Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 230937 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 537 AM EDT WED JUL 23 2014 .SYNOPSIS... A COLD FRONT WILL PUSH SOUTHEAST ACROSS THE COMMONWEALTH LATE TODAY AND TONIGHT. A REFRESHING...COOLER AND LESS HUMID AIRMASS WILL OVERSPREAD THE COMMONWEALTH FOR THE END OF THE WEEK INTO THE WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WEAK RIDGING OVER THE REGION AT THE SURFACE AND ALOFT...COMBINED WITH VERY WARM MID LEVEL TEMPS OF 9-11C WILL KEEP CONDITIONS MAINLY CLEAR BUT MUGGY INTO THE LATE MORNING HOURS. CURRENT DEWPOINTS IN THE MID TO UPPER 60S ARE A FEW DEG SHY OF THE EXPECTED MIN TEMPS AROUND SUNRISE. CIRRUS BLOWOFF FROM A WEAKENING LINE OF SHOWERS AND THUNDERSTORMS OVER LAKE ERIE WILL OVERSPREAD THE NW MTNS THIS MORNING...BUT THEN DISSIPATE FOR THE MIDDAY HOURS BEFORE NEW CONVECTION INITIATES ALONG/AHEAD OF AN APPROACHING COLD FRONT. THE BKN LINE OF SHRA/TSRA SLIDING SE ACROSS CENTRAL LAKE ERIE ATTM IS OVER LOCALLY COOLER AND MORE STABLE LLVLS...AND IS PROGGED BY THE LAST FEW RUNS OF THE HRRR TO STEADILY WEAKEN...AND EVEN DISSIPATE AS IT MOVES ONTO THE SOUTH SHORE DURING THE NEXT FEW HOURS AND ENCOUNTERS THE VERY STRONG MID-LEVEL CAP ACROSS NWRN PENN. 15-MINUTE LIGHTNING FREQUENCY HAS DROPPED OFF DRAMATICALLY OVER THE PAST HOUR. STILL PAINTED CHC POPS FOR SHOWERS OR A RUMBLE OF THUNDER ACROSS NW WARREN COUNTY AROUND 12Z SINCE EARLIER RUNS OF THE HRRR HAD NO SIGN OF CONVECTION EVEN REACHING THE CENTRAL WATERS OF LAKE ERIE ATTM. A DRY START TO THE DAY AND MAINLY SUNNY SKIES ACROSS ALL BUT THE FAR NW ZONES...WILL GIVE WAY TO INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS THIS AFTERNOON AS LARGE SCALE FORCING INCREASES ASSOCIATED WITH THE APPROACHING COLD FRONT. SPC HAS MAINTAINED A /SEE TEXT/ FOR ALL OF PENN WITHIN THEIR DAY 1 CONVECTIVE OUTLOOK...WITH EASTERN NEW YORK AND NEW ENGLAND UNDER THE GUN FOR A SLIGHT RISK OF SVR TSRA GIVEN THE BETTER COMBINATION OF STRONGER DEEP LAYER SHEAR AND CAPE. STILL...MODERATE-HIGH SFC BASED CAPE IN EXCESS OF 2000 J/KG...COMBINED WITH ABOUT 20 KTS OF 0-6KM BULK SHEAR SHOULD BE SUFFICIENT FOR A FEW OCCURENCES OF DAMAGING MICROBURSTS AND HAIL ACROSS THE CWA THIS AFTERNOON INTO THIS EVENING. THE LOW-LEVEL...WSW DOWNSLOPE FLOW/COMPRESSIONAL WARMING OF THE AIRMASS AHEAD OF THE CFRONT...WILL LEAD TO THE HIGHEST TEMPS OF THE WEEK. AFTERNOON MAX TEMPS WILL RANGE FROM THE LOWER 80S ACROSS THE HIGH TERRAIN OF THE NORTH AND WEST...TO THE MID AND UPPER 80S IN THE CENTRAL VALLEYS...AND LOWER 90S IN THE GREATER YORK/HARRISBURG AREA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... THE FOCUS FOR SHOWERS AND THUNDERSTORMS /SOME WITH HEAVY RAIN...GUSTY WINDS...FQT LIGHTNING AND EVEN SOME FAIRLY LARGE HAIL/ WILL OCCUR ACROSS THE LOWER SUSQ VALLEY THIS EVENING... WHILE THE FAR NW SEES SHOWERS DECREASE/MOVE OFF TO THE SOUTH AS THE CFRONT PUSHES THROUGH THE KBFD AREA LATE THIS AFTERNOON...AND REACHES THE CENTRAL ZONES AOB 00Z THUR. SCATTERED SHOWERS AND A STRAY TSRA WILL LINGER ACROSS THE CENTRAL RIDGE AND VALLEY REGION THROUGH EARLY THIS EVENING. 24-HOUR...STORM TOTAL RAINFALL WILL BE ABOUT 4-5 TENTHS OF AN INCH...WITH THE BULK OF IT FALLING FROM JUST ONE OR TWO THUNDERSTORMS. GIVEN THE ANOMALOUSLY HIGH PWATS OF 1.5-2 INCHES ACROSS THE STATE...THERE IS A CHANCE FOR LOCALLY HEAVY RANFALL OF OVER 1 INCH. TEMPS TONIGHT WILL STILL BE QUITE MUGGY IN THE SOUTHEAST. LOWS WILL RANGE FROM THE UPPER 60S ACROSS THE LOWER SUSQ REGION...TO THE MUCH MORE COMFORTABLE UPPER 50S ACROSS THE NORTHERN MTNS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... OVERALL SCENARIO REMAINS UNCHANGED IN THE LONG TERM PERIOD AS A LARGE UPPER RIDGE BUILDING OVER THE FOUR CORNERS REGION IS FORECAST TO EXPAND NORTH AND EAST INTO THE ROCKIES AND PLAINS DURING THE PERIOD. DOWNSTREAM...THIS WILL LEAD TO LONG WAVE TROFFING OVER THE EASTERN THIRD OF THE COUNTRY. UPPER LOW TO THE EAST OF HUDSON BAY WILL BE STRENGTHENED AT TIMES BY SHORTWAVE ENERGY IN THE STRONGER JET STREAM FLOW ACROSS CANADA. SOUTHWARD EXTENSION OF THIS LOW/TROF WILL AT TIMES DURING THE PERIOD STRENGTHENING THE TROFFING ACROSS THE NORTHEASTERN U.S./OUR REGION. THE TREND OF MEDIUM RANGE MODEL GUIDANCE IS FOR STRONGER/DEEPER TROFFING DOWNSTREAM ACROSS THE EASTERN U.S...DEVELOPING AN ALMOST FULL LATITUDE TROF EXTENDING FROM THE EASTERN CANADA LOW SWD TO FLORIDA. THIS WILL LIKELY SERVE TO EXPAND AND PROLONG THE CHANCES FOR PCPN THIS WEEKEND. GUIDANCE FORECASTS CONTINUE TO BRING A FRONT AND INCREASED CHANGES FOR PRECIPITATION TOWARD PA IN THE WEDNESDAY/THURSDAY TIME FRAME AND SHOW A SECOND...POTENTIALLY STRONGER SYSTEM LATE NEXT WEEKEND. THE TREND OF STRONGER TROUGHING MENTIONED ABOVE HAS LEAD TO SLOWER ARRIVAL AND DEPARTURE OF THE FRONTAL SYSTEM IN THE DAILY PROGS. THE ECMWF IN LATEST RUN HAS SLOWED UP THE PROGRESSION OF THIS UPPER LEVEL LOW...WHERE THE GFS OPERATIONAL AND ENSEMBLES HAVE SPED UP ITS PROGRESSION THROUGH THE GREAT LAKES REGION. A WARM FRONT WILL BE ON THE DOORSTEP OF PA SUNDAY...AS THE EC CONTINUES TO SLOW ITS PROGRESSION SO EXPECT THE WARM FRONT TO MOVE IN CLOSER TO MIDDAY SUNDAY. HAVE THUS ADJUSTED POPS/TIME. ASSOCIATED COLD FRONT DOES NOT CROSS THE STATE TIL MONDAY...WHERE SURPRISINGLY AT THIS POINT...THE EC AND GFS COME CLOSELY IN PHASE. THIS LARGE UPPER LEVEL LOW COULD BECOME QUASI STATIONARY OVER SOUTHERN CANADA...GREAT LAKES REGION WHICH COULD LEAD TO A POTENTIAL PROLONGED PERIOD OF SHOWERS AND THUNDERSTORM THROUGH THE MIDDLE OF NEXT WEEK. && .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/... 23/06Z...CUT BACK ON FOG THIS MORNING GIVEN OBS TRENDS AND LGT S-SW GRADIENT SFC WIND IN ADVANCE OF COLD FRONT SEWD ACRS LWR MI TWD THE ERN LKS. LINE OF STORMS IN ADVANCE OF COLD FRONT MOVG ACRS LK ERIE ARE FCST BY COSPA/HRRR/SPC 4KM WRF TO WEAKEN OR DISSIPATE AS THEY REACH NW PA AROUND DAYBREAK. AFTER SOMEWHAT OF A LULL IN CONVECTION DURING THE MID TO LATE MORNING...EXPECT SCT TO NMRS SHWRS AND TSTMS TO DEVELOP FROM THIS AFTN INTO THE EVE ALONG AND AHEAD OF THE COLD FRONT..AS IT SHIFTS SEWD ACRS THE AIRSPACE. CVRG SHOULD BE GREATEST OVER THE CNTRL AND ERN PRTNS OF THE AIRSPACE WITH SOME STG TO LCLY SVR STORMS POSSIBLE. PREVAILING CONDS WILL VFR WITH BRIEF MVFR-IFR VIS REDUCTIONS IN TSRA IMPACTS. WND SHIFT FROM SW TO NW BY TONIGHT WITH MAIN PCPN ACTIVITY BCMG CONFINED TO SERN AREAS INTO THU. POST-FRONTAL MVFR SEEMS PROBABLE OVER WRN SXNS TNGT. OUTLOOK... THU...SCT TSTM IMPACTS PSBL SERN AIRFIELDS AS COLD FRONT SLOWS ALONG THE MID-ATLC COAST. FRI...PATCHY MORNING FOG...OTHERWISE VFR/NO SIG WX. SAT...PATCHY MORNING FOG...OTHERWISE VFR. ISOLD PM TSTM PSBL. SUN...TSTM IMPACTS LKLY AS WARM FRONT LIFTS NWD ACRS AIRSPACE. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...LAMBERT/CERU AVIATION...STEINBUGL

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