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Area Forecast Discussion
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000
FXUS61 KCTP 180934
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
434 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/...
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 /09Z 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...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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