FXUS61 KPHI 150836
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
336 AM EST TUE DEC 15 2009

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION TODAY. COLD CANADIAN AIR WILL
ARRIVE IN THE WAKE OF THE FRONT AND LINGER THROUGH THE WORK WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WE START WITH A STABLE, MOIST AND RELATIVELY MILD FLOW OVER THE
AREA EARLY THIS MORNING. THAT WAS RESULTING IN LOW CLOUDS, AREAS
OF FOG AND SOME DRIZZLE. MEANWHILE, A FRONTAL BOUNDARY WAS MOVING
THROUGH WESTERN PA. COLD AIR ADVECTION WAS LAGGING BEHIND THAT
BOUNDARY BY SEVERAL HOURS. 

WE THINK THAT THE PASSAGE OF THE BOUNDARY WILL OCCUR HERE MAINLY
DURNING THE MORNING HOURS, AND THAT SHOULD CAUSE AN END TO THE
LOW CLOUDS, DRIZZLE AND FOG. IN THE INTERIM BETWEEN THE STABLE
CONDITIONS AND THE COLD AIR ADVECTION, THE DEVELOPING CATABATIC
FLOW MAY CAUSE TEMPERATURES TO REACH THE MILDER MAV GUIDANCE. THAT
IS CONSISTENT WITH CONTINUITY, AND SO WE WILL GO THAT WAY. WINDS
SHOULD BEGIN TO PICK UP SOME BEHIND THE FRONT AND SOMEWHAT MORE
ONCE THE COLD AIR BEGINS TO ARRIVE. 

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
FOR MOST OF THE AREA, THE COLD AIR ADVECTION SHOULD BRING CLEARING
SKIES TONIGHT. FOR THE NORTHWESTERN ZONES, THE COLD FLOW OFF THE LAKE
AND A ROTATING VORT MAX MAY RESULT IN SOME SNOW SHOWER ACTIVITY.
THE SOUNDINGS ARE CAPPED BELOW 5K FT, SO WE ARE JUST MAINTAINING
THE LOW CHANCE POPS THAT WE HAVE BEEN CARRYING. THERE IS GOOD
AGREEMENT ON MIN TEMPS BETWEEN THE MAV, THE MET AND CONTINUITY. 

WE KEEP THE CHANCE OF SNOW SHOWERS DURING THE MORNING IN THE
NORTHWEST AND THEN WAIT FOR A REINFORCING SHOT OF COLD AIR ON
WEDNESDAY NIGHT TO BRING THE CHANCE BACK FOR A LITTLE WHILE.
OTHERWISE, WE GO DRY WITH ONLY A FEW CLOUDS. WINDS LOOK TO BE
BRISK, AND THE H925 TEMPERATURE PROGS FROM THE ECMWF, GFS AND NAM
WOULD SUGGEST THAT THE ONLY REASON NOT TO CUT THE COLDER GUIDANCE
FROM WEDNESDAY THROUGH THURSDAY IS THE DOWNSLOP FLOW. WE HAVE GONE
WITH THE COLDER GUIDANCE. 

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
THE STRONG UPPER LOW TO OUR NORTH IS FORECAST TO RETROGRADE THROUGH
THE WEEKEND KEEPING US IN A COLD PATTERN. FAIR WEATHER WILL PREVAIL
THURSDAY NIGHT INTO SATURDAY AS SURFACE HIGH PRESSURE MOVES ACROSS. 
A LOBE OF VORTICITY IS THEN FORECAST TO ROTATE AROUND THE UPPER LOW.
THIS WILL CAUSE A COASTAL LOW TO FORM ALONG THE SOUTH ATLANTIC COAST.
THIS LOW IS THEN EXPECTED TO MOVE NORTHEAST WELL OFF THE COAST.
NEVERTHELESS, IT MAY GET CLOSE ENOUGH TO SPREAD SOME RAIN OR SNOW
INTO OUR SOUTHERN COASTAL AREAS LATE SATURDAY NIGHT INTO SUNDAY
NIGHT. MEANWHILE, THE UPPER TROUGH WILL BE DROPPING DOWN ACROSS
OUR AREA. THIS WILL ALSO BRING THE CHANCE FOR SOME PRECIPITATION
FOR THE SAME TIME PERIOD. ONCE THE UPPER TROUGH MOVES OFF TO THE
EAST, ANOTHER BATCH OF COLD ARCTIC AIR WILL RUSH INTO OUR AREA
LATER SUNDAY NIGHT INTO MONDAY.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

THE GREAT SLIDE INTO IFR CONDITIONS WAS THE THEME FOR THE TERMINALS 
OVERNIGHT AS DECENT LOW(EST) LEVEL MOISTURE AND GENTLY WAA LIFT 
PRECEDE AN ADVANCING COLD FRONT. THIS FRONT WILL CROSS THE AREA THIS 
MORNING AND A RETURN TO BETTER FLYING CONDITIONS WILL BEGIN 
THEREAFTER. IT APPEARS THE THE IFR WILL HOLD IN THROUGH THE MORNING 
RUSH AT KPHL BUT A DECENT WRLY WIND THIS AFTERNOON WILL SCOUR OUT 
THE LOW CIGS FAIRLY QUICKLY. WINDS WILL TEND MORE NWRLY AND REMAIN 
GUSTY INTO THE EVENING. VFR TONIGHT WITH MAINLY CLR SKIES. 

OUTLOOK...
GENERALLY VFR CONDITIONS ARE FORECAST FOR MUCH OF THE REST OF THIS 
WEEK.

&&

.MARINE...
PREFRONTAL CONDITIONS OVER THE WATERS ARE BENIGN WITH SOUTH TO 
SOUTHWEST WINDS AROUND 10 KNOTS AND SOME FOG. A FEW GUSTS UP TO 20 
KNOTS HAVE OCCURRED EARLIER. WINDS AND SEAS ARE EXPECTED TO REMAIN 
SUB-SCA EARLY TODAY BUT THEN PICK UP LATE TODAY AND TONIGHT. THE 
REASONING BEHIND THE SCA FLAG FROM EARLIER LOOKS FINE. THE ONLY 
CHANGED WAS AN EARLIER START TIME AND AN EXTENSION INTO THE 4TH 
PERIOD. A FEW GALE GUSTS MAY OCCUR AROUND 12Z WED...BUT IT DOESN'T 
APPEAR TO BE ENOUGH TO WARRANT ANY GALE FLAGS AT THIS POINT.  

WINDS AND SEAS WILL DECREASE BY LATE WEEK AS HIGH PRESSURE BUILDS 
OVER THE WATERS. ANOTHER DISTURBANCE WILL PASS EAST OF THE WATERS 
LATE THIS WEEKEND WITH SOME BUILDING WINDS AND SEAS THEN. 

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 6 AM EST 
     THURSDAY FOR ANZ430-431-450>455.

&&

$$
SYNOPSIS...DELISI
NEAR TERM...DELISI
SHORT TERM...DELISI
LONG TERM...RPW
AVIATION...O'HARA
MARINE...O'HARA