FXUS61 KCTP 301202
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
702 AM EST MON NOV 30 2009
.SYNOPSIS...
A COLD FRONT CONTINUES TO SLIDE EAST OF PENNSYLVANIA TODAY WITH
MUCH COOLER AIR FILTERING INTO THE REGION BEHIND THE FRONT.
SCATTERED RAIN SHOWERS WILL BECOME LESS NUMEROUS AND BEGIN TO
CHANGE OVER TO SNOW SHOWERS ACROSS THE NORTHWEST MOUNTAINS. AN
AREA OF HIGH PRESSURE QUICKLY BUILDS INTO THE REGION LATE TUESDAY
THROUGH WEDNESDAY. AN ACTIVE WEATHER PATTERN RETURNS FOR THE
SECOND HALF OF THE WEEK WITH AN AREA OF LOW PRESSURE ACROSS THE
MIDDLE ATLANTIC STATES LATE WEDNESDAY AND THURSDAY. ADDITIONAL
RAIN SHOWERS ARE EXPECTED FOR THURSDAY AND MAY POSSIBLY BECOME
MIXED WITH SNOW SHOWERS WITH COOLER TEMPERATURES FOR THE UPCOMING
WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
CHALLENGES FOR TODAY RESIDE ARND TIMING OF P-TYPE CHG FROM RA TO SN.
FRONTAL BNDRY SLOWLY SLIPPING THRU THE REGION IS UP AGAINST A REGION
OF ELEVATED POTENTIAL TEMP OVER THE SUSQ-VALLEY...WHICH IS HELPING
WITH A WEAKENING OF THE INITIAL SLUG OF PRECIP. TROUGH AXIS QUICKLY
PIVOTS TOWARDS MID-ATLANTIC REGION BY MIDDAY AS NOSE OF
ANTI-CYCLONIC FLOW POKES INTO NW PA.
FLOW TURNS NWSTRLY OFF OF LK ERIE WITH TEMPS STEADILY COOLING ENUF
TO CHG PRECIP TO A RA/SN MIX BEFORE ALL SN LATER TODAY. MIXED LYR
TODAY RISES TOWARDS 1500-2000FT AGL...FILTERING TO THE SFC A CORE OF
15-25KTS. EXPECT GUSTS ARND 15-25MPH BEGINNING FROM THE NW TO
CENTRAL. WEAK DOWNSLOPING MAY PROVIDE FOR A FEW BREAKS IN A THINNING
CLOUD SHIELD FOR PORTIONS OF THE CWFA THIS AFTN.
PRECIP WILL REMAIN LGT...WITH BTWN .05 TO .15 INCHES ACROSS THE CWFA
THRU MIDDAY. NON-DIURNAL CURVE ANTICIPATED FOR TODAY...MOST LIKELY
MAX TEMPS WILL HAVE BEEN ACHIEVED PRIOR TO 15Z FOR MOST LOCATIONS
WITH NEAR STEADY OR FALLING TEMPS THRU THE AFTN INTO THE M30S
NW...ARND 40 CENTRAL...M40S SE CWFA. CONTINUED COLD AIR ADVECTION
WILL PUSH TEMPS COOLER TOWARDS EARLY EVE.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
THE QUESTION FOR TONIGHT IS IF TOO MUCH DRY AIR WILL ENTRAIN INTO
THE BNDRY LYR AND CHOKE OFF LES FROM DEVELOPING UNTIL AFT 06Z.
500MB TROUGH AXIS QUICKLY PIVOTS THRU THE REGION UNDER A
PROGRESSIVE FLOW...WITH A WEAK LOBE OF VORTICITY ACROSS SOUTHERN
ONTARIO OVERNIGHT. BASED ON MESOSCALE SOUNDINGS THE DENDRITIC
GROWTH ZONE REMAINS ELEVATED WITH TOO MUCH DRY IN THE 5-8KFT RANGE
ACROSS OUR FAVORED LES CWFA TO SUPPORT ANY ORGANIZED BANDS OR
PROLONGED INTENSITY OF SN. WEAK UPSLOPE MECHANISM COULD SPAWN SOME
SCT SHSN BTWN 06-12Z FOR MUCH OF THE ALLEGHENY MTNS WITH ARND AN
INCH OF TWO PSBL. HAVE ADJUSTED POPS TO REFLECT THE TYPICAL
UPSLOPE AND LES REGION OF OUR CWFA...TO HIGH CHC. DOWNSTREAM
EXPECT DRY CONDS OVERNIGHT FOR THE SUSQ-VALLEY. CLOUD SHIELD WILL
CONTINUE TO THIN ACROSS THE SUSQ- VALLEY WITH PROLONGED
SUBSIDENCE...WITH OVERNIGHT TEMPS IN THE LOW TO MID 30S. UPSTREAM
TEMPS WILL BE COOLER IN THE MID 20S NW TO LOW 30S CENTRAL.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
VERY CHANGEABLE CONDITIONS FOR THE EXTENDED WILL TRANSITION TO
NEAR TO BELOW NORMAL TEMPERATURES BY LATE IN THE PERIOD...AS COLD
AIR ENVELOPS MUCH OF THE LOWER 48 BY NEXT WEEKEND.
ENSEMBLES AND DETERMINISTIC RUNS INDICATE A RAPID REGIME CHANGE
FROM BRIEF LAKE EFFECT ON TUESDAY TO STRONG OVERRUNNING WARM
ADVECTION LATER WEDNESDAY INTO THURSDAY AS SOUTHWEST UNITED STATES
CUTOFF PHASES WITH STRONG NORTHERN STREAM UPPER TROF WHICH DROPS
THROUGH THE NORTHERN ROCKIES INTO THE NORTHERN AND CENTRAL PLAINS
LATE TUESDAY AND WEDNESDAY. GEFS CONSENSUS SFC LOW TRACK TRENDING
FURTHER WESTWARD OVER THE LAST 24 HOURS WITH WARMER AIR FLOODING
NORTHWARD ALONG THE MID ATLANTIC SEABOARD AND NORTHWARD INTO
CENTRAL PA...WITH NO CAD TO SPEAK OF GIVEN SFC HIGH TRACKING WELL
OFF THE COASTLINE ON WEDNESDAY. THUS...CONFIDENCE APPEARS TO BE
INCREASING FOR A RAIN STORM THROUGHOUT CENTRAL PA WEDNESDAY
AFTERNOON INTO EARLY THURSDAY AS A FAIRLY DEEP SFC CYCLONE RIDES
NEWD ALONG THE SPINE OF THE APPALACHIANS...REACHING NORTHERN NEW
ENGLAND THURSDAY EVENING.
IT APPEARS SEASONABLY COOL CONDITIONS MAY PREVAIL FOR A WHILE IN
THE WAKE OF THIS SYSTEM...WITH BROAD TROFFING TRANSITIONING TO
ZONAL FLOW LATE NEXT WEEKEND INTO EARLY NEXT WEEK. THIS MAY
PROVIDE OPPORTUNITIES FOR PACIFIC SYSTEMS TO TRACK ACROSS THE
CONUS AND PERHAPS FAVOR PTYPES IN THE FORM OF SNOW VS. RAIN ACROSS
THE REGION DURING THE 2ND WEEK OF DECEMBER.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
POOR FLYING CONDS FOR MUCH OF TDY AS WINDS TURN W/NWSTRLY BEHIND
FRONTAL PASSAGE. MIXED LYR SUGGESTS PSBL GUSTS TDY BTWN
15-20KTS...WHICH WILL PROVIDE SOME UPSLOPE CONDS FOR THE HIGHER
TERRAIN AIRFIELDS OF THE ALLEGHENIES AIDING IN PROLONGED IFR
PATCHY LIFR CONDS FOR JST/BFD. AOO/UNV SHUD SEE SLIGHT IMPROV
CONDS TO MVFR. SCT SHRA WILL PERSIST THRU MIDDAY THEN BEGIN TO
DIMINISH AS DRY AIR SLIDES IN. ACROSS THE SUSQ-VALLEY AIRFIELDS
WILL IMPROV CIGS TO MVFR MIXED AT TIMES TO VFR. AFT 21Z TEMPS
COULD BE COOL ENUF ARND BFD FOR SN TO FALL...TEMPO VSBYS TO IFR.
OVERALL EXPECT MVFR CIGS/VSBYS FOR WESTERN THIRD OF PA.
DOWNSLOPING WILL KEEP DRY CONDS FOR IPT/MDT THRU EARLY TUE.
OUTLOOK...
TUE...IFR/MVFR CIGS WEST WITH -SN. VFR EAST.
WED...VFR.
WED PM- FRI...MVFR TO IFR CIGS. -SN NW/RA CENT AND SE.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...BEACHLER
NEAR TERM...BEACHLER
SHORT TERM...BEACHLER
LONG TERM...DEVOIR/MARTIN
AVIATION...BEACHLER
