Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291642 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1242 PM EDT MON JUN 29 2015 .SYNOPSIS... A WEAK RIDGE OF HIGH PRESSURE WILL BRING DRY WEATHER AND MILDER TEMPERATURES TO MOST OF CENTRAL PENNSYLVANIA TODAY. A FRONTAL SYSTEM MOVING THROUGH THE OHIO VALLEY INTO THE LOWER GREAT LAKES WILL LIKELY BRING INCREASING CLOUDS AND SHOWERS TO THE AREA LATER TONIGHT INTO TUESDAY MORNING...FOLLOWED BY SCATTERED THUNDERSTORMS TUESDAY AFTERNOON. EXPECT AN UNSETTLED WEATHER PATTERN TO PERSIST INTO THE UPCOMING HOLIDAY WEEKEND AS A BROAD BUT WEAKENING UPPER LEVEL TROUGH REMAINS POSITIONED OVER THE LOWER 48 EAST OF THE CONTINENTAL DIVIDE. && .NEAR TERM /THROUGH TONIGHT/...
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WEAK SFC RIDGE DRIFTING NE ACROSS THE REGION THIS AFTERNOON WILL CONTINUE TO PROVIDE FAIR/DRY WEATHER THIS AFTERNOON /AND EARLY THIS EVENING FOR MOST LOCATIONS EAST OF THE ALLEGHENIES/. THE SW EDGE OF COOLER TEMPS/STEEPER LOW-MID LEVEL LAPSE RATES WAS DEPARTING THE CWA...BUT WILL RESULT IN SCT-BKN FLAT CU THIS AFTERNOON. LATER TODAY...QUICKLY NE ADVANCING WARM FRONT AND THE LEADING EDGE OF ANOMALOUSLY STRONG SSWRLY FLOW AT 850 MB AND HIGHER PWAT AIR WILL ACCOMPANY A WARM FRONT TO BRING A QUICK INCREASE IN CLOUDS WITH A CHC FOR SHOWERS BY EARLY THIS EVENING ACROSS MAINLY THE NW MTNS. AREAS EAST OF THE ALLEGHENY PLATEAU WILL SEE INCREASING CLOUDS LATE TODAY/EARLY TONIGHT...BUT THE CHC FOR SHOWERS WILL BE MUCH LOWER UNTIL AT LEAST 04Z TUESDAY. MODEL CONSENSUS FAVORS SHOWERS OVER NW PA TONIGHT WITH MODEST QPF AMOUNTS IN THE 0.25 TO 0.50 INCH RANGE AS THE SFC LOW REACHES LAKE ERIE BY 12Z TUE. HIGH TEMPS THIS AFTERNOON WILL VARY FROM THE L70S NORTH TO AROUND 80F IN THE SE.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... THE LEAD SHORTWAVE IS FCST TO WEAKEN INTO THE LOWER GREAT LKS EARLY TUESDAY. HOWEVER...SEVERAL ADDITIONAL SHORTWAVES CRESTING THE WRN CONUS MEAN RIDGE WILL DIG SEWD THROUGH THE UPPER/MID MS VALLEY...HELPING TO CARVE OUT A SIGNIFICANT MID LVL TROUGH THAT SHOULD GRADUALLY SHIFT EWD ACROSS THE OH VALLEY ON TUESDAY/D2 AND THE NORTHERN MID ATLC STATES ON WEDNESDAY/D3. THE LATEST SHORT RANGE MODEL GUIDANCE INDICATES CENTRAL PA WILL BE IN THE WARM SECTOR BY TUESDAY AFTERNOON...WITH SEASONALLY STRONG BOUNDARY LAYER HEATING EXPECTED AHEAD OF WEAK COLD FRONT OR WIND SHIFT APPROACHING FROM THE OH VALLEY. TSTMS ARE PROJECTED TO DEVELOP WITHIN A CORRIDOR OF MODEST INSTABILITY AND STEEP LOW LLVL LAPSE RATES FROM THE MID SOUTH NEWD ALONG THE APPALACHIANS INTO CENTRAL PA. DEEP LAYER SHEAR VALUES WITHIN THIS CONVECTIVE ZONE ARE SUPPORTIVE OF ORGANIZED MULTI-CELL UPDRAFTS AND LINE SEGMENTS...AND THEREFORE SPC HAS MAINTAINED A MARGINAL RISK FOR D2. TSTM ACTIVITY WILL BE TIED TO DIURNAL HEATING MAXIMUM WITH A DECREASING COVERAGE/WEAKENING TREND EXPECTED DURING THE EVENING HOURS. THE SEVERE WEATHER RISK IS FCST TO SHIFT EWD ON D3/WED AS THE MAIN MID-LVL TROUGH EJECTS NEWD ACROSS THE UPPER OH VALLEY INTO UPSTATE NY/CENTRAL PA BY 18Z. THE CONVECTIVE ENVIRONMENT SHOULD BE SIMILAR TO D2 WITH THE AXIS OF BEST INSTABILITY/LOW LVL LAPSE RATES SHIFTED SLIGHTLY EWD INTO ERN PA. LOOK FOR ANOTHER ROUND OF TSTMS TO DEVELOP ALONG/AHEAD OF SFC COLD FRONT AND POSE AT LEAST A LOW RISK OF DAMAGING WINDS AND PERHAPS SOME HAIL. && .LONG TERM /THURSDAY THROUGH MONDAY/... THE LATEST GLOBAL DETERMINISTIC MODELS AND ENSEMBLE MEANS ARE STARTING TO SUGGEST THAT THE HIGHLY AMPLIFIED RIDGE/TROUGH PATTERN OVER THE LOWER 48 WILL START TO FLATTEN OUT WITH TIME...PERHAPS REVERTING BACK TO A MORE TYPICAL SUMMERTIME MID- LATITUDE FLOW REGIME WITH THE MAIN BELT OF ZONAL WESTERLIES ALIGNED NEAR THE US/CANADIAN BORDER AND SUBTROPICAL RIDGING EXPANDING ACROSS THE SOUTHERN UNITED STATES. DESPITE A SERIES OF MID-LEVEL DISTURBANCES MOVING DOWNSTREAM OF THE WRN THROUGH FROM THE UPPER/MID MS VALLEY THROUGH THE MID ATLC REGION...500MB HEIGHTS SHOULD BE IN RECOVERY MODE WHICH SHOULD ALLOW DAYTIME TEMPERATURES TO TREND WARMER INTO THE JULY 4TH HOLIDAY WEEKEND. CONFIDENCE IN THE PCPN PATTERN REMAINS LOW ALTHOUGH THERE SEEMS TO BE SOME MODEL AGREEMENT IN FOCUSING RAINS THU/FRI ALONG THE D3/WEDNESDAY COLD FRONT...WHICH APPEARS TO BECOME QUASI-STNRY FROM SRN NJ WSWWD ALONG THE MASON DIXON LINE LATE THIS WEEK. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... ALL AIRFIELDS HAVE RETURNED TO VFR CONDITIONS AND THEY ARE EXPECTED TO PERSIST THROUGH MUCH OF THE DAY. UNSETTLED PATTERN WITH A SERIES OF FRONTS AFFECTING THE REGION MUCH OF NEXT WEEK. BEST CHANCES OF RESTRICTIONS WILL BE TUESDAY INTO WEDNESDAY. OUTLOOK... TUE- WED...MAINLY VFR...BUT SOME POSSIBLE RESTRICTIONS IN SHRA/TSRA. THU-THU...AGAIN MAINLY VFR....BUT RESTRICTIONS POSSIBLE IN SHRA AND POSSIBLE TSRA. && .CLIMATE... JUNE 2015 HAS BEEN A WET MONTH ACROSS MUCH OF CENTRAL PA. THROUGH 6/28...OUR TWO LCD CLIMATE SITES /HARRISBURG AND WILLIAMSPORT/ ARE RANKED 8TH AND 6TH RESPECTIVELY FOR THE WETTEST JUNE ON RECORD. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT/STEINBUGL NEAR TERM...LAMBERT/STEINBUGL SHORT TERM...STEINBUGL LONG TERM...STEINBUGL AVIATION...JUNG/LAMBERT/GARTNER CLIMATE...

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