Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211145 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 645 AM EST SUN DEC 21 2014 .SYNOPSIS... HIGH PRESSURE OVER PENNSYLVANIA WILL RETREAT INTO THE CANADIAN MARITIMES EARLY NEXT WEEK...AS WEAK LOW PRESSURE LIFTS UP THE EAST COAST. A DEEP UPPER TROUGH AND ASSOCIATED SFC LOW WILL LIFT NORTHEAST THROUGH THE GREAT LAKES DURING THE MIDDLE OF NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WATER VAPOR LOOP SHOWS SHORTWAVE EXITING NORTHEAST PA AS OF 12Z. FALLING INVERSION HGTS IN WAKE OF SHORTWAVE SHOULD CAUSE STRATOCU TO BEGIN BREAKING UP TODAY EAST OF THE APPALACHIANS. HOWEVER...NOT CONFIDENT IN CLEARING ACROSS THE W MTNS...WHERE MDL SOUNDINGS IMPLY LINGERING LOW CLOUDS. WENT CLOSE TO CONSALL GUIDANCE WITH MAXES REACHING THE LOW 30S OVER THE ALLEGHENIES TO THE UPPER 30S ACROSS THE LOWER SUSQ VALLEY. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... COMBINATION OF RETREATING HIGH PRES OVR NEW ENG AND WEAK LOW LIFTING UP THE E COAST WILL SPREAD AN INCREASINGLY MOIST SERLY FLOW INTO CENTRAL PA ON MONDAY. THE INCREASING MOISTURE...COMBINED WITH LG SCALE FORCING AHEAD OF SHORTWAVE LIFTING OUT THE OHIO VALLEY...COULD SPREAD A BIT OF LIGHT RAIN INTO SOUTHERN PA MONDAY PM. BLEND OF LATEST MDL GUIDANCE SUPPORTS CHC POPS ACROSS THE SOUTHERN COUNTIES MON AFTN. MAIN CONCERN WILL BE POTENTIAL OF SOME FZRA GIVEN COLD AIR DAMMING SIGNATURE AND IMPLIED LOW-LEVEL AGEOSTROPHIC NORTHERLY FLOW HOLDING LOW-LEVEL COLD AIR IN. OPER MDL SOUNDINGS AND ENS PTYPES SUGGEST THE BEST CHC OF LATE DAY -FZRA WOULD BE OVR THE LAUREL HIGHLANDS AND HIGHER TERRAIN OF THE SC MTNS. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... MOIST SERLY FLOW OFF THE ATLANTIC AND ASSOC OROGRAPHIC FORCING OF SHALLOW MOISTURE LYR WILL LIKELY PRODUCE PATCHY LGT RAIN/DRIZZLE MON NIGHT AND TUESDAY. SFC TEMP FIELDS OF BOTH OPER AND ENSEMBLE DATA SUGGEST THERE COULD BE SOME LINGERING ICING CONCERNS MON NIGHT OVER THE HIGHER TERRAIN OF CENTRAL PA. THE MOST SIGNIFICANT FORECAST ISSUE IN THE LONG TERM REMAINS THE EVOLUTION OF DEEP TROUGH AND ASSOC SFC LOW TO OUR WEST 23-25 DECEMBER. STRONG SOUTHERLY FLOW AHEAD OF THIS SYSTEM WILL BRING WARM AIR INTO THE REGION TUESDAY AND WEDNESDAY. BY TUESDAY AND WEDNESDAY MANY LOW-LEVEL TEMPERATURE AND MOISTURE FIELDS RISE WELL ABOVE THEIR SEASONAL VALUES. THIS IMPLIES VERY WARM WEATHER...ESP WEDNESDAY...WHEN THE SHALLOW COLD AIR SCOURS OUT EAST OF THE MOUNTAINS. TUESDAY THE STRONG CYCLONE...WITH SOME OF THE LOWEST SURFACE PRESSURES IN THE EASTERN US ON 24 DECEMBER IN THE PAST 30 YEARS WILL MOVE INTO THE GREAT LAKES. PRESSURE ANOMALIES ARE -3 TO -4 SIGMA BELOW NORMAL WITH A RETURN PERIOD ON THE ORDER OF 30 YEARS IN SOME FORECAST SYSTEMS. THE FRONT ASSOCIATED WITH THE CYCLONE PUSHES INTO OUR REGION WEDNESDAY...AT THIS TIME THE 850 MB SOUTHERLY WINDS ARE FORECAST TO BE ABOUT +3 SIGMA ABOVE NORMAL. THE STRONG SOUTHERLY FLOW...THE HIGH PRECIPITABLE WATER...THE STRONG FRONT ALL IMPLY A FRONTAL RAIN EVENT AND PERHAPS SOME RARE LATE DECEMBER (ELEVATED) CONVECTION. IF THIS WERE AUTUMN OR SPRING WE MIGHT BE THINKING QLCS. BUT SURFACE CAPE IS VIRTUALLY NON-EXISTENT BUT SHOWERY RAIN AND PERHAPS ISOLATED THUNDER POSSIBLE. DO NOT LIKE HAVING POPS ABOVE 60 TO 66 PERCENT AT DAY 4...BUT GIVEN DIMINISHING SPREAD AMONGST MDL MEMBERS AND INCREASING CONFIDENCE IN FRONTAL TIMING...WILL MAINTAIN CATEGORICAL POPS WEDNESDAY/WED EVENING. THE PATTERN...SHARP NORTH-SOUTH FRONT TO OUR WEST...IMPLIES MOST OF THE RAIN SHOULD FALL WITHIN 3-6 HOURS OF THE FRONT. THE COLD FRONT WILL LIKELY PUSH THRU THE REGION WED NIGHT...ACCOMPANIED BY GUSTY WINDS AND LIKELY FOLLOWED BY OROGRAPHIC SNOW SHOWERS ACROSS THE W MTNS CHRISTMAS MORNING. CHRISTMAS EVE AND EARLY CHRISTMAS IS THE AREA OF HIGH UNCERTAINTY AS TO WHEN THE COLD AIR COMES IN. THIS WILL DICTATE WHEN THE RAIN COMES AND WHEN THE GUSTY WINDS SET IN. GRADIENTS ARE WHERE FORECASTS ARE THEIR POOREST. BUT BY CHRISTMAS MORNING MOST IF NOT ALL OF THE REGION SHOULD BE BELOW 0C AT 850 AND THE STRONG WESTERLY WINDS SHOULD BE MIXING DOWN BEHIND THE FRONTAL BOUNDARY. WINDY OVERNIGHT CHRISTMAS EVE INTO CHRISTMAS DAY. ANY RESIDUAL PRECIPITATION SHOULD BE SNOW/SNOW SHOWERS AND FLURRIES. TEMPERATURES SHOULD REBOUND FRIDAY AHEAD OF ANOTHER NORTHERN STREAM WAVE MOVING INTO THE MID-WEST. THIS SHOULD RAISE OUR HEIGHTS AND TEMPERATURES FRIDAY INTO EARLY SATURDAY. IT APPEARS A SERIES OF WAVES MAY EVENTUALLY CARVE OUT A TROUGH OVER THE EAST-CENTRAL US. IF SO...WE COULD END DECEMBER A BIT ON THE CHILLY SIDE. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... A WEAK AND SHALLOW STRATOCU DECK REMAINS TRAPPED BENEATH SUBSIDENCE. THE CIG RESTRICTIONS WILL SPREAD AND INCREASE DUE TO THE STRENGTHENING OF THE INVERSION OVERNIGHT...THOUGH LOW CLOUDS SHOULD NOT BE QUITE AS EXPANSIVE AS PREVIOUS NIGHTS. A SHORTWAVE WILL TRACK ACROSS THE REGION BRINGING A THICKENING MID- LVL DECK AS WELL. THAT MID DECK WILL DECREASE THE PROBABILITY FOR A THICKER LOW DECK. THE SURFACE WINDS WILL CONTINUE TO BE LIGHT...WITH SW FLOW ALOFT BEGINNING TO INCREASE AS A LARGE LOW PRESSURE SYSTEM BEGINS TO DEEPEN OVER THE CENTRAL U.S. EXPECT MVFR CIGS AT THE CENTRAL SITES AOO...JST AND UNV. IFR REMAINS POSSIBLE AT JST BETWEEN 09 TO 13Z...AND BFD SHOULD BE IFR THROUGH MOST OF THE PERIOD. MAINLY VFR THROUGH THE EASTERN TAF SITES. BFD SHOULD LIFT TO MVFR BY LATE TOMORROW MORNING...THOUGH MVFR SHOULD REMAIN POSSIBLE AT BFD THROUGH TOMORROW...AND IFR RETURNING AT BFD TOMORROW EVENING. OUTLOOK... SUN...NO SIG WX EXPECTED. MON...LOW CIGS WITH LGT RAIN/SNOW POSSIBLE. BECOMING BREEZY. TUE...LOW CIGS WITH RAIN LIKELY. BREEZY. WED...MILD WITH PERIODS OF RAIN OF VARYING INTENSITY...LEADING TO MVFR TO IFR. ALSO...WINDY WITH LLWS. THU...WINDY AND COLDER WITH SCT MVFR CIGS AND -SHSN. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...FITZGERALD NEAR TERM...FITZGERALD SHORT TERM...FITZGERALD LONG TERM...GRUMM/FITZGERALD AVIATION...RXR

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