A couple AFDs from Mount Holly leading up to the Dec 2009 KU. Pretty interesting reads. Seems the Euro sniffed this one out first, as it often did.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1109 AM EST WED DEC 16 2009
.SYNOPSIS...
STRONG HIGH PRESSURE WILL BUILD IN FROM THE NORTH AND WEST AND
THEN WEAKEN THROUGH THE WORK WEEK. A SYSTEM THAT WILL DEVELOP
NEAR THE GULF OF MEXICO AND MOVE OUT OVER THE ATLANTIC MAY HAVE
SOME EFFECT ON US LATE IN THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
FLURRY ACTIVITY HAS BEEN LIMITED TO THE NORTHWESTERN AREAS OF THE
CWA. A VORT MAX IS EXPECTED TO ROTATE THROUGH THE AREA THIS
AFTERNOON AND AS A RESULT FLURRIES MAY SPREAD SLIGHTLY FARTHER
SOUTH THAN PREVIOUS THINKING. WE HAVE EXTENDED THE CHANCE FOR
FLURRIES INTO THE LEHIGH VALLEY, ALTHOUGH MOST AREAS PROBABLY
WILL NOT SEE TOO MANY FLAKES FALL AS THEY MAY EVAPORATE BEFORE
REACHING THE GROUND. LAKE EFFECT CLOUDS WILL CONTINUE TO STREAM
INTO THE AREA TODAY, AS THE FETCH OFF THE LAKES REMAINS.
WINDS ARE GUSTY AND WILL REMAIN SO THROUGH THE DAY TODAY BEFORE
STARTING TO DECREASE THIS EVENING.
GUIDANCE TEMPERATURES WERE IN PRETTY GOOD AGREEMENT WITH
CONTINUITY AND WERE ACCEPTED.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY/...
ANOTHER VORT MAX MOVES ACROSS THE AREA TONIGHT WITH SOME
REINFORCING COLD AIR. THE ATMOSPHERE LOOKS TO BE DRIER, SO WE ARE
CONFINING SNOW FLURRIES TO THE NORTHWEST AND GOING MOSTLY CLEAR
ELSEWHERE FOR NOW. WINDS MAY PICK UP SOME AS THE SECONDARY PUSH
OCCURS. GUIDANCE TEMPS AGAIN ARE IN GOOD AGREEMENT WITH CONTINUITY
AND ARE ACCEPTED.
THURSDAY THROUGH FRIDAY LOOKS DRY, ALTHOUGH WARM AIR ADVECTION
ALOFT AND AN UPPER JET MAY BRING SOME MID AND HIGH CLOUDINESS INTO
THE AREA THURSDAY NIGHT INTO FRIDAY. WINDS SHOULD BE DIMINISHING
THROUGH THE PERIOD, AND WERE IT NOT FOR THE POSSIBILITY OF CLOUDS
WE WOULD HAVE UNDERCUT GUIDANCE MINS ON THURSDAY NIGHT WITH
EXCELLENT RADIATING CONDITIONS. AS IT IS, WE CONTINUED TO WALK A
GUIDANCE-CONTINUITY LINE, WHICH HAS WORKED REASONABLY WELL.
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
THE MODELS CONTINUE TO DIFFER AS TO HOW THEY HANDLE THE ROTATING
UPPER LOW TO OUR NORTH ALONG WITH THE ASSOCIATED SHARPENING TROUGH.
AT THE SURFACE, ALL MODELS DEVELOP A LOW ALONG THE SE COAST AND
HEAD IT NE. MOST OF THE MODELS KEEP IT FAR ENOUGH S AND E OF OUR
AREA SO THAT IT JUST BRUSHES OUR SE SECTIONS. THE OUTLIER AT THIS
TIME IS THE ECMWF WHICH SHARPENS THE TROUGH AND DEVELOPS AN INTENSE
EAST COAST STORM. IT IS ALSO MUCH FASTER THAN THE REST OF THE MODELS
AND WOULD HAVE THE BIGGEST IMPACT LATE SATURDAY AND SATURDAY NIGHT
RATHER THAN LATE SATURDAY NIGHT AND SUNDAY. FOR NOW WE WILL GO WITH
THE MAJORITY AND BRING INCREASING CLOUDINESS IN LATE SATURDAY INTO
SATURDAY NIGHT AND CALL FOR A CHANCE OF SNOW INLAND AND RAIN OR SNOW
ALONG THE COAST LATE SATURDAY NIGHT AND SUNDAY. ONCE THE LOW MOVES
OFF TO THE NE, HIGH PRESSURE WILL BRING ANOTHER BATCH OF COLD AIR
INTO OUR AREA FOR THE BEGINNING OF NEXT WEEK.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
658 PM EST FRI DEC 18 2009
.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE TO MOVE OFF TO THE NORTHEAST THIS
EVENING ALLOWING A MASSIVE LOW PRESSURE SYSTEM TO FILL IN BEHIND
THIS WEEKEND. THIS LOW PRESSURE WILL BE ARRIVING BY EARLY MORNING
SATURDAY AND HEADING TO THE NORTHEAST THROUGHOUT THE DAY. THE LOW
SHOULD PULL FAR ENOUGH TO THE NORTHEAST ON SUNDAY THAT WE WILL SEE A
BRIEF RETURN OF HIGH PRESSURE ON SUNDAY. THE HIGH PRESSURE WILL GIVE
WAY TO ANOTHER LOW PRESSURE SYSTEM MOVING IN FROM THE NORTHWEST ON
MONDAY AND TUESDAY.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A 20Z SURFACE ANALYSIS SHOWS AN INTENSE AREA OF LOW PRESSURE OVER
THE SOUTHEASTERN UNITED STATES WHILE HIGH PRESSURE CONTINUES TO SIT
OVER THE NORTHEAST. WINDS WILL REMAIN FAIRLY CALM THIS EVENING BUT
WITH TEMPERATURES WELL BELOW FREEZING WINDS CHILLS WILL BE IN THE
SINGLE DIGITS TO THE TEENS. WHILE FOLLOWING THE STORM SYSTEM DOWN IN
THE SOUTHEAST UNITED STATES WE BROUGHT THE ONSET OF PRECIPITATION IN
WILL START LATE TONIGHT IN THE FAR SOUTHERN ZONES AND PROGRESSIVELY
SPREAD TO THE NORTH DURING THE DAY.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
AS IF THINGS COULD NOT GET ANY MORE COMPLICATED WITH THIS MASSIVE
LOW PRESSURE SYSTEM IT APPEARS AS THOUGH THE EARLY MORNING NAM
LEAVES US HIGH AND DRY...HOWEVER 6 HOURS LATER, WE ARE ONCE AGAIN
WET. BOTH THE NAM AND ECMWF HAVE BEEN PRETTY GOOD RECENTLY WITH
THEIR INITIALIZATIONS FIELDS AND OVERALL PERFORMANCE, SO IT IS
REALLY HARD TO DISCREDIT THEIR RECENT SOLUTIONS. WITH THAT BEING
SAID, BELIEVE A BLEND OF THE TWO MODELS WOULD PROVIDE THE BEST
SOLUTION FOR SNOWFALL AMOUNTS ACROSS THE REGION.
UPPER LEVEL DYNAMICS ADD TO THE DEEPENING OF THE LOW PRESSURE SYSTEM
WHILE IT MOVES TO THE NORTHEAST. OUR CWA IS PLACED IN A GREAT REGION
BETWEEN A COUPLED 250H JET STREAK TO SEE AN ENHANCEMENT OF UVM
PROVIDING AN AREA OF MASS DIVERGENCE LEADING TO THE OFFSHORE LOW
DEEPENING. THE INTERACTION WITH THE MID-LEVEL LOW IS A LITTLE MORE
PRECARIOUS RIGHT NOW. BOTH MODELS ARE SHOWING SOME SLIGHT PHASING OF
THE TWO REGIONS LATE SATURDAY WITH THE NAM BEING SLIGHTLY FASTER
THAN THE EURO. THIS PHASING WOULD PROVIDE AN OVERALL SLOWING OF THE
SYSTEM AND POSSIBLE OCCLUSION LEADING TO A GREATER CHANCE OF WRAP
AROUND MOISTURE TO BE SLUNG OVER THE REGION ON SUNDAY. BOTH MODELS
ALSO HINT AT A SLIGHT TROWAL EVENT WITH A DEFORMATION ZONE TO THE
NORTHWEST OF THE PHILADELPHIA METRO AREA ALLOWING ENHANCED
PRECIPITATION TO OCCUR. LOOKS LIKE THE HEAVIEST SNOW WILL BEGIN LATE
SATURDAY EVENING THROUGH EARLY SUNDAY MORNING SOUTH OF I-95 CORRIDOR
WHERE THE BEST OMEGA WILL BE MAINTAINED.
THIS SYSTEMS TRACK HAS BEEN HANDLED FAIRLY WELL WITH PREVIOUS
FORECASTS AND AMOUNT OF QPF. THIS SYSTEM WILL BE THE FIRST
WIDE-SPREAD PLOW-ABLE SNOWFALL EVENT IN THIS EARLY SEASON. RECORDS
SHOW THAT PHILADELPHIA HAS ONLY THREE SEPARATE OCCASIONS IN
DECEMBER WITH DOUBLE DIGIT SNOWFALLS, 12/26/1909, 12/12/1960, AND
12/24/1966, COULD THIS BE THE FOURTH ONE? ACCUMULATIONS LOOK
STAGGERING WITH AT LEAST AN 8 INCH SNOWFALL IN THE METRO AREA WITH
LOCALLY HIGHER AMOUNTS SOUTH AND EAST OF THE CITY WHERE MESOSCALE
BANDING APPEARS TO HAVE THE BEST CHANCE TO FORM.