159  
FXUS61 KPHI 210809  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
409 AM EDT TUE APR 21 2015  
   
SYNOPSIS
 
 
A COLD FRONT WILL MOVE RAPIDLY OFFSHORE THIS MORNING. REINFORCING  
COLD FRONTS WILL MOVE THROUGH THE MID ATLANTIC STATES ON WEDNESDAY  
AND THURSDAY. A LOW PRESSURE SYSTEM SHOULD THEN SLIDE SOUTH OF  
THE AREA PASSING OFF THE CAROLINA COAST ON SATURDAY. A HIGH  
PRESSURE WILL GRADUALLY BUILD IN FROM THE WEST THROUGH THE  
REMAINDER OF THE WEEKEND INTO MONDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
THE COLD FRONT CONTINUES TO PUSH ACROSS THE AREA EARLY THIS MORNING  
AND WILL MAKE ITS WAY OFF THE COAST BY SUNRISE. THERE REMAINS  
WIDESPREAD SHOWERS AND A FEW ISOLATED THUNDERSTORMS ACROSS MUCH OF  
THE AREA. THIS ACTIVITY WILL LIFT OUT OF THE AREA THROUGH SUNRISE AS  
A SHORT WAVE APPROACHES AND LIFTS NORTH OF THE AREA. THE SHOWERS MAY  
LINGER FOR A COUPLE OF HOURS ACROSS THE NORTHERN TIER OF THE AREA,  
BUT SHOULD END BY MID-MORNING. SKIES SHOULD BEGIN TO CLEAR OUT  
THROUGH THE DAY, AND A FAIR AMOUNT OF SUNSHINE SHOULD DEVELOP ACROSS  
MUCH OF THE AREA.  
 
ANOTHER SHORT WAVE/VORTICITY IMPULSE IS FORECAST TO APPROACH THE  
AREA LATER IN THE DAY. WITH STEEP LOW/MID LEVEL LAPSE RATES AND SOME  
LOW/MID LEVEL MOISTURE FORECAST ACROSS OUR NORTHERN AREAS, THERE  
COULD BE SOME ISOLATED SHOWERS DEVELOP LATER IN THE DAY. SO WE  
INCLUDE A SLIGHT CHANCE OF SHOWERS THIS AFTERNOON ACROSS THE  
NORTHERN TIER OF THE AREA.  
 
A BLEND OF MAV/MET MOS, MOSGUIDE, AND MIXED 925 MB ECMWF  
TEMPERATURES WAS USED FOR HIGHS TODAY, WHICH BRINGS EVERYONE PRETTY  
CLOSE TO NORMAL.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/
 
 
ANY SHOWERS THAT DEVELOP DURING THE DAY ARE EXPECTED TO HAVE  
DIMINISHED BY SUNSET AS WE LOSE DAYTIME HEATING. WE DO EXPECT AN  
INCREASE IN MID-LEVEL CLOUD COVER AS A SHORT WAVE/VORTICITY IMPULSE  
SLIDES ACROSS THE AREA. RIGHT NOW IT DOES NOT LOOK LIKE THERE WILL  
BE DEEP ENOUGH MOISTURE TO CREATE ANY SHOWERS, SO WE KEEP THE  
FORECAST DRY.  
 
A BLEND OF MAV/MET MOS AND MOSGUIDE WAS USED FOR OVERNIGHT LOWS,  
WHICH BRINGS EVERYONE PRETTY CLOSE TO NORMAL.  
 

 
   
LONG TERM /WEDNESDAY THROUGH MONDAY/
 
 
THE LONG TERM WILL FEATURE AN ALL TOO FAMILIAR PATTERN OF CLOSED  
LOWS LINGERING ACROSS SOUTHEAST CANADA AND NORMAL TO COOLER THAN  
NORMAL WEATHER PATTERN PREVAILING. THE GFS AND WRF 500MB  
INITIALIZATION LOOKED GOOD. THEY BOTH WERE INTERMITTENTLY TOO COLD  
AT 850MB AND 925MB AT UPSTREAM SITES.  
 
ON WEDNESDAY, A REINFORCING COLD FRONT IS PREDICTED TO MOVE  
THROUGH OUR CWA. THIS HAS DECENT MID AND UPPER LEVEL SUPPORT (QVEC  
CONVERGENCE, EXIT REGION OF THE 250MB JET) AS WELL AS PREDICTED  
LOW LEVEL THETA E RIDGING. COMING QUICKLY ON THE HEELS OF THE  
CURRENT SYSTEM THERE WILL NOT BE MUCH AIR MASS RECOVERY FOR  
HEAVIER PCPN. BUT FORECAST SOUNDINGS ARE SHOWING THE INVERTED V  
LOOK AND THERE COULD BE SOME GUSTY SHOWERS OR TSTMS AS PCPN MOVES  
ACROSS THE AREA. BOTH THE NAM AND GFS ARE FAIRLY BULLISH WITH WIND  
GUSTS REACHING OR EXCEEDING 35 MPH. GIVEN DECENT MODELING  
CONSENSUS ABOUT SHOWERS, WE UPPED POPS TO LIKELY. THERE ARE  
DIFFERENCES AS TO WHETHER OR NOT A RIBBON OF INSTABILITY CAPABLE  
OF PRODUCING THUNDER WILL BE SUFFICIENT. WE ADDED LOW CHANCES  
DURING THE AFTERNOON OVER THE SOUTHEASTERN TWO THIRDS OF OUR CWA  
WHERE DAYTIME HEATING SHOULD HAVE MORE TIME TO GENERATE  
INSTABILITY. ODDLY A FASTER CFP DID NOT TRANSFER INTO LOWER GFS  
MOS MAX TEMPS AND WE PREFER THEIR HIGHER NUMBER BASED ON FCST  
925MB TEMPS.  
 
UNLIKE NOW WHERE PCPN IS LINGERING AND LINGERING AND LINGERING,  
SHOWERS/TSTMS WEDNESDAY SHOULD BE MORE DIURNALLY DRIVEN AND DECREASE  
RAPIDLY WITH SUNSET. THE ONE EXCEPTION IS FAR NORTHWEST WHERE A  
SHORT WAVE ROUNDING THE BASE OF THE 500MB TROF COULD KEEP PCPN  
CHANCES GOING INTO THE NIGHT AND THURSDAY MORNING. HIGHER TERRAIN  
LOCATIONS WOULD BE COLD ENOUGH FOR POSSIBLY SOME SNOW SHOWERS.  
 
BETWEEN THE CHANNELIZED VORT MAX AND CONVECTIVE TEMPS WITHIN REACH,  
SELF DESTRUCT SUNSHINE SHOULD BE OCCURRING ON THURSDAY. ONCE  
AGAIN GFS MOS AGREES MORE WITH THE NAM'S THERMAL PROFILES THAN ITS  
COLDER OWN. NOT MUCH CHANGE FROM CONTINUITY, A COOLER STEP DOWN  
OF MAX TEMPS.  
 
WITH THE SURFACE AND UPPER LOW LINGERING OVER SOUTHEASTERN CANADA, THERE  
SHOULD BE TOO MUCH OF A GRADIENT FOR RADIATIONAL COOLING IN PLACES WHERE  
THE GROWING SEASON HAS MADE STRIDES THE LAST WEEK OR SO. SUB FREEZING  
MINS WERE KEPT FAR NORTH.  
 
ANOTHER BREEZY BUT DRY DAY FRIDAY. POSSIBLY LESS SELF DESTRUCT  
SUNSHINE THAN THURSDAY AS PREDICTED MOISTURE IS LESS. MAX TEMPS  
THOUGH ARE FORECAST TO BE SIMILAR TO THURSDAY, COOLER THAN NORMAL.  
FRIDAY NIGHT HAS A GREATER CHANCE TO BE A FROSTY ONE AS WEAK HIGH  
PRESSURE COMES CLOSER TO OUR CWA.  
 
ON SATURDAY (THIS SOUNDS LIKE A WINTER SCENARIO), A SOUTHERN SLIDER  
LOW PRESSURE SYSTEM IS PREDICTED TO PASS OFF THE CAROLINA COAST. AS  
LONG AS THE ANTECEDENT UPPER CLOSED/SFC LOW REMAIN LINGERING OVER  
THE CANADIAN MARITIMES, THIS NEW LOW MAY NOT HAVE THE ABILITY TO  
TURN THE CORNER AND AFFECT US. THE LATEST ECMWF BACKED OFF ON PCPN  
EXTENT AND WE KEPT THE LOW CHANCE FAR SOUTH BECAUSE OF ITS CLOSER  
PROXIMITY TO THE EXITING LOW.  
 
THEN NOT MUCH CHANGE FOR SUNDAY AND MONDAY AS THE AIR MASS SHOULD  
RECOVER SLIGHTLY AS THE MARITIME SYSTEM'S COLD AIR SUPPLY BECOMES  
STALER.  
 

 
   
AVIATION /08Z TUESDAY THROUGH SATURDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
THE COLD FRONT CONTINUES TO PUSH ACROSS THE AREA EARLY THIS MORNING  
AND WILL MAKE ITS WAY OFF THE COAST BY SUNRISE. THERE REMAINS  
WIDESPREAD SHOWERS AND A FEW ISOLATED THUNDERSTORMS ACROSS THE TAF  
SITES. WHERE THE HEAVIEST RAIN HAS FALLEN, MVFR OR IFR CONDITIONS  
HAVE BEEN OCCURRING. FOG HAS ALSO DEVELOPED AT RDG. AS THE SHOWERS  
END AND WEST-NORTHWEST WINDS DEVELOP ACROSS THE AREA, CONDITIONS ARE  
EXPECTED TO BECOME VFR EVERYWHERE. ONCE VFR CONDITIONS RETURN, THEY  
WILL REMAIN THROUGH THE TAF PERIOD.  
 
WINDS WILL INCREASE OUT OF THE WEST-NORTHWEST, ESPECIALLY AFTER  
SUNRISE AND WE BEING TO MIX STRONG WINDS FROM ALOFT. WIND GUSTS OF  
25-30 KNOTS ARE EXPECTED THROUGH THE DAY. THE GUSTS WILL DROP OFF  
AROUND OR AFTER SUNSET TONIGHT AND BECOME MORE SOUTHWEST OVERNIGHT.  
 
OUTLOOK...  
WEDNESDAY...MAINLY VFR CONDITIONS EXPECTED WITH SUB-VFR SHOWERS AND  
TSTMS POSSIBLE AS A COLD FRONT CROSSES THE REGION. GUSTY SOUTHWEST  
TO WEST WINDS SHOULD EXCEED 30 KNOTS, ESPECIALLY IN PROXIMITY TO  
ANY SHOWERS.  
 
WEDNESDAY NIGHT THROUGH FRIDAY NIGHT...MAINLY VFR CONDITIONS  
EXPECTED. SOME GUSTY DAYTIME NORTHWEST WINDS EXPECTED.  
 
SATURDAY...MAINLY VFR CONDITIONS...LOWEST CONFIDENCE  
SOUTHERN AIRPORTS AS SHOWERS MIGHT OCCUR THERE.  
 

 
   
MARINE
 
 
THE SMALL CRAFT ADVISORY REMAINS ON THE OCEAN AS WIND GUSTS OF 25  
KNOTS SHOULD INCREASE TODAY BEHIND THE COLD FRONT AND SEAS WILL  
REMAIN ELEVATED. THE ADVISORY REMAINS IN PLACE ON THE LOWER DELAWARE  
BAY AND WE HAVE EXPANDED THE ADVISORY INTO THE NORTHERN DELAWARE BAY  
AS WINDS WILL INCREASE TODAY BEHIND THE FRONT ON THE BAY. ALL OF THE  
ADVISORIES END AT 6 PM TONIGHT, ALTHOUGH IT IS POSSIBLE THE ADVISORY  
ON THE OCEAN MAY NEED AN EXTENSION IN TIME FOR A FEW HOURS THIS  
EVENING IF SEAS TAKE LONGER TO SUBSIDE.  
 
OUTLOOK...  
WEDNESDAY...AN INCREASING SOUTHWEST GRADIENT PRECEDING THE  
NEXT COLD FRONT COULD BRING SMALL CRAFT ADVISORY CONDITIONS  
BACK TO ALL OF THE AREA WATERS.  
 
WEDNESDAY NIGHT THROUGH THURSDAY...BORDERLINE SMALL CRAFT  
ADVISORY CONDITIONS ARE OUTLOOKED AS A NORTHWEST GRADIENT  
WIND WILL PERSIST.  
 
THURSDAY NIGHT AND FRIDAY...NEAR SMALL CRAFT ADVISORY CONDITIONS  
ARE OUTLOOKED. THE PERSISTENT NORTHWEST FLOW MIGHT WEAKEN SLIGHTLY.  
 
FRIDAY NIGHT AND SATURDAY...GREATER CONFIDENCE ABOUT SUB SMALL  
CRAFT ADVISORY CONDITIONS.  
 

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

 
 

 
SYNOPSIS...GIGI/MEOLA  
NEAR TERM...GAINES/GIGI/ROBERTSON  
SHORT TERM...ROBERTSON  
LONG TERM...GIGI  
AVIATION...GIGI/ROBERTSON/MEOLA  
MARINE...GIGI/ROBERTSON/MEOLA  
 
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