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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 221741
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
141 PM EDT WED MAY 22 2013

.SYNOPSIS...
LOW PRESSURE OVER THE MIDWEST WILL TRACK NORTHEAST THROUGH THE
LOWER GREAT LAKES REGION TODAY AND UP THE ST. LAWRENCE RIVER
VALLEY ON THURSDAY. A COLD FRONT TRAILING THE LOW WILL CROSS THE
REGION ON THURSDAY...FOLLOWED BY A SECONDARY COLD FRONT ON FRIDAY.
A CANADIAN HIGH PRESSURE SYSTEM WILL USHER IN COOLER AND DRIER
AIR THAT WILL KEEP TEMPERATURES BELOW NORMAL FOR MEMORIAL DAY
WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
EARLY AFTERNOON VISIBLE LOOP SHOWS STRATIFIED CU ACROSS THE
ALLEGHENY HIGHLANDS. LAPS SOUNDINGS STARTING TO DESTABLIZE WITH
SFC TEMPS APPROACHING CONVECTIVE TEMPS...AND UP TO 1400 J/KG ABOVE
THE LFC. UPSTREAM ACTIVITY OVER WV HAS CONTINUED TO BUT THIS AREA
HAS OVERALL BEEN WEAKENING AND SLIGHTLY SHRINKING IN COVERAGE OVER
THE PAST 2 HOURS.

MAIN FORECAST CONCERN IN THE NEAR TERM IS CONVECTIVE INITIATION
AND EVENTUAL INTENSITY THIS AFTERNOON AND TONIGHT. WITH THE AREA
IS ON THE WESTERN PERIPHERY OF AMPLIFIED UPPER RIDGE...AND
ADDITIONAL SHORTWAVES LIFTING THROUGH THE OHIO VALLEY... WESTERN
PA WILL BE IN AN INCREASINGLY CONVERGENT BOUNDARY LAYER FLOW AS
30-40 KT 850 MB JET NOSES INTO EASTERN OHIO. WITH CIN APPEARING TO
DISSIPATE ON SCHEDULE EXPECT TO SEE SCATTERED THUNDERSTORMS
DEVELOP AFTER 18Z OVER THE HIGHER TERRAIN AND WEST. WITH SPEED
SHEAR OF 25 TO 40 KTS AND MODERATE CAPE...SOME OF STORMS MAY BE
CAPABLE OF DAMAGING WIND GUSTS FROM BOWING LINE SEGMENTS AND
CLUSTERS INTO THIS EVENING. PEAK INTENSITY LKLY BTWN APPROX
21-03Z.

ANOTHER VERY WARM AND MUGGY AFTERNOON IS IN STORE WITH MAXES
REACHING WELL INTO THE 80S...~10F ABOVE NORMAL FOR THIS TIME OF
YEAR.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
CONTINUED EWD PROGRESSION OF THE EXPANSIVE ERN CONUS TROUGH IS
EXPECTED THIS PERIOD...HOWEVER IT MAY BE AT SLOWER PACE AS SOME
MODEL DATA IS TRENDING SLOWER/SHARPER BY THE END OF THE PERIOD.
THE ATTENDANT COLD FRONT WILL TRAVERSE THE AREA DURING THE AFTN
AND EVENING BEFORE EXITING THE ERN PART OF THE CWA AROUND MIDNIGHT.

GENERALLY WEAK INSTABILITY IS PROGGED IN THE PRE-FRONTAL WARM
SECTOR. HOWEVER...MODERATE FLOW/0-6KM SHEAR AROUND 40 KTS COULD
ALLOW FOR A FEW STRONG STORMS TO ORGANIZE WHERE POCKETS OF GREATER
HEATING/DESTABILIZATION CAN OCCUR. THIS APPEARS MOST LKLY OVER THE
ERN 1/3 OF THE CWA...WHICH IS HIGHLIGHTED BY THE SPC DAY 2 SEE TEXT
CATEGORICAL OUTLOOK.

A LIGHTER...DEFORMATION PCPN AXIS IS PROGGED TO SET UP OVER THE
AREA THURS NIGHT INTO FRI AS A SHORTWAVE EMBEDDED IN THE LARGER-
SCALE TROUGH DIGS FROM THE GRT LKS TWD WV. THERE ARE SOME NOTABLE
MODEL DIFFS HEADING INTO DAY 3 SURROUNDING THE DEPTH AND SPEED OF
THE H5 TROUGH CROSSING THE MID-ATLC REGION. MORE ON THIS IN THE
LONG TERM SECTION.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
THE 22/00Z NAM/GFS AND NOW ECWMF ARE SLOW AND SHARP WITH THE BASE
OF THE H5 TROUGH CROSSING THE MID-ATLC/NORTHEAST STATES FRI-SUN.
THESE DATA ALSO SHOW A CLOSED MID-LEVEL LOW ROTATING WITHIN THE
LARGER-SCALE TROUGH ACRS NRN VA FRI BEFORE PIVOTING NWD INTO NEW
ENGLAND THIS WEEKEND. WPC IS STILL LEANING AWAY FROM THE CLOSED
SOLUTION HOWEVER THEY HAVE GIVEN A LITTLE MORE WEIGHT TO THE OPRN
GFS/ECMWF TRENDS. THE IMPLICATIONS ARE IMPORTANT ESPECIALLY IN THE
DAY 4 PERIOD WHERE THE GUIDANCE SPREAD IS THE GREATEST/MOST
NOTICEABLE. TO COMBAT THIS...USED A INTERMEDIATE APPROACH TAKING A
BLEND OF THE 00Z ECMWF AND GFS...WITH SLIGHTLY MORE WEIGHTING
TOWARD THE GFS GIVEN WPC PREFERENCE TOWARD THE GEFS MEAN AND AN
OVERALL BETTER FIT TO THE OPRN/ENSEMBLE CONSENSUS.

EXPECT PLENTY OF CLOUDS AND LGT RAIN IN THE DEFORMATION ZONE ON
FRIDAY...WITH TEMPS FALLING BACK TO 55-65F. THE ECMWF SOLN WOULD
LINGER LIGHT RAIN OVER THE AREA /ESP IN THE EAST/ ON
SATURDAY...BUT DID NOT FULLY BUY-INTO THIS GIVEN HOW STRONG IT WAS
WITH THE CLOSED H5 LOW COMPARED TO THE OTHER GLOBAL GUIDANCE.
CANADIAN HIGH PRES EXTENDING SWD FROM NUNAVUT INTO THE UPPER
MIDWEST WILL SHIFT EWD ACRS THE GREAT LAKES AND EVENTUALLY TAKE UP
RESIDENCE OVER THE NORTHEAST BY MEMORIAL DAY. ENS DATA CONTINUES
TO SHOW NEGATIVE THERMAL/MOISTURE ANOMS SUPPORTING AN UNSEASONABLY
COOL AND DRY WEEKEND WITH THE POTENTIAL FOR FROST IN THE NRN AND
WRN MTNS SAT/SUN AM. THE GROWING SEASON IS UNDERWAY IN THIS AREA
/AS OF MAY 20TH/ AND THEREFORE WILL CONTINUE TO MENTION FROST IN
HWO. ELSEWHERE LOW TEMPS WILL BE CHILLY BY LATE-MAY STANDARDS...BUT
NOT QUITE COLD ENOUGH FOR FROST.

Q-STNRY/WARM FRONTAL ZONE INITIALLY CENTERED FROM IA-WV SHOULD
SLOWLY RETURN NWD THROUGH THE OH VLY EARLY NEXT WEEK. GFS/EC DIFFS
IN THE PATTERN EVOLUTION CONTINUE INTO THE END OF THE MEDIUM RANGE
PARTICULARLY UPSTREAM. IN GENERAL...THERE SHOULD BE A GRADUAL
EARLY-MID WEEK WARMING TREND WITH HTS RISING AS THE UPPER TROUGH
CONTINUES TO MOVE AWAY FROM THE NORTHEAST.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR CONDS WILL GIVE WAY TO SCT -TSRA AND MVFR CIGS THIS AFTERNOON
AND EVENING FROM WEST TO EAST. ISOLD IFR CIGS/VSBY AND STRONG WIND
GUSTS TO 40 KTS MAY BE POSSIBLE NEAR ANY THUNDERSTORMS INTO THIS
EVENING.

COOLER AND BREEZY FOR FRIDAY INTO SUNDAY...AS A STRONG COLD
FRONT DROPS SE OF PA.

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

&&

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

&&

$$
SYNOPSIS...STEINBUGL
NEAR TERM...DEVOIR/STEINBUGL
SHORT TERM...STEINBUGL
LONG TERM...STEINBUGL
AVIATION...DEVOIR