719
FXUS61 KPBZ 031815
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
215 PM EDT WED SEP 3 2025
SYNOPSIS
SHOWERS AND THUNDERSTORMS RETURN THURSDAY WITH THE APPROACH AND
PASSAGE OF A COLD FRONT. GUSTY WIND AND ISOLATED SEVERE STORMS
MAY BE POSSIBLE. COOLER CONDITIONS ARE EXPECTED OVER THE
WEEKEND.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- PRE-FRONTAL SHOWERS POSSIBLE THIS EVENING MAINLY SOUTH OF
PITTSBURGH
- TEMPERATURES TREND WARMER THAN RECENT DAYS/NIGHTS
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AS A POTENT TROUGH STRENGTHENS INTO A CLOSED LOW IN SOUTH-
CENTRAL CANADA AND ADVANCES INTO THE NRN GREAT LAKES, WARM
ADVECTION STRENGTHENS IN TURN, SUPPORTING TEMPS BROADLY
APPROACHING 80F TODAY AMID GENERALLY SUNNY CONDITIONS.
HEATING ALONG RIDGE LINES ALSO IS SUPPORTING DEEPER UPDRAFT
GROWTH WITHIN THE DEEPLY MIXED ENVIRONMENT. IN THIS AREA OF NRN
WV, THE POSSIBILITY OF ISOLATED SHOWERS/STORMS EXISTS FOR A
BRIEF WINDOW THIS AFTERNOON, THOUGH LIMITED MOISTURE AND A MID-
LEVEL THERMAL INVERSION WILL LIMIT INTENSITY OF ANY DEEP, MOIST
CONVECTION AS THE CAPE PROFILE WILL BE HEAVILY CENTERED IN THE
LOWER LEVELS OF THE ATMOSPHERE.
AHEAD OF THE CLOSED UPPER LOW, AND AS AN EMBEDDED SHORTWAVE
TROUGH APPROACHES THE REGION, INCREASING WARM, MOIST ADVECTION
WILL SUPPORT RAPID INCREASE IN CLOUD COVER AND POTENTIAL ONSET
OF SHOWERS BY SUNRISE.
SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/
KEY MESSAGES:
- SHOWERS AND LOCALIZED THUNDERSTORMS FAVORED THURSDAY, LIKELY
IN A MORNING AND AFTERNOON WAVE
- MARGINAL RISK FOR DAMAGING WIND DEPENDENT ON HEATING AHEAD OF
AFTERNOON WAVE
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WITHIN THE INCREASED FLOW AHEAD OF A CLOSED LOW/EMBEDDED
SHORTWAVE TROUGH, MODEST ELEVATED CAPE MAY YIELD WEAK, BROAD
CONVECTIVE DEVELOPMENT WITHIN A PRE-FRONTAL SFC TROUGH THU
MORNING. WITH A LACK OF MID-LEVEL DRY AIR AND ELEVATED UPDRAFTS,
ANY MORNING SHOWERS/STORMS DO NOT SUGGEST POTENTIAL FOR A
SEVERE-WEATHER RISK.
THE PRE-FRONTAL TROUGH ADVANCES EWD TO THE RIDGES BY EARLY
AFTERNOON, FOCUSING A PRIMARY SEVERE WEATHER RISK NEAR AND EAST
OF THE RIDGES. ADDITIONAL STORM POTENTIAL EXISTS THU AFTERNOON
ALONG THE SYSTEM'S COLD FRONT BEGINNING EARLY AFTERNOON THRU
EARLY EVENING.
SEVERE-WEATHER POTENTIAL IN THE AFTERNOON REMAINS UNCLEAR,
HOWEVER, AND WILL BE HIGHLY DEPENDENT ON RECOVERY IN THE WAKE OF
MORNING SHOWERS/STORMS. THE CHANCE OF THIS RECOVERY APPEARS LOW,
GIVEN THAT CLOUD COVER WILL BE ABUNDANT AND FRONTAL TIMING MAY
BE QUICK BEHIND THE MORNING RAIN. HOWEVER, THERE REMAINS
UNUSUALLY LARGE UNCERTAINTY WITH RESPECT TO THE TIMING OF
FRONTAL ARRIVAL, AND A DELAYED FRONTAL TIMING WOULD BETTER FAVOR
AFTERNOON RECOVERY AND POTENTIAL FOR GREATER STORM INTENSITY.
IN THE INTEREST OF CONDITIONAL-THREAT AWARENESS, IF STORMS CAN
FORM ALONG THE FRONTAL ZONE, MID-LEVEL DRY AIR, COUPLED WITH A
DEEP-SHEAR VECTOR LARGELY PARALLEL TO THE BOUNDARY, SUGGESTS A
QUICK GROWTH TO LINEAR MODE WITH THREATS FOR WIND GUSTS AND A
MESOVORTEX TORNADO.
FARTHER SOUTH, IN THE VICINITY OF MGW AND ADJACENT NRN WV/SW
PA, SHEAR WILL BE MORE OBLIQUE TO THE BOUNDARY, SUGGESTING
POTENTIAL FOR DISCRETE UPDRAFTS SHOULD RECOVERY OCCUR.
OVERALL, A LOW UNCONDITIONAL SEVERE THREAT (WIND GUSTS AND
POSSIBLY A MESOVORTEX TORNADO) SEEMS REASONABLE, AND MESSAGING
WILL HIGHLIGHT THE GREATEST PROBABILITY FOCUSED IN NRN WV/FAR
SWRN PA AS NOTED BY PRIOR SHIFTS.
FRONTAL PASSAGE OUT OF THE REGION IS ANTICIPATED BY EARLY
EVENING. CLEARING BEHIND THE FRONT WILL BE QUICK, AS A STRONGER
TROUGH DEVELOPS TO THE WEST, FAVORING RAPID WEAKENING OF HIGH
PRESSURE AND RETURN TO LIGHT SLY FLOW BY FRI MORNING.
LONG TERM /FRIDAY THROUGH WEDNESDAY/
KEY MESSAGES:
- ARRIVAL OF A STRONG COLD FRONT WILL INCREASE PRECIPITATION
CHANCES LATE FRIDAY INTO SATURDAY
- DRY, BUT SEASONABLY COOL WEATHER, IS LIKELY SUNDAY AND MONDAY
BEFORE A RETURN TO NEAR-NORMAL TEMPERATURE MID-WEEK
-------------------------------------------------------------------
STRONG SWLY FLOW ALOFT WILL PERSIST FRI TO THE SOUTH OF A DEEP
CLOSED LOW OVER CENTRAL CANADA. A SERIES OF SHORTWAVE TROUGHS
EMBEDDED IN THE FLOW WILL INFLUENCE THE UPPER OHIO VALLEY
FRI/FRI NIGHT, WITH A PARTICULARLY STRONG TROUGH ADVANCING A
STRONG COLD FRONT ACROSS THE REGION ON SAT.
AFTER A QUICK POST-FRONTAL RECOVERY FROM THU'S FRONT, FRI MAXIMA
ARE LIKELY TO RETURN TO NEAR- OR SLIGHTLY ABOVE-SEASONAL LEVELS
IN THE 80S ALONG WITH GUSTY SYNOPTIC WIND. HOWEVER, ATTENDANT
CLOUDS/PRECIPITATION AND POST-FRONTAL COLD ADVECTION WILL
CONTINUE THE THERMAL ROLLER COASTER, WITH SAT MAXIMA BACK IN THE
60S ONCE FRI NIGHT/SAT RAIN CLEARS OUT BY MID-AFTERNOON.
PRIMARY UNCERTAINTY DRIVING THE FRI/SAT TIME PERIOD REVOLVES
AROUND TIMING OF SHORTWAVE TROUGHS EMBEDDED IN THAT STRONGER
FLOW ALOFT, AND MODULATED BY VARIANCES IN SPATIAL POSITIONING OF
THE CLOSED UPPER LOW.
GIVEN THESE RELATED UNCERTAINTIES, BEST TIMING FOR RAIN ONSET
ASSOCIATED WITH THE FRONTAL APPROACH APPEARS TO BE AFTER 8PM
FRI, BUT IT COULD BEGIN AS EARLY AS LATE FRI AFTERNOON IN ERN
OH.
EVENTUAL POST-FRONTAL CLEARING AND SLACKENING OF THE NWLY FLOW
AS HIGH PRESSURE BUILDS WILL SUPPORT RADIATIONAL COOLING WITHIN
A COOLER AIRMASS, SUGGESTING OVERNIGHT LOWS COULD FALL INTO THE
40S SAT NIGHT THRU MON NIGHT, WITH SEASONABLY COOL MAXIMA
PERSISTING IN THE 60S DURING THIS TIME.
AMID CONTINUED WRN-CONUS RIDGING AND A DEPARTING NERN-CONUS
TROUGH, CONSIDERABLE MODEL VARIANCE DEVELOPS EARLY NEXT WEEK.
CLUSTER ANALYSIS SUGGESTS STRONG MID-LEVEL FLOW OVER THE REGION
WITH TWO PRIMARY SOURCES OF UNCERTAINTY DRIVING POTENTIAL
OUTCOMES: THE FIRST BEING THE AMPLITUDE OF THE DEPARTING ERN-
CONUS TROUGH, AND THE SECOND BEING POTENTIAL FOR AN EMBEDDED
SHORTWAVE TROUGH ADVANCING THRU THE STRONGER FLOW. IN EITHER
CASE, COOLER AIR IS LIKELY TO PERSIST ON MON, WITH SOME VARIANCE
IN RECOVERY ON TUE.
THEREAFTER CONSIDERABLE UNCERTAINTY EXISTS IN THE FORECASTED
WEATHER PATTERN FOR THE UPPER OHIO VALLEY, AS A RESULT OF
VARIANCE IN THE AMPLITUDE OF THE LINGERING WRN-CONUS RIDGE. AT
THIS TIME, THE BLENDED MEAN (SUGGESTING A MODEST THERMAL
RECOVERY THRU LATE WEEK) WILL YIELD MINIMIZED FORECAST ERROR,
AND WILL BE ACCEPTED.
AVIATION /17Z WEDNESDAY THROUGH SUNDAY/
VFR CONTINUES THROUGH WEDNESDAY NIGHT. DIURNALLY DRIVEN CUMULUS
THIS AFTERNOON WILL DISSIPATE AND GIVE WAY TO INCREASING MID
AND UPPER LEVEL CLOUD COVER AS LOW PRESSURE DEEPENS OVER THE
UPPER GREAT LAKES TO OUR NORTHWEST. SOUTHWEST WIND WILL BE ON
THE INCREASE THIS AFTERNOON WITH SOME GUSTS UP TO 15 KNOTS AT
TIMES, BUT THERMODYNAMIC PROFILES LARGELY SUGGEST SUSTAINED
AROUND 8-12 KNOTS. CAN'T RULE OUT A FEW SHOWERS OVER NORTHERN WV
(MGW) AND EXTREME SOUTHWEST PA (SOUTH OF PIT/AGC), THOUGH NO
IMPACTFUL RESTRICTIONS ARE ANTICIPATED, AND CONFIDENCE WASN'T
HIGH ENOUGH FOR ANY MENTION IN TAFS AT THIS TIME.
AFTER SUNSET TONIGHT, WIND GUSTS WILL CEASE AND GIVE WAY TO LIGHT
SOUTH/SOUTHWEST FLOW OVERNIGHT. THICKENING CLOUD COVERAGE WILL
WORK IN AND LOWER, THOUGH STILL REMAIN VFR, FROM THE WEST AHEAD
OF AN APPROACHING COLD FRONT.
PROBABILITY FOR RESTRICTIONS INCREASES GREATLY ON THURSDAY
MORNING AS AN UPPER LEVEL TROUGH AND SURFACE COLD FRONT MOVE
THROUGH. TWO ROUNDS OF PRECIP IS LIKELY; ONE IN THE MORNING
ALONG A PRE-FRONTAL TROUGH THAT MAY BRING PERIODS OF MVFR
RESTRICTIONS IN RAIN TO ZZV AFTER 10Z, PIT AND SURROUNDING SITES
AFTER 13Z, AND LBE AFTER 15Z. THUNDER IS POSSIBLE WITH THIS
ROUND THOUGH NO NOTABLY GUSTY WIND IS LIKELY, SO HAVE INCLUDED A
TEMPO FOR TSRA.
DEPENDING ON THE EXTENT OF CLEARING AFTER THE MORNING BATCH,
SOME OF THE STORMS WITH THE SECOND ROUND COULD BRING GUSTY WIND.
CONFIDENCE ON THE EVOLUTION OF THIS ROUND IS LOW AT THIS TIME,
SO OPTED FOR A PROB30 GROUP TO REINTRODUCE TSRA IN THE
AFTERNOON, AND WILL CONTINUE TO UPDATE AS CONFIDENCE GROWS. ENSEMBLE
PROBABILITY SUGGESTS CONDITIONS IMPROVING WEST TO EAST AFTER
FRONTAL PASSAGE. NON-CONVECTIVE WIND IS LIKELY TO INCREASE AS
WELL WITH GUSTS AS HIGH AS 20-25 KNOTS THURSDAY AND FRIDAY
AFTERNOONS.
OUTLOOK.
ADDITIONAL SHORTWAVE MOVEMENT MAY OFFER ADDITIONAL
RAIN AND RESTRICTIONS CHANCES LATE FRIDAY INTO SATURDAY BEFORE
DRY WEATHER DEVELOPS TO START THE NEXT WEEK.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...KRAMAR/HEFFERAN
NEAR TERM...KRAMAR
SHORT TERM...KRAMAR
LONG TERM...KRAMAR
AVIATION...MLB
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