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Area Forecast Discussion
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000
FXUS61 KCTP 221525
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1025 AM EST MON DEC 22 2014

.SYNOPSIS...
HIGH PRESSURE WILL RETREAT NORTHEAST INTO THE CANADIAN MARITIMES
EARLY THIS WEEK...AS A WEAK LOW PRESSURE SYSTEM LIFTS UP THE MID
ATLANTIC COAST. AN INTENSIFYING STORM SYSTEM WILL TRACK WEST OF
PENNSYLVANIA WEDNESDAY NIGHT...PUSHING A COLD FRONT THROUGH
THE STATE. ANOTHER LESS POTENT COLD FRONT IS LIKELY TO IMPACT THE
REGION BY NEXT WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
15Z UPDATE** LOW CLOUDS LIFTING CENTRAL MOUNTAINS AT MID
MORNING WITH DEEPER MOISTURE STARTING TO POOL SOUTH OF THE MASON
DIXON LINE...IN RESPONSE TO INCREASING MARITIME INFLUENCE IN
INCREASING EASTERLY/ONSHORE FLOW BETWEEN CAPE HATTERAS LOW
PRESSURE AND NORTHERN NEW ENGLANHIGH PRESSURE. THE INCREASING
MOISTURE...COMBINED WITH LG SCALE FORCING AHEAD OF SHORTWAVE
LIFTING OUT THE SE STATES...COULD SPREAD A BIT OF LIGHT RAIN INTO
SOUTHERN PA THIS AFTN. BLEND OF LATEST MDL GUIDANCE SUPPORTS CHC
POPS ACROSS THE SOUTHERN COUNTIES THIS AFTN.

FOR THE DAY...THE MAIN CONCERN FOCUSES ON POTENTIAL OF SOME ICING
LATER ON... GIVEN COLD AIR DAMMING AND LLVL AGEOSTROPHIC NLY FLOW
LOCKING THE COLD AIR IN. LATEST HRRR AND 4KM HRW-ARW DIFFER
SIGNIFICANTLY ON ARRIVAL OF PRECIP INTO SOUTH CENTRAL PA. LATEST
HRW-ARW HAS COME INTO LINE WITH PREVIOUS HRRR HOWEVER...IN
DELAYING PRECIP UNTIL AFTER 20Z...AND MOST OF THAT BEING RAIN
OVERF THE LOWER SUSQ RIVER VALLEY. 

THUS...LATEST HI RES RUNS...FORECAST SOUNDINGS AND ENS PTYPES
SUGGEST THE BEST ICING CHANCE LATE THIS AFTERNOON...STARTING NEAR
THE MASON DIXON LINE MID TO LATE AFTERNOON...AND LIFTING NORTHWARD
INTO THE LAURELS AND SOUTH CENTRAL MOUNTAINS BEFORE DARK.

STILL NO ADVY TO BE POSTED AT THIS TIME DUE TO THE LOW CERTAINTY
OF MEASURABLE FZRA...BUT CONFIDENCE INCREASING FROM ADAMS COUNTY
WESTWARD THAT AN ADVISORY MAY BE NEEDED FROM ADAMS COUNTY WESTWARD
MID TO LATE AFTERNOON. WILL MONITOR TRENDS AND ISSUE ACCORDINGLY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
MOIST SERLY FLOW OFF THE ATLANTIC AND ASSOC OROGRAPHIC FORCING OF 
SHALLOW MOISTURE LYR WILL LIKELY PRODUCE PATCHY LGT RAIN/DRIZZLE
TONIGHT AND TUESDAY. BEST CHC OF MEASURABLE PRECIP SHOULD COME
BTWN 00Z-06Z THIS EVENING WITH BENEFIT OF LG SCALE FORCING AHEAD
OF MID LVL SHORTWAVE. SFC TEMP FIELDS OF BOTH OPER AND ENSEMBLE
DATA SUGGEST THERE COULD BE ICING CONCERNS OVER THE HIGHER TERRAIN
OF CENTRAL PA. HOWEVER...TEMPS WILL BE VERY MARGINAL WITH ICING
MOST LIKELY ON THE RIDGETOPS. ALSO...NOT ENTIRELY SURE MEASURABLE
PRECIP WILL EVEN REACH FAR ENOUGH WEST TO CREATE A CONCERN. WILL
THEREFORE CONTINUE TO MENTION THREAT OF ICY ROADS IN THE HWO AND
AWAIT 12Z GUIDANCE TO GET A BETTER HANDLE ON THIS EVENT.

ANY ICING THREAT SHOULD END BY DAYLIGHT TUESDAY...WHEN ALL PLUME
MEMBERS RISE ABV FREEZING. RAINFALL AMTS TUESDAY SHOULD BE VERY
LIGHT...WITH SHALLOW MOISTURE IN MDL SOUNDINGS IMPLYING OCNL
DRIZZLE RATHER THAN RAIN.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
THE MOST SIGNIFICANT FORECAST ISSUE IN THE LONG TERM REMAINS THE
EVOLUTION OF DEEP TROUGH AND ASSOC SFC LOW TRACKING WEST OF PA
WED/WED NITE. STRONG SOUTHERLY FLOW AHEAD OF THIS SYSTEM SHOULD SCOUR
OUT LINGERING SHALLOW COLD AIR EAST OF THE APPALACHIANS. LOW-LEVEL
TEMPERATURE AND MOISTURE FIELDS RISE WELL ABOVE THEIR SEASONAL
VALUES...IMPLYING IT WILL BE A BALMY CHRISTMAS EVE FOR ALL.

ALL MED RANGE GUIDANCE TIMES THE TRAILING COLD FRONT THRU CENTRAL
PA WED NITE. A STRONG SOUTHERLY LL JET AND ASSOC PWAT ANOMALIES
ABOUT +3 SIGMA ABOVE NORMAL ARE PROGGED BY GEFS TO PASS THRU THE
AREA IN ADVANCE OF THE FRONT WED NITE. THIS STRONG SOUTHERLY
FLOW...HIGH PRECIPITABLE WATER AND SHARP CDFRONT ALL IMPLY A
FRONTAL RAIN EVENT WITH PERHAPS SOME RARE LATE DECEMBER (ELEVATED)
CONVECTION. HAVE ADDED CHC OF THUNDER BASED ON EXPECTED STRONG LG
SCALE FORCING IN ADVANCE OF UPPER TROF AND PRESENCE OF SOME MEAGER
MDL CAPES.

INTENSIFYING SFC LOW PASSING NORTH OF PA IS A FAVORABLE PATTERN
FOR STRONG WINDS ACROSS CENTRAL PA DURING THE COLD SEASON...SO STILL
MONITORING THE POTENTIAL OF STRONG WINDS COINCIDENT AND FOLLOWING
PASSAGE OF CDFRONT LATE WED NITE AND THURSDAY. WILL MENTION
POTENTIAL IN HWO.

COLDER AIR WORKING IN BEHIND COLD FRONT WILL LIKELY PRODUCE
OROGRAPHIC SNOW SHOWERS ACROSS THE ALLEGHENY PLATEAU ON CHRISTMAS
DAY. HOWEVER...AIR MASS NOT LOOKING PARTICULARLY COLD AND SFC
TEMPS LIKELY TO BE ABV FREEZING...LIMITING THE POTENTIAL OF
ACCUMS.

TEMPERATURES SHOULD REBOUND FRIDAY AHEAD OF ANOTHER NORTHERN STREAM 
WAVE MOVING INTO THE MID-WEST. ECENS OUTPUT SUGGESTS THIS
SHORTWAVE WILL LIFT NORTH OF PA NEXT WEEKEND...PUSHING A DYING COLD
FRONT INTO THE REGION.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
COMBINATION OF RETREATING HIGH PRES OVR THE CANADIAN MARITIMES AND
WEAK LOW LIFTING UP THE MID ATLANTIC COAST WILL SPREAD AN
INCREASINGLY MOIST SERLY FLOW INTO CENTRAL PA ON TODAY. LOWER CIGS
LIFTING NORTHWARD THIS MORNING IN RESPONSE TO DEEPENING LLVL
MOISTURE AND ONSHORE FLOW. THE INCREASING MOISTURE...COMBINED
WITH LG SCALE FORCING AHEAD OF SHORTWAVE LIFTING OUT THE SE
STATES...COULD SPREAD A BIT OF LIGHT RAIN INTO SOUTHERN PA LATE
THIS AFTN.

MAIN CONCERN WILL BE POTENTIAL OF SOME LIGHT ICING...GIVEN COLD
AIR DAMMING SIGNATURE AND IMPLIED LOW-LEVEL AGEOSTROPHIC NORTHERLY
FLOW HOLDING LOW-LEVEL COLD AIR IN. OPER MDL SOUNDINGS AND ENS
PTYPES SUGGEST THE BEST CHC OF LATE DAY LIGHT -FZRA WOULD BE OVR
THE LAUREL HIGHLANDS AND HIGHER TERRAIN OF THE SC MTNS...WITH A
BETTER CHANCE TONIGHT ACROSS THE CENTRAL MTNS. 

OUTLOOK...

TUE...LOW CIGS WITH DRIZZLE/LIGHT RAIN LIKELY. BECOMING BREEZY
MAINLY ACROSS HIGHER TERRAIN. LLWS POSS N/W.

WED...PERIODS OF RAIN ALONG WITH WIDESPREAD REDUCTIONS. BREEZY.
LLWS LIKELY.

THU...WINDY AND COLDER WITH SCT MVFR CIGS AND -SHSN. LLWS.

FRI...FAIR AND MOSTLY VFR.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...FITZGERALD
NEAR TERM...DEVOIR/FITZGERALD
SHORT TERM...FITZGERALD
LONG TERM...FITZGERALD
AVIATION...RXR



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