156
FXUS61 KPBZ 121700
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
100 PM EDT SAT SEP 12 2026
WHAT HAS CHANGED
THE FLOOD WATCH HAS BEEN EXPANDED TO THE REST OF THE FORECAST AREA.
ISOLATED SEVERE STORM THREATS ALSO NOW ENCOMPASS MORE OF THE AREA
TODAY. CONFIDENCE IN THE SUNDAY SEVERE THREAT IS DECREASING.
KEY MESSAGES
1) WIDESPREAD RAIN AND ISOLATED THUNDERSTORMS EXPECTED ON SATURDAY
WITH FLOODING AND ISOLATED DAMAGING GUSTS POSSIBLE
2) SEVERE THUNDERSTORMS STILL POSSIBLE SUNDAY AFTERNOON AND EVENING
WITH A COLD FRONT, BUT THE LEVEL OF THE THREAT IS UNCERTAIN
3) A BRIEF BOUT OF DRY WEATHER RETURNS EARLY NEXT WEEK
DISCUSSION
KEY MESSAGE 1...
A RENEWED PUSH OF MOISTURE WITH LONG MOISTURE TRANSPORT VECTORS ON
MORNING MESOANALYSIS IS ONGOING THIS MORNING IN STRENGTHENING
SOUTHWEST FLOW. LATER THIS AFTERNOON, A SHORTWAVE RIDING UP THE OHIO
VALLEY WILL CROSS OUR REGION AND ENHANCE SUPPORT FOR LIFT. OUR 12Z
SOUNDING SHOWED A 1.54" PWAT VALUES, THOUGH UPSTREAM AT WILMINGTON,
THEIRS WAS 2", AND LATEST ACARS SOUNDINGS FROM CMH AND PIT ARE
SHOWING INCREASING DEEP LAYER MOISTURE WITH EVENTUAL 99TH PERCENTILE
VALUES BY THIS AFTERNOON AREAWIDE. WITH INITIAL HIGH CLOUDS
PROVIDING ONLY MODEST HINDRANCE TO HEATING, NO CAPPING OF NOTE ON
MODEL SOUNDINGS, AND INCREASING SUPPORT FOR LIFT FROM WARM ADVECTION
AND THE APPROACHING WAVE, CAMS SUGGEST THAT SCATTERED SHOWERS AND
THUNDERSTORMS BEGIN TO FIRE DURING THE LATE MORNING AND EARLY
AFTERNOON HOURS. THE ENVIRONMENT WILL ALREADY BE SUPPORTIVE OF WARM
RAIN PROCESSES AT THAT POINT GIVEN THE INCREASING PWAT, INCREASINGLY
SATURATED COLUMN, AND DEEPENING WARM CLOUD DEPTHS.
AS THE AFTERNOON WEARS ON, THESE FACTORS CONTINUE TO IMPROVE, AND A
MORE ROBUST SHIELD OF RAIN AND EMBEDDED THUNDERSTORMS IS LIKELY AS
THE SHORTWAVE APPROACHES. AREAS EAST OF PITTSBURGH MAY SEE ENHANCED
LOW-LEVEL CONVERGENCE AS STRENGTHENING SOUTH/SOUTHWEST FLOW BUTTS UP
AGAINST SOUTHEAST FLOW JUST TO OUR EAST AS SURFACE HIGH PRESSURE
MOVES FARTHER AWAY FROM THE NEW ENGLAND COAST. THIS COULD LOCALLY
ENHANCE RAINFALL RATES TO CONCERNING LEVELS CAPABLE OF FLASH
FLOODING. HREF PROBABILITIES OF GREATER THAN 1" ARE VERY HIGH AT 70-
95% FROM PITTSBURGH SOUTH AND EAST, GREATER THAN 2" AT 60-80% EAST
OF PITTSBURGH, AND GREATER THAN 3" AT 40-50%. LPPM VALUES STILL
REACH UP TO 5-6". SUCH TOTALS REPRESENT THE HIGH-END SCENARIO, BUT
THE ENVIRONMENT IS CERTAINLY CAPABLE OF SUPPORTING THEM. MUCH OF THE
CWA HAS SOIL MOISTURE LEVELS IN EXCESS OF 50% ACCORDING TO MRMS.
ALTHOUGH LOW-LEVEL FORCING MAY NOT BE AS ROBUST AS AREAS TO THE
EAST, THE SAME FAVORABLE ENVIRONMENTAL PARAMETERS FOR HEAVY RAIN
(HIGH PWAT/SATURATED SOUNDINGS/ETC) ARE PRESENT, AND AT LEAST
ISOLATED FLOODING ISSUES ARE POSSIBLE. WPC HAS EXPANDED THE SLIGHT
RISK FOR EXCESSIVE RAINFALL TO VIRTUALLY ALL OF THE FORECAST AREA.
THE FLOOD WATCH REMAINS IN EFFECT FOR THE ENTIRE AREA THROUGH
TONIGHT.
IN ADDITION TO THE FLOODING THREAT, A WINDOW FOR STRONG TO ISOLATED
SEVERE THUNDERSTORMS EXISTS. JOINT 10KM NEIGHBORHOOD PROBABILITIES
OF 1000 J/KG OF SBCAPE AND 30 KNOTS OF 0-6KM SHEAR REACH 70-90%
ACROSS MUCH OF THE AREA THIS AFTERNOON. WHILE MID-LEVEL LAPSE RATES
WILL BE POOR GIVEN THE DEEP SATURATION, AND SOUNDINGS EVENTUALLY
LEAD TO TALL AND SKINNY CAPE PROFILES, THERE MAY BE ENOUGH STORM
ORGANIZATION AND STEEP LOW-LEVEL LAPSE RATES TO PRODUCE DAMAGING
WIND POTENTIAL WITH SMALL-SCALE BOWING STRUCTURES POSSIBLE. EVEN A
TORNADO CANNOT BE TOTALLY RULED OUT PRIMARILY EAST OF PITTSBURGH
WHERE LOCALLY BACKED LOW-LEVEL FLOW ELONGATES HODOGRAPHS A TOUCH. ML
GUIDANCE PEGS A LOW-END TORNADO AND WIND THREAT TODAY.
THE HEAVY RAIN THREAT SHOULD BEGIN TO WANE DURING THE LATE
EVENING/MIDNIGHT PERIOD AS THE SHORTWAVE CROSSES, LEAVING SOME
SCATTERED SHOWERS IN ITS WAKE. LINGERING LOW-LEVEL MOISTURE SHOULD
LEAD TO ABUNDANT STRATUS COVERAGE BY SUNDAY MORNING.
KEY MESSAGE 2...
ANOTHER SEVERE WEATHER THREAT COULD EMERGE ON SUNDAY AS
DEVELOPING GREAT LAKES TROUGHING DROPS A SURFACE COLD FRONT INTO
OUR REGION DURING THE LATE AFTERNOON AND EVENING HOURS. THE
TROUGH WILL PROVIDE SUFFICIENT DEEP SHEAR ON THE ORDER OF 35-45
KNOTS, WITH HIGHER VALUES CLOSER TO THE LAKES. MOISTURE
CERTAINLY REMAINS PRESENT WITH SURFACE DEWPOINTS REMAINING IN
THE UPPER 60S TO AROUND 70. HOWEVER, THERE REMAINS SOME QUESTION
AS TO THE LEVEL OF CLEARING AND THUS DESTABILIZATION THAT CAN
TAKE PLACE, AS ENSEMBLES CONTINUE TO SUGGEST A RANGE OF SKY
COVER OUTCOMES. THIS RESULTS IN 25TH/75TH PERCENTILE SBCAPE
SPREADS OF BELOW 800 J/KG TO ABOVE 1200 J/KG. PERHAPS MORE
INHIBITIVE IS A SUBSIDENT WARM LAYER AROUND 800 MB THAT WAS
EVIDENT IN FRIDAY'S CAM RUNS AND IS EVEN MORE PREVALENT ACROSS
TODAY'S SUITE. IN FACT, A COUPLE WARM LAYERS ARE SHOWING UP IN
MODEL SOUNDINGS. THE RRFS WAS THE ONLY MODEL THAT HAD BEEN LESS
CAPPED, BUT EVEN NOW THE LATEST RUN IS JUMPING SHIP AND ERRING
MORE TOWARD THE REST OF THE SOLUTIONS. SO, CONFIDENCE IN
ORGANIZED SEVERE WEATHER ON SUNDAY IS DECREASING. SOME CAMS DO
SHOW AT LEAST WIDELY SCATTERED STORM COVERAGE DURING FRONTAL
PASSAGE, AND GIVEN THE SHEAR, ANY STORM WILL BE CAPABLE OF
MARGINALLY SEVERE WIND AND HAIL THREATS PROVIDED THE WARM LAYERS
CAN BE OVERCOME. A MORE WIDESPREAD THREAT COULD EMERGE IF LATER
RUNS SHOW BETTER POTENTIAL FOR DESTABILIZATION AND A LACK OF
CAPPING.
KEY MESSAGE 3...
MINOR TIMING ISSUES REMAIN, BUT ENSEMBLES HAVE CLUSTERED INTO SOME
BETTER AGREEMENT THAT THE TROUGH AXIS CROSSES THE REGION EARLY
MONDAY AND MAINTAINS SHOWERS THROUGH THE EARLY MORNING HOURS BEFORE
MID-LEVEL RIDGING PROVIDES A DRY INTERLUDE BY MONDAY AFTERNOON. THIS
BREAK MAY LAST UNTIL TUESDAY NIGHT OR WEDNESDAY, DEPENDING ON THE
PROGRESS OF THE NEXT FRONT.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
VFR IS EXPECTED THROUGH EARLY AFTERNOON FOR MOST AIRPORTS,
THOUGH INCREASING CUMULUS AND MID LEVEL CLOUDS ARE EXPECTED
AHEAD OF AN APPROACHING SHORTWAVE TROUGH. EXPECT A BROKEN LINE
OF SHOWERS AND THUNDERSTORMS TO IMPACT FKL FROM EARLY TO MID
AFTERNOON ALONG AN AREA OF WARM ADVECTION. EXPECT ADDITIONAL
SCATTERED THUNDERSTORMS TO DEVELOP ACROSS PORTIONS OF WRN PA AND
NRN WV WHERE SURFACE HEATING HAS OCCURRED, WITH MORE
CONCENTRATED SHOWERS/STORMS AHEAD OF THE APPROACHING SHORTWAVE
TROUGH THIS AFTERNOON AND EVENING. INCLUDED A TEMPO FOR THE MOST
LIKELY TIME TO SEE THUNDERSTORMS. IFR AND HEAVY RAIN ARE
EXPECTED IN SOME OF THESE STORMS.
EXPECT MVFR IN SHOWERS FOR 3 OR 4 HOURS AFTER THE STORMS EXIT
LATE THIS EVENING AND OVERNIGHT. IFR IN FOG AND STRATUS IS THEN
EXPECTED TO DEVELOP TONIGHT WITH LOW LEVEL MOISTURE IN PLACE.
OUTLOOK...
IFR SHOULD CONTINUE INTO SUNDAY MORNING BEFORE A GRADUAL
IMPROVEMENT TO VFR BY AFTERNOON. A CROSSING COLD FRONT WILL
BRING SCATTERED THUNDERSTORM CHANCES TO THE AREA LATE SUNDAY
AFTERNOON AND EVENING. OUTSIDE OF MORNING VALLEY FOG, VFR
RETURNS MONDAY AND TUESDAY UNDER HIGH PRESSURE. SHOWER AND
THUNDERSTORM CHANCES INCREASE FROM N-S ON WEDNESDAY WITH AN
APPROACHING COLD FRONT.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...FLOOD WATCH THROUGH LATE TONIGHT FOR PAZ007>009-013>016-
020>022-029-031-073>078.
OH...FLOOD WATCH THROUGH LATE TONIGHT FOR OHZ039>041-048>050-
057>059-068-069.
WV...FLOOD WATCH THROUGH LATE TONIGHT FOR WVZ001>004-012-021-
509>514.
DISCUSSION...MLB/CL
AVIATION...WM
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