527
FXUS61 KPBZ 041431 AAA
AFDPBZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
1031 AM EDT THU SEP 4 2025
SYNOPSIS
SHOWERS AND THUNDERSTORMS RETURN TODAY 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:
- SHOWERS AND LOCALIZED THUNDERSTORMS FAVORED TODAY, LIKELY IN
TWO MAIN WAVES: THIS MORNING AND THIS AFTERNOON/EVENING
- MARGINAL RISK FOR DAMAGING WIND DEPENDENT ON HEATING AHEAD OF
AFTERNOON/EVENING 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 THIS
MORNING. WITH A LACK OF MID-LEVEL DRY AIR AND ELEVATED
UPDRAFTS, ANY MORNING SHOWERS/STORMS SHOULD NOT CARRY NOTABLE
POTENTIAL FOR A SEVERE- WEATHER RISK.
THE PRE-FRONTAL TROUGH ADVANCES TO THE RIDGES BY EARLY
AFTERNOON, FOCUSING A PRIMARY SEVERE WEATHER RISK NEAR AND EAST
OF THE RIDGES DURING AND AFTER THAT TIME. TRAILING THIS WILL BE
THE FRONT ITSELF, WHICH COULD SUPPORT AN ADDITIONAL ROUND OF
THUNDERSTORM DEVELOPMENT AS IT TRACKS EASTWARD ACROSS THE AREA
THROUGH AFTERNOON AND EVENING HOURS. THIS SECOND WAVE (AND ITS
ASSOCIATED SEVERE WEATHER THREAT) WILL DEPEND HEAVILY ON HOW
MUCH HEATING CAN OCCUR TO RECOVER SURFACE-BASED INSTABILITY
FOLLOWING THE MORNING WAVE.
THE PRIMARY FACTORS INFLUENCING THIS RECOVERY WILL BE CLOUD
COVER AND FRONT SPEED/TIMING. LESS CLOUD COVER AND A SLOWER
FRONT WOULD BETTER FAVOR STRONGER STORM DEVELOPMENT AND A HIGHER
SEVERE WEATHER THREAT, WHILE MORE ABUNDANT CLOUD COVER AND A
FASTER FRONT WOULD FAVOR THE OPPOSITE. UNFORTUNATELY, HI-RES
GUIDANCE STILL EXHIBITS AN UNCHARACTERISTICALLY LARGE SPREAD
WITH RESPECT TO THE TIMING OF THE FRONT. THUS, IT MAY END UP
BEING A SCENARIO WHERE WE HAVE TO WAIT AND SEE HOW THE MORNING
WAVE PLAYS OUT BEFORE GAINING CONFIDENCE IN THE AFTERNOON AND
EVENING OUTLOOK.
IN THE CASE WHERE STRONGER STORMS DO 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 A PRIMARY THREAT FOR DAMAGING WIND GUSTS,
THOUGH A BRIEF MESOVORTEX TORNADO COULDN'T BE ENTIRELY RULED OUT.
FARTHER SOUTH (NEAR AND SOUTH OF THE MASON-DIXON), SHEAR WILL
BE MORE OBLIQUE TO THE BOUNDARY, SUGGESTING POTENTIAL FOR MORE
DISCRETE UPDRAFTS AND THEREFORE A SLIGHTLY HIGHER CHANCE FOR A
BRIEF TORNADO IN ADDITION TO DAMAGING WIND GUSTS (AGAIN,
CONDITIONAL ON RECOVERY OCCURRING).
FRONTAL PASSAGE OUT OF THE REGION IS ANTICIPATED BY LATE EVENING.
CLEARING BEHIND THE FRONT WILL BE QUICK, EXCEPT PERHAPS THE
RIDGES AND ADJACENT LOWLANDS WHERE POST-FRONTAL UPSLOPE FLOW
(AT LEAST INITIALLY) COULD SUPPORT LINGERING LOW STRATUS. A
STRONG TROUGH DEVELOPING TO THE WEST WILL FAVOR RAPID WEAKENING
OF HIGH PRESSURE AND RETURN TO LIGHT SOUTHERLY FLOW BY EARLY
FRIDAY MORNING.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
KEY MESSAGES:
- DRY AND SEASONABLE WEATHER FAVORED FRIDAY WITH INCREASING RAIN
CHANCES IN THE EVENING
- RAIN LIKELY SATURDAY WITH NEAR RECORD LOW MAXIMUM TEMPERATURE
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THE UPPER LEVEL PATTERN WILL EXPERIENCE A QUICK PIVOT BACK TO
SOUTHWESTERLY FLOW AHEAD OF THE NEXT DEEP SHORTWAVE ROUNDING
THROUGH THE BROADER GREAT LAKES TROUGH. MODEST WARM ADVECTION
AND INITIALLY SUNNIER SKIES ARE LIKELY TO AID TEMPERATURE
RETURNING NEAR THE DAILY AVERAGE HIGH. SUBSIDENCE AHEAD OF THE
APPROACHING MID-LEVEL JET ALSO WILL AID IN FRIDAY INITIALLY
STARTING DRY.
MODELS FAVOR THE APPROACH AND PASSAGE OF A FAIRLY POTENT COLD
FRONT BETWEEN LATE FRIDAY AFTERNOON INTO EARLY SATURDAY MORNING
AS THE UPPER TROUGH AXIS DEEPENS OVER THE LOWER OHIO RIVER
VALLEY. VARIABILITY CONTINUES TO EXIST IN TIMING OF THE MID-
LEVEL JET AIDED ASCENT AND THE SURFACE FRONT, OF WHICH EACH MAY
INFLUENCE ONSET OF PRECIPITATION AND AREAS OF MORE FOCUS RAIN.
REGARDLESS, WARM AIR ALOFT IS HIGHLY LIKELY TO MUTE SEVERE
CONCERNS DESPITE STRONG SHEAR BEFORE THE COLD FRONT PASSAGES
ENDS ANY SURFACE BASED BUOYANCY. THE BULK OF THE EVENT THEN WILL
BE WAVES OF STRATIFORM RAIN OVERNIGHT FRIDAY INTO SATURDAY UNTIL
THE UPPER TROUGH AXIS MORE CLOSELY INCHES EAST AND DRY-SLOTTING
PLUS LIFT SHIFT ACCORDINGLY, END PRECIPITATION WEST TO EAST.
THE COMBINATION OF EXCESSIVE CLOUD COVER, RAIN, AND NEAR SURFACE
COLD ADVECTION SATURDAY MEANS AREA HIGH TEMPERATURE IS LIKELY
TO FALL WITHIN THE TOP 10 LOWEST MAXIMUMS ON RECORD FOR AREA
CLIMATE SITES AND THE COLDEST MAXIMUM TEMPERATURE READINGS FOR
SEPTEMBER 6TH SINCE 2011. SPECIFICALLY FOR PITTSBURGH'S CLIMATE,
CURRENT MODELING SUGGESTS A 10% PROBABILITY OF THE HIGH
TEMPERATURE TYING THE RECORD LOW MAXIMUM OF 60 DEGREES SET IN
1924.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
KEY MESSAGES:
- DRY, BUT SEASONABLY COOL WEATHER, IS LIKELY SUNDAY AND MONDAY
BEFORE A RETURN TO NEAR-NORMAL TEMPERATURE MID-WEEK
- A LAKE ENHANCED SHOWER NORTH OF PITTSBURGH CAN'T BE RULED OUT
SUNDAY AFTERNOON
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ENSEMBLE MEANS FAVOR THE TRANSITION OF THE DEEP UPPER TROUGH
AXIS WEST TO EAST THROUGH THE REGION SUNDAY THAT PORTENDS TO
GRADUAL HEIGHT RISES WITHIN NW FLOW TO START THE NEXT WORK WEEK.
THE COMBINATION OF RESIDUAL COLD ADVECTION AND COLD AIR ALOFT
WILL KEEP TEMPERATURE READINGS WELL BELOW NORMAL SUNDAY WITH A
NON-ZERO CHANCE FOR AFTERNOON LAKE ENHANCED SHOWERS NORTH OF
PITTSBURGH; GLOBAL MODELING MAY BE UNDERSELLING THIS POTENTIAL
GIVEN LOWER RESOLUTION ATTEMPTING TO CAPTURE LAKE DYNAMICS.
SURFACE HIGH PRESSURE IS LIKELY TO DEVELOP OVER THE AREA MONDAY
THEN TRANSITION EAST BY MIDWEEK TO AID IN PROMOTING DRY WEATHER
WHILE SUBTLE HEIGHT RISES FAVOR RISING TEMPERATURE. LONG RANGE
OUTLOOKS ARE MORE VARIED BEYOND TUESDAY DUE TO VARIANCE IN THE
AMPLITUDE/DEPTH OF THE NEXT UPPER TROUGH AND THE INFLUENCES OF
LOW PRESSURE MOVEMENT ALONG THE WEST COAST. THE KEY IS THAT
CLUSTER ANALYSIS SUGGESTS THE MORE PLAUSIBLE SCENARIOS ARE
UNLIKELY TO FEATURE STARK TEMPERATURE CHANGES AND/OR BE
CONDUCIVE TO HAZARDOUS WEATHER.
AVIATION /15Z THURSDAY THROUGH MONDAY/
CIGS HAVE LOWERED TO MVFR BEHIND AN EXITING AREA OF SHOWERS THIS
MORNING. THESE LOWER CIGS SHOULD CONTINUE TO SPREAD EASTWARD
WITH INCREASED LOW LEVEL MOISTURE AHEAD OF AN APPROACHING COLD
FRONT.
ADDITIONAL SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGH THIS
AFTERNOON AND EARLY EVENING AS THE COLD FRONT CROSSES THE
REGION. MVFR/LOCAL IFR CONDITIONS ARE POSSIBLE IN ANY OF THESE
STORMS, ALONG WITH GUSTY WINDS. MAINTAINED PREDOMINANT SHOWERS
WITH THIS FRONT, WITH TEMPOS FOR THE POTENTIAL FOR STORMS AHEAD
OF AND ALONG THE FRONT. ML CAPE FROM 500-800 J/KG IS EXPECTED
THIS AFTERNOON, ALONG WITH SOME SHEAR.
MVFR/LOW VFR IS EXPECTED BEHIND THE FRONT, THOUGH WITH LOW LEVEL
MOISTURE IN PLACE, IFR IS EXPECTED TO DEVELOP MAINLY EAST OF PIT
OVERNIGHT.
OUTLOOK.
LOW CIGS ARE POSSIBLE INTO FRIDAY MORNING WITH LOW LEVEL
MOISTURE IN PLACE. ADDITIONAL SHOWERS ARE LIKELY, WITH POSSIBLE
THUNDERSTORMS, LATE FRIDAY INTO SATURDAY WITH A CROSSING
REINFORCING COLD FRONT. MAINLY VFR IS THEN EXPECTED THROUGH
MONDAY, THOUGH A CROSSING UPPER TROUGH AND COLD AIR ALOFT COULD
LEAD TO CIG RESTRICTIONS N OF PIT SUNDAY INTO MONDAY.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...KRAMAR/HEFFERAN
NEAR TERM...CERMAK/KRAMAR/RACKLEY
SHORT TERM...FRAZIER
LONG TERM...FRAZIER
AVIATION...WM
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