FXUS61 KPHI 120905
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
405 AM EST SAT DEC 12 2009
.SYNOPSIS...
HIGH PRESSURE WILL RIDGE ACROSS THE AREA TODAY AND MOVE OFF THE
MID ATLANTIC COAST TONIGHT. A FRONTAL SYSTEM WITH AN ASSOCIATED
AREA OF LOW PRESSURE WILL APPROACH ON SUNDAY AND MOVE BY SUNDAY
EVENING. WEAK AND TRANSIENT HIGH PRESSURE WILL MOVE ACROSS THE
AREA ON MONDAY. A FRONTAL BOUNDARY IS FORECAST TO MOVE ACROSS THE
AREA ON TUESDAY. HIGH PRESSURE IS EXPECTED TO REMAIN TO OUR WEST
THROUGH THE MIDDLE OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
SURFACE HIGH PRESSURE WILL MOVE BY JUST TO OUR SOUTH TODAY, AND
THAT WILL CAUSE WINDS AT AND NEAR THE SURFACE TO BACK AND WEAKEN
SOMEWHAT. STRATOCUMULUS OVER THE NORTHERN ZONES EARLY IN THE DAY
SHOULD DISSIPATE IN RESPONSE, ALTHOUGH CIRRUS SHOULD START TO
ADVANCE INTO THE AREA AS THE SHALLOW MID LEVEL RIDGE AXIS PASSES
OVERHEAD. STILL, TEMPERATURES SHOULD REBOUND SOME FROM YESTERDAY'S
COLD VALUES. WE BASICALLY HAVE BLENDED GUIDANCE AND CONTINUITY, AS
ON THE ONE HAND THE HIGH IS CENTERED JUST TO OUR SOUTH AND SHOWS
LITTLE IN THE WAY OF AIR MASS MODIFICATION TODAY, AND, ON THE
OTHER, TEMPERATURES AT MANY LOCATIONS EARLY THIS MORNING HAVE BEEN
BEHAVING AS IF A LITTLE WARM AIR ADVECTION ALREADY HAD BEGUN /THIS
IS UNEVEN AROUND THE FORECAST AREA, AS SOME DECOUPLED PLACES ARE
QUITE COLD/.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
HIGH AND THEN MID LEVEL CLOUDS SHOULD BE INCREASING TONIGHT. I300
ISENTROPIC LIFT WILL APPROACH THE AREA BUT MAY REMAIN JUST TO THE
SOUTHWEST. SOME Q-VECTOR CONVERGENCE, UPPER JET SUPPORT AND LOWER
LEVEL FRONTOGENESIS WILL APPROACH, BUT THE MODELS AND STAT
GUIDANCE SEEM TO WANT TO KEEP US DRY THROUGH TONIGHT. WE CARRY
JUST A SLIGHT CHANCE OF PRECIPITAION IN THE SOUTHWEST. BECAUSE WE
MAY RADIATE SOME DURING THE FIRST PART OF THE NIGHT, WE MAY GET
COLD ENOUGH TO EXPERIENCE SOME LIGHT NUISANCE FREEZING OR FROZEN
PRECIPITATION DURING THE OVERNIGHT IF PRECIPITATION DOES OCCUR. WE
HAVE ACCOUNTED FOR THIS IN THE FORECAST, BUT AT THIS POINT DO NOT
THINK IT WARRANTS AN ADVISORY OR A MENTION IN THE HWO. ALSO, WE
HAVE PUT THE MIN TEMPERATURES JUST AFTER MIDNIGHT, BECAUSE THE
INCREASING CLOUDS SHOULD CAUSE TEMPERATURES TO STEADY OR EVEN RISE
A LITTLE DURING THE LATE OVERNIGHT.
THERE IS GOOD ISENTROPIC LIFT AND FRONTOGENESIS, SOMETHING OF AN
UPPER JET AND FAIR Q-VECTOR CONVERGENCE, AND NO INSTABILITY OR
SIGNS OF SLANTWISE CONVECTION WITH THE FRONTAL SYSTEM AND
ASSOCIATED AREA OF LOW PRESSURE. OUR QPF VALUES ARE LESS THAN AN
INCH, AND IN THE WAKE OF THE PREVIOUS SYSTEM WE ARE HOPEFUL THAT
THIS IS CORRECT. THE EVENT, ACCORDING TO THE GFS AND NAM BUFKIT
SOUNDINGS, LOOKS TO BE MAINLY A RAIN EVENT, BUT SOUNDINGS ABOVE
THE SURFACE ARE COLD ENOUGH FOR SNOW EARLY IN THE DAY IN THE NORTH
AND NORTHWEST, AND BECAUSE OF THE POSSIBILITY OF RADIATING DURING
THE PREVIOUS PERIOD WE MAY HAVE TO DEAL WITH A PERIOD OF FREEZING
PRECIPITATION OVER THE NORTHWEST AND OVER THE BEST RADIATING SPOTS
ELSEWHERE IN THE MORNING. RIGHT NOW, THE SOUNDINGS SAY THAT
ACCUMULATIONS/ACCRUAL WOULD BE LIGHT, AND SO WE AGAIN WILL NOT PUT
UP AN ADVISORY OR MENTION THIS IN THE HWO WITH THIS PACAKGE. THE
NEXT SHIFT WILL NO DOUBT TAKE A FRESH LOOK AT THIS.
PRECIPITATION IS EXPECTED TO END FROM SOUTHWEST TO NORTHEAST ON
SUNDAY NIGHT, AND THEN MONDAY LOOKS FAIR IN THE TEMPORARILY ZONAL
FLOW AS ANOTHER SYSTEM LOOKS TO APPROACH FOR MONDAY NIGHT. WE HAVE
MAINTAINED CONTINUITY ON POPS AND TEMPERATURES FOR MONDAY AND
MONDAY NIGHT /NIL POPS MONDAY AND LOW POPS MONDAY NIGHT/ AS STAT
GUIDANCE SUPPORTS THIS.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
ANOTHER ARCTIC BLAST IS ON TAP FOR OUR CWA DURING THE LONG TERM.
BUT AT THE START OF THE LONG TERM, A RELATIVELY MILD NIGHT IS
EXPECTED MONDAY NIGHT. AS THE COLD FRONT APPROACHES, CHANCES FOR
SHOWERS WILL START INCREASING. THE LATEST ECMWF HAS SLOWED THE
CDFNTL PASSAGE CLOSER TO THE GFS'S TIMING. SO POPS FOR MONDAY
NIGHT HAVE BEEN LIMITED TO AFTER MIDNIGHT. THE AIR MASS ALOFT IS
RELATIVELY MILD AND PTYPE IS MAINLY RAIN. HIGHER TERRAIN LOCATIONS
THE PTYPE ISSUE MIGHT IN REALITY BE MORE FREEZING RAIN VS RAIN
THAN RAIN VS SNOW. THIRD DAY IN A ROW THAT THE SOUTHERN STREAM
CONTRIBUTION TO THIS SYSTEM REMAINS ON THE WEAK SIDE MAKING
TUESDAY DAY ALMOST A TYPICAL COLD FRONTAL TYPE OF DAY. THE ONLY
MODEL THAT IS SHOWING A SHORT ANAFRONT PRECIP SHOT IS THE CAN
GGEM. BUT THAT MODEL AS OF TODAY WOULD STILL HAVE PCPN CUT OFF
BEFORE A WIDESPREAD CHANGE TO FROZEN PRECIPITATION.
ON WEDNESDAY THROUGH FRIDAY OUR CWA WILL BE DOMINATED BY AN ARCTIC
HIGH PRESSURE SYSTEM THAT WILL WORK ITS WAY TO THE EASTERN SEABOARD.
THE LAKE EFFECT MACHINE SHOULD BE WORKING VERY WELL INTO THURSDAY
DAY AT THE LEAST. CHANCES ARE SOME LAKE EFFECT STREAMERS OR
RESIDUALS SHOULD MAKE IT INTO OUR CWA. FOR NOW WE LIMITED THE
MENTION OF FLURRIES (WHICH MIGHT BE SNOW SHOWERS) TO OUR HIGHER
TERRAIN.
ON FRIDAY, THE GFS IS FORECASTING AN ALBERTA TYPE LOW TO MAKE IT
INTO THE GREAT LAKES. THE LATEST ECMWF DOES NOT. THIS HAS TO
DO WITH HOW EACH MODEL IS HANDLING A POLAR VORTEX MOVING INTO THE
CANADIAN MARITIMES. BOTH RETROGRADE IT, BUT THE GFS IS FARTHER SOUTH
THAN THE ECMWF WITH ITS RETROGRESSION AND THUS PASSES THE LOW INTO
OUR CWA. THE ECMWF AND ALL OF THE OTHER MEDIUM RANGE MODELS ARE NOT
AS FAR SOUTH. FOR NOW WE KEPT FRIDAY DRY.
THE GFS REMAINS AT THE FOREFRONT OF THE COLDEST TEMPS DURING THIS
PERIOD WHICH STILL REMAINS LOGICAL GIVEN THIS HIGH PRESSURE IS
ARRIVING FROM THE NORTH POLE, WE LEANED CLOSER TO ITS THERMAL FIELDS
THAN THE ECMWF.
BEYOND OUR DETERMINISTIC FORECAST, THE NEGATIVE NAO PATTERN WHICH
NORMALLY MEANS COLDER WEATHER, IS EXPECTED TO PERSIST. THE CANADIAN
MARITIMES POLAR VORTEX IS ON THE SOUTH SIDE OF A FORECAST REX BLOCK
WITH A CLOSED RIDGE FORECAST TO BE OVER GREENLAND. BOTH ENMASS ARE
EXPECTED TO RETROGRADE WESTWARD AND WEAKEN SOMEWHAT. ON THE PACIFIC
SIDE THE STRONG (BASED ON CURRENT WEEKLY CPC VALUES) EL NINO KEEPS
ON TRYING TO SMASH THE PACIFIC RIDGE, THIS HAS CAUSED VERY LITTLE
RUN TO RUN CONTINUITY WITH ACTUAL GFS OR ECMWF MODEL RUNS. EITHER
WAY BLOCKING PATTERNS TAKE TIME TO UNRAVEL, SO OUR WEATHER SHOULD
REMAIN ON THE COLDER THAN NORMAL SIDE AS WE REACH ASTRONOMICAL
WINTER.
&&
.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
GREAT VFR FLYING WEATHER WILL BE ACROSS ALL OF THE TERMINALS TODAY
AND TONIGHT. THE SFC WINDS HAVE DECREASED OVERNIGHT AND TODAY THEY
SHOULD NOT REACH THE DEGREE OF GUSTINESS THAT THEY HAVE HAD THE PAST
FEW DAYS. GENERALLY WEST WINDS AROUND 10 KTS AT THE TERMINALS
TODAY...PERHAPS A BIT LIGHTER AND MORE SWRLY LATER THIS AFTERNOON.
OUTLOOK...
A FRONTAL SYSTEM ARRIVING FROM THE WEST AND A LOW RIDING NORTHWARD
ALONG IT WILL BRING MOISTURE AND POORER FLYING WEATHER SUNDAY AND
EARLY SUNDAY NIGHT. IF THE GUIDANCE IS TO BE BELIEVED...IFR
CONDITIONS WILL ARRIVE AT THE TERMINALS SUNDAY MORNING AND PERSIST
UNTIL AT LEAST EVENING. VFR CONDITIONS SHOULD RETURN LATER SUN NIGHT
AND LAST INTO MONDAY.
&&
.MARINE...
WINDS CONTINUE TO SLOWLY DECREASE. WINDS SPEEDS AND GUSTS ARE NOW IN
THE SCA RANGE AND SEAS ARE 4 TO 5 FT AT THE BUOYS SO A SCA FLAG WILL
CONTINUE TODAY. THE DAY SHIFT CAN EXPIRE IT EARLIER THAN WHAT IS
PRESENTLY IN THERE IF NEEDED. THERE WILL THEN BE A PERIOD OF SUB-SCA
CONDITIONS TONIGHT AND SUNDAY-DAYTIME WHEN THE HIGH PULLS TO THE
EAST AND THE NEXT FRONT/LOW MOVE TOWARDS THE WATERS. LOOKS LIKE
ANOTHER MAINLY SCA CRITERIA SITUATION AS OF NOW FOR SUN NGT INTO
MON. STRONGER WINDS (GALES) BEHIND THE NEXT STRONG COLD FRONT LOOK
TO ARRIVE OVER THE WATERS TUE NGT INTO WED.
&&
.TIDES/COASTAL FLOODING...
THE PREVIOUS LOW TIDE BROUGHT SOME LOW-WATER CONDITIONS TO THE OCEAN
AND DELAWARE BAY. THE NEXT LOW TIDE (THE HIGHER ON THE TWO LOW
TIDES) SHOULD HAVE A GREATER (POSITIVE) DEPARTURE THAN THE PREVIOUS
ONE WHICH SHOULD KEEP IT ABOVE LOW WATER CRITERIA. I WILL NOT ISSUE
ANY STATEMENTS ABOUT THIS NOW, BUT ADVISE THE DAY SHIFT TO MONITOR,
IN CASE THE SITUATION CHANGES. THE SPS FOR THE DELAWARE RIVER WILL
EXPIRE SHORTLY, ONCE THE LOW TIDE FINISHES IN THE DELAWARE RIVER.
&&
.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...DELISI
NEAR TERM...DELISI
SHORT TERM...DELISI
LONG TERM...GIGI
AVIATION...O'HARA
MARINE...O'HARA
TIDES/COASTAL FLOODING...O'HARA
