL  
LAST BUT IT SHOULD BEGIN TO DISSIPATE WHEN HEAVIER PRECIP ARRIVES  
LATER THIS EVENING. CURRENT ADVISORY RUNS UNTIL MIDNIGHT.  
 
SOCIAL MEDIA HAS THE UPDATED WED EVENING BRIEFING PACKAGE AND  
REQUEST FOR OBSERVATIONS. WE WILL BE MONITORING MOSTLY OUR SKYWARN  
ACCOUNT AND PHI FB. THANK YOU VERY MUCH FOR ALL YOUR ASSISTANCE  
INCLUDING THE ENERGY TO HELP US DURING THE NIGHT. SAFETY FIRST.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/
 
 
RECORD DAILY SNOWFALLS POSSIBLE AT KILG AND KACY. PLS SEE CLIMATE  
SECTION FOR DETAILS ON THE BIG FOUR CLIMATE SITES.  
 
THE WARM NOSE WILL STILL BE PRESENT, AND SHOULD IN FACT BE A BIT  
DEEPER OVER SOUTHERN DELMARVA AS THEY DROP NEAR AND BELOW FREEZING  
NEAR SUNRISE. AS SUCH, COULD SEE A MIX OF FREEZING RAIN AND SLEET  
BEFORE IT CHANGES OVER TO ALL SNOW NO LATER THAN MID MORNING. ON  
THE OTHER SIDE OF THE REGION, DRIER AIR MOVING INTO THE POCONOS  
AND NW NJ COULD ERODE AND END THE PRECIPITATION FOR THOSE AREAS BY  
MID DAY.  
 
DRY AIR ADVECTION WILL DEVELOP OVER MUCH OF THE REST OF THE AREA  
THROUGH THE AFTERNOON, ALLOWING THE PRECIPITATION TO TAPER OFF  
ALMOST EVERYWHERE BY LATE AFTERNOON EXCEPT SUSSEX COUNTY  
DELAWARE.  
 
FGEN WHILE DECENT DOES NOT NECESSARILY FAVOR 1/4 TO ONE HALF MI  
VSBY IN MDT TO HEAVY SNOW. WE'VE PUT IT IN THERE, PER WPC QPF.  
 

 
   
LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/
 
 
FAIRLY QUIET WITH A GENERAL NORTHWEST FLOW PATTERN OF ALTERNATING  
COLD FRONTS AND WEST-SOUTHWESTERLY FLOW WARM-UPS AHEAD OF THESE  
FRONTS. SLIGHT TO LOW PRECIPITATION CHANCES AHEAD OF THESE FRONTS,  
FOCUSED NORTH.  
 
THURSDAY NIGHT THROUGH SATURDAY: A COLD FRIDAY MORNING IS ON TAP  
WITH SNOWCOVER IN PLACE, CLEAR SKIES AND MAINLY LIGHT WINDS UNDER 10  
MPH. RADIATIONAL COOLING SHOULD ALLOW FOR A QUICK TEMPERATURE DROP  
AFTER CLOUDS CLEAR. WENT COLDER THAN MAV AND MET GUIDANCE SETS  
CLOSER TO THE MODELED TWO METER TEMPERATURES FROM THE GFS. HIGH  
PRESSURE BUILDS INTO THE REGION KEEPING THIS PERIOD DRY WITH A  
EVENTUAL SWING FROM NORTHWEST TO SOUTHWEST WINDS AND MODERATING  
TEMPERATURES BY SATURDAY. TRENDED COLDER THAN THE MET AND MAV AT  
NIGHT DUE TO SNOWCOVER AND WARMER DURING THE DAY. THESE GUIDANCE  
SETS HAVE BEEN RUNNING WITH A COLD BIAS IN THE DAYTIME. SOUNDINGS  
ALSO YIELD THE POTENTIAL FOR SOME WIND GUSTS AROUND 15 MPH  
SATURDAY AFTERNOON.  
 
 
SATURDAY NIGHT AND SUNDAY: A COLD FRONT WILL DECAY INTO A TROUGH  
ACROSS NEW ENGLAND BY SUNDAY MORNING PROVIDING AN INCREASE IN  
CLOUDS AND PERHAPS A LOW CHANCE FOR RAIN AND SNOW SHOWERS ACROSS FAR  
NORTHERN PARTS OF THE REGION, CLOSER TO THE FRONT. A FEW 06Z GEFS  
MEMBERS HAVE MOISTURE FROM THE GULF COMING NORTH AS WELL, FOR NOW  
WILL GO WITH THE MODEL CONSENSUS AWAY FROM THIS IDEA. SNOWCOVER  
SHOULD LESS OF A CONCERN WITH TEMPERATURES BY SUNDAY. WITH MORE  
CLOUDS AROUND THE ENSEMBLE GUIDANCE FROM WPC IS PREFERRED FOR MOST  
ELEMENTS. WINDS ARE MORE IN LINE WITH THE NAM/GFS MODELS THOUGH.  
 
 
SUNDAY NIGHT THROUGH WEDNESDAY: ONCE AGAIN HIGH PRESSURE IS IN CONTROL  
IN THE REGION WITH GENERAL WEST WINDS. THIS WILL RESULT IN A BRIEF  
PERIOD OF COOLER TEMPERATURES SUNDAY NIGHT BEFORE SPRING LIKE DAYS  
ON MONDAY THROUGH WEDNESDAY. A WEAK FRONTAL BOUNDARY AGAIN LOOKS TO  
FOCUS ON NEW ENGLAND FOR MONDAY, ANOTHER LOW CHANCE OF  
PRECIPITATION. THEN THIS WILL BE FOLLOWED BY ANOTHER HIGH PRESSURE  
SYSTEM. THE AIRMASS BY TUESDAY AND WEDNESDAY WILL BE THE WARMEST IN  
SOME TIME ACROSS THE REGION. LIKED THE DIRECTION OF THE ENSEMBLE  
GUIDANCE TO TREND TEMPERATURES SEVERAL DEGREES WARMER THAN THE  
MODELED TWO METER TEMPERATURES. THE MODELED TWO METER TEMPS LOOK  
TO COOL SHOULD SOME SOUTHERLY COMPONENT GET INVOLVED, THIS LOOKS  
LIKE IT HAS A FAIR CHANCE OF OCCURRING BY WEDNESDAY. FORECAST  
HIGH OF 56 AT PHL WEDNESDAY, I'M SURE THIS WILL BE WELCOME TO  
MANY. LOW PRESSURE THAT FORMS IN THE GULF OF MEXICO TUE-WED LOOKS  
TO STAY SOUTH OF OUR REGION ATTM.  
 

 
   
AVIATION /02Z THURSDAY THROUGH MONDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...MVFR CONDS IN RAIN/FOG VARIABLE LIFR IN PATCHY DENSE FOG  
THIS EVENING. THEN AS THE COLDER NORTHWEST WIND INCREASES, THE  
CHANGE FROM RAIN TO SLEET/FREEZING RAIN FOR 1-2 HOURS AND THEN IFR  
SNOW OCCURS. PLEASE SEE THE 00Z TAFS FOR DETAILS. CONFIDENCE IN  
MDT 1/2 MILE SNOW IS BELOW AVERAGE FOR THURSDAY. HOWEVER, I AM  
CONFIDENT THAT WIDESPREAD PLOWING AND EXTENSIVE DELAYS WILL  
DEVELOP BY SUNRISE THURSDAY FROM PHILADELPHIA NORTH AND THEN  
SPREAD SOUTHWARD DURING THE MORNING AFTER 12Z. NORTH WIND GUSTS TO  
18 KT BY 11Z THURSDAY.  
 
THURSDAY...IFR SNOW IN THE MORNING WITH TEMPERATURES FALLING INTO  
THE 20S AT ALL TAF SITES BY 15Z. NORTH WIND GUSTING TO 20 KT.  
CONDITIONS SHOULD IMPROVE TO VFR FROM NORTH TO SOUTH DURING THE  
AFTERNOON. PLOWING OPERATIONS AND EXTENSIVE DELAYS ARE ANTICIPATED  
WITH WIDESPREAD EVENT TOTALS OF 4 TO 8 INCHES.  
 
OUTLOOK...  
 
THURSDAY NIGHT: IMPROVING TO VFR BY MID-EVENING. NORTHWEST WIND  
AROUND 10 KNOTS.  
 
FRIDAY AND FRIDAY NIGHT: VFR, NORTHWEST WIND 10 KNOTS OR LESS.  
 
SATURDAY THROUGH SUNDAY NIGHT: VFR, WEST TO SOUTHWEST WIND AROUND 10  
KNOTS, GUSTS AROUND 15 KNOTS SATURDAY AFTERNOON. MID-LEVEL CLOUDS  
SATURDAY NIGHT AND SUNDAY MORNING, PASSING RAIN/SNOW SHOWER CAN NOT  
BE RULED OUT FOR ABE.  
 
MONDAY AND MONDAY NIGHT: VFR, MID-LEVEL CLOUDS.  
 

 
   
MARINE
 
 
WAVES ALONG THE COASTAL WATERS WILL CONTINUE TO REMAIN NEAR OR ABOVE  
5 FT. AFTER MIDNIGHT, WINDS INCREASE WITH GUSTS ABOVE 25 KT POSSIBLE.  
THEREFORE THE SMALL CRAFT ADVISORY CONTINUES THROUGH THURSDAY EVENING  
ALONG THE COASTAL WATERS. ON THE BAY, A FEW GUSTS NEAR 20KT ARE POSSIBLE,  
BUT CONDITIONS SHOULD GENERALLY REMAIN BELOW SCA CRITERIA.  
 
OUTLOOK..  
 
SEAS LOOK TO REMAIN BELOW FIVE FEET THROUGHOUT THE ENTIRE OUTLOOK  
PERIOD, WITH SEAS NEAR FIVE FEET EARLY THURSDAY NIGHT. THE FORECAST  
IS ABOUT A FOOT HIGHER THAN WAVEWATCH. NORTHWEST WIND GUSTS AROUND  
20 KNOTS MAY OCCUR THURSDAY EVENING. OTHERWISE WIND GUSTS SHOULD  
STAY UNDER 20 KNOTS. SOME FREEZING SPRAY MAY OCCUR THURSDAY NIGHT  
AND EARLY FRIDAY IN ICE FREE WATERS. CONFIDENCE IS NOT HIGH FOR ANY  
MODERATE FREEZING SPRAY IN TERMS OF DURATION AND LIKELIHOOD, MAY  
JUST LAST A FEW HOURS IF IT OCCURS. WITH SOME MODERATE FREEZING  
SPRAY IN THE GRIDS, DID INCLUDE MENTION IN THE HWO.  
 

 
   
HYDROLOGY
 
 
MODELS CONTINUE TO SHOW A DECENT AMOUNT OF QPF ACROSS THE AREA  
TONIGHT INTO THURSDAY. IN GENERAL AND BREAKING THE CWA INTO  
THIRDS, A CHANGEOVER TO SLEET OR SNOW IS EXPECTED ACROSS THE  
NORTHERN THIRD BY AROUND MIDNIGHT, THE MIDDLE THIRD BY DAYBREAK,  
AND THE SOUTHERN THIRD BY MID-MORNING TOMORROW.  
 
WITH THE GROUND BEING FROZEN EVERYWHERE, ANY RUNOFF WILL BE VERY  
EFFICIENT BEFORE THE CHANGEOVER.  
 
MORNING MODELS CONTINUE TO PRODUCE BETWEEN 0.50 TO 1.00 INCH OF QPF  
BEFORE THE CHANGEOVER. WITH THIS AMOUNT, WE FEEL NUISANCE POOR  
DRAINAGE AND LOW LYING FLOODING WILL BE THE MOST LIKELY OUTCOME.  
WITH MORE SNOW OR SLEET EXPECTED ACROSS THE NORTHERN HALF OF THE  
CWA, WE'RE LESS CONCERNED ABOUT FLOODING THERE.  
 
MODELED SOLUTIONS SUGGEST WE WOULD NEED BETWEEN 1.50 TO 2.00 INCHES  
OF LIQUID (OVER A 6 TO 12 HOUR PERIOD), EITHER IN THE FORM OF ALL  
RAIN OR RAIN AND MELTING SNOW TO HAVE OUR SOUTHERN CREEKS AND  
STREAMS LEAVE THEIR BANKS. NONE OF OUR RIVER FORECAST POINTS ARE  
FORECAST TO HIT FLOOD STAGE OR EVEN CAUTION STAGE.  
 
THE SHORT TERM GOOD NEWS IS THAT RAIN WILL CHANGE OVER TO SNOW  
QUICKER ACROSS PLACES THAT HAVE A SNOWPACK AND WHERE MORE RAIN IS  
EXPECTED, THERE IS LESS SNOW PACK.  
 
THE LONGER TERM BAD NEWS IS THAT WE'RE POTENTIALLY KICKING THE CAN  
DOWN THE LINE AND JUST ADDING TO OUR SNOWPACK FOR A FUTURE MELT.  
 
WITH THE RAINFALL, THE FLOW ON AREA CREEKS AND STREAMS WILL  
INCREASE. THIS COULD START TO MOVE ICE, AND IN A WORST CASE  
SCENARIO, CREATE RESTRICTIONS OR JAMS. THE GOOD NEWS IS WE'VE  
SEEN SOME RECESSION/MELT THE LAST FEW DAYS.  
 

 
   
CLIMATE
 
 
CLIMATE: WITH A SNOWCOVER IN PLACE AND ANOTHER MODIFIED ARCTIC  
AIRMASS SETTLING INTO THE REGION AND RADIATIONAL COOLING OCCURRING,  
WE HAVE ANOTHER CHANCE FOR MORE RECORD LOWS ACROSS THE REGION.  
 
FRIDAY 3/6  
 
RECORD LOWS  
 
ACY 10 1888  
PHL 10 1978  
ILG 11 1926  
ABE 7 1960  
TTN 7 1872  
GED 10 1978  
RDG 7 1978  
MPO -5 1909  
 
THE CURRENT FORECAST CURRENTLY HAS MOST LOCATIONS BREAKING THERE  
RECORD LOW ON FRIDAY MORNING. THE ONE EXCEPTION WOULD BE MOUNT  
POCONO.  
 
SATURDAY 3/7  
 
RECORD LOWS  
 
ACY 10 1890  
PHL 9 1960  
ILG 11 1960  
ABE 1 1960  
TTN 7 1890  
GED 3 1960  
RDG 10 1989  
MPO -18 1911  
 
MOST LOCATIONS ARE FORECASTED TO BE SEVERAL DEGREES WARMER THAN THE  
RECORD LOWS FOR SATURDAY MORNING.  
 
RECORD DAILY SNOWFALL FOR THURSDAY MARCH 5  
 
KACY 0.3 - 1960  
KILG 3.7 - 1981  
KABE 7.0 - 1917  
KPHL 8.8 - 1981  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR PAZ054-055-  
061-062.  
WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR PAZ060-  
101>106.  
DENSE FOG ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR PAZ070-071-  
101>106.  
WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR PAZ070-071.  
NJ...WINTER WEATHER ADVISORY UNTIL 7 PM EST THURSDAY FOR NJZ001-007-  
008.  
WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR NJZ009-010-  
012-015.  
DENSE FOG ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR NJZ015>027.  
WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR NJZ013-014-  
016>027.  
DE...DENSE FOG ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR DEZ001>004.  
WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR DEZ001-002.  
WINTER STORM WARNING FROM 3 AM TO 7 PM EST THURSDAY FOR DEZ003-  
004.  
MD...DENSE FOG ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ008-012-  
015-019-020.  
WINTER STORM WARNING UNTIL 7 PM EST THURSDAY FOR MDZ008-012-  
015-019-020.  
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THURSDAY FOR ANZ450>455.  
 

 
 

 
SYNOPSIS...GAINES  
NEAR TERM...AMC/DRAG 915  
SHORT TERM...DRAG  
LONG TERM...GAINES  
AVIATION...DRAG/GAINES  
MARINE...DRAG/GAINES/JOHNSON  
HYDROLOGY...  
CLIMATE...  
 
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