604
FXUS61 KPBZ 132344
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
744 PM EDT SUN SEP 13 2026
WHAT HAS CHANGED
STILL SOME UNCERTAINTY WITH THE AFTERNOON SEVERE WEATHER THREAT
TODAY, THOUGH CONDITIONALLY WARMER SURFACE TEMPERATURES COULD
BODE SLIGHTLY MORE FAVORABLE.
KEY MESSAGES
1) SEVERE THUNDERSTORMS STILL POSSIBLE SUNDAY AFTERNOON AND EVENING
WITH A COLD FRONT, BUT THE LEVEL OF THE THREAT IS UNCERTAIN
2) A BRIEF BOUT OF DRY WEATHER EARLY NEXT WEEK BEFORE RAIN RETURNS
BY MID-WEEK
DISCUSSION
KEY MESSAGE 1...
MORNING FOG AND STRATUS FROM SATURDAY'S RAIN WILL SLOWLY LIFT AND
MIX OUT BY EARLY AFTERNOON AND ALLOW FOR, AT MINIMUM, FILTERED
SUNSHINE AND POCKETS OF HEATING AHEAD OF THE APPROACH OF TODAY'S
COLD FRONT. BOTH THERMODYNAMICS AND KINEMATICS WILL BE FAVORABLE FOR
ORGANIZED STRONG TO SEVERE THUNDERSTORMS ALONG THE FRONT TODAY. HREF
AND REFS MEAN SBCAPE IS >1500 J/KG, AND AS A MID-LEVEL TROUGH
ENCROACHES WITH INCREASING WESTERLY 45-55 KNOT FLOW OVERSPREADING
NORTH TO SOUTH, EFFECTIVE SHEAR VALUES RAMP UP TO 40-50 KNOTS WITH
HIGHEST VALUES IN NW PA (40-60% PROBABILITY OF >1500 J/KG OF SBCAPE
AND >40 KNOTS OF DEEP LAYER SHEAR). PLENTY OF SURFACE MOISTURE IS IN
PLACE THIS MORNING WITH UPPER 60S TO LOW 70S DEW POINTS, THOUGH IF
CLOUDS DO END UP SCATTERING OUT BY EARLY AFTERNOON, THERE WILL
LIKELY BE SOME MIXING OF DEW POINTS. BUT, THE TYPICALLY OVER-MIXED
HRRR STILL MAINTAINS UPPER 60S BY MID-AFTERNOON. ALL THAT SAID, THE
PRIMARY INHIBITING FEATURE OVER THE PAST 24-36 HOURS HAS BEEN A
SUBSIDENT WARM LAYER AROUND 800 MB AND PERHAPS ANOTHER WEAKER ONE
ABOVE 500 MB. ONE NOTED DIFFERENCE IN THE SUNDAY MORNING 12Z CAMS IS
THAT PRE-FRONTAL SURFACE TEMPERATURES ARE FORECAST TO RISE A BIT
HIGHER THAN PREVIOUS RUNS HAD SUGGESTED. THE CAP(S) ARE STILL THERE,
BUT WITH WARMER SURFACE TEMPS, THE ML PARCEL TRACE COULD SKIRT BY
THE CAPS, OR AT LEAST HAVE AN EASIER TIME ERODING THEM WITH STRONGER
FORCING ALONG THE FRONT. IT'LL LIKELY TAKE THE STRONGER FORCING TO
REALLY GET THINGS GOING TODAY, SO WOULDN'T EXPECT TOO MUCH PRE-
FRONTAL STUFF, THOUGH A LAKE BREEZE COULD SPARK OFF SOME PRIMING
CONVECTION, BUT MOST DEVELOPMENT SHOULD OCCUR WITHIN THE STRONGEST
CONVERGENCE RIGHT ALONG THE BOUNDARY. ENVIRONMENTAL MID-LEVEL LAPSE
RATES AREN'T ALL THAT GREAT EITHER, BUT THERE IS SOME ROOM TO WET-
BULB, SO IT'S CERTAINLY PLAUSIBLE THAT SOME STORMS DO DO THIS AND
CAN IMPROVE THEM ON THE MESOSCALE. SPC HAS INTRODUCED AN UPGRADE TO
A SLIGHT RISK (2/5) FOR THE NORTHERN HALF OF OUR AREA (PITTSBURGH
NORTH).
TIMING REMAINS RELATIVELY CONSISTENT AMONG MOST MODELS WITH
INITIATION AROUND 4-5PM, PERHAPS AN HOUR EARLIER ACCOUNTING FOR CAM
BIASES, IN NW PA AND THEN WORKING SOUTHWEST. THAT'S WHERE THE BEST
SEVERE THREAT WILL BE, AND HOW FAR SOUTHWEST IT PERSISTS WILL BE
DEPENDENT ON PROGRESSION OF CONVECTION AS WE'LL BE RUNNING OUT OF
DAYLIGHT GIVEN SUNSET MOVING EARLIER AND EARLIER BY MID SEPTEMBER.
PRIMARY THREATS WILL BE LARGE HAIL AND DAMAGING WIND WITH A LOW
TORNADO THREAT AS HODOGRAPHS LOOK STRAIGHT AND MORE SUPPORTIVE OF
SPLITTING STORMS. THEY ALSO LOOK TO BE PROGRESSIVE, SO HYDRO
CONCERNS SHOULD BE MORE LIMITED TODAY ONLY TO AREAS THAT WERE
ESPECIALLY HIT HARD ON SATURDAY.
KEY MESSAGE 2...
ENSEMBLES HAVE CLUSTERED INTO BETTER AGREEMENT THAT THE TROUGH AXIS
CROSSES THE REGION EARLY MONDAY AND MAINTAINS SCATTERED SHOWER
OVERNIGHT THAT EXIT OUR EASTERN RIDGES BY THE MORNING HOURS. MID-
LEVEL RIDGING BUILDS AND PROVIDES A DRY INTERLUDE THROUGH AT LEAST
MOST OF TUESDAY BEFORE ANOTHER TROUGH APPROACHES, CROSSES TO OUR
NORTH, AND RETURNS SHOWERS TUESDAY EVENING (FASTER SOLUTION) OR
WEDNESDAY MORNING (MORE LIKELY SLOWER SOLUTION). MACHINE LEARNING
SUGGESTS A LOW-END SEVERE AND FLOODING THREAT BOTH WEDNESDAY AND
THURSDAY AS DEW POINTS START TO RECOVER A BIT BACK INTO THE 60S ON
THE SOUTH SIDE OF AN EAST-WEST BAROCLINIC ZONE.
AVIATION /00Z MONDAY THROUGH FRIDAY/
THE LINE OF SHOWERS AND THUNDERSTORMS ASSOCIATED WITH THE
FRONTAL PASSAGE HAS MOVED THROUGH MOST OF THE AREA. IT WILL BE
EAST OF MGW BY 03Z. WITH LESSER AVAILABLE INSTABILITY, THEY ARE
MORE LIKELY TO BE JUST SHOWERS.
EXPECT A WIND SHIFT TO THE NW AFTER FROPA, WITH VFR STRATOCU,
HOWEVER, SOME MVFR CLOUDS ARE POSSIBLE IN MGW OVERNIGHT. THESE
CLOUDS SHOULD SCATTER OUT LATE TONIGHT, HOWEVER, SOME FOG IS POSSIBLE
IN MGW. SCATTERED DIURNAL CU EXPECTED ON MONDAY AS HIGH
PRESSURE AND DRIER AIR BUILD IN.
OUTLOOK...
OUTSIDE OF MORNING VALLEY FOG, VFR IS EXPECTED THROUGH TUESDAY
UNDER HIGH PRESSURE. SHOWER AND THUNDERSTORM CHANCES INCREASE
FROM N-S LATE WEDNESDAY INTO LATE THURSDAY WITH THE APPROACH AND
PASSAGE OF A COLD FRONT. VFR SHOULD RETURN FRIDAY AS THE FRONT
EXITS AND HIGH PRESSURE BUILDS IN.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
DISCUSSION...MLB
AVIATION...WM/LUPO
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