-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 211113
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
713 AM EDT TUE MAY 21 2013

.SYNOPSIS...
A WARM AND HUMID...SUMMERTIME AIRMASS WILL CONTINUE TO BRING ABOVE
NORMAL TEMPERATURES TO CENTRAL PENNSYLVANIA THROUGH WEDNESDAY. A
COLD FRONT WILL CROSS THE REGION ON THURSDAY. A LARGE AREA OF HIGH
PRESSURE WILL BUILD SOUTH AND EAST FROM CENTRAL CANADA INTO THE
NORTHEAST AND MID-ATLANTIC STATES...BRINGING COOLER AND DRIER AIR
TO THE AREA FOR MEMORIAL DAY WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
IR SATL/SFC OBS INDICATE FOG IS QUICKLY DEVELOPING ESP ACRS
S-CNTRL AND SERN PA. SOME OF THE FOG WILL BE LCLY DENSE EARLY THIS
MORNING WITH VIS AOB 1/2-1/4SM. FOG AND LOW ST WILL GIVE WAY TO
M/SUNNY SKIES BY MID-LATE MORNING WITH TEMPS 75-80F BY NOON.

AN UPPER-LEVEL RIDGE WILL BE IN PLACE OVER CNTRL PA DURING THE
DAY 1 PERIOD...GRADUALLY WEAKENING AND SLIDING EWD THROUGH
TONIGHT. SOUTHWEST LLVL FLOW WILL CONTINUE TO ADVECT VERY WARM AND
MOIST AIR INTO THE REGION WITH AFTERNOON TEMPS IN THE 80S AND SFC
DEWPOINTS IN THE LOWER TO MID 60S. DESPITE WEAK LG SCALE FORCING
FOR ASCENT...MODERATE INSTABILITY /MEAN ML CAPE VALUES BETWEEN
1000-2000 J/KG/ SHOULD SUPPORT ISOLD-SCT CONVECTION DURING THE
AFTN-EVE. THE OVERALL SVR THREAT LOOKS MARGINAL GIVEN THE ABSENCE
OF A SIGNIFICANT TRIGGER...HOWEVER THE SPC CATG OUTLOOK HIGHLIGHTS
NRN PA IN THE SEE TEXT WITH 5% PROB OF DMGG WINDS. THIS AREA
MAY BE INFLUENCED BY WEAK HT FALLS ASSOCD WITH S/W CRESTING THE
UPPER RIDGE OVER THE UPPER GRT LKS...AND NOSE OF STG LLJ IN THE
UPPER OH VLY/NW PA BY 00Z. THE MODELS SHOW A MCS WITH THIS FEATURE
MOVG EWD ACRS THE ERN GRT LKS/ST. LAWRENCE VLY INTO NRN NEW
ENGLAND. HIGHEST POPS OVERNIGHT ARE ACRS THE NRN TIER...WITH NWD
DISPLACEMENT MDL BIAS ARGUING FOR A MORE SRN MCS TRACK.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
A S/W MOVG EWD ACRS THE UPPER MS VLY INVOF IA WILL PHASE WITH A
CANADIAN UPPER LOW/TROUGH DROPPING SWD ACRS HUDSON/JAMES BAY DURING
THE DAY WEDNESDAY...REACHING THE MIDWEST BY F72. AT THE SFC...A
COLD FRONT PUSHING EWD THRU THE OH VLY WILL BE THE MAIN FOCUS FOR
TSTM DEVELOPMENT/SVR POTENTIAL THIS PERIOD.

AM CLOUDS WITH SOME PCPN IS EXPECTED TO LIMIT DIURNAL HEATING
TO SOME EXTENT ACRS THE DAY 2 SPC SLGT RISK AREA - WHICH COVERS
NEARLY ALL OF THE CWA WITH THE EXCEPTION OF THE FAR SERN ZONES.
DESPITE THE TEMPERED DESTABILIZATION...EXPECT AN AFTN INCREASE IN
TSTM COVERAGE ALONG WITH SOME PICK-UP IN INTENSITY AS BELT OF
STRONGER FLOW ALOFT SHIFTS EWD AHEAD OF THE MID-UPPER TROUGH.
BANDS OF TSTMS CAPABLE OF PRODUCING DMGG WNDS/MARGINAL HAIL WILL
BE POSSIBLE AND THUS WILL CONTINUE TO HIGHLIGHT AN ELEVATED SVR WX
THREAT IN THE HWO FOR WEDNESDAY. BETTER FORCING PORTENDS HIGHER
POPS RANGING FROM THE MED-HIGH CHC RANGE IN THE SE TO LOW LKLYS IN
THE NW. SHOWERS/TSTMS MAY PERSIST AFTER DARK INTO WED NGT.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
ERN NOAM TROUGH AXIS EXTENDING FROM JAMES BAY SWD THRU THE GRT
LKS/MID-SOUTH TO THE CENTRAL GULF COAST AT THE START OF THE PERIOD
WILL PUSH SLOWLY EWD AND SHOULD REACH THE EAST COAST BY 00Z SAT.
THE GUIDANCE IS SHOWING SOME NOTABLE DIFFS WITH THE H5 SYSTEM. THE
NAM/GFS/GEFS ARE SLOWER AND SHARPER WITH TROUGH AS IT CROSSES THE
OH VLY INTO THE MID-ATLC. THE 00Z GFS EVEN CLOSES OFF THE H5 LOW
OVER NRN VA FRI EVE. THE LAST TWO RUNS OF THE CMC HAVE BEEN TRYING
TO GENERATE A TROPICAL CYCLONE-LIKE SYSTEM NEAR THE OUTER BANKS.
THE KNOWN SLOW/TROPICAL BIASES OF THE NAM/CMC AND STRONG/CLOSED
SOLN OF THE GFS LEADS TO A UKMET/ECMWF PREFERRED SOLN WHICH FAVORS
MORE EWD PROGRESSION WITH THE TROUGH AND ITS ASSOCD COLD FRONT.

THE COLD FRONT WILL CROSS THE CWA ON THURS ACCOMPANIED BY SCT TO
NMRS SHOWERS AND TSTMS. MUCH LIKE ON DAY 2...THE PRE-FRONTAL WARM
SECTOR /LOCATED OVER THE ERN 1/2 OF PA/ WILL BE CHARACTERIZED BY
35-40KTS OF DEEP-LAYER SHEAR WITH WEAK INSTABILITY. THEREFORE THE
OVERALL SVR POTENTIAL APPEARS RELATIVELY LOW ATTM. THE SPC DAY 3
OUTLOOK DOES INCLUDE ERN PA IN THE SEE TEXT/5% SVR FOR ISOLATED
HAIL AND WIND THREAT.

BEHIND THE DEPARTING COLD FRONT...A STG AND LARGE ANTICYCLONE
SHOULD DOMINATE PATTERN IN THE FRI-MON TIMEFRAME...BUILDING SEWD
FROM NUNAVUT ACRS THE GRT LKS INTO THE NORTHEAST. AN UNSEASONABLY
COLD/DRY AIRMASS WILL ACCOMPANY THE HIGH RESULTING IN BLW NORMAL
TEMPS FOR MEMORIAL DAY WEEKEND. ECENS MOS DATA SHOWS TEMPS ON
FRI/SAT STRUGGLING TO CRACK THE 60F MARK LOCALLY...WITH SEVERAL
OPPORTUNITIES FOR A LATE-SEASON FROST OVER THE NRN MTNS SAT/SUN/MON
MORNINGS. THERE SHOULD BE A MODERATION INTO THE MIDDLE OF NEXT
WEEK WITH TEMPS GETTING BACK TO NEAR NORMAL AROUND 5/28.

&&

.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
AM FOG IS IN THE PROCESS OF BURNING OFF AND SHOULD DO SO
COMPLETELY BY 13-14Z. AFTER THAT...THERE IS A HIGH DEGREE OF
CONFIDENCE IN WIDESPREAD VFR CONDS FROM LATE AM THRU THIS EVENING.
HOWEVER...SCT PM TSRA WILL AGAIN BE AN AVIATION CONCERN. THE BEST
CHC OF AN AFTN TSRA AND ACCOMPANYING BRIEF VSBY REDUCTION WILL BE
ACROSS THE N MTNS AND SOUTHWARD ALONG THE LAUREL HIGHLANDS.
HOWEVER...LATEST MDL DATA INDICATES SOME POSSIBILITY OF A LINE OF
TSRA SWEEPING SE ACROSS THE ENTIRE REGION LATE THIS EVENING.

.OUTLOOK...
WED-THU...SCT THUNDERSTORM IMPACTS POSSIBLE...MAINLY IN THE PM.
FRI-SAT...NO SIG WX EXPECTED.
-- End Changed Discussion --

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...STEINBUGL
NEAR TERM...STEINBUGL
SHORT TERM...STEINBUGL
LONG TERM...STEINBUGL
AVIATION...FITZGERALD/GARTNER