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Area Forecast Discussion
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000
FXUS61 KCTP 191156
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
756 AM EDT TUE AUG 19 2014

.SYNOPSIS...
AN UPPER LOW OVR THE W GRT LKS WILL DRIFT SLOWLY SE ACROSS UPSTATE
NY AND NEW ENG BY LATE THIS WEEK. A LARGE SFC HIGH OVR THE CANADIAN
MARITIMES WILL RIDGE SOUTHWARD INTO PA DURING THE UPCOMING WEEKEND
AND EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
WEAK UPPER-LEVEL LOWS ARE STRUGGLING TO MAKE IT UNDER THE
RETROGRADING UPPER LEVEL RIDGE. MODELS FOR DAYS NOW HAVE BEEN
WETTER THAN REALITY. THE SREF AND GEFS ARE MORE ROBUST WITH SHOWER
POTENTIAL TODAY THAN THE HIGH RESOLUTION CONVECTIVE FOLLOWING
MODELS.

LATEST 4KM NAM AND 3KM HRRR IMPLY SOME VERY ISOLATED CONVECTION
ABOUT CENTRAL PA THIS AFTERNOON AND EARLY EVENING. NOTHING
ORGANIZED OR SIGNIFICANT. SORT OF A QUANDARY HOW TO EFFECTIVELY
USE THESE DATA VERSE THE LARGER SCALE MODELS WHERE CONVECTION IS
GENERATED BY RELEASING INSTABILITY IN THE CONVECTIVE
PARAMETERIZATION SCHEMES (CPS). BIASED POPS LOWER TOWARD
CONVECTIVE ALLOWING MODELS THAT DO NOT USE CPS.

MODELS IMPLY PARTLY TO MOSTLY CLOUDY TODAY. FIRST BATCH OF LOW
CLOUDS IN SW PA WILL SHRINK AS IT ADVECTS ACROSS THE STATE.
TEMPERATURE WISE CLOSE TO NORMAL.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
ANY SHOWER ACTIVITY THAT DEVELOPS SHOULD FADE FAST AROUND SUNSET. 

BUILDING 5940M RIDGE IN SOUTHERN US AND BLOCKING RIDGE TO OUR
NORTH. WE ARE STUCK IN THE SQUEEZE PLAY BETWEEN THEM. AN ANEMIC
FRONTAL SYSTEM TRIES TO PUSH THROUGH THE REGION. SREF LARGER SCALE
MODELS SHOW SOME SURGE OF SLIGHTLY ABOVE NORMAL PW AND SOME CAPE
INTO WESTERN PA. POPS SHOULD DROP OFF TO EAST AS THIS SYSTEM WILL
WEAKEN AS IT MOVES BENEATH THE BLOCK. BEST CHANCE...AS MENTIONED
BELOW FOR SEVERAL TENTHS WOULD BE IN WEST VERY LIGHT RAINFALL IN
EASTERN AREAS. 

PREVIOUS: PASSAGE OF SHORTWAVE AND COOLING OF BLYR SHOULD CAUSE
ANY EARLY EVENING SHOWERS TO DIMINISH SHORTLY AFTER SUNSET.
HOWEVER...APPROACH OF UPPER LOW AND ASSOC LL JET/PLUME OF
ANOMALOUS PWATS COULD SPREAD SHRA/TSRA INTO THE NW MTNS TOWARD
DAWN WED.

HAVE RAISED POPS MARKEDLY ACROSS THE AREA WED...AS MDLS NOW IN
AGREEMENT WITH TIMING OF LL JET/PLUME OF ANOMALOUS PWATS. BLEND OF
OPER AND ENSEMBLE GUIDANCE SUGGESTS MOST LIKELY RAINFALL WED WILL
RANGE FROM LESS THAN 0.10 INCHES SE OF HARRISBURG...TO ARND A HALF
INCH ACROSS WARREN CO. HOWEVER...MUCH HIGHER LOCALIZED AMTS ARE
LIKELY ACROSS THE W MTNS...WHERE ENVIRONMENT OF MODERATE INSTABILITY
AND HIGH PWATS WILL MAKE LOCALLY HVY TSRA POSSIBLE. CONVECTION-
ALLOWING MDLS SUPPORT THIS SCENARIO WITH SPOT AMTS OF ARND 2
INCHES ON WED ACROSS THE W MTNS. A MORE STABLE MARITIME AIR MASS
OVR EASTERN PA WILL MAKE TSRA UNLIKELY THERE.

GEFS 925 TEMPS ARE SUPPORTIVE OF HIGH TEMPS WED FROM THE M70S OVR
THE ALLEGHENY PLATEAU...TO THE L80S OVR THE SUSQ VALLEY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
THURSDAY LOOKS LIKE ANOTHER UNSETTLED DAY...AS UPPER LOW MAKES
IT/S CLOSEST PASS TO PA...TRACKING ACROSS UPSTATE NY. COOL TEMPS
ALOFT...COMBINED WITH DIURNAL HEATING...SHOULD YIELD NUMEROUS SHRA
AND TSRA BY AFTN. HAVE RAISED POPS TO THE LIKELY CATEGORY BASED ON
00Z OPER AND GEFS OUTPUT. SOUTHERLY LL JET AND PLUME OF HIGH
PWATS WILL HAVE PASSED NE OF THE AREA THURSDAY...LIMITING THE
THREAT OF ANY HVY RAINFALL. MDL BLENDED QPF IS IN THE QUARTER TO
HALF INCH RANGE THURSDAY. THE NUMEROUS SHOWERS AND COOLER TEMPS
ALOFT WILL RESULT IN HIGH TEMPS BLW NORMAL FOR AUGUST...WITH
MAXES MAINLY IN THE 70S.

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 WARMUP 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 /12Z TUESDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL GIVE WAY TO FOG AND LOWERING VSBYS OVERNIGHT
UNDER CLEAR SKIES AND LIGHT WINDS. EXPECT WIDESPREAD MVFR TO IFR
VSBYS AND CIGS TO DEVELOP OVERNIGHT AT MOST CENTRAL AND NORTHERN
AIRFIELDS. HOWEVER...HAVE NOT INCLUDED FOG IN THE LOWER
SUSQUEHANNA TAFS OF KMDT AND KLNS...AS CONFIDENCE OF FORMATION IS
LOWER. IF FOG DOES DEVELOP...LIKELY TO BE IN THE MVFR RANGE AT
THESE LOCATIONS.

CURRENT TIMING OF FOG IS FOR DEVELOPMENT AROUND 07Z IN MOST
LOCATIONS...WITH THE DENSEST FOG BETWEEN 09Z AND 12Z. 

AFTER MORNING FOG...EXPECT GENERALLY VFR CONDITIONS. THERE IS A
THREAT FOR SHRA/TSRA...MOST LIKELY IN THE SOUTHWEST AND LEAST
LIKELY IN THE NORTHEAST.

A VERY SLOW APPROACHING UPPER LOW WILL SLOWLY INCREASE CHANCES FOR
DAILY SHOWERS AND POTENTIAL AFTERNOON TSRA FOR THE BALANCE OF THE
WEEK. CURRENTLY...LATER WEDNESDAY AND THURSDAY LOOK LIKE THE
HIGHEST LIKELIHOOD OF PRECIPITATION...WITH SURFACE FRONT CROSSING
THE REGION.

OUTLOOK...

TUE...MORNING FOG...THEN MAINLY VFR...WITH SHRA/TSRA POSSIBLE.
WED-FRI...MORNING FOG CHANCES EACH DAY. OVERALL VFR...BUT
INCREASING CHANCES OF MAINLY AFTERNOON SHRA/TSRA AND ASSOCIATED
RESTRICTIONS.
SAT...MAINLY VFR. STILL CHANCE OF SHRA...BUT DECREASING CHANCES.

&&

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

&&

$$
SYNOPSIS...FITZGERALD
NEAR TERM...GRUMM
SHORT TERM...GRUMM/FITZGERALD
LONG TERM...FITZGERALD
AVIATION...JUNG/GARTNER



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