381  
FXUS61 KPHI 230013  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
813 PM EDT WED MAY 22 2019  
   
SYNOPSIS
 
 
HIGH PRESSURE WILL SLIDE OFFSHORE THIS EVENING. A WARM FRONT WILL  
CROSS THE REGION TONIGHT FOLLOWED BY A STRONG COLD FRONT ON THURSDAY  
NIGHT. HIGH PRESSURE WILL RETURN FOR FRIDAY INTO SATURDAY. ANOTHER  
COLD FRONT WILL DROP DOWN INTO THE AREA LATE SATURDAY INTO SUNDAY,  
STALLING NEARBY THROUGH EARLY NEXT WEEK.  
 

 
   
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/
 
 
FORECAST MAINLY ON TRACK. WILL MAKE MINOR ADJUSTMENTS TO HOURLY  
GRIDS BASED ON THE LATEST SURFACE OBS.  
 
OTHERWISE, THE MAIN STORY TONIGHT WILL BE SHOWERS BEHIND THE  
WARM FRONT LIFTING NORTH OVER THE REGION. EVEN THOUGH THIS WILL  
BE A LATE NIGHT (MOSTLY AFTER MIDNIGHT) EVENT, A FEW RUMBLES OF  
THUNDER ARE POSSIBLE ONCE THE WARMER AIR MASS ARRIVES. THE  
BOUNDARY LAYER WILL BE RELATIVELY DRY, SO MAY PRECLUDE ANY HEAVY  
DOWNPOURS THROUGH THE OVERNIGHT PERIOD DESPITE INCREASING  
PRECIPITABLE WATER VALUES.  
 

 
   
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/
 
 
AS THE LOW PRESSURE SYSTEM OVER THE GREAT LAKES SLIDES EAST, OUR  
REGION WILL SEE FIRST A PRE-FRONTAL TROUGH IN THE LATE  
AFTERNOON/EVENING, FOLLOWED BY A COLD FRONT LATE THURSDAY NIGHT.  
 
ALTHOUGH SHOWERS, AND POSSIBLY A THUNDERSTORM OR TWO, WILL CONTINUE  
TO BE POSSIBLE IN THE WARM SECTOR THROUGH THE MORNING, THE MAIN  
ROUND OF STORMS WE ARE CONCERNED ABOUT ARE STORMS THAT ARE EXPECTED  
TO DEVELOP ALONG AND AHEAD OF THE PRE-FRONTAL TROUGH LATE THURSDAY  
AFTERNOON INTO THURSDAY EVENING. SOME OF THESE STORMS COULD BE  
SEVERE. MOST MODELS DEPICT ML CAPE VALUES NEAR OR ABOVE 1000 J/KG IN  
THE 21 TO 00Z TIME FRAME ALONG WITH 0-6KM BULK SHEAR VALUES OF 40 TO  
50 KT. NOT ONLY IS THIS A SIGNIFICANT AMOUNT OF SHEAR, BUT MODEL  
SOUNDINGS DEPICT PLENTY OF VEERING WITH HEIGHT (ESPECIALLY WITHIN  
THE FIRST 3 KM). THIS FURTHER ENHANCES THE RISK THAT UPDRAFTS COULD  
BE PERSISTENT. THERE ARE A FEW POTENTIAL CAVEATS. FIRST, LOW/MID  
LEVEL CLOUDS MAY NOT ERODE THROUGH THE MORNING. THIS WILL LIMIT  
DIURNAL HEATING (IN ANTICIPATION THAT THIS MAY BE THE CASE, HAVE  
GONE WITH THE COOLER GUIDANCE FOR HIGHS ON THURSDAY), WHICH WOULD  
LIMIT INSTABILITY/CAPE VALUES. SECONDLY, RELATED TO THE FIRST  
CAVEAT, THE NAM DEPICTS A LOW LEVEL INVERSION (AROUND 900 MB) WHICH  
NEVER FULLY ERODES THROUGH THE DAY (UNLIKE THE GFS WHICH DEPICTS  
THIS ERODING BETWEEN 21 AND 00Z). EVEN IF WE ARE COOLER AND THE  
INVERSION STAYS IN PLACE, I THINK WE WILL CONTINUE TO HAVE AT LEAST  
SOME SEVERE THREAT AS LIFT ALONG THE TROUGH COULD BE ENOUGH TO LIFT  
ELEVATED PARCELS ABOVE THE INVERSION. THE FINAL CAVEAT IS THAT  
REMARKABLY, MODEL SOUNDINGS ARE DEPICTING SEVERAL DRY (AND ONE VERY  
DRY) LAYERS THROUGH THE AFTERNOON AND EVENING. THIS MEANS THE LCL  
WILL BE HIGHER THAN NORMAL, AND WILL HAVE AN IMPACT ON THE RISK FOR  
WIND, TORNADO, AND HEAVY RAIN. SPEAKING OF HAZARDS:  
 
DAMAGING WIND: THIS LOOKS TO BE THE PRIMARY HAZARD THANKS TO A LOW  
AND MID LEVEL JET, AND PLENTY OF SHEAR. THE LOW LEVEL INVERSION  
MENTIONED ABOVE MAY LIMIT HOW EFFICIENT THE MIXING IS DOWN TO THE  
SURFACE, BUT THE DRY LEVELS WILL HELP TO INCREASE THE RISK OF  
DOWNBURSTS THANKS TO AN INCREASED RISK OF DRY AIR ENTRAINMENT.  
 
HAIL: SEVERE HAIL (1" IN DIAMETER OR GREATER) IS CERTAINLY POSSIBLE,  
ESPECIALLY IF WE WARM UP AS MUCH AS WHAT THE GFS IS DEPICTING AND  
ARE ABLE TO REALIZE THE HIGHER CAPE VALUES. THE HIGHEST THREAT FOR  
HAIL LOOKS TO BE OVER DELMARVA AND FAR SE PA WHERE THE HIGHEST CAPE  
VALUES ARE POSSIBLE.  
 
TORNADO: THE VEERING WIND PROFILES INCREASE THE RISK FOR ROTATING  
UPDRAFTS. HOWEVER, AS MENTIONED ABOVE THE LCL WILL BE HIGHER THAN  
NORMAL WHICH COULD LIMIT THE THREAT FOR TORNADOES.  
 
HEAVY RAIN: ALTHOUGH LOCALIZED DOWNPOURS WILL BE POSSIBLE, STORMS  
SHOULD BE MOVING FAST ENOUGH TO PRECLUDE A WIDESPREAD FLOODING  
THREAT.  
 
STORMS SHOULD MOVE OFF SHORE BY LATE THURSDAY EVENING. A COLD FRONT  
IS THEN EXPECTED TO ARRIVE IN THE REGION DURING THE PRE DAWN HOURS  
ON FRIDAY.  
 

 
   
LONG TERM /FRIDAY THROUGH WEDNESDAY/
 
 
HIGH PRESSURE SLIDES ACROSS THE GREAT LAKES REGION AND INTO THE MID-  
ATLANTIC FOR FRIDAY, SLIDING OFFSHORE ON SATURDAY. THIS WILL ALLOW  
US TO REMAIN DRY ACROSS THE REGION AND HAVE A COUPLE OF NICE DAYS  
BEFORE THE NEXT SYSTEM ARRIVES. TEMPERATURES ON FRIDAY AND SATURDAY  
SHOULD GENERALLY BE IN THE 70S TO LOWER 80S ACROSS THE FORECAST  
AREA. WITH DRY AIR IN PLACE AND DEW POINTS IN THE 50S, IT SHOULD  
FEEL QUITE NICE OUTSIDE DURING THE DAY, ALTHOUGH THE DEW POINTS MAY  
START TO CREEP UP A BIT ON SATURDAY. WITH THE INCREASING MOISTURE  
COMBINED WITH SURFACE HEATING, WE MAY SEE SOME SCATTERED SHOWERS AND  
THUNDERSTORMS ON SATURDAY AFTERNOON/EVENING.  
 
A COLD FRONT WILL START TO DROP DOWN FROM THE NORTHWEST LATER ON  
SATURDAY AS THE PARENT LOW TRACKS ACROSS ONTARIO. THE FRONT SAGS  
SOUTHWARD THROUGH THE REGION THROUGH THE DAY SUNDAY AND PUSHING JUST  
OFFSHORE SUNDAY NIGHT. THE FRONT APPEARS TO STALL THOUGH AND IT  
LOOKS LIKE IT HAS PLANS TO HANG AROUND THROUGH THE BEGINNING OF THE  
WEEK, WHICH WOULD KEEP OUR UNSETTLED SO WE CONTINUE TO MENTION SOME  
SHOWERS THROUGH AT LEAST MONDAY, WHEN IT LOOKS LIKE THE FRONT MIGHT  
START MOVING NORTHWARD AS A WARM FRONT.  
 
THE MODELS APPEAR TO BE COMING CLOSER TOGETHER FOR THE  
TUESDAY/WEDNESDAY TIMEFRAME BUT STILL HAVE ENOUGH DIFFERENCES TO  
LOWER FORECAST CONFIDENCE. ONCE THE WARM FRONT LIFTS NORTH OF THE  
AREA ON TUESDAY, IT LOOKS TO BE FAIRLY NICE ACROSS THE REGION WITH  
SOME WARMING TAKING PLACE ON TUESDAY IN THE SOUTHWESTERLY FLOW AND  
INCREASED WARMING EXPECTED FOR WEDNESDAY. THERE IS THE POSSIBILITY  
FOR SHOWERS THROUGH THIS PERIOD BUT WILL KEEP ANY MENTION PRETTY LOW  
FOR NOW.  
 

 
   
AVIATION /00Z THURSDAY THROUGH MONDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,  
KILG, KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...MOSTLY VFR CONDITIONS ARE EXPECTED. HOWEVER, SHOWERS  
AND EVEN A THUNDERSTORM OR TWO ARE POSSIBLE, MAINLY AFTER 09Z.  
ANY THUNDERSTORMS ARE EXPECTED TO MAINLY AFFECT ABE, PNE, RDG,  
AND TTN, AND MAY TEMPORARILY LEAD TO LOWER CONDITIONS. WINDS ARE  
GENERALLY SOUTH TO SOUTHWEST AROUND 5-10 KNOTS THIS EVENING,  
AND WILL LIKELY BECOME LIGHT AND VARIABLE FOR MANY LOCATIONS  
LATER TONIGHT.  
 
THURSDAY...THERE COULD BE SOME ONGOING SHOWERS OR THUNDERSTORMS  
DURING THE MORNING HOURS, WHICH MAY TEMPORARILY LEAD TO LOWER  
CONDITIONS. ONCE THIS AREA OF SHOWERS MOVES THROUGH, ADDITIONAL  
SCATTERED SHOWERS ARE POSSIBLE THROUGH THE DAY, UNTIL A LINE  
OF THUNDERSTORMS MOVES INTO THE AREA AFTER 20Z AND MOVES FROM  
NORTHWEST TO SOUTHEAST. GUSTY AND VARIABLE WINDS WILL BE  
POSSIBLE IN THE VICINITY OF ANY STORMS. OTHERWISE, SOUTHWESTERLY  
WINDS INCREASE TO 5-15 KT THROUGH THE DAY, WITH GUSTS 15-20  
KNOTS DURING THE AFTERNOON (EXCLUDING IN THE VICINITY OF  
STORMS).  
 
OUTLOOK...  
 
THURSDAY NIGHT...STORMS SHOULD MOVE EAST OF THE TAF SITES NO LATER  
THAN 06Z. CONDITIONS SHOULD RETURN TO VFR THROUGH THE LATER HALF OF  
THE NIGHT. WINDS SHOULD START SOUTHWESTERLY 5 TO 10 KT, BEFORE  
SHIFTING TO WESTERLY BY 03Z AT 5 TO 10 KT. FINALLY, AN ABRUPT SHIFT  
TO NORTHWESTERLY AT 10 TO 15 KT IS EXPECTED AFTER 06Z.  
 
FRIDAY...MAINLY VFR CONDITIONS EXPECTED. NORTHWEST WINDS AROUND  
AROUND 10 TO 15 KNOTS WITH GUSTS AROUND 20 TO 25 KNOTS THROUGH THE  
AFTERNOON. GUSTING UP TO 20 KT, BECOMING NORTHEASTERLY AND  
DECREASING FRIDAY NIGHT.  
 
FRIDAY NIGHT...MAINLY VFR CONDITIONS EXPECTED. NORTH TO NORTHEAST  
WINDS AROUND 5 TO 10 KNOTS EARLY THEN DROPPING OFF TO LIGHT AND  
VARIABLE OVERNIGHT.  
 
SATURDAY THROUGH SATURDAY NIGHT... MAINLY VFR CONDITIONS EXPECTED.  
SHOWERS AND THUNDERSTORMS POSSIBLE FROM LATE SATURDAY AFTERNOON  
THROUGH THE OVERNIGHT PERIOD WITH MVFR OR LOWER CONDITIONS POSSIBLE.  
SOUTHEAST TO SOUTH WINDS AROUND 10 KNOTS THROUGH THE DAY BECOMING  
SOUTHWEST TO WEST OVERNIGHT.  
 
SUNDAY...MAINLY VFR CONDITIONS EXPECTED. MVFR OR LOWER CONDITIONS  
POSSIBLE IN SHOWERS AND THUNDERSTORMS, MAINLY IN THE AFTERNOON AND  
EVENING. WEST TO NORTHWEST WINDS AROUND 5 TO 10 KNOTS, BECOMING  
MORE NORTHERLY OVERNIGHT.  
 
MONDAY...MAINLY VFR CONDITIONS EXPECTED. MVFR OR LOWER CONDITIONS  
POSSIBLE IN SHOWERS AND THUNDERSTORMS. NORTHWEST WINDS AROUND 5  
KNOTS.  
 

 
   
MARINE
 
 
WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY  
CONDITIONS TONIGHT AND INTO MID DAY ON THURSDAY. WIND GUSTS NEAR 25  
KT AND WAVE HEIGHTS AT 5 FEET ARE POSSIBLE THURSDAY AFTERNOON AND  
EVENING, BUT WILL HOLD OFF ON ISSUING AN SCA AT THIS TIME AS  
CONDITIONS LOOK MARGINAL AND BRIEF. THUNDERSTORMS ON THURSDAY  
EVENING WILL BE CAPABLE OF PRODUCING WIND GUSTS ABOVE 34 KT.  
 
OUTLOOK...  
 
FRIDAY THROUGH MONDAY...RELATIVELY QUIET CONDITIONS ON THE AREA  
WATERS. WINDS MAY GUST NEAR 25 KNOTS ON FRIDAY. SEAS GENERALLY  
AROUND 2 TO 4 FEET ON THE OCEAN AND 1 TO 2 FEET ON THE DELAWARE  
BAY.  
 
RIP CURRENTS...  
THERE IS A MODERATE RISK FOR THE DEVELOPMENT OF DANGEROUS RIP  
CURRENTS FRIDAY AFTERNOON, MAINLY AT THE NEW JERSEY BEACHES.  
 

 
   
EQUIPMENT
 
 
THE KDIX RADAR IS BACK ONLINE AND REPAIRS HAVE BEEN COMPLETED.  
HOWEVER, IT WILL BE IN A TEST PHASE THROUGH THURSDAY TO ENSURE  
IT IS STABLE.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...NONE.  
MD...NONE.  
MARINE...NONE.  
 

 
 

 
SYNOPSIS...MEOLA  
NEAR TERM...JOHNSON/MPS  
SHORT TERM...JOHNSON  
LONG TERM...MEOLA  
AVIATION...JOHNSON/ROBERTSON/MEOLA  
MARINE...JOHNSON/MEOLA  
EQUIPMENT...  
 
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