Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 230954
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
554 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 OCCURRENCES 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 RAINFALL 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/...
23/09Z...UPDATE...IR STLT/SFC OBS DEPICT SIGNIFICANTLY LESS FOG/ST
IMPACTING TERMINALS THAN IN RECENT MORNINGS. RADAR SHOWS LINE OF
STORMS CROSSING LK ERIE HAS WEAKENED CONSIDERABLY AS PREV FCST
BELOW. A SECOND LINE OF SCT SHOWERS RECENTLY DEVELOPED NEAR AFJ-
DUJ LINE AND SHOULD ALSO WEAKEN AS THEY APPROACH THE LAURELS BY 12Z.

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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