Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 240145
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
845 PM EST FRI JAN 23 2015

.SYNOPSIS...
LOW PRESSURE OVER THE WESTERN PANHANDLE OF FLORIDA THIS AFTERNOON
WILL MOVE QUICKLY NORTHEAST TO THE DELMARVA COAST BY EARLY
SATURDAY...BEFORE PASSING EAST OF NEW ENGLAND SATURDAY NIGHT. THIS
STORM WILL BRING A HIGH IMPACT...MODERATE TO HEAVY SNOWFALL TO THE
SOUTHEAST HALF OF PENNSYLVANIA. ANOTHER LOW...IN THE FORM OF AN
ALBERTA CLIPPER WILL TRACK JUST SOUTH OF PENNSYLVANIA SUNDAY
NIGHT. AN UPPER LVL TROUGH WILL REMAIN OVER THE NORTHEAST CONUS
THRU THE REST OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
640 PM...
RAIN/SNOW ON THE DOORSTEP JUDGING BY OBS AND INCREASING RADAR
ECHOES ON THE MD BORDER. TEMPS ALONG THERE ARE M30S...SO IT COULD
START AS RAIN OR SNOW. BUT THE EVAP COOLING PROCESS WILL TURN IT
TO SNOW AS THE LOWER ATMOS MOISTENS UP. MILD SRLY WIND IN MD/VA
COULD STILL LIFT SOME MILDER AIR INTO THE AREA AND PROLONG THE
RAIN CHCS THRU THE NIGHT...AND THIS ALREADY IN THE FCST.

PREV...
MID AFTERNOON SATELLITE LOOP SHOWS THICKENING CLOUD SHIELD RACING
INTO OUR AREA FROM THE SW...AHEAD OF A POTENT SOUTHERN STREAM
TROUGH AND IT/S ASSOCIATED...GRADUALLY STRENGTHENING SFC LOW
/1007 MB/ CENTERED NEAR KPNS.

EXPECT THE CLOUD BASES TO LOWER TO AN ALTOSTRATUS...7-10 KFT AGL
BY 22Z ACROSS THE SOUTH...AND DURING THE EARLY EVENING HOURS NORTH
OF INTERSTATE 80.

WINDS FOR THE REST OF TODAY/EARLY TONIGHT WILL BE LIGHT AND
GRADUALLY BACK THROUGH THE SOUTH...THEN TO THE SE OR EAST.

TEMPS FOR THE REST OF THE DAYLIGHT HOURS WILL BE IN THE MID 20S
ACROSS THE NORTH...AND LOWER TO MID 30S AS YOU HEAD SOUTH ACRS
CENTRAL AND SRN PENN.

09Z SREF AND 12Z U.S. OPER MODEL CONSENSUS POINTS TWD A SWATH OF
SIGNIFICANT/HEAVY SNOWFALL OCCURRING NEAR AND A FEW LAYERS OF
COUNTIES TO THE NORTHWEST OF I-81 TONIGHT AND SAT MORNING...WITH
THE SLIGHTLY SUB-1000 MB SFC LOW ANTICIPATED TO TRACK ACROSS THE
SRN DELMARVA PENINSULA BETWEEN 10-12Z SATURDAY.

MADE JUST SOME MINOR UPWARD MODIFICATIONS TO SNOWFALL ACROSS THE
COUNTIES NEAR THE ALLEGHENY FRONT...AND SLIGHTLY TRIMMED AMOUNTS
NEAR KTHV AND KLNS...WHERE A TRANSITION TO LIGHTER INTENSITY
PRECIP /SNOW...RAIN OR FREEZING RAIN/ MAY OCCUR EARLY SATURDAY AS
SUBSIDENCE OCCURS IN ASSOCIATION WITH THE NEWD DEPARTURE OF THE
HIGHER SEEDER-FEEDER CLOUDS...AND PASSAGE OF THE UNFAVORABLE LEFT
ENTRANCE REGION OF A 140 KT UPPER JET.

AN ADVISORY TYPE SNOWFALL OF 3-5 INCHES STILL APPEARS HIGHLY LIKELY
TONIGHT INTO EARLY SAT JUST TO THE SE OF THE ALLEGHENY FRONT IN
CENTRAL PENN /AND ACROSS THE FAR SE/ WHILE LOW END...WINTER STORM
WARNING AMOUNTS OF 6-8 INCHES SHOULD FALL ACROSS THE BULK OF THE
REGION BETWEEN I-81 AND THE I99/ROUTE 22O CORRIDOR.

NO OTHER CHANGES/ADDITIONS MADE TO THE WARNING AND ADVISORY
AREAS WITH THIS MID AFTERNOON UPDATE.

RADAR AND LATEST HIGH RES MODEL DATA ALL POINT TOWARD SNOW
ARRIVING ACROSS THE S TIER ARND 00Z AND REACHING IT/S FURTHEST
WESTWARD EXTENT ACROSS THE NW MTNS BY ARND MIDNIGHT. 12Z MDL
BLENDED QPF /AND MEDIAN VALUES ON THE 09Z SREF/ RANGES FROM
PRACTICALLY NOTHING OVR WARREN CO...TO 0.3 TO 0.5 INCHES ACROSS
THE LAURELS...CENTRAL MTNS...AND MIDDLE SUSQ VALLEY...TO PERHAPS
0.75 INCHES NEAR THE I-81 CORRIDOR.

THE PASSAGE OF SOUTHERLY LL JET LATE TONIGHT WILL DRAW MILDER AIR
INTO FAR SE PA...LIKELY MIXING OR CHANGING THE PTYPE TO EITHER
LIGHTER RAIN OR -FZRA FOR UP TO SEVERAL FROM ARND KLNS SOUTH AND
EASTWARD. STILL...EXPECT SEVERAL INCHES OF ACCUM BEFORE ANY
CHANGEOVER ACROSS THE SE. FURTHER NORTH...SNOW/WATER RATIOS LOOK
TO BE ARND 12/1...TYPICAL FOR COASTAL STORMS.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
BY DAWN SATURDAY...LL JET AND BEST ISENTROPIC LIFT SHOULD HAVE
SHIFTED EAST OF THE REGION. HOWEVER...LIGHTER /TO BRIEFLY MDT/ SNOW
/ASSOC WITH MID LVL SHORTWAVE AND LINGERING 850-700 MB DEFORMATION BAND/
IS LIKELY TO LAST THRU ARND MIDDAY...AND PERHAPS A BIT LONGER OVR
THE NE COUNTIES.

NW FLOW IN WAKE OF THIS SYSTEM SHOULD BRING PARTIAL CLEARING LATE
TO EASTERN PA. HOWEVER...A FAST MOVING AND WEAK CLIPPER TYPE
SHORTWAVE WILL BE DIVING INTO THE REGION FROM THE GRT LKS TOWARD
EVENING...LIKELY PRODUCING -SHSN ACROSS THE ALLEGHENY PLATEAU SAT
EVENING.

THE AIR MASS BEHIND TONIGHT/S LOW IS NOT PARTICULARLY COLD AND
ENS MEAN 925 TEMPS SUPPORT HIGHS SATURDAY IN THE M/U30S OVR MUCH
OF THE AREA...WHICH SHOULD RESULT IN MUCH IMPROVED ROAD CONDS BY
SAT AFTN.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
TROFFY NW FLOW PATTERN WILL PERSIST THROUGH MUCH OF THE PERIOD IN
THE WAKE OF THE EARLY WEEKEND STORM. THIS WILL LEAD TO LIMITED
OPPORTUNITIES FOR PHASING WITH ANY SRN STREAM ENERGY.

MED RANGE MDLS ALL TRACKING A POTENT ALBERTA CLIPPER JUST SOUTH
OF PA SUN NIGHT. LATEST TRENDS ARE FARTHER SOUTH ON THE TRACK AND
HAVE BACKED OFF ON QPF AND THUS SNOW TOTALS. PLENTY OF COLD AIR
AVAILABLE AND EXPECT NO PRECIP TYPE ISSUES WITH THIS EVENT.

AS THE LOW INTENSIFIES OFF THE THE ATLANTIC COAST ON MONDAY...WE
COULD SEE LIGHT SNOW/SHOWERS CONTINUING THROUGH THE DAY WITH
TEMPERATURES REMAINING STEADY OR SLOWLY FALLING THROUGH THE 20S.

COLDEST AIR OF THE WEEK DIVES IN BEHIND THE DEPARTING SYSTEM ON
TUESDAY WITH STATEWIDE HIGHS A FEW DEGREES EITHER SIDE OF 20F.
SUB-ZERO LOWS POSSIBLE ACROSS A GOOD PART OF CENTRAL PA TUESDAY...AS
SFC HIGH BUILDS OVR THE AREA. CLEARING SKIES...A CALM WIND AND
FRESH SNOW COVER COULD RESULT IN AN IDEAL RADIATIONAL COOLING
SCENARIO.

MODERATING CHILL IS IN STORE FOR THE MID TO LATE WEEK...AS
RIDGING AT THE SURFACE AND ALOFT MOVES IN AHEAD OF NEXT IN SERIES
OF ALBERTA CLIPPERS.

ANOTHER POTENT SHORTWAVE WILL BRING A COLD FRONT THROUGH THE
REGION THUR NIGHT INTO FRIDAY WITH MAIN SCATTERED SNOW SHOWERS.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...

SNOW IS SLOWLY SPREADING NORTHWARD AND IS ONLY STARTED TO SNOW
THROUGH THE SOUTHERN HALF OF PENNSYLVANIA. SNOW WILL OVERSPREAD
THE REMAINDER OF THE AREA BY LATE EVENING. THE SNOW WILL BE
ACCOMPANIED BY LOWERING CIGS/VSBYS WITH MAJORITY OF TERMINALS
DROPPING TO IFR BY MID EVENING AND LINGERING THROUGH MUCH OF THE
OVERNIGHT. SOME FREEZING RAIN LIKELY WORKS INTO THE SOUTHERN MTNS
AND LOWER SUSQ AFTER MIDNIGHT...WHICH COULD BRING ICING ISSUES.
ANY PRECIPITATION WILL WEAKEN AND TAPER OFF MID TO LATE SATURDAY
MORNING...WITH AREAS CLEARING AS WINDS SHIFT TO THE WEST
NORTHWEST...SATURDAY AFTERNOON. EXPECT CIGS AND VSBYS TO LIFT
THROUGH THIS TIMEFRAME. AS A MORE NORTHWESTERLY FLOW TAKES
HOLD...WINDS WILL BECOME BREEZY WITH CONDITIONS ONCE AGAIN
DROPPING TOMORROW NIGHT AT BFD AND JST...BEGINNING BETWEEN 22Z TO
02Z.



OUTLOOK...

SUN...VFR INTO THE AFTERNOON...THEN SNOW DEVELOPING ACROSS THE
WEST IN THE AFTERNOON OR EVENING...AND OVERSPREADING ALL OF
CENTRAL PENN AND THE SUSQ VALLEY AT NIGHT.

MON...AM SNOW WITH WIDESPREAD MVFR TO IFR LIKELY.

TUE...NO SIG WEATHER EXPECTED.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 1 PM EST SATURDAY FOR PAZ019-024-
025-033-042-045-046-064>066.
WINTER STORM WARNING UNTIL 1 PM EST SATURDAY FOR PAZ026>028-
034>036-049>053-056>059-063.

&&

$$
SYNOPSIS...LAMBERT
NEAR TERM...DANGELO/LAMBERT
SHORT TERM...LAMBERT
LONG TERM...FITZGERALD/GARTNER
AVIATION...LAMBERT/CERU



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