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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 210738
AFDCTP

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

.SYNOPSIS...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
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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.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
THE LARGE UPPER LEVEL LOW BRINGING SEVERE WEATHER THROUGHOUT THE
MIDWEST WILL SLOWLY MAKE ITS WAY EASTWARD. THIS FLOW SHOULD BRING A
RATHER UNSETTLED PERIOD THROUGH THE WORK WEEK. AS THE UPPER LEVEL
RIDGE CONTINUES TO BREAK DOWN...STORMS WILL SLOWLY APPROACH.  SEVERE
OUTLOOK FOR DAY3/WED HAS THE WESTERN HALF OF THE CWA IN THE SLIGHT
RISK. SOUTHEASTERLY MOISTURE...COUPLED WITH INSTABILITY FROM THE
FRONT AND DAYTIME HIGHS IN THE 80S SHOULD ALLOW FOR A SUFFICIENT
ENVIRONMENT FOR DAYTIME STORMS/SHOWERS. SHEAR SHOULD BE
DECENT...ESPECIALLY AS MID RANGE MODELS ARE HINTING AT A LLJ THROUGH
WEDNESDAY AFTERNOON. THURSDAY WILL AGAIN FEATURE SCT/NMRS TSRA. THE
MED RANGE GUID IS NOW PRETTY SOLID WITH A THURS NIGHT/EARLY FRIDAY
PASSAGE OF THE COLD FRONT ASSOCD WITH THE SYNOPTIC SCALE STORM. MUCH
COOLER AIR AND DRIER CONDITIONS SHOULD FOLLOW FOR THE WEEKEND. ECMWF
HAS BACKED OFF ON THE COLD-NESS OF THE AIR MOVING DOWN WITH THE BIG
1030MB HIGH FOR THE WEEKEND...THOUGH IT LOOKS LIKE THE ZERO C LINE
AT 8H COULD CLIP THE NORTHWESTERN CORNER OF PA. MIN TEMPS FOR
SATURDAY MORNING WILL BE COOL BUT HAVE KEPT THEM IN THE LOW 40S TO
UPPER 30S. DRIER AIR ASSOCIATED WITH THIS FRONT SHOULD KEEP
PRECIPITATION OUT OF THE FORECAST THROUGH THE WEEKEND...WITH WEAK
HIGH PRESSURE BUILDING THROUGH SUNDAY. MEMORIAL DAY MAY SEEM SOME
CLOUDINESS AS THE RIDGE BREAKS DOWN TO DUE NORTHWESTERLY FLOW.
MOISTURE FROM A WEAK SHORTWAVE COULD BRING PRECIPITATION ALONG THE
MASON DIXON MONDAY EVENING...YET DUE TO IT BEING ON THE EDGE OF THE
FORECAST MUCH COULD CHANGE.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
THE MAIN AVIATION CONCERN OVERNIGHT IS THE POTENTIAL OF FOG. HIGH
DEWPOINTS AND LIGHT WINDS WILL LEAD TO AREAS OF FOG...MAINLY AFTER
06Z. BULK OF MDL GUIDANCE CONTINUES TO TARGET THE EASTERN THIRD OF
THE STATE FOR THE LOWEST VSBYS DUE TO A NEARLY CALM WIND AND LOWER
DWPT DEPRESSIONS IN THIS AREA. THE COMBINATION OF MDL DATA AND 03Z
SFC DWPT DEPRESSIONS SUGGEST KLNS AND KMDT ARE VERY LIKELY TO
EXPERIENCE A PERIOD OF IFR VSBYS LATE TONIGHT. KAOO ALSO APPEARS
LIKELY TO EXPERIENCE A PERIOD OF IFR VSBYS...DUE IN PART TO WET
GROUND FROM A LATE DAY SHRA. ELSEWHERE...THE FOG THREAT NOT QUITE
AS GREAT. HOWEVER...A BRIEF PERIOD OF LOW VSBYS IS POSSIBLE JUST
BEFORE DAWN.

AM FOG SHOULD BURN OFF BY ARND 13Z TUESDAY. AFTER THAT...THERE IS
A HIGH DEGREE OF CONFIDENCE IN WIDESPREAD VFR CONDS FROM LATE AM
THRU TUE 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 TUE EVENING.

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

&&

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

&&

$$
SYNOPSIS...STEINBUGL
NEAR TERM...STEINBUGL
SHORT TERM...STEINBUGL
LONG TERM...LA CORTE/CERU
AVIATION...FITZGERALD