Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 031627
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1227 PM EDT MON AUG 3 2015

.SYNOPSIS...
A LARGE UPPER LOW CENTERED OVER NORTHERN ONTARIO WILL TRANSLATE
EASTWARD OVER THE NEXT FEW DAYS. IT WILL DRIVE A COLD FRONT
THROUGH THE STATE TODAY AND EARLY TONIGHT. LARGELY CONFLUENT
NORTHWEST FLOW ALOFT OVER THE GREAT LAKES DURING THE MID WEEK
WILL HELP HIGH PRESSURE SETTLE IN BEHIND THE FRONT. HOWEVER...THE
FRONT WILL HANG UP JUST TO THE SOUTH OF THE REGION AND MAY RETURN
NORTHWARD AS A WARM FRONT LATER THIS WEEK.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...

WAITING GAME IS ON FOR CONVECTION TO BEGIN FIRING OVER THE NEXT
SEVERAL HOURS IN THE MODERATELY UNSTABLE/MDTLY SHEARED ENVIRONMENT
OVER CENTRAL PENN. AN AREA OF CONVECTIVE DEBRIS/LAYERED MID AND
HIGH CLOUDS WILL CONTINUE TO SLOWLY DISSOLVE AS IT DRIFTS EAST AT
20-25 KTS ACROSS THE CENTRAL AND EASTERN PART OF THE CWA THROUGH
THE AFTERNOON HOURS.

IT APPEARS THAT HIGH RES MODELS /4 KM WRF...AND HRRR - HRRRX/ ARE
LATCHING ONTO THE WESTERN PERIPHERY OF THIS MID/HIGH CLOUD DECK TO
ACT AS A DECENT BOUNDARY FOR DIFFERENTIAL HEATING...AND LLVL
CONVERGENCE /AS A RESULT OF DEEPER VERTICAL MIXING OF WESTERLY
MOMENTUM OCCURS IN THE CLEARING SKIES OVER THE WESTERN HIGH
TERRAIN/.

SUNSHINE THROUGH THINNING HIGH CLOUDS ACROSS NWRN PENN WILL
COMBINE WITH AN APPROACHING CFRONT TO TRIGGER ANOTHER LINE OR TWO
OF STG TO POTENTIALLY SEVERE TSRA ACROSS NRN OHIO AND NEAR THE
LAKE ERIE BREEZE BOUNDARY IN FAR NWRN PENN.

LIGHT SOUTHWEST WINDS AT THE SFC WILL VEER A BIT THROUGH THE DAY
AS THE COLD FRONT NEARS. THE FRONT THEN WASHES OUT AND WILL BE
TOUGH TO DISCRIMINATE THIS AFTERNOON AND EVENING.

SPC DAY ONE OUTLOOK KEEPS THE SLIGHT RISK OVER ALMOST ALL OF
CENTRAL PA. THE EXCEPTION IS THE FAR SERN COS. THIS IS PRESUMABLY
DUE TO THE LOSS OF CAPE AS THE HEAT OF THE DAY GOES AWAY.

HOWEVER...THE MIXED LAYER CAPES OF 1-2K JOULES AND GOOD DEEP LAYER
SHEAR MAKE FOR AN ENVIRONMENT WHERE STORMS WILL GROW TALL AND MOVE
FAIRLY QUICKLY W-E. 0-3KM BULK SHEAR WILL INCREASE TO 30-35
KTS...WITH 0-6KM VALUES ABOUT 10 KTS FASTER. THE MAIN SEVERE
WEATHER THREAT SHOULD BE SEVERAL...EMBEDDED ORGANIZED BOWS WITHIN
THE FEW BKN LINES OF SHOWERS/TSRA...CONSIDERING THE NEARLY
UNI-DIRECTIONAL VERTICAL WIND PROFILE. IN ADDITION...DOWNDRAFT
CAPE PER SPC MESO ANALYSIS PAGE HAS INCREASED TO 1000-1200 J/KG
ACROSS ROUGHLY THE SERN HALF OF THE CWA AT 16Z.

MARGINALLY LARGE HAIL IS THE SECONDARY SEVERE THREAT IN THIS
CASE.

HEAVY RAIN DOES NOT SEEM TO POSE A THREAT TODAY WITHOUT SLOW-
MOVING STORMS OR MUCH POTENTIAL FOR BACK-BUILDING. SUNSHINE WITH
HELP FROM A WEST/DOWNSLOPE SFC WIND WILL HELP THE MAXES TOUCH 90
IN THE SERN THIRD OF THE AREA. AFTERNOON DEWPOINTS IN THE UPPER
50S AND LOWER 60S WILL KEEP HEAT-RELATED FLAGS ON THE SHELF TODAY.

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM TUESDAY/...
MOST LIKELY...A BROKEN ASSORTMENT OF STORMS WILL BE ON-GOING AT
THE START OF THE SHORT-TERM. SOME ORGANIZATION FROM MULTI-CELL
CLUSTERS TO BOWING SEGMENTS SHOULD EMERGE DUE TO THE UNI-DIR WIND
PROFILE. THE CURRENT CROP OF MESO MDLS HAS A POOR LEVEL OF
CONTINUITY AMONG THEM WHEN IT COMES TO HOW LONG CONVECTION WILL
LAST AND WHEN THE ALL-CLEAR WILL SOUND. THE COLD FRONT CURRENTLY
ACROSS THE LOWER LAKES WILL MOVE INTO THE STATE LATER TODAY...BUT
GETS LOST IN THE DISTURBANCES IN THE P-FILED CAUSED BY CONVECTIVE
COLD POOLS. HOWEVER...BY MIDNIGHT THE FRONT SHOULD START TO EMERGE
OVER THE EASTERN END OF THE STATE. WILL KEEP POPS IN THE LIKELY
RANGE CONSIDERING THE UNCERTAINTY OF WHERE THE CONVECTION WILL
OCCUR.

LOWS WILL GET INTO THE 50S IN THE NW BUT FOG MAY NOT BE A PROBLEM
DUE TO SOME AIR MOVEMENT. THIS USUALLY SPELLS LOW CLOUDS INSTEAD
OF FOG.

TUESDAY SEEMS LIKE A DRY DAY AS HIGH PRESSURE BUILDS IN. BUT...
THE HEATING COULD AGAIN POP AN ISOLATED SHOWER IN THE NRN MTNS AND
PERHAPS THE LAURELS. THE COVERAGE OF ANYTHING WHICH WOULD MAKE
PRECIP REACH THE GROUND IS GOING TO BE WIDELY SCT. HAVE HELD ONTO
THE IDEA OF A LOW POP IN THE FAR SE AS WELL SINCE THE FRONT
SHOULD NOT MOVE TOO FAR AWAY. MAXES IN THE 70S NW HALF AND 80S SE
HALF. NOT TOO FAR OFF NORMALS FOR LATE SUMMER.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
THE UPPER LOW OVER NORTHERN QUEBEC SHOULD CONTINUE TO DRIFT TO
THE NORTHEAST AND ZONAL TO SLIGHTLY NORTHWEST FLOW IS EXPECTED TO
FOLLOW AS A QUASI-STATIONARY BOUNDARY HANGS OUT JUST TO THE SOUTH
OF THE STATE. EARLIER RUNS OF THE GFS/EC HAD MOVED THE BOUNDARY
FURTHER NORTH BUT THEY HAVE RETURNED SOUTHWARD A BIT WITH THIS
PACKAGE. UNCERTAINTY IN THE PLACEMENT OF THE BOUNDARY WILL KEEP
SOME POP IN THE SRN PART OF THE STATE...BUT MOST LOCATIONS WILL BE
DRY UNTIL WED NIGHT OR THURS. THEN A STACKED LOW WILL SLIDE
EASTWARD FROM THE MID MISSISSIPPI VALLEY AND MAY MAKE A MORE-OR-
LESS CONSTANT RAIN INSTEAD OF SHOWERY/CONVECTIVE PRECIP. THE
UPPER LEVEL LOW WILL FINALLY MOVE OFF NEXT WEEKEND WHICH WILL BE A
HERALD FOR QUIETER WEATHER. TEMPERATURES SHOULD TREND COOLER
LATER IN THE WEEK.

&&

.AVIATION /16Z MONDAY THROUGH FRIDAY/...
AN APPROACHING COLD FRONT AND PRECEDING SFC/LEE TROUGH DEVELOPING
ACROSS CENTRAL PENN WILL ACT AS TWO AREAS OF FOCUS FOR LATE
AFTERNOON/EVENING SHRA TSRA WITH SCT/BRIEF MVFR CIGS AND VSBYS.

A FEW OF THE STORMS MAY BE STRONG TO SEVERE...WITH VERY BRIEF IFR
VSBY IN +RA AND HIGHLY-LOCALIZED WESTERLY SFC WIND GUSTS AOA
40KTS. WILL CONTINUE TO USE -SHRA WITH VCTS BTWN 18-22Z TO SHOW
TSTM IMPACT RISK AT ALL TERMINALS.

OUTLOOK...

TUE...VFR. VERY ISOLD P.M. SHRA PSBL XTRME NRN AIRSPACE.

WED...VFR. NO SIG WX.

THU-FRI...VFR/MVFR WITH RAIN PSBL AS LOW PRES TRACKS SOUTH OF
CENTRAL PA.

&&

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

&&

$$
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT/DANGELO
SHORT TERM...DANGELO
LONG TERM...DANGELO/CERU
AVIATION...LAMBERT/GARTNER


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