Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211917 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 317 PM EDT SUN SEP 21 2014 .SYNOPSIS... A COLD FRONT WILL PUSH EAST ACROSS THE STATE LATE THIS AFTERNOON AND THIS EVENING...ACCOMPANIED BY SHOWERS AND ISOLATED THUNDERSTORMS. A POTENT UPPER AIR DISTURBANCE AND UNSEASONABLY COLD AIR ALOFT WILL DROP SOUTHEAST FROM LAKE ERIE THIS EVENING BRINGING NUMEROUS SHOWERS...MAINLY TO THE NORTHWEST MOUNTAINS OVERNIGHT. A LARGE AREA OF HIGH PRESSURE WILL BUILD OUT OF CENTRAL CANADA AND PROVIDE GENERALLY FAIR AND COOL WEATHER FOR MOST IF NOT ALL OF THIS WEEK. && .NEAR TERM /UNTIL 10 PM THIS EVENING/... A FEW AREAS OF SHOWERS WILL ACCOMPANY A PREFRONTAL TROUGH AND COLD FRONTAL PASSAGE ACROSS THE CWA LATE THIS AFTERNOON AND THIS EVENING. BEST LARGE SCALE FORCING /ASSOCIATED WITH THE RIGHT ENTRANCE REGION OF A SWRLY 100 KT 300 MB JET/ WILL BE ACROSS CENTRAL AND NRN PENN THROUGH 22Z. THAT/S WHERE THE GREATEST CONCENTRATION OF SHOWERS WILL OCCUR WITH BASIN AVG QPF OF 2-3 TENTHS OF AN INCH LIKELY. ALTHOUGH LESS RAINFALL IS EXPECTED ON AVERAGE ACROSS SOUTHERN PENN /INCLUDING THE LOWER SUSQ VALLEY/ A FEW GUSTY... LOW-TOPPED TSRA ARE POSSIBLE IN ANY LOCATION AS POCKETS SUNSHINE...TEMPS IN THE 70S TO LOWER 80S SE...AND DEWPOINTS IN THE L-M 60S WILL CREATE SFC BASED CAPES OF 1000-1500 J/KG AND PINPOINT RAINFALL AMOUNT AOA 0.25 INCH. IN THE WAKE OF THE CFROPA...A DRY SLOT LASTING 2-4 HOURS ACROSS THE NW MTNS /AND LONGER ELSEWHERE/ PUSHES IN LATE THIS AFTERNOON/EARLY EVENING. THIS WILL BE FOLLOWED BY A POTENT UPPER VORT MAX AND THE LEADING EDGE OF QUITE COLD 850 MB AIR /DROPPING TO SLIGHTLY BELOW ZERO ACROSS THE NORTH ON MONDAY/. MORE ON THE IMPACT OF THIS COLDER AIR ALOFT IN THE SHORT TERM SECTION BELOW. && .SHORT TERM /10 PM THIS EVENING THROUGH 6 AM MONDAY/... WHILE SKIES GO SCATTERED-BKN LATER THIS EVENING WITH A FEW SPRINKLES POSSIBLE EAST OF THE ALLEGHENIES...NUMEROUS UPSLOPE AND LAKE EFFECT RAIN SHOWERS WILL IMPACT THE NW MTNS AND LAUREL HIGHLANDS BEGINNING LATER THIS EVENING. DELTA-T DIFF BETWEEN THE LAKE TEMPS OF AROUND 20C AND THE MUCH COLDER AIR ALOFT WILL BE AROUND 20C /AND WELL-BEYOND THE THRESHOLD FOR LAKE EFFECT PRECIP/. A GUSTY WEST-NORTHWEST GRADIENT WIND WILL FOLLOW THE FRONT THIS EVENING. WIND GUSTS OF 25-30 MPH ARE LIKELY ACROSS THE WEST TONIGHT. WINDS SHOULD BE A TAD LIGHTER FOR MUCH OF THE NIGHT ACROSS THE EASTERN HALF OF THE CWA AS BOUNDARY LAYER DECOUPLES WITHIN THE CLEAR SLOT PRIOR TO THE DEEP COLD AIR ADVECTION. LOW TEMPS TONIGHT WILL VARY FORM THE MID TO UPPER 40S ACROSS THE NORTHERN AND WRN MTNS...TO THE LOWER AND MID 50S IN THE CENTRAL AND SOUTHERN PORTIONS OF THE STATE. && .LONG TERM /MONDAY THROUGH SUNDAY/... TYPICAL POST-FRONTAL SET-UP WILL BE WITH US DURING THE DAY MONDAY AND THE RESIDUAL AND LAKE MOISTURE ASCENDING THE MTNS AND COLD AIR MOVING IN ALOFT WILL GENERATE INSTABILITY AND SCT SHRA FOR THE NWRN THIRD OF THE AREA THROUGH THE MORNING HOURS MONDAY. 8H TEMPS DO DIP INTO THE LOWER SINGLE DIGITS MONDAY AND MAXES MAY BE LIMITED TO THE M50S IN THE MTNS BUT STILL GET CLOSE TO 70F IN THE DOWNSLOPE- WARMED SOUTHEASTERN PIEDMONT. HIGH PRESSURE BUILDS IN AS THE LONG TERM IS BEGINNING AND IT SORT OF PARKS ITSELF OVER NEW YORK AND NEW ENGLAND WITH +2 TO +3 SIGMA ABOVE NORMAL MSLP ANOMALIES BY WEDNESDAY-THURSDAY. THE MODELS SEEM TO BE IN FAIR AGREEMENT SHOWING A BLOCKING 500 HPA ANTICYCLONE TO THE NORTHWEST AS A MASSIVE 500 HPA POSITIVE HEIGHT ANOMALY OF +2 TO +3 SIGMA DEVELOPS OVER CENTRAL CANADA BY THURSDAY AND INTO FRIDAY. THE MODELS AND EFS DO WELL FORECASTING ANTICYCLONES SO THERE SEEMS TO BE MORE OF A CONSENSUS. ON THE FAIR WEATHER FORECAST NEXT WEEK. EXPECT DIURNAL VALLEY FOG AND LOW CLOUDS LIKELY TO AFFECT THE REGION EACH MORNING ONCE THE BIG HIGH TAKES HOLD....AND CONTINUING DAILY INTO NEXT WEEKEND. THAT MASSIVE HIGH SHOULD CONTINUE THE DRY FAIR WEATHER THROUGH NEXT WEEKEND. TEMPERATURES ON MONDAY AND MONDAY EVENING WILL BE BELOW NORMAL...HOWEVER OUTSIDE OF MONDAY...TEMPERATURES THERE WILL BE A PERIOD OF NEAR NORMAL TEMPERATURES. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... LOCALIZED MVFR AND VSBYS WILL ACCOMPANY FAST-MOVING SHOWERS AND PERHAPS A FEW BRIEF TSRA ALONG AND AHEAD OF A COLD FRONT LATE THIS AFTERNOON AND EARLY THIS EVENING. OTHERWISE...CONDITIONS WILL BE MAINLY VFR THROUGH 00Z. A POTENT UPPER LEVEL DISTURBANCE AND ASSOCIATED POOL OF UNSEASONABLY COLD AIR ALOFT WILL PUSH SOUTHEAST ACROSS THE REGION OVERNIGHT. NUMEROUS...LAKE EFFECT AND UPSLOPE SHOWERS WILL IMPACT THE NORTHERN AND WRN MTNS OF PENN WITH IFR CIGS /AND PERIODS OF MVFR VSBYS/ IN THE 00Z-15Z MONDAY PERIOD OCCURRING FROM KBFD...TO KFIG AND KJST. ELSEWHERE ACROSS THE CENTRAL RIDGE AND VALLEY REGION OF THE STATE... PERIODS OF BKN STRATO CU WILL BE IN THE LOW- END VFR TO UPPER END MVFR CATEGORY. VFR CONDITIONS SHOULD PREVAIL INTO MID/LATE WEEK WITH THE EXCEPTION OF SOME PATCHY MORNING FOG. OUTLOOK... MON...AM LOW CIGS WITH SCATTERED SHOWERS POSSIBLE ACROSS THE NRN AND WRN MTNS. TUE...AM FOG POSS W MTNS. WED...AM FOG POSS...MAINLY NORTHERN PA. THU AND FRI...PATCHY AM FOG POSSIBLE. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...GRUMM/CERU AVIATION...LAMBERT

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