Dec 24-25 MidAtl/NE Storm, Reality: Short Range (0-4 Days Out) Forecasts Options

[Ryan Duff]

AFDCTP

.NEAR TERM /THROUGH TONIGHT/...
A SHALLOW WEDGE OF COLDER AIR HAS ADVECTED SOUTH TO COVER MUCH OF
THE REGION EARLY TODAY. SLIGHTLY MILDER/ABOVE FREEZING AIR AT 850 MB
WAS ADVANCING EAST ACROSS THE GREATER PITTSBURGH AREA ATTM...JUST
ABOVE THE NEARLY STALLED OUT...EAST TO WEST 925 MB FRONT. HIGH RES
NAM AND RUC MODELS SHOW THAT A BKN-OVC STRATO CU LAYER AROUND 2-3KFT
AGL WILL PERSIST THE NEXT FEW HOURS ACROSS THE NRN TIER COUNTIES...
BEFORE ERODING AROUND SUNRISE. HIGH CLOUDS WILL STREAM IN FROM THE
WSW AND THICKEN UP LATER THIS MORNING.

TEMPS AT DAYBREAK WILL BE COLDEST ACROSS THE SOUTHERN HALF OF THE
STATE /MAINLY IN THE LOWER 20S/...WHILE THE CLOUD BLANKET ACROSS THE
NORTH RESULTS IN SLIGHTLY WARMER MINS IN THE MID 20S.

00Z MODEL SUITE AND LATEST ENSEMBLE GUIDANCE SHOWS A HIGH
PROBABILITY FOR A LIGHT SNOWFALL OF AN INCH OR TWO ACROSS THE REGION
THIS AFTERNOON INTO TONIGHT AS A WEAK AREA OF LOW PRESSURE MOVES ENE
UP THE OHIO RIVER VALLEY. HIGH RES MODEL THERMAL/WET BULB THERMAL
PROFILES WITHIN 2 KFT AGL INDICATE THAT MUCH OF THE LIGHT PRECIP
WILL FALL IN THE FORM OF SNOW. THE LOWEST 1 KFT AGL MAY WARM BRIEFLY
INTO THE MID AND UPPER 30S ACROSS THE SOUTHEAST VALLEYS TO CAUSE THE
LIGHT SNOW TO MIX WITH LIGHT RAIN.

OTHERWISE...925-850 MB WET-BULB TEMPS WILL BE A FEW TO SVRL DEG C
BELOW ZERO FOR THE DURATION OF THIS EVENT...SUPPORT PRIMARILY SNOW.

THE ONLY LOCATION AT THIS POINT THAT WILL SEE A LAYER OF SLIGHTLY
ABOVE FREEZING AIR ALOFT WILL BE PORTIONS OF THE LAUREL HIGHLANDS.
THERE...SOME LIGHT FREEZING RAIN AND SLEET SHOULD MIX IN AT
TIMES...PERHAPS LEADING TO TREACHEROUS HOLIDAY TRAVEL. A WINTER
WEATHER ADVISORY WAS POSTED FOR SOMERSET COUNTY FROM 17Z TODAY
THROUGH 06Z CHRISTMAS.

SFC TEMPS THIS AFTERNOON IN THE LOWER TO MID 30S ACROSS MUCH OF THE
REMAINDER OF CENTRAL PENN SHOULD ALLOW TREATED/PRIMARY ROADS TO STAY
MAINLY WET AS SNOWFALL RATES SHOULD BE QUITE LIGHT...PERHAPS AROUND
0.25 INCH PER HOUR.

AFTER THE MAIN WAVE OF PRECIP COMES THROUGH EARLY THIS EVENING...
VERY WEAK FORCING AND SPOTTY LIGHT PRECIP WILL CONTINUE
OVERNIGHT...AND LLVL WINDS GO WESTERLY. THIS WILL PROLONG THE
NEAR-FREEZING TEMPS AND POSSIBILITY FOR -FZDZ ACROSS THE AREA...ESP
THE WRN MTS. ALL OF THE HIGH/COLD CLOUDS GO AWAY IMMEDIATELY AFTER
THE MAIN PUSH...SO GOOD SEEDING OF ICE CRYSTALS IS GONE AND MUCH OF
THE AREA COULD SEE PATCHY FZDZ. AGAIN...ALL TOO FAR AWAY AND MINOR
PRECIP AMOUNTS TO MAKE A CALL ON THIS YET.

TEMPS GREETING SANTA AND HIS REINDEER TEAM EARLY CHRISTMAS MORNING
WILL VARY FROM THE L20S UP NORTH...TO THE MID AND UPPER 20S ACROSS
CENTRAL AND SOUTHERN PENN.

[Ryan Duff]

HWO

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE STATE COLLEGE PA
322 AM EST MON DEC 24 2012

PAZ004>006-010>012-017>019-024>028-034>037-041-042-045-046-049>053-
056>059-063>066-250830-
WARREN-MCKEAN-POTTER-ELK-CAMERON-NORTHERN CLINTON-CLEARFIELD-
NORTHERN CENTRE-SOUTHERN CENTRE-CAMBRIA-BLAIR-HUNTINGDON-MIFFLIN-
JUNIATA-BEDFORD-FULTON-FRANKLIN-TIOGA-NORTHERN LYCOMING-SULLIVAN-
SOUTHERN CLINTON-SOUTHERN LYCOMING-UNION-SNYDER-MONTOUR-
NORTHUMBERLAND-COLUMBIA-PERRY-DAUPHIN-SCHUYLKILL-LEBANON-CUMBERLAND-
ADAMS-YORK-LANCASTER-
322 AM EST MON DEC 24 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL PENNSYLVANIA.

.DAY ONE...TODAY AND TONIGHT.

WEAK LOW PRESSURE HEADING UP THE OHIO RIVER VALLEY TODAY WILL
SPREAD LIGHT SNOW INTO THE REGION DURING THE MIDDAY AND AFTERNOON
HOURS TODAY. THE LIGHT SNOW WILL CONTINUE INTO TONIGHT...POSSIBLY
MIXING WITH SOME LIGHT SLEET OR FREEZING DRIZZLE AT
TIMES...ESPECIALLY ACROSS SOUTHERN PENNSYLVANIA. AN INCH OR TWO IS
SNOW ACCUMULATION IS LIKELY...POSSIBLY TOPPED BY A THIN COATING OF
FREEZING DRIZZLE IN SOME LOCATIONS TONIGHT AND EARLY CHRISTMAS
DAY.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.
A MORE SIGNIFICANT STORM WILL FORM OVER THE LOWER MISSISSIPPI
VALLEY CHRISTMAS DAY AND INTENSIFY AS IT MOVES NORTHEAST TOWARD
THE CENTRAL APPALACHIANS WEDNESDAY. THERE IS STILL UNCERTAINTY
WITH RESPECT TO THE TIMING AND INTENSITY OF A SECONDARY LOW THAT
WILL FORM...AND THEN STRENGTHEN NEAR THE MID ATLANTIC COAST
WEDNESDAY NIGHT...WHICH WILL PLAY A KEY ROLE ON THE TYPE AND
INTENSITY OF THE PRECIPITATION ACROSS THE COMMONWEALTH. A MODERATE
TO HEAVY SNOWFALL STILL APPEARS LIKELY ACROSS MAINLY THE NORTHWEST
HALF OF THE STATE WEDNESDAY INTO THURSDAY...WHILE A LAYER OF
SLIGHTLY ABOVE FREEZING AIR STREAMING IN ALOFT FROM THE SOUTH MAY
CAUSE THE SNOW TO MIX WITH...OR CHANGE TO SLEET OR RAIN AT TIMES
THROUGHOUT THE VALLEYS OF SOUTH-CENTRAL AND SOUTHEASTERN
PENNSYLVANIA.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ENCOURAGED TO RELAY REPORTS OF SNOW AND ICE ACCUMULATION
TO THE THE NATIONAL WEATHER ACCORDING TO STANDARD PROCEDURES.

[NorEaster07]

OBS thread opened.. http://forums.accuweather.com/index.php?showtopic=30327