Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 200635
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
235 AM EDT WED AUG 20 2014

.SYNOPSIS...
A MASSIVE RIDGE WILL BUILD OVER EAST-CENTRAL CANADA FOR THE NEXT
WEEK. ANOTHER STRONG RIDGE WILL BUILD OVER THE SOUTHERN UNITED
STATES. SHORT-WAVES EMBEDDED IN THE WEAK FLOW MOVING UNDER THE
CANADIAN BLOCK WILL SLOW DOWN AND WEAKEN AS THEY MOVE THROUGH OUR
REGION. THIS WILL LEAD TO A POTENTIALLY PROLONGED PERIOD OF
UNSETTLED WEATHER. BUT IT SHOULD PROTECT US FROM THE LATE SEASON
HEAT BUILDING TO OUR SOUTH.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
EARLY AM WATER VAPOR LOOP SHOWS UPPER LOW OVR THE UPPER PENINSULA
OF MICHIGAN...WHILE FURTHER SE SHRA/TSRA NOTED ALONG AXIS OF ASSOC
LL JET AND PLUME OF ANOMALOUS PWATS FROM LK ERIE SOUTHWARD TO THE
OHIO VALLEY. BASED ON LATEST RADAR TRENDS...HAVE INCREASED POPS TO
NR 100 PCT EARLY THIS MORNING OVR THE NW MTNS AND WILL INTRODUCE
CHC OF SHRA OVR THE CENTRAL MTNS ARND DAWN...AS LG SCALE FORCING
OVERSPREADS THE REGION IN ADVANCE OF UPPER LOW.

DWPT DEPRESSIONS QUITE LOW AS OF 05Z...SO EXPECT LITTLE ADDITIONAL
COOLING OVERNIGHT WITH LOWS IN THE 60S. PARTLY CLOUDY SKIES STILL
ALLOWING FOR A BIT OF RAD COOLING ACROSS THE CENTRAL MTNS EASTWARD
AS OF 05Z...WHICH WILL PROMOTE PATCHY FOG EARLY THIS AM.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
SHORTWAVE ROTATING THRU BASE OF UPPER LOW WILL SWING THRU CENTRAL
PA LATER TODAY...BRINGING NUMEROUS SHRA/TSRA. THE HIGHEST
CONFIDENCE IN SHOWERS WILL COME ARND 12Z OVR THE NW MTNS IN
CONJUNCTION WITH PASSAGE OF ANOMALOUS PWATS AND BEST LG SCALE
FORCING AS IMPLIED BY MDL 500-300MB Q-VEC CONVERGENCE FIELDS.
WANING LG SCALE FORCING ANTICIPATED BY AFTN...AS SHORTWAVE LIFTS
TO THE NORTH. HOWEVER...HEATING OF MOIST/UNSTABLE AIR MASS IS
EXPECTED TO RESULT IN MODERATE CAPES BY AFTN ACROSS THE WESTERN
HALF OF THE STATE. NO CAPPING INVERSION IN PLACE...SO EXPECT
NUMEROUS SHRA/TSRA TO DEVELOP AS WE REACH CONVECTIVE TEMP DURING
THE AFTN HOURS. LATEST GEFS DATA AND OPER MDL QPF IMPLY MOST AREAS
WILL SEE MEASURABLE RAINFALL ACROSS CENTRAL PA WITH THE POSSIBLE
EXCEPTION OF THE EXTREME SE COUNTIES.

MDL BLENDED QPF SUGGESTS RAINFALL WILL AVERAGE CLOSE TO 0.25 INCHES
TODAY. HOWEVER...COMBINATION OF HIGH PWAT/CAPES ACROSS THE W MTNS
IMPLY THE POTENTIAL OF MUCH HIGHER AMTS IN THUNDERSTORMS.
CONVECTION-ALLOWING MDLS SUPPORT THIS SCENARIO WITH SPOTS AMTS
ARND 2 INCHES ACROSS THE W MTNS BY LATE TODAY.

ALTHOUGH CLOUDS WILL PREDOMINATE TODAY...ENOUGH BREAKS EXPECTED TO
PUSH READINGS TO NEAR SEASONAL NORMS WITH HIGHS FROM THE M70S OVR
THE HIGH TERRAIN OF THE ALLEGHENIES...TO THE M80S ACROSS THE LOWER
SUSQ VALLEY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
THE WEAKENING RIDGE OVER EASTERN CANADA WILL ALLOW FOR DIVERGENT
FLOW AS THE UPPER LEVEL LOW SLOWLY MOVES EASTWARD. DAYTIME
HEATING...DECREASING PRESSURE...MOIST SOUTHEASTERLY SFC FLOW...AND
WEST TO NORTHWESTERLY FLOW ALOFT SHOULD ALLOW FOR ENOUGH
SHEAR...FOR CHANCE TO LIKELY POPS EARLY WEDNESDAY EVENING. CAPE
VALUES ARE LOW...WITH AN AVG OF 500-1K J/KG THROUGHOUT MOST OF
CENTRAL PA. SO SCATTERED SHOWERS AND THUNDERSTORMS REMAIN POSSIBLE
EARLY WEDNESDAY EVENING. THESE WILL SLOWLY FADE AS THE EVENING
CONTINUES.

THURSDAY LOOKS LIKE ANOTHER UNSETTLED DAY...AS UPPER LOW MAKES
IT/S CLOSEST PASS TO PA...TRACKING ACROSS UPSTATE NY...WITH THE
850MB LOW MOVING THROUGH PA. COOL TEMPS ALOFT...COMBINED WITH
DIURNAL HEATING...SHOULD YIELD NUMEROUS SHRA AND TSRA BY THE
AFTERNOON. HAVE CONTINUED POPS IN THE LIKELY CATEGORY BASED ON 12Z
OPERATIONAL AND GEFS OUTPUT. DUE TO THE CHANGING POSITION AND
TIMING OF THE LOW...HAVE SLIGHTLY LOWERED POPS ALONG THE SOUTHERN
HALF OF THE CWA. THE SOUTHERLY LL JET AND PLUME OF HIGH PWATS WILL
HAVE PASSED NE OF THE AREA THURSDAY...LIMITING THE THREAT OF ANY
HVY RAINFALL. MODEL BLENDED QPF IS IN THE QUARTER TO HALF INCH
RANGE THURSDAY. BEFORE THE LOW PASSES...TEMPS COULD REACH UP TO
THE LOW 80S. AFTER THURSDAY/S NUMEROUS SHOWERS AND THE ADVECTION
OF COOLER TEMPS ALOFT...HIGH TEMPS SHOULD DROP BELOW NORMAL FOR
AUGUST...WITH MAXES MAINLY IN THE 70S THROUGH THE END OF THE WORK
WEEK INTO THE WEEKEND.

LATEST MED RANGE GUIDANCE POINTING TOWARD DRIER WX FRIDAY INTO
EARLY NEXT WEEK...AS SUBTROPICAL HIGH IS PROGGED TO EDGE TOWARD
THE REGION FROM THE MIDWEST. DAILY RING OF FIRE CONVECTION ON NE
PERIPHERY OF THIS RIDGE WILL THREATEN WESTERN PA DURING THE
FRI-SUN TIME FRAME...WHILE EASTERN PA IS LIKELY TO REMAIN DRY.
DESPITE APPROACH OF UPPER RIDGE...NO BIG WARM UP EXPECTED...AS
LARGE SFC HIGH OVR THE CANADIAN MARITIMES WILL CIRCULATE AN
EASTERLY FLOW INTO CENTRAL PA. THERE MAY BE ISSUE WITH AM LOW
CLOUDS/FOG DUE TO THE EXPECTED MOISTLY SERLY FLOW OVR THE AREA.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AN ISOLATED SHOWER WILL BE POSSIBLE THROUGH 1 AM ACROSS SOUTH
CENTRAL PA.

MOST OF THE ACTIVITY IS OVER OH AND MOVING EAST. TOPS WERE
COOLING...BUT NOW STORMS ARE WEAKENING SOME.

MINOR CHANGES MADE ON THE 03Z PACKAGE.

OTHERWISE THE MAIN CONCERN WILL BE MVFR AND IFR CONDITIONS
LATE...GIVEN LIGHT WINDS...MAINLY CLEAR SKIES...AND DEWPOINTS
HIGHER THAN WE HAVE SEEN THEM FOR MUCH OF THE SUMMER SEASON SO
FAR.

EXPECT THINGS TO IMPROVE WED MORNING...BUT THE REMAINS OF
CONVECTION TO THE WEST AND THE UPPER LVL TROUGH MOVING IN
WILL RESULT IN AT LEAST SOME SHOWERS. SOME THUNDERSTORMS
WITH HEAVY RAIN WILL BE POSSIBLE.

NOT A LOT OF CHANGE IN THE PATTERN BEFORE THE WEEKEND IF
THEN.

OUTLOOK...
THU-SAT...MORNING FOG CHANCES EACH DAY. OVERALL VFR...BUT CHC
OF MAINLY AFTERNOON SHRA/TSRA AND ASSOCIATED RESTRICTIONS.
SUN...MAINLY VFR. STILL CHANCE OF SHRA IN THE MORNING.

&&

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

&&

$$
SYNOPSIS...LAMBERT
NEAR TERM...FITZGERALD/LAMBERT
SHORT TERM...GRUMM/FITZGERALD/LAMBERT
LONG TERM...FITZGERALD/CERU
AVIATION...MARTIN


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