563
FXUS61 KPBZ 201738
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
138 PM EDT THU AUG 20 2026
WHAT HAS CHANGED
THE FLOOD WATCH WILL BE ALLOWED TO EXPIRE AT 2 PM. THE POTENTIAL
COVERAGE AREA OF SHOWERS/STORMS ON FRIDAY HAS SHRUNK A BIT.
UNCERTAINTY REGARDING SEVERE STORM POTENTIAL ON SATURDAY
CONTINUES.
KEY MESSAGES
1) THE THREAT OF LOCALIZED HEAVY RAIN REMAINS UNTIL LATE
AFTERNOON, WITH DRIER WEATHER DEVELOPING THIS EVENING.
2) AFTER LIMITED SHOWER/STORM ACTIVITY FRIDAY, NEW ROUNDS OF
RAINFALL ARE POSSIBLE OVER THE WEEKEND. SATURDAY MAY PRESENT A
LOCALIZED THREAT FOR DAMAGING WIND GUSTS, DEPENDING ON FRONTAL
TIMING AND CLOUD COVER.
DISCUSSION
KEY MESSAGE 1...
THE MCV WHICH CAUSED MORE WIDESPREAD HEAVY RAIN HAS MOVED EAST
OF THE REGION. HOWEVER, LOW-LEVEL CONVERGENCE CONTINUES ON THE
STALLED BOUNDARY ALONG THE I-70 CORRIDOR, ALONG WITH
PRECIPITABLE WATER VALUES STILL IN THE 1.6 TO 1.8 INCH RANGE.
THIS IS CONTINUING TO CREATE BANDS OF MODERATE TO HEAVY RAIN
ALONG AND SOUTH OF THE BOUNDARY SOUTH OF I-70. THE VARIOUS CAMS
SUGGEST THIS ACTIVITY WILL CONTINUE THROUGH 22Z OR SO, TAPERING
OFF FROM NORTH TO SOUTH AS THE BOUNDARY GETS A PUSH FROM A
SHORTWAVE CROSSING THE UPPER OHIO VALLEY. WITH MUCH OF THE
ONGOING FLOOD WATCH ALREADY COVERED BY WARNINGS AND WITH A
RELATIVELY LOW THREAT OF NEW FLOODING, WILL LET THE WATCH EXPIRE
AT 2 PM. QUIETER WEATHER TAKES HOLD AFTER SUNSET WITH THE
ARRIVAL OF SURFACE HIGH PRESSURE, WITH FOG LIKELY TO DEVELOP
OVERNIGHT WHERE THE SKY CAN CLEAR.
KEY MESSAGE 2...
WEAK SURFACE HIGH PRESSURE STILL TRIES TO BUILD SOUTH ON FRIDAY.
MODEL GUIDANCE APPEARS A BIT LESS BULLISH ON SHOWER/STORM
DEVELOPMENT DURING THE AFTERNOON. MOISTURE DEPTH/SUBSIDENCE-
INDUCED CAPPING MAY LARGELY SUPPRESS DEVELOPMENT AT LEAST NORTH
OF THE PA TURNPIKE, AND POTENTIALLY FURTHER SOUTH THAN THAT. WILL
KEEP NBM SUGGESTION OF POPS SOUTH OF I-70/EAST OF I-77, ALTHOUGH
SOME MINOR MODIFICATION MAY BE NEEDED WITH FUTURE MODEL RUNS.
THE NEXT 500MB SHORTWAVE TROUGH PIVOTS ACROSS THE GREAT LAKES
LATER FRIDAY NIGHT/SATURDAY MORNING, AND LINGERS ACROSS THE
UPPER OHIO VALLEY INTO SUNDAY WITH ADDITIONAL VORTICITY MAXIMA
MAINTAINING LOWER HEIGHTS. AN ASSOCIATED FRONTAL BOUNDARY LOOKS
TO SWING THROUGH DURING LATE AFTERNOON/EVENING ON SATURDAY,
ALTHOUGH THE TIMING STILL IS QUESTIONABLE. THERE ARE STILL
SCENARIOS, GIVEN FAVORABLE TIMING/CLEARING, THAT SHOW SUFFICIENT
CAPE AND DCAPE FOR A DOWNBURST WIND THREAT. THE 12Z RRFS, FOR
EXAMPLE, DOES SHOW UP TO 1500 J/KG CAPE/800-1000 J/KG DCAPE IN
AREAS EAST OF PITTSBURGH DURING THE AFTERNOON THAT COULD SUPPORT
THE SEVERE THREAT. MUCH OF THE AVAILABLE MACHINE-LEARNING
GUIDANCE DOES CONTINUE TO HIGHLIGHT THE POTENTIAL. STILL,
CHANGES IN FRONTAL TIMING OR CLOUD COVER COULD REDUCE THE
OVERALL THREAT, AND FUTURE CAMS RUNS WILL BE EVALUATED TO
REASSESS THE RISK.
THAT THEN SERVES AS A PRECURSOR TO ADDITIONAL SHORTWAVE TROUGH
MOVEMENT ALOFT COMBINING WITH A MORE DEFINED SURFACE COLD FRONT
THAT PASSES THROUGH SOMETIME SATURDAY AFTERNOON INTO SUNDAY.
VARIANCES IN UPPER TROUGH DEPTH/POSITIONING AND TIMING OF THE
WAVE MAKES IT DIFFICULT TO ASSESS POTENTIAL STORM ENVIRONMENTS
AND POTENTIAL HAZARDOUS WEATHER THREATS. ENSEMBLE GUIDANCE,
DRIVEN PRIMARILY BY CANADIAN MODELING, DOES SHOW SCENARIOS WITH
ENOUGH CAPE/DCAPE FOR A DAMAGING WIND THREAT (THOUGH WEAK SHEAR
WON'T BE A BOON) THAT SEEMS TO BE CAPTURED BY A FEW OTHER
MACHINE-LEARNING CONVECTIVE OUTLOOK MODELS. THIS SCENARIO IS
MAINLY TIED TO CLEAN HEATING PRIOR TO THE FRONT/SHORTWAVE AND
SATURDAY AFTERNOON/EARLY EVENING STORM OCCURRENCE; EARLIER/LATER
ARRIVALS OR MORE CLOUD COVER IS JUST AS LIKELY THAT WOULD
DAMPEN OR COMPLETELY SQUASH THAT RISK. TRENDS WILL BE MONITORED
TO UNDERSTAND HOW THINGS MAY TRACK. SCATTERED SHOWERS/STORMS
REMAIN POSSIBLE ON SUNDAY, BUT CONVECTIVE PARAMETERS APPEAR A
LITTLE LESS FAVORABLE FOR A SEVERE THREAT.
ENSEMBLES CONTINUE TO LEND CONFIDENCE TO A DRIER FORECAST FOR
THE FIRST PART OF NEXT WEEK, AS SURFACE HIGH PRESSURE RETURNS
UNDER A WEAKENING TROUGHING PATTERN.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
SHOWERS ARE STARTING TO EXIT THE REGION TO THE EAST TO KICK OFF
THE 18Z TAF CYCLE, WITH AREAS ALONG AND WEST OF A ZZV-PIT-DUJ
LINE ALREADY CLEAR OF THE STEADIER RAINFALL AND ASSOCIATED
RESTRICTIONS. EXPECT MVFR/IFR CEILINGS TO LINGER A BIT EVEN
AFTER RAIN HAS DEPARTED BEFORE DAYTIME HEATING WANES AND THE CU
FIELD DISSIPATES. ANY LATE AFTERNOON OR EVENING IMPROVEMENTS IN
CIGS/VSBYS APPEAR TO BE SHORT-LIVED AS CLEARING SKIES AND A
STAGNANT, MOIST NEAR-SURFACE AIRMASS FAVOR FOG AND STRATUS
DEVELOPMENT OVERNIGHT INTO FRIDAY MORNING. GENERALLY DRY VFR
CONDITIONS RETURN BY LATE MORNING OR AFTERNOON.
OUTLOOK...
OUTSIDE OF A FEW AFTERNOON SHOWERS POSSIBLE ALONG THE HIGHER
TERRAIN, DRY WEATHER AND VFR CONDITIONS PREVAIL THROUGH THE DAY
FRIDAY. ADDITIONAL ROUNDS OF RAIN AND RESTRICTIONS ARE LIKELY
THIS WEEKEND WITH ANOTHER PASSING DISTURBANCE.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...FLOOD WATCH UNTIL 2 PM EDT THIS AFTERNOON FOR PAZ021-029-031-
073>076.
OH...FLOOD WATCH UNTIL 2 PM EDT THIS AFTERNOON FOR OHZ039-040-
048>050-057>059-068-069.
WV...FLOOD WATCH UNTIL 2 PM EDT THIS AFTERNOON FOR WVZ001>004-012-
021-509>512.
DISCUSSION...CL
AVIATION...CERMAK
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page