985
FXUS61 KCTP 220153
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
853 PM EST TUE JAN 21 2025
SYNOPSIS
* FRIGID TEMPERATURES WILL CONTINUE TO GRIP THE COMMONWEALTH
TONIGHT THROUGH WEDNESDAY
* MODERATING, BUT STILL SEASONABLY COLD TEMPERATURES WILL FOLLOW
FOR THURSDAY AND FRIDAY, CONTINUING INTO THE WEEKEND
NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/
EVENING WATER VAPOR LOOP SHOWS A SHORTWAVE ENTERING WESTERN PA
AT THE BASE OF THE DEEP UPPER TROUGH OVER THE REGION. DESPITE
LIMITED MOISTURE, STRONG LARGE SCALE FORCING AND LOW LEVEL
CONVERGENCE IS PRODUCING A BAND OF LIGHT SNOW SHOWERS ALONG THE
ASSOCIATED COLD FRONT, WHICH LIES FROM JUST WEST OF KBFD TO JUST
EAST OF KPIT AT 01Z. EXPECT A LIGHT COATING OF SNOW OF <0.5
INCHES THIS EVENING ALONG THE SPINE OF THE ALLEGHENIES AS THIS
FEATURE MOVES THROUGH. SUBSIDENCE DOWNWIND OF THE ALLEGHENIES
SHOULD PRECLUDE SNOW SHOWERS FURTHER EAST.
THE COLDEST TEMPS ALOFT WITH OUR CURRENT COLD SNAP ARE PROGGED
TO SPREAD INTO CENTRAL PA TONIGHT BEHIND THE EXITING COLD FRONT.
THE COMBINATION OF CLEARING SKIES, DRY AIR AND SNOW COVER
SHOULD RESULT IN EFFICIENT RADIATIONAL COOLING LATE TONIGHT,
ESPECIALLY OVER THE LAUREL HIGHLANDS, CLOSEST TO SURFACE HIGH
PRESSURE BUILDING IN FROM THE OHIO VALLEY. BASED ON THIS, HAVE
UNDERCUT NBM MIN TEMPS BY A COUPLE OF DEGREES OVER THE LAURELS.
EXPECT A WIDE RANGE IN MIN TEMPS FROM RIDGETOPS TO VALLEYS DUE
TO DECOUPLING. LOWS SHOULD RANGE FROM AROUND -20F IN THE COLDER
VALLEYS OF THE LAUREL HIGHLANDS, TO AROUND 5 ABOVE IN THE MORE
URBANIZED SPOTS OF THE LOWER SUSQ VALLEY. LIGHT WINDS LATE
TONIGHT SHOULD NOT RESULT IN SIGNIFICANTLY LOWER WIND CHILLS.
SHORT TERM /7 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/
FAIR AND COLD CONDITIONS WITH LIGHT WIND ARE EXPECTED
WEDNESDAY, AS SURFACE RIDGE BUILDS ACROSS PA. WARM ADVECTION
PRECEDING LOW PRESSURE OVER THE GRT LKS WILL SPREAD MID LEVEL
CLOUDINESS INTO THE REGION BY AFTERNOON, ESPECIALLY OVER THE NW
MTNS. LOW LEVELS ARE PROGGED TO REMAIN VERY DRY, BUT CAN'T RULE
OUT A FEW FLURRIES OVER THE NW MTNS LATE IN THE DAY. MAX TEMPS
WEDNESDAY SHOULD BE IN THE TEENS OVER THE BULK OF THE FORECAST
AREA, WHICH IS AROUND 20 DEGREES BELOW AVERAGE FOR JANUARY.
MODEL RH PROFILES SUPPORT A CLEARING TREND WED NIGHT, AS THE
BEST MID LEVEL WARM ADVECTION SHIFTS NORTH OF PA. THE WEAKEST
GRADIENT AND BEST RADIATIONAL COOLING SHOULD BE OVER SOUTHEAST
PA, CLOSEST TO THE RETREATING SURFACE RIDGE. THE RESULT SHOULD
BE FAIRLY UNIFORM MIN TEMPS IN THE SINGLE DIGITS ABOVE ZERO.
MARKEDLY LESS COLD CONDITIONS ARE ANTICIPATED THURSDAY, AS A
SOUTHWEST FLOW DEVELOPS BETWEEN HIGH PRESSURE OFF OF THE EAST
COAST AND AN UPSTREAM COLD FRONT OVER THE GRT LKS. SEE NO REASON
TO DEVIATE FROM NBM MAX TEMPS, WHICH ARE IN THE 20S. RH
TIMESECTIONS SUPPORT CLOUDS ARRIVING FROM WEST TO EAST DURING
THE AFTERNOON AHEAD OF THE APPROACHING COLD FRONT. MODEL
SOUNDINGS INDICATE THE RETURN MOISTURE AHEAD OF THE FRONT WILL
BE SHALLOW, BUT COULD SUPPORT A BIT OF VERY LIGHT SNOW WHERE
THE SSW FLOW IS FORCED TO ASCEND THE NW MTNS LATE IN THE DAY.
EXPECT MAINLY DRY AND COLD CONDITIONS INTO THE WEEKEND. TOWARDS
THE END OF THIS WEEK A WEAK UPPER LEVEL SHORT WAVE WILL SWING
OFF THE GREAT LAKES. A SURFACE TROUGH WILL ARRIVE BY FRIDAY
MORNING, BRINGING WITH IT ANOTHER MOISTURE STARVED COLD FRONT.
DESPITE THE SYNOPTIC FORCING THERE WILL NOT BE ENOUGH MOISTURE
TO ALLOW FOR MUCH PRECIPITATION. EVEN WIND FLOW WILL REMAIN
MOSTLY WESTERLY BEHIND THIS FRONT MAKING LAKE EFFECT SNOW IN THE
NORTHWEST UNLIKELY AT THE BEGINNING OF THE EXTENDED PERIOD.
STILL ENOUGH OF A CHANCE TO ENTER SLIGHT CHANCE POPS ACROSS THE
HIGHER TERRAIN.
LONG TERM /SATURDAY THROUGH TUESDAY/
WEAK FRONTAL SYSTEMS WILL MOVE ACROSS THE REGION FROM TIME TO
TIME. AFTER THE ONE LATER TODAY AND AGAIN LATER ON THURSDAY
INTO EARLY FRIDAY, LOOKS LIKE THE NEXT ONE WOULD MOVE ACROSS THE
AREA LATE SUNDAY INTO MONDAY. GFS AND EC SHOW A STRONG JET
STREAM FROM THE CENTRAL PLAINS OF CANADA, SOUTHEAST ACROSS THE
GREAT LAKES AREA BY NEXT MONDAY. A LARGE HIGH PRESSURE SYSTEM
BEHIND THE SYSTEM MAY TRY TO BUILD INTO THE AREA LATER NEXT
WEEK, BUT THE TENDENCY WILL BE FOR ANY HIGH PRESSURE SYSTEMS TO
SPLIT IN TWO, WITH THE REAL COLD AIR STAYING OVER SOUTHERN
ONTARIO AND QUEBEC, AND THE OTHER HIGH CENTER BEING FURTHER
SOUTH. CAN THANK THE GREAT LAKES WARMER WATERS TO AID IN HAVING
THE HIGH CENTERS SPLIT APART. ALSO WILL LIKELY HAVE SEVERAL
CLIPPERS MOVE ACROSS THE AREA BEFORE THIS.
TEMPERATURES WILL TREND TOWARD NORMAL BY LATE WEEK INTO SUNDAY,
WHICH WILL HELP EASE THE PROBLEMS THAT CAN DEVELOP WITH THE
EXTENDED COLD SPELL.
AVIATION /01Z WEDNESDAY THROUGH SUNDAY/
AN UPPER LEVEL TROUGH ALONG WITH A MOISTURE STARVED COLD FRONT WILL
MOVE ACROSS THE REGION OVERNIGHT. SCATTERED SNOW SHOWERS ARE
POSSIBLE WITH WESTERLY WINDS PROVIDING UPSLOPE CONDITIONS IN
THE WESTERN HALF OF OUR AIRSPACE, MAINLY AT BFD AND JST. MVFR
CEILINGS AND VISBY RESTRICTIONS WILL BE CONFINED TO THESE SITES.
ANY OVERNIGHT RESTRICTIONS WILL QUICKLY IMPROVE WEDNESDAY
MORNING. BROKEN TO SCATTERED MEDIUM AND HIGH CLOUDS WILL BE
PRESENT AND VFR CONDITIONS ARE EXPECTED DURING THE DAYTIME HOURS
WEDNESDAY.
REPEATED WEAK DISTURBANCES WILL PASS OVER PENNSYLVANIA THROUGH
THE REMAINDER OF THIS WEEK, BUT A LACK OF MOISTURE WILL PROHIBIT
WIDESPREAD PRECIPITATION. LIGHT BRIEF SNOW SHOWERS WILL REMAIN
POSSIBLE IN THE WESTERN HALF OF THE STATE THROUGH THIS COMING
WEEKEND.
OUTLOOK...
THU-SUN...PRIMARILY VFR WITH BRIEF RESTRICTIONS POSSIBLE ACROSS
NW PA THURS PM IN SCATTERED -SHSN.
CLIMATE
RECORD LOW MAXIMUM TEMPERATURES FOR JANUARY 22:
HARRISBURG 14F IN 2014
WILLIAMSPORT 14F IN 1961
ALTOONA 10F IN 2014
BRADFORD 6F IN 2014
STATE COLLEGE 7F IN 1936
CTP WATCHES/WARNINGS/ADVISORIES
COLD WEATHER ADVISORY UNTIL NOON EST WEDNESDAY FOR PAZ004>006-
010>012-017>019-025>028-034>037-041-042-045-046-049>053-
056>059-063>066.
EXTREME COLD WARNING UNTIL NOON EST WEDNESDAY FOR PAZ024-033.
SYNOPSIS...GUSEMAN/LAMBERT
NEAR TERM...FITZGERALD
SHORT TERM...GUSEMAN/FITZGERALD
LONG TERM...MARTIN
AVIATION...BOWEN
CLIMATE...STEINBUGL
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