FXUS61 KCTP 242353
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
653 PM EST THU DEC 24 2009
.SYNOPSIS...
A STRONG LOW PRESSURE SYSTEM OVER THE MIDWEST WILL PUSH RAIN INTO
THE REGION CHRISTMAS DAY. SUB-FREEZING AIR TRAPPED NEAR THE
SURFACE WILL CREATE POTENTIALLY ICY CONDITIONS ACROSS ALMOST ALL
OF CENTRAL PENNSYLVANIA CHRISTMAS MORNING...INTO THE MID AFTERNOON
HOURS...ESPECIALLY THE LAUREL HIGHLANDS. MOST LOCATIONS WILL TURN
TO PLAIN RAIN BY FRIDAY EVENING. COLD AIR WILL MOVE IN LATE
SATURDAY AND SUNDAY...CHANGING THE RAIN BACK TO SNOW SHOWERS. THE
COLD AIR WILL LAST THROUGH MOST OF NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
AS THE SFC-850 RIDGE SLIDES EAST OF THE PENN/NJ BORDER LATE TODAY
THE MEAN WIND IN THAT LAYER WILL VEER FROM THE NORTHEAST OR EAST
TO SERLY ACROSS THE REGION.
MAINLY CLEAR SKIES FOR THIS EVENING EAST OF THE SUSQ VALLEY...WITH
LAYERED (MID AND HIGH) CLOUDS INCREASING ACROSS CENTRAL PENN ATOP
THE EXPECTED REFORMATION OF A LOW STRATUS DECK TONIGHT.
MEAN LLVL WIND BECOMING WELL ALIGNED FROM THE SOUTHEAST (AND
INCREASING TO 20-30 KTS WITHIN THE LOWEST 500M OF THE GROUND) WILL
ADVECT LOW CLOUDS QUICKLY BACK TO THE NW TONIGHT. 09Z SREF
PROBABILITY OF IFR CIGS (LESS THAN 1000 FT AGL) BLOSSOMS RAPIDLY
AFTER 06Z - TO 90-100 PERCENT (LESS NEAR THE NY BORDER). THE
PROBABILITY FOR THE LOW OVC IS 95-100 PERCENT ACROSS THE ENTIRE
CWA...EXCEPT FOR AREAS JUST TO THE WEST OF A LINE FROM KJST TO
KDUJ AND KBFD WHERE THE MEAN LLVL FLOW WILL PROVIDE A
DOWNSLOPE/DRYING FLOW.
THE MAIN CONCERN VERY LATE TONIGHT IS THE RISK FOR BARELY
MEASURABLE -FZDZ TO OCCUR ESPECIALLY ACROSS THE CENTRAL MTNS AND
SUSQ VALLEY (MAINLY AFTER 08Z FRI). TEMPS TONIGHT WILL FALL OFF
QUICKLY THIS EVENING...THEN LEVEL OFF TO A LOW IN THE LOWER TO MID
20S FOR THE SECOND HALF OF THE NIGHT.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
WINTER WEATHER ADVISORY IN EFFECT FOR ALL AREAS FROM CHRISTMAS
MORNING THROUGH MUCH OF THE AFTERNOON. PRECIP TYPE WILL BE MAINLY
-FZDZ AROUND AND BEFORE DAYBREAK...WITH STEADIER -FZRA (POSSIBLY
MIXED WITH SNOW/SLEET) ARRIVING DURING THE LATE MORNING/EARLY
AFTERNOON HOURS. THERMAL PROFILES FROM THE NAM/GFS REMAIN
MARGINALLY COLD AT 850 THRU THE MORNING...BEFORE THE STG WAA
STREAMS IN ALOFT. EVAP COOLING OR ENHANCED PRECIP RATES...MAINLY
AT THE ONSET OF STEADIER PRECIP...COULD BRIEFLY PULL THERMAL
PROFILES TO THE LEFT ENOUGH FOR INITIAL FZRA/RA TO REVERT TO
SNOW/IP FOR A TIME. THEREFORE...WE DECIDED (IN CONJUNCTION WITH
SURROUNDING OFFICES) TO ISSUE A WINTER WEATHER ADVY VS. A FREEZING
RAIN ADVY.
AFTER THE POSSIBLE -FZDZ EARLY...THE DEEPER MSTR CLIMBS INTO THE
WRN HIGH TERRAIN ON A 30-35KT SRLY TO SERLY LLVL JET CHRISTMAS
MORNING AND SPREADS SW-NE DURING THE DAY. 12Z GFS BUFKIT THERMAL
STRUCTURE IS MUCH MORE BORDERLINE ACROSS THE NORTH - WITH ITS KBFD
GRIDPOINT CONTAINING JUST A FEW ELEVATED LAYERS OF +1C AIR AND UP
TO SEVERAL INCHES OF SNOW. 12Z GEFS PLUMES...AND 12Z NAM ARE IN
STARK CONTRAST TO THIS COLD OUTLIER UP NORTH...AND PAINT MAINLY
RAIN AT KBFD - EAST TO KELM... AFTER UP TO SEVERAL HOURS OF
FREEZING RAIN.
THE SHALLOW COLD AIR AT THE SFC IN THE MORNING WILL CONTINUE TO
BE REINFORCED BY ENELY AGEO FLOW EAST OF THE MTNS DUE TO COLD AIR
DAMMING. EXPECT A GRADUAL CHANGEOVER TO PLAIN RAIN DURING THE
AFTN AS BL TEMPS ARE FCST TO WARM ABV FZG. ICE ACCUMS OF UP TO A
TENTH OF AN INCH ARE POSSIBLE IN MOST LOCATIONS...WHICH A LOW
PROBABILITY OF 0.25" OVR THE LAUREL HIGHLANDS.
OCCLD FNTL BNDRY WILL PIVOT SLWLY NEWD ON SAT...AS A SFC LOW FORMS
OVR THE SRN MID ATLC. THIS MAY ACT TO KEEP TEMPS COOLER OVR THE
NRN TIER AND STILL COULD SEE A CHANGEOVER TO SNOW SOONER THAN THE
MDLS ARE DEPICTING. A RICH PLUME OF MSTR AND STG SELY LLJ WILL
KEEP PRECIP GOING INTO SAT...WITH POSSIBLE WRAP-AROUND SNOW AS THE
LOW DEEPENS SOME GOING UP THE COAST. TEMPERATURES OVR ERN PENN
MAY APPROACH 50F IN THE WARM SECTOR...BEFORE TEMPS DROP BEHIND THE
OCCLD FNTL PASSAGE. MANUAL 36HR GRIDDED QPF SHOWS MUCH OF THE AREA
PICKING UP 0.75-1.00" RNFL AMNTS THRU 00Z SUNDAY. THIS...ALONG
WITH SNOW MELT WILL CAUSE MINOR TO MODERATE RISES IN THE WEST
BRANCH AND LOWER SUSQ BASINS...AND MAY PUSH SOME SMALLER TRIBS TO
CAUTIONS STAGE. HYDRO FCSTS FROM THE MARFC DO NOT INDICATE ANY
FLOODING ATTM AND GIVEN THAN ANY PROBLEMS WOULD LKLY NOT OCCUR FOR
ANOTHER 36HRS...DECIDED AGAINST A FLOOD WATCH...BUT WL MENTION
SOME SPECIFICS IN HWO AND HYDRO SECTION BELOW.
COLDER AIR WILL BEGIN TO MIX WITH/CHANGE ANY LINGERING RAIN
SHOWERS TO SNOW SHOWERS SAT NGT WITH LITTLE OR NO ACCUMS XPCD.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
COLD MID LVL VORT WILL WOBBLE E ACROSS THE OH VLY AND INTO THE
MID ATLC REGION SUN/MON. BRISK/WINDY CONDS AND LES SHWRS WILL
ACCOMPANY A REINFORCING SURGE OF COLDER AIR MON NGT/TUE. HIGH PRES
SHOULD BRING SOME IMPROVEMENT BY THE MIDDLE OF NEXT WEEK.
STRONG NEG AO/NAO...+ PNA AND A SRN STREAM EL NINO CONNECTION
WL CONT TO OFFER A SET UP FAVORABLE FOR EAST COAST WINTER STORMS.
GFS/ECMWF MEAN SHOW A STORM SYSTEM ORGANIZED ALONG THE ECOAST
AROUND THE NEW YEAR...STAY TUNED.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR CONDS SHUD HOLD THRU AT LEAST 06Z FOR MUCH OF CENTRAL PA
AIRFIELDS...EXCEPT FAR SW PA. LLVL FLOW WILL REMAIN EASTERLY AS
MID/HIGH LVL MOISTURE SLOWLY PUSHES NE AHEAD OF AN INTENSE WINTER
STORM. EXPECT CIGS TO GRADUALLY DIMINISH TO AOA BKN-OVC 2KFT AGL
ARND 9-12Z FROM SW/W AIRFIELDS STEADILY PROGRESSING NE TOWARDS
UNV/IPT/MDT BY 13-15Z. CIGS WILL CONTINUE TO LOWER TOWARDS
IFR/LIFR AS PRECIP ARRIVES. VSBYS IN STEADIER PRECIP WILL
FLUCTUATE BTWN 2-5SM. ATTM IT APPEARS TEMPS SUPPORT PRECIP AT
ONSET BEGINNING AS FZRA. ARND 18-21Z TEMPS WILL WARM AND PUSH
PRECIP OVER TO RA AS IFR/LIFR CIGS PERSIST. IN ADDITION TO THE
POOR FLYING CONDS...A VIGOROUS LLVL JET PUSHES NE INTO CENTRAL PA
WITH WINDS OFF THE DECK AT 1400-1800FT AGL AOA 40-50KTS. HAVE THUS
MENTIONED WIND SHEAR THRU EARLY SAT.
OUTLOOK...
FRI NGT...IFR TEMPO LIFR CIGS WITH STEADY RA. WS OF 40-50KTS AOA
1400-1600FT AGL.
SAT...IFR CONDS...SLT IMPROV TO MVFR CENTRAL/EAST. WS WILL RELAX.
SUN- TUE...MVFR CIGS W/IFR WEST IN SHSN. CNTRL/EAST VFR/MVFR.
&&
.HYDROLOGY...
GENERALLY MINOR CHANGES IN RIVER LEVELS ARE EXPECTED OVER THE
NEXT 24 HOURS...WITH A RISE OF UP TO SEVERAL FEET EXPECTED LATER
IN THE PERIOD. WILLIAMSPORT IS FCST TO APPROACH CAUTION STATE
SUN/MON.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 8 AM TO 7 PM EST FRIDAY FOR
PAZ037-041-042-046-051>053.
WINTER WEATHER ADVISORY FROM 3 AM TO 5 PM EST FRIDAY FOR
PAZ004>006-010>012-017>019-024>028-033>036-045-049-050-056>059-
063>066.
&&
$$
SYNOPSIS...DANGELO/LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...LAMBERT/STEINBUGL
LONG TERM...STEINBUGL
AVIATION...BEACHLER
HYDROLOGY...STEINBUGL
