Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 181218 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 718 AM EST THU DEC 18 2014 .SYNOPSIS... NORTHWEST WINDS WILL KEEP SCATTERED SNOW SHOWERS GOING OVER THE NORTH AND WEST INTO FRIDAY MORNING. HIGH PRESSURE WILL SLIDE DOWN FROM THE UPPER GREAT LAKES AND PROVIDE A GENERALLY FAIR PERIOD FOR MOST OF THE WEEKEND. A HIGHLY COMPLEX PATTERN WILL SET UP IN THE FIRST PART OF THE NEW WEEK. A WEAK LOW PRESSURE AREA COULD BRING LIGHT RAIN OR SNOW TO THE AREA ON MONDAY. THEN A SIGNIFICANT AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE MIDWEST AND UPPER GREAT LAKES. THIS WILL LIKELY PRODUCE WIDEPSREAD RAIN FOR THE STATE ON WEDNESDAY...FOLLOWED BY STRONG WEST WINDS AND SCATTERED MOUNTAIN SNOW SHOWERS FOR CHRISTMAS DAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 630 AM UPDATE... RADAR RETURNS CONTINUE TO DIMINISH AND THE SLIGHTLY COLDER CLOUD TOPS ARE SLIDING TO THE EAST. ALL THIS IS HANDLED NICELY...BUT THE POPS MAY BE INITIALLY TOO HIGH IN THE NW WHERE NO PRECIP IS ON THE SCOPE OR IN ANY OBS. PREV... SNOW SHOWERS DIMINISHING AT THIS HOUR AS THE MAIN SHORT WAVE TROUGH IS OVERHEAD AND PUSHING QUICKLY TO THE EAST. A CONTINUED WNW FLOW AND NEUTRAL TEMPERATURE ADVECTION MEAN LITTLE CHANGE IS IN STORE FOR TODAY. SCT POPS ARE ON ORDER FOR THE WRN HIGHLANDS...BUT ONLY FLURRIES ELSEWHERE. WINDS WILL BE RELAXING BY ONLY A FEW MPH THROUGH THE DAY. MAXES CLOSE TO GUID BLEND IS CONSISTENT WITH PREV FCSTS AND FOLLOWED HEREIN. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... THE AXIS/CENTER OF HIGH PRESSURE AREA TO OUR NORTHWEST WILL MOVE LITTLE TONIGHT AND JUST A BIT MORE ON FRIDAY. SCT TO NMRS SHSN ARE EXPECTED...BUT ACCUMS WILL BE VERY MINOR AND MAINLY HELD TO THE WRN HIGHLANDS. THERE IS A WAVE ROLLING FROM W-E ACROSS THE SRN APPALACHIANS TONIGHT...AND DESPITE A DISCONNECT WITH THE MAIN TROUGH...IT WILL LIKELY ADD ENOUGH FORCING TO MAKE AN INCH OR TWO OF SNOW ACCUMULATION IN THE LAURELS OVERNIGHT. THIS FORCING ZIPS QUICKLY TO THE EAST ON FRIDAY MORNING. THE SUBSIDENCE INVERSION ASSOCIATED WITH THE GIANT HIGH PRESSURE AREA OVER THE UPPER GREAT LAKES FINALLY BEGINS TO SETTLE OVER THE LOCAL AREA. THUS...THE AMOUNT/COVERAGE OF THE SNOW SHOWERS AND FLURRIES SHOULD DIMINISH COMPLETELY ON FRIDAY. MINS WILL STAY A LITTLE MILDER THAN CLIMO WITH CLOUDS AROUND. MAXES ON FRIDAY VERY SIMILAR TO TODAY...WITH 30S FOR THE MOUNTAINS AND NEAR 40 IN THE LOW LANDS WITH THE HELP OF SOME DOWNSLOPE WARMING. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... THE FLOW REMAINS RATHER FLAT OVER THE SERN U.S. AND MID ATLANTIC STATES THIS WEEKEND. SO THE WEAK LOW WHICH HAS BEEN PROJECTED TO PASS JUST TO THE SOUTH OF THE AREA THIS WEEKEND SHOULD DO SO...AND EVEN WELL SOUTH OF THE AREA AT THAT. ALL MED RANGE GUIDANCE KEEPS THE SFC LOW ALONG A PATH FROM KATL TO KCHS. THEREFORE...WILL REMOVE ANY REMAINING POPS IN THE SAT-SUN TIME FRAME. TEMPS WILL STAY VERY SIMILAR TO WHAT WE SEE IN THE NEAR TERM...GENERALLY COOLER THAN NORMAL DURING THE DAYS. FRIDAY NIGHT SHOULD BE THE COLDEST NIGHT UNTIL AFTER CHRISTMAS WITH MINS IN THE TEENS WEST AND 20S ELSEWHERE. THE PATTERN TURNS VERY COMPLICATED/CONVOLUTED FOR THE FIRST PART OF THE WEEK. A BIG TROUGH STARTS TO DEVELOP OVER THE UPPER PLAINS/MIDWEST AND THE RESULTING HEAVE TO THE HEIGHTS OFF THE EASTERN SEABOARD WILL ALLOW ANOTHER AREA OF LOW PRESSURE TO ROLL TO THE NORTHEAST FROM THE GULF COAST ON MONDAY. THE LOW WILL STILL STAY DECENTLY FAR AWAY FROM THE LOCAL AREA. BUT THE ATLANTIC MOISTURE WILL PROBABLY AT LEAST BRUSH THE SOUTHEASTERN HALF OF THE AREA. TIMING DIFFERENCES BETWEEN THE GFS AND EC ARE ABOUT 12 HRS - WITH THE EC FASTER IN MOVING THE WAVE TO THE EAST. PRECIP TYPE AT THIS POINT LOOKS LIKE IT COULD BE LIGHT SNOW...IF IT FALLS DURING THE NIGHT. BUT A DAYLIGHT EVENT WOULD BE MORE OF A MIX OR SNOW ON THE NORTHERN END OF THE PRECIP SHIELD AND RAIN INTO THE LOWER SUSQ. POPS AT THIS POINT ARE NOT WORTH MUCH MORE THAN CHCS...DUE TO TIMING DIFFERENCES AND THE FACT THAT THE WEEKEND SYSTEM IS NOW PROGGED TO GO WELL OFF TO OUR SOUTH. THIS SYSTEM MAY END UP ROWING DOWN THE SAME STREAM...AND HAVE HEDGED FORECASTS OF THE PRECIP SHIELD TO THE SE A BIT. EASTERLY WINDS MAY PILE THE LLVL MARITIME AIR UP INTO THE CENTRAL PA MTNS FOR TUESDAY AND A DARK DAY WITH LIGHT SHOWERS OR DRIZZLE IS POSSIBLE. THE TEMPS START WARMING UP SIGNIFICANTLY ALOFT....THOUGH. THE BIG STORY IS THE EXPECTED DEVELOPMENT OF A VERY SIGNIFICANT LOW PRESSURE AREA DURING THE MID WEEK OVER THE MID MS VALLEY AND UPPER GREAT LAKES ON TUES/WED. SOME MDLS HAD PLACED A 960HPA LOW OVER LAKE HURON ON WEDNESDAY. BUT THE MOST RECENT RUNS OF THE GFS AND ECMWF PLACE A 990HPA LOW UNDER THE MAIN UPPER LOW OVER THE UPPER GREAT LAKES...AND A RAPIDLY DEEPENING BUT INITIALLY EQUAL- STRENGTH SFC LOW RUNNING UP THE PIEDMONT EAST OF THE APPALACHIANS ON WED MORNING. THIS SECOND LOW WILL THROW COPIOUS MOISTURE BACK INTO THE STATE AS IT WHIPS NORTHEAST ON CHRISTMAS EVE. THE TEMPS LOOK LIKE THEY WILL BE WARM ENOUGH FOR MAINLY RAIN OVER THE ENTIRE AREA...BUT IF THE TRACK IS SLIGHTLY MORE TO THE EAST - THE TEMPS WILL BE JUST A HAIR COLDER AND THE MOUNTAINS MAY HAVE SNOW ACCUMULATIONS. AFTER THE SECONDARY LOW ZIPS AWAY...THE CYCLONIC FLOW AROUND THE CLOSED UPPER LOW AND STRONG COLD ADVECTION WILL CERTAINLY MAKE WIDESPREAD SNOW SHOWERS OVER THE WRN MOUNTAINS...AND VERY GUSTY WINDS. TIMING DIFFERENCES WITH THE MAIN SLUG OF PRECIP ARE MINOR FOR THIS RANGE. HPC GUID OF LIKELY POPS SEEMS VERY PLAUSIBLE...AND WILL HOLD IT TO A 70 POP AT THIS POINT FOR WED DURING THE DAY. QPF IN THE GEFS PLUMES IS ON A GIANT SPREAD AT THIS POINT...BUT THE MEAN NUMBERS ARE AROUND AN INCH AND THE MEDIANS SLIGHTLY HIGHER. WILL MENTION THE STORM AND THE MOST LIKELY OUTCOMES IN THE HWO AT THIS POINT...DUE TO THE FACT THAT THE TIMING LOOKS TO BE ON ONE OF THE BUSIEST TRAVEL DAYS - DIDN/T WE JUST DO THIS A MONTH AGO - AND A SMALL CHANGE TO THE EAST IN TRACK OF THE SECONDARY LOW COULD MEAN SNOW - AT LEAST FOR THE ALLEGHENIES. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... LOW LVL MOISTURE TRAPPED BENEATH INVERSION WILL KEEP STRATO CU IN PLACE ACROSS MOST OF CENTRAL PA TODAY. LATEST MDL SOUNDINGS POINT TOWARD PREDOMINANTLY MVFR CIGS/VSBYS AT KBFD. HOWEVER...A FEW BRIEF DIPS IN VSBY TO BTWN 1-2SM ARE QUITE POSSIBLE FROM PASSING LAKE EFFECT SNOW SHOWERS. ELSEWHERE...MDL SOUNDINGS SUPPORT CIGS ARND 1500FT AT KJST TODAY...WHILE DRYING/DOWNSLOPING FLOW YIELDS PROGRESSIVELY HIGHER CIGS FURTHER EAST. A TROUGH OF LOW PRESSURE WILL PUSH THRU THE REGION TONIGHT...PERHAPS PRODUCING A PERIOD OF STEADIER LGT SNOW AT KBFD BTWN 00Z-06Z FRIDAY WITH VSBYS IN THE 1-2SM RANGE. OUTLOOK... FRI...EARLY AM -SHSN/REDUCED VSBYS POSS AT KJST. SAT-SUN...NO SIG WX EXPECTED. MON...LOW CIGS WITH LGT RAIN/SNOW POSSIBLE. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DANGELO NEAR TERM...DANGELO SHORT TERM...DANGELO LONG TERM...DANGELO AVIATION...FITZGERALD

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