277
FXUS61 KCTP 220351
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1051 PM EST SAT DEC 21 2024
SYNOPSIS
* SCATTERED LAKE EFFECT & UPSLOPE SNOW SHOWERS LINGER INTO THIS
EVENING
* COLDEST AIRMASS OF THE SEASON SO FAR BRINGS SINGLE DIGIT LOW
TEMPERATURES BY MONDAY MORNING
* CHRISTMAS EVE SYSTEM WITH MIXED PRECIP IMPACTS TRAVEL WHILE
TEMPERATURES CONTINUE TO MODERATE THROUGH THE END OF THE WEEK.
NEAR TERM /THROUGH SUNDAY/
10 PM UPDATE... A COUPLE OF CHANGES WERE MADE LATE THIS EVENING.
A LAKE HURON-ERIE CONNECTED BAND HAS RECENTLY INTENSIFIED FROM
WEST-CENTRAL PA INTO SOUTHERN CAMBRIA/NORTHERN SOMERSET
COUNTIES. THIS BAND IS LIKELY TO PERSIST UNTIL CLOSE TO
MIDNIGHT, WITH GOOD LAKE GENERATED INSTABILITY, SOME SYNOPTIC
UPGLIDE FROM A PASSING SHORT-WAVE, AND A SUFFICIENCY OF LOW-
LEVEL MOISTURE. A QUICK 1-2" OF SNOW IS POSSIBLE OVER THE NEXT
COUPLE OF HOURS AND A SPECIAL WEATHER STATEMENT WAS WRITTEN TO
ADDRESS THIS.
LATER TONIGHT, WE STILL EXPECT LAKE BANDS TO WEAKEN AND CONTRACT
BACK TOWARDS THE NORTHWEST, AS DRYING, SUBSIDENCE, AND WEAKENING
FLOW TAKE HOLD.
THE OTHER ISSUE IS RAPIDLY FALLING TEMPERATURES (ALREADY DOWN
NEAR ZERO OVER PARTS OF THE NORTHERN TIER AS OF 10 PM).
ESPECIALLY WHERE SKIES ARE CLEAR TO THE EAST AND THERE IS SOME
FRESH SNOW COVER, WE NOW HAVE LOWS LARGELY IN THE SINGLE DIGITS
BY DAYBREAK, WITH SOME SUB-ZERO READINGS IN PARTS OF POTTER,
TIOGA, AND SULLIVAN COUNTIES.
7 PM UPDATE... AS EVIDENCED BY RECENT AIRCRAFT SOUNDINGS ACROSS
PA AND OH, AS WELL AS REGIONAL RADAR TRENDS, LAKE ENHANCED
STREAMERS OFF HURON AND ERIE ARE GRADUALLY WEAKENING THIS
EVENING, OWING TO DRY ADVECTION/SUBSIDENCE JUST ABOVE THE
BOUNDARY LAYER. WE ANTICIPATE A CONTINUED REDUCTION OF SNOW
SHOWERS/FLURRIES OVER THE LAUREL HIGHLANDS OVER THE NEXT FEW
HOURS, AS THE CAPPING INVERSION LOWERS AND OVERALL MOISTURE
DEPTHS DECREASE.
ELSEWHERE ACROSS NORTHWEST AND CENTRAL PA, PERSISTENT
STRATOCUMULUS CLOUDS OVER THE ALLEGHENIES AND THE NORTHERN TIER
SHOULD HANG IN MUCH OF THE NIGHT, PERHAPS WITH SOME CLEARING
DURING THE PRE-DAWN HOURS. MAINLY CLEAR SKIES ANTICIPATED
ELSEWHERE.
ALTHOUGH BRISK WINDS WILL SLOWLY SUBSIDE FROM WEST TO EAST, IT
WILL BE A VERY COLD NIGHT, WITH AIR TEMPERATURES DOWN INTO THE
SINGLE DIGITS OVER THE NORTHERN TIER AND THE TEENS IN THE
SUSQUEHANNA VALLEY. APPARENT TEMPERATURES WILL GENERALLY RANGE
FROM FIVE BELOW TO ABOUT 10 ABOVE ZERO MUCH OF THE TIME.
PREVIOUS DISCUSSION... THE BASE OF AN UPPER TROUGH IS ROTATING
THROUGH CENTRAL PA TODAY AND GENERATING WIDESPREAD LAKE-ENHANCED
STREAMER BANDS THROUGHOUT THE FORECAST AREA. OCCASIONAL
REDUCTIONS IN VISIBILITY AND A QUICK DUSTING OF SNOW HAVE BEEN
OBSERVED ON SOME OF THE ROAD WEATHER CAMERAS AROUND THE STATE SO
FAR. THESE SNOW SHOWERS WILL GRADUALLY TAPER OFF INTO THE
EVENING AS THE UPPER TROUGH MOVES EAST. LINGERING LAKE- ENHANCED
OROGRAPHIC SNOW SHOWERS MAY LINGER INTO THE OVERNIGHT HOURS
ACROSS THE LAUREL HIGHLANDS AND NORTHERN MOUNTAINS. MAIN AREA OF
CONCERN THROUGH THE AFTERNOON IS A HEFTY BAND WITH A LAKE HURON
TO LAKE ERIE CONNECTION THAT HAS ALREADY BROUGHT A QUICK
ACCUMULATION OF 3+ INCHES NORTH OF PITTSBURGH. THAT BAND IS
POINTING RIGHT TOWARD EXTREME SOUTHWEST SOMERSET COUNTY AND
COULD DROP 2 TO 3 INCHES OF SNOW THERE THROUGH DINNER TIME. AS
SUCH, HAVE ISSUED A SPECIAL WEATHER STATEMENT TO REFLECT THE
REDUCED VISIBILITIES, ACCUMULATING SNOW POTENTIAL, AND RAPIDLY-
CHANGING WEATHER CONDITIONS FOR MOTORISTS.
A DEEPENING SURFACE LOW LIFTING INTO THE CANADIAN MARITIMES
HAS PRODUCED A FAIRLY TIGHT PRESSURE GRADIENT OVER PA TODAY,
WITH GUSTY NORTHWEST WINDS. BUFKIT SOUNDINGS SUGGEST 20 TO 30KT
GUSTS ARE LIKELY, MAINLY DURING THE AFTERNOON HOURS. EARLY
MORNING SATELLITE IMAGERY IS SHOWING DEVELOPING BREAKS IN THE
STRATOCU, ESPECIALLY EAST OF THE ALLEGHENIES. HOWEVER, DIURNAL
HEATING AND COLD TEMPS ALOFT SHOULD RESULT IN CLOUDS FILLING IN
EARLY THIS AFTERNOON, WITH MOSTLY CLOUDY SKIES EVEN ACROSS THE
SUSQ VALLEY AT TIMES.
CLOUD COVER AND LOW LEVEL COLD ADVECTION SHOULD RESULT IN
LITTLE WARMING TODAY. MIXING DOWN MODEL 850MB TEMPS OF
-14C TO -16C YIELDS EXPECTED HIGHS FROM ONLY AROUND 20F ACROSS
THE N MTNS, TO THE LOW 30S IN THE LOWER SUSQ VALLEY. THE GUSTY
NORTHWEST WIND SHOULD RESULT IN MIDDAY WIND CHILLS IN THE SINGLE
DIGITS OVER THE N MTNS AND TEENS MOST OTHER LOCATIONS.
SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/
DWINDLING LAKE EFFECT SNOW SHOWERS/FLURRIES OVER THE NW
MTNS/LAUREL HIGHLANDS ARE EXPECTED TONIGHT, AS HIGH PRESSURE
APPROACHES FROM THE GREAT LAKES. THE COLD WILL BE THE MAIN
STORY, WITH MIN TEMPS IN THE SINGLE DIGITS OVER THE N MTNS TO
MID TEENS IN THE SOUTHEAST COUNTIES. ALTHOUGH WINDS ARE EXPECTED
TO DIMINISH TONIGHT, RADIATIONAL COOLING WILL NOT BE IDEAL DUE
TO A LINGERING BREEZE OVER THE EASTERN COUNTIES AND LINGERING
LAKE EFFECT STRATOCU OVER THE LAURELS AND NW MTNS.
MOSTLY SUNNY AND COLD WEATHER WITH LIGHT WINDS ARE EXPECTED
SUNDAY, AS HIGH PRESSURE BUILDS OVER THE STATE. GEFS 2M TEMP
ANOMALIES ARE 10-15 DEGREES BELOW AVERAGE, TRANSLATING TO HIGHS
RANGING FROM THE MID TO UPPER TEENS OVER THE N MTNS, TO THE MID
AND UPPER 20S IN THE VALLEYS OF SOUTHERN PA. EVEN THOUGH HIGHS
WILL BE SEVERAL DEGREES BELOW THOSE OF SATURDAY, THE
COMBINATION OF SUNSHINE AND LIGHTER WINDS MAY ACTUALLY MAKE IT
SLIGHTLY MORE PLEASANT TO BE OUTSIDE ON SUNDAY AFTERNOON.
WITH HIGH PRESSURE OVERNIGHT SUNDAY NIGHT, IDEAL CONDITIONS FOR
RADIATIONAL COOLING WILL UNDOUBTEDLY LEAD TO THE COLDEST LOW
TEMPERATURES YET THIS WINTER BY MONDAY MORNING. LOWS WILL
GENERALLY BE IN THE SINGLE DIGITS WITH BELOW ZERO TEMPERATURES
FAVORED IN NORTHEAST PA.
RETURN SOUTHERLY FLOW BEHIND THE DEPARTING HIGH WILL HELP
TEMPERATURES REBOUND SOME ON MONDAY AS HIGH CLOUDS STREAM IN
AHEAD OF THE NEXT SYSTEM. CURRENT MEDIUM RANGE GUIDANCE
INDICATES MOST OF THE DAY WILL BE DRY, BUT PRECIPITATION COULD
ARRIVE IN NORTHWEST PA BY MONDAY EVENING.
A FAIRLY FAST MOVING, NORTHERN STREAM SHORTWAVE WILL CROSS PA
LATE MONDAY INTO TUESDAY AND BRING SOME LIGHT SNOW TO THE AREA.
BEST CHANCE FOR -SN AND A LIGHT ACCUM OF A COATING TO 2 INCHES
WILL BE ACROSS THE NORTHERN MTNS OF THE STATE. SOME TRAVEL
DISRUPTIONS ARE POSSIBLE FOR I-80, BUT SIGNIFICANT ACCUMULATIONS
APPEAR UNLIKELY AT THIS POINT. GFS AND ITS ENSEMBLES ARE
FARTHER NORTH WITH THE TRACK OF THE MID AND UPPER LEVEL TROUGH,
BUT QPF ALONG THE TRAILING COLD FRONT LEADS TO A SIMILAR
OUTCOME TO THE EC WITH RESPECT TO SNOW PROBS/AMOUNTS.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
ON THE LARGE-SCALE, THE AMPLIFIED, COLD EASTERN
CANADIAN/NORTHEASTERN CONUS UPPER TROUGH DOMINATING AT THE
PRESENT TIME SHOULD BE A THING OF THE PAST BY CHRISTMAS DAY, AS
THIS FEATURE LIFTS OUT INTO THE NORTHERN ATLANTIC. IT WILL
REPLACED BY BUILDING HEIGHTS AND A GENERALLY MORE ZONAL FLOW
PATTERN ALOFT. THIS TRANSLATES INTO MORE SEASONABLE TEMPERATURES
FOR LATE DECEMBER ACROSS PA, EVEN TRENDING ABOVE CLIMO TOWARDS
NEXT WEEKEND.
AS FOR THE SENSIBLE WEATHER, THERE IS INCREASING CONFIDENCE THAT
SURFACE HIGH PRESSURE FROM SOUTHEASTERN CANADA DOWN INTO THE
NORTHEASTERN U.S. WILL KEEP THE WEATHER DRY FOR THE COMMONWEALTH
FROM CHRISTMAS DAY INTO AT LEAST THURSDAY.
UNCERTAINTY GROWS LATER IN THE WEEK, AS LOW-LEVEL EASTERLY FLOW
AND THE APPROACH OF WEAK SHORT-WAVE ENERGY FROM THE MIDWEST
COULD BRING BOUTS OF LIGHT PRECIPITATION, ESPECIALLY FOR
SOUTHERN AND WESTERN SECTIONS OF THE STATE. AT THIS EARLY
JUNCTURE, LIGHT RAIN APPEARS TO BE THE MOST PROBABLE
PRECIPITATION TYPE, BUT POCKETS OF LIGHT WINTRY MIX ARE NOT BY
ANY MEANS OFF THE TABLE.
AVIATION /04Z SUNDAY THROUGH THURSDAY/
AS EXPECTED, BANDS OF SNOW SHOWERS ARE ON THE DECREASE
EARLY THIS EVENING. MAIN IMPACTS WOULD BE VERY BRIEF DROP IN
VISIBILITIES BELOW 2 MILES, AT SPOTS LIKE BFD AND PERHAPS JST.
EXPECT MOST IF NOT ALL THE ACTIVITY TO BE OVER WITH BY MIDNIGHT.
LIKEWISE, WINDS WILL SLOWLY WEAKEN OVERNIGHT.
LOW CIGS WILL LIKELY OCCUR FROM TIME TO TIME AT JST
AND BFD, PERHAPS FOR A BRIEF TIME AT AOO AND UNV INTO
EARLY SUNDAY MORNING. FURTHER EAST, MAINLY CLEAR SKIES
WILL PREVAIL.
HIGH PRESSURE BUILDING INTO THE AREA ON SUNDAY SHOULD
GIVE MOST PLENTY OF SUNSHINE. EXPECT LOW CIGS AT SPOTS
LIKE JST AND BFD TO BE GONE BY EARLY AFT.
LIGHT WINDS AND CLEAR SKIES EXPECTED FOR SUNDAY NIGHT INTO
THE FIRST PART OF MONDAY.
MAIN ISSUE FOR THE AREA AFTER MONDAY WOULD BE FOR LOWER
CIGS AND EVEN SOME MIXED PRECIPITATION FROM TIME TO TIME,
MAINLY AFTER EARLY MONDAY EVENING, AS A MILDER AND HIGHER
DEWPOINT AIRMASS WORKS INTO THE AREA.
OUTLOOK...
MON...NO SIG WX.
TUE...SNOW ENTERS W PA AM, OVERSPREADS AREA BY AFTERNOON.
WED...NO SIG WX.
WED NIGHT...PATCHY FREEZING RAIN POSSIBLE.
THU...LIGHT RAIN POSSIBLE SOUTH.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...BANGHOFF
NEAR TERM...JUREWICZ/FITZGERALD/BANGHOFF
SHORT TERM...FITZGERALD/BANGHOFF
LONG TERM...JUREWICZ
AVIATION...MARTIN
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