Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 310619 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 119 AM EST SAT JAN 31 2015 .SYNOPSIS... ARCTIC AIR WILL BRING BITTER COLD TEMPERATURES AND SUBZERO WIND CHILLS TO MUCH OF CENTRAL PENNSYLVANIA TONIGHT INTO EARLY SATURDAY. CONFIDENCE IS INCREASING FOR A WIDESPREAD...HIGH IMPACT WINTER WEATHER EVENT SUNDAY INTO MONDAY...WITH THE POTENTIAL FOR SIGNIFICANT SNOW ACCUMULATION...ALONG WITH SOME MIXED WINTRY PRECIPITATION ACROSS SOUTHERN PENNSYLVANIA. ANOTHER SHOT OF ARCTIC AIR WILL FOLLOW FOR MONDAY AFTERNOON INTO TUESDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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INVERSION HEIGHTS FALLING RAPIDLY NEXT FEW HOURS AS HIGH PRESSURE NEAR COLUMBUS OHIO BUILDS EAST AND THE MEAN...850-700MB THERMAL TROUGH DRIFTS TWD THE NEW JERSEY COAST. REGIONAL RADAR MOSAIC STILL DETECTING NARROW BANDS OF SNOW SHOWERS FEEDING INTO THE LAUREL HIGHLANDS. BLOWING SNOW IS LIKELY MORE RESPONSIBLE FOR VSBY REDUCTIONS THAN THAN THE SNOWFALL ITSELF. WESTERN UPSLOPE AREAS AND OUR FAR NORTHEASTERN ZONES WILL HANG ONTO THE CLOUDS AND LINGERING FLURRIES THE LONGEST. SKIES WILL SLOWLY CLEAR ACROSS MOST OF THE REGION IN THE PRE DAWN HOURS AS THE MEAN LLVL WIND BACKS TO THE WEST. WINDS REMAINING IN THE 10-15 MPH RANGE LATE TONIGHT...WITH HIGHER GUSTS WILL KEEP WIND CHILLS IN THE 10-20 BELOW ZERO RANGE OVER THE WESTERN HIGHER TERRAIN,..AND FROM ZERO TO 10 BELOW THROUGHOUT THE CENTRAL RIDGE AND VALLEY REGION. ACTUAL LOWS AROUND SUNRISE SATURDAY WILL VARY FROM ZERO TO 5 BELOW ACROSS THE NORTHWEST MOUNTAINS...TO AROUND 10 ABOVE IN THE SOUTHEAST.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... SATURDAY WILL START BRIGHT IN MOST AREAS AS THE HIGH CRESTS JUST TO OUR SOUTH. HIGH CLOUDS MAY BEGIN TO INVADE FOR THE LAST HALF OF THE AFTERNOON...BUT THEY SHOULD DO LITTLE TO MAR AN OTHERWISE FAIR ALBEIT COLD MID WINTER`S DAY. HIGHS FROM THE MID TEENS TO MID 20S NORTH TO SOUTH WILL BE ABOUT 15 DEG BELOW NORMAL ON AVERAGE. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... *SIGNIFICANT WINTER WEATHER/SNOW EVENT POSSIBLE SUNDAY-MONDAY *BITTER COLD TEMPERATURES AND DANGEROUS WIND CHILLS POSSIBLE MONDAY NIGHT INTO TUESDAY MINOR CHANGES SEEN IN 18Z/21Z OPER AND ENS MODEL GUIDANCE W/RESPECT TO SFC LOW TRACK AND ANTICIPATED SNOW AMOUNTS SUNDAY INTO EARLY MONDAY /ALONG WITH THE APPROX AREA ACROSS SOUTHERN PENN WHERE SNOW SHOULD AT LEAST MIX WITH SLEET AND FZRA SUNDAY NIGHT/. PREVIOUS LATE AFTERNOON DISCUSSION FOLLOWS BELOW... A POTENTIALLY WIDESPREAD HIGH IMPACT WINTER WX EVENT APPEARS TO BE SHAPING UP ACROSS CENTRAL PENNSYLVANIA FOR SUNDAY INTO MONDAY. A WINTER STORM WATCH CONTINUES IN EFFECT FOR ALL CENTRAL PA COUNTIES AND IS VALID FROM NOON EST SUNDAY THROUGH NOON EST MONDAY. CONFIDENCE IN THE EVENT OCCURRING IS AVERAGE WITH SLIGHTLY LOWER CONFIDENCE IN THE DETAILS SUCH AS LOCATION AND SNOW ACCUM NUMBERS GIVEN THE UNCERTAINTY IN THE TRACK OF THE SYSTEM...AND POTENTIAL FOR MIXED PCPN/WARMER TEMPS IN THE SRN 1/3 OF THE AREA. A SHORTWAVE NOW ENTERING CENTRAL BRITISH COLUMBIA WILL BE DIGGING SOUTHEAST DOWN INTO THE NORTHERN/CENTRAL PLAINS LATER SAT AND INTO SUN. THIS ENERGY COUPLED WITH A MORE SUBTLE SHORTWAVE ON ITS HEELS DROPPING DOWN FROM THE NORTHWEST TERRITORIES WILL PLAY A KEY ROLE IN THE EVOLUTION OF SURFACE LOW PRESSURE THAT IS CURRENTLY FORECAST TO DEVELOP OVER THE LOWER MO AND MID MS VALLEY REGION BY EARLY SUN BEFORE THEN AIMING EAST TOWARD THE OH VALLEY AND MID- ATLANTIC STATES SUN NIGHT AND MON. AS THIS STORM DEVELOPS...MUCH COLDER AIR WILL BUILD NOT ONLY BEHIND THE SYSTEM AS A LARGE ARCTIC ANTICYCLONE HEADS SOUTHWARD INTO THE NORTHERN PLAINS...BUT COLDER AIR WILL ALSO BLEED EASTWARD AS PRESSURES RISE OVER SOUTHEASTERN CANADA AND NORTHERN NEW ENGLAND IN ASSOCIATION WITH A PRONOUNCED UPPER CONFLUENCE ZONE. THE COMBINATION OF THESE TWO SYSTEMS WILL HELP GENERATE A INCREASINGLY TIGHT BAROCLINIC ZONE UPON WHICH THE DEVELOPING SURFACE LOW WILL MOVE ALONG. THE PREVAILING SHIFT IN THE 12Z MODELS WAS TO CONTINUE A MORE NORTHERLY TRACK WITH THIS SYSTEM...WHICH IS REFLECTED IN THE WPC FORECAST WHICH WAS WEIGHTED HEAVILY IN THE FINAL GRIDDED SNOW/ICE ACCUMULATIONS. HOWEVER FORECAST CONFIDENCE IS TEMPERED BY THE RUN- TO- RUN INCONSISTENCIES THE MODELS HAVE SHOWN ALONG THE WITH DISTINCT POSSIBILITY THAT THE MODELS MAY REVERSE TRENDS IN SUBSEQUENT RUNS. WITH SEVERAL FORECAST CYCLES COMING UP ANTICIPATE SOME CHANGES REGARDING NUMBERS AND LOCATIONS OF SNOWFALL TOTALS. A SHOT OF ARCTIC AIR IS FORECAST TO SURGE INTO THE AREA BEHIND THE EARLY WEEK STORM WITH POTENTIAL FOR DANGEROUS WIND CHILLS MONDAY NIGHT INTO TUESDAY. THIS COULD ADD TO STORM-RELATED IMPACTS. HIGH PRESSURE SHOULD BRING COLD BUT QUIET WEATHER INTO MIDWEEK. MODELS AND ENSEMBLES SHOW A COASTAL TYPE SYSTEM SOMETIME NEXT WED-FRI BUT IT IS WAY TOO EARLY TO SPECULATE ON THIS SYSTEM. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... IFR AT KJST WILL CONTINUE INTO THE EARLY MORNING HOURS AS SNOW SHOWERS AND LOW CIGS PERSIST IN THE NWRLY UPSLOPE FLOW. UPSLOPE WINDS ALSO CONTINUE TO SUPPORT MVFR CIGS AT KBFD AND KAOO. VFR HAS RETURNED ELSEWHERE AND SHOULD PREVAIL INTO TOMORROW...THOUGH A STRAY REMAINING SNOW SHOWER COULD BRING SOME TEMP REDUCTIONS OVERNIGHT. GUSTY WINDS WILL CONTINUE INTO THE OVERNIGHT BUT DIMINISHING SOMEWHAT TO BETWEEN 15-20KT. OUTLOOK... SAT...VFR. SUN...WIDESPREAD IFR/MVFR DEVELOPING ASSOCIATED WITH A STORM MOVING TOWARD THE REGION. MON...REDUCED CONDS EARLY...IMPROVING AS THE STORM MOVES AWAY FROM THE AREA. TUE-WED...NO SIG WX. && .CTP WATCHES/WARNINGS/ADVISORIES...
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WINTER STORM WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY MORNING FOR PAZ004>006-010>012-017>019-024>028-033>037-041-042- 045-046-049>053-056>059-063>066. WIND CHILL ADVISORY UNTIL 11 AM EST THIS MORNING FOR PAZ004>006-010>012-017>019-024-033-037-041-042-045-046-049- 051>053-058.
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&& $$ SYNOPSIS...LAMBERT NEAR TERM...DEVOIR/LAMBERT SHORT TERM...LA CORTE LONG TERM...STEINBUGL AVIATION...LA CORTE/CERU

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