Area Forecast Discussion
Issued by NWS State College, PA

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319 FXUS61 KCTP 090533 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1233 AM EST TUE FEB 9 2016 .SYNOPSIS... A LONG-DURATION PERIOD OF SNOW WILL LIKELY RESULT IN A WIDESPREAD LIGHT TO MODERATE ACCUMULATION FOR MUCH OF CENTRAL PA TONIGHT INTO EARLY WEDNESDAY. LAKE EFFECT AND UPSLOPE SNOW SHOWERS WILL FOLLOW FROM MID WEEK INTO THE FIRST PART OF THE WEEKEND...WITH ADDITIONAL ACCUMULATION LIKELY IN THE FAVORED NORTHWEST SNOWBELT AND HIGHER TERRAIN ALONG THE ALLEGHENIES AND LAURELS. THE COLDEST AIRMASS OF THE WINTER IS POISED TO BRING FRIGID TEMPERATURES AND DANGEROUS WIND CHILLS FOR VALENTINES WEEKEND. && .NEAR TERM /UNTIL 8 AM THIS MORNING/...
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1230 AM UPDATE... JUST A COATING SO FAR...BUT IT IS JUST THE BEGINNING. BOTH MDT AND IPT CAME IN WITH 0.2IN OF SF AT MIDNIGHT. WEBCAMS PLAY UP A BIT MORE SNOW OVER THE LAURELS...BUT MOST PLACES DRY OR JUST WET ROADS AT THIS POINT. IT JUST SKIPPED RIGHT OVER HAPPY VALLEY. HRRR AND RUC INDICATE THAT A WEAK TROUGH FORMS TO THE E OF UNV AND AOO AND FOCUS THE LIGHT SNOW ALONG THE MID-LOWER SUSQ THROUGH THE REST OF THE NIGHT. SLUG OF PRECIP MOVING UP FROM CENTRAL MD...SHOULD RISE INTO THE SRN TIER/FAR LOWER SUSQ IN THE NEXT COUPLE OF HRS. STILL...SF RATES WILL LIKELY NOT GET TO INCH/HR RATES OVERNIGHT. PREV... 03Z RADAR LOOP SHOWS SPOTTY LIGHT SNOW HAS OVERSPREAD NEARLY ALL OF CENTRAL PA AHEAD OF SHORTWAVE LIFTING NE FROM THE OHIO VALLEY. LACK OF SIG MOISTURE OVER THE REGION /SATL DERIVED PWATS ONLY NR SEASONAL AVG/ AND EXPECTATION THAT WEAKENING SHORTWAVE WILL PASS NE OF THE AREA AFTER 06Z...BOTH POINT TOWARD ONLY LIGHT PRECIP OVERNIGHT. IN ADDITION...MARGINAL BLYR TEMPS MAY RESULT IN AN INITIAL PERIOD OF LGT RAIN OVR THE LOWER ELEVS OF SOUTHERN PA AND COULD LIMIT SNOW ACCUMS THEREAFTER. WEB CAMS ACROSS THE SUSQ VALLEY INDICATING ONLY WET ROADS AT 03Z. FOR NOW WILL MAINTAIN THE IDEA OF AN INCH OR SO OF SNOW ACCUM ACROSS MUCH OF CENTRAL PA BY DAWN. HOWEVER...GIVEN LIGHT SNOW RATES AND TEMPS AOA FREEZING...DON/T ANTICIPATE BIG TRAVEL PROBLEMS FOR THE AM COMMUTE. BLEND OF LATEST GUIDANCE POINTS TOWARD OVERNIGHT MIN TEMPS IN THE U20S- L30S.
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&& .SHORT TERM /8 AM THIS MORNING THROUGH WEDNESDAY NIGHT/... AFTER DISCUSSION WITH PHI AND LWX...ALONG WITH NEW WPC GRAPHICS...HAVE ISSUED WINTER WX ADVISORY FOR MUCH OF SOUTHERN PA AND A WARNING FOR THE ADAMS/YORK/LANCASTER...WHERE WPC GUIDANCE SUPPORTS TOTALS TO ARND 6 INCHES BY TUES NIGHT. AFTER A LULL IN THE LGT SNOW EARLY TUE AM...SECOND SHORTWAVE ROUNDING THE BASE OF UPPER LOW OVR THE GRT LKS WILL APPROACH BY MIDDAY TUESDAY...PRODUCING A STEADIER LIGHT SNOW ALONG NEG TILTED INVERTED SFC TROUGH AXIS AND ASSOC PLUME OF HIGHER PWATS OVR CENTRAL PA. BEST LG SCALE FORCING...AS INFERRED BY MDL 500-300MB QVEC CONV FIELDS...WILL BE FOCUSED ACROSS SOUTHERN PA...WHERE MDL BLENDED QPF SUPPORTS SEVERAL INCHES OF ADDITIONAL ACCUM BTWN MIDDAY TUES AND LATE TUES EVENING. MARGINAL BLYR TEMPS MAY CONTINUE TO HINDER SNOW ACCUMS IN THE VALLEYS...AS NCAR MESO ENSEMBLE AND SPC SSEO BOTH SUGGEST. SO...CONFIDENCE IN WARNING TYPE SNOW IN THE POPULATION CENTERS OF SE PA IS NOT NEARLY AS HIGH AS FOR THE RIDGETOP LOCATIONS. OTHER FACTOR TO CONSIDER IS THAT LIGHT SNOW FALLING WITH SFC TEMPS AOA FREEZING DURING THE DAYLIGHT HRS WILL LIKELY RESULT IN A GOOD DEAL OF MELTING ON ROAD SURFACES AND COULD POTENTIALLY MAKE THIS A RELATIVELY LOW IMPACT ADVISORY/WARNING. EXPECT A TRANSITION TOWARD A LAKE EFFECT/UPSLOPE SNOW PATTERN LATE TUES NIGHT INTO WEDNESDAY NIGHT...AS INVERTED SFC TROUGH LIFTS NE AND BLYR FLOW TURNS TO THE WEST. && .LONG TERM /THURSDAY THROUGH MONDAY/... *IMPACT WEATHER HIGHLIGHTS INCLUDE ADDITIONAL LAKE EFFECT AND UPSLOPE SNOW ACCUMULATIONS THURSDAY-SATURDAY...FOLLOWED BY FRIGID TEMPERATURES AND DANGEROUSLY COLD WIND CHILLS FOR VALENTINES WEEKEND. ANOMALOUS WESTERN RIDGE/EASTERN TROUGH PATTERN WILL REMAIN IN PLACE THROUGH THE WEEKEND. THE GLOBAL ENSEMBLE MEANS GENERALLY KEEP THIS PATTERN CONFIGURATION INTACT INTO NEXT WEEK BUT AT A DECREASING AMPLITUDE. AS THE BROAD UPPER LEVEL CIRCULATION DEPARTS OVER THE NORTHEAST TOWARD THE END OF THE WEEK...IT WILL BE REPLACED BY A POLAR VORTEX DROPPING SOUTH ACROSS HUDSON BAY INTO SE CANADA. COLD AIR WILL BEGIN SPILLING SOUTHWARD LATER IN THE WEEK...REINFORCED INITIALLY BY A SECONDARY FRONT ON THURSDAY. CONFIDENCE CONTINUES TO INCREASE IN A SIGNIFICANT ARCTIC AIR INTRUSION/COLD OUTBREAK FOR VALENTINE`S WEEKEND. LAKE EFFECT/UPSLOPE SNOWS FOR SEVERAL DAYS THU-SAT WILL BRING ADDITIONAL LGT-MDT ACCUMULATION OVER THE FAVORED NORTHWEST SNOWBELT DOWNWIND OF LAKE ERIE AND IN THE HIGHER TERRAIN OF THE ALLEGHENIES/LAURELS. A NEW ELEMENT IN THE FCST IS DEVELOPING LOW PRESSURE OFF THE MID-ATLANTIC/NORTHEAST COAST BY EARLY SATURDAY. AT THIS TIME THE 08/00Z ECMWF LIES ON THE WESTERN EDGE OF THE GUIDANCE ENVELOPE. CONFIDENCE IS HIGH IN THE FCST COLD PATTERN/WELL-BELOW NORMAL TEMPERATURES THROUGH THE PERIOD. THE COLDEST AIRMASS OF THE WINTER APPEARS POISED TO ARRIVE THIS WEEKEND WITH GFS/EC BOTH BRINGING -30C AIR AT 850MB INTO PA. MAX/MIN TEMPERATURE DEPARTURES OF -20 TO -25 DEGREES BELOW CLIMO ARE PROBABLE SATURDAY AND SUNDAY. WIDESPREAD SINGLE DIGIT TEMPERATURES +/- ZERO ARE FCST SATURDAY NIGHT INTO EARLY SUNDAY. A STRONG GRADIENT BETWEEN LOW PRESSURE OFF THE NEW ENGLAND COAST AND 1040+MB ARCTIC HIGH DROPPING INTO THE UPPER MS VALLEY WILL PRODUCE GUSTY WINDS AND DANGEROUSLY COLD WIND CHILLS -10F TO -25F DEGREES BELOW ZERO. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... FIRST OF THE SNOW SHOWERS NOW WORKING INTO THE WESTERN MOUNTAINS. WHILE OVERALL FORECAST CALLS FOR DETERIORATING CONDITIONS THIS EVENING FROM WEST TO EAST...THE TIMING OF THE ONSET OF THE STEADY SNOW IS THE CHALLENGING ASPECT OF THIS FORECAST. EXPECT CONDITIONS TO VARY FOR SEVERAL HOURS AT THE ONSET OF THE PRECIPITATION...LIKELY SWITCHING FROM VFR TO MVFR AND THEN BACK AGAIN TO IFR. THIS THINKING IS DIFFICULT TO TRANSLATE INTO THE TAFS. HAVE DECIDED TO GO WITH PREVAILING AREAS OF STEADY SNOW...WITH LOWERING CONDITIONS...BUT REALIZING THE POTENTIAL FOR HIGH VARIABILITY FOR A GOOD PORTION OF THE EVENING. IFR CONDITIONS SHOULD DEVELOP OVERNIGHT...AND LAST THROUGH MUCH OF THE TAF PERIOD IN WIDESPREAD SNOW. SOME AREAS OF LIFR MAY DEVELOP IN BANDING OF HEAVIER SNOW...BUT DIFFICULT TO PUT IN AN EXACT LOCATION AT THIS TIME. THE COMPLEX WEATHER PATTERN WILL RESULT IN WIDESPREAD... BUT MAINLY LIGHT TO OCCASIONALLY MODERATE SNOW OVERNIGHT TONIGHT INTO TUESDAY NIGHT. WHILE THERE MAY BE BREAKS FROM TIME TO TIME...EXPECT FAIRLY WIDESPREAD SNOW/SNOW SHOWERS AND ASSOCIATED RESTRICTIONS OVER MUCH OF THE REGION THROUGH THAT PERIOD. LOOKING AHEAD...SNOW SHOWERS BECOME MORE CONFINED TO WESTERN HIGHER TERRAIN MID/LATE WEEK AS SHOT OF QUITE COLD AIR ARRIVES ON NW FLOW. OUTLOOK... TONIGHT INTO TUE NIGHT...PERIODS OF LIGHT SNOW. IFR CONDITIONS DEVELOPING. LOCALIZED LIFR POSSIBLE. WED...MAINLY IFR IN SNOW WRN AIRSPACE. MVFR-VFR CIGS CENTRAL/EAST. THU-SAT...MVFR IN -SHSN W MTNS. VFR ELSEWHERE. && .CTP WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 7 PM EST WEDNESDAY FOR PAZ024- 033. WINTER WEATHER ADVISORY UNTIL 5 AM EST WEDNESDAY FOR PAZ025>028-034>036-056-057-059-063. WINTER STORM WARNING UNTIL 5 AM EST WEDNESDAY FOR PAZ064>066. && $$ SYNOPSIS...STEINBUGL NEAR TERM...DANGELO/FITZGERALD SHORT TERM...FITZGERALD/GARTNER LONG TERM...STEINBUGL AVIATION...JUNG/GARTNER

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