817
FXUS61 KPBZ 021716
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
116 PM EDT SUN AUG 2 2026
WHAT HAS CHANGED
A FLOOD WATCH REMAINS IN EFFECT WHILE AFTERNOON THUNDERSTORMS
POSE A LIMITED DAMAGING WIND AND TORNADIC THREAT. SCENARIOS FOR
ANOTHER ACTIVE PERIOD FEATURING NON-ZERO SEVERE CHANCES START
AGAIN WEDNESDAY INTO NEXT WEEKEND.
KEY MESSAGES
1) FLOOD WATCH IN EFFECT THROUGH MIDNIGHT DUE TO HEAVY RAIN
POTENTIAL, WITH STORMS ALSO POSING LIMITED DAMAGING WIND AND
TORNADIC THREATS.
2) AN ACTIVE PATTERN DEVELOPS WEDNESDAY INTO NEXT WEEKEND THAT
COULD FEATURE VARYING HAZARDOUS WEATHER RISKS.
DISCUSSION
KEY MESSAGE 1...
JET-INDUCED ASCENT ALONG THE WESTERN PERIPHERY OF A SAGGING OH
RIVER VALLEY TROUGH IN COMBINATION WITH A SIGNIFICANTLY MOIST
ENVIRONMENT AND ENOUGH DIURNAL HEATING TO FOSTER SHOWERS AND
THUNDERSTORMS THROUGH THIS EVENING. THE FOCUS FOR ACTIVITY IS
EAST OF I-77 IN OH AS SATELLITE IMAGERY HIGHLIGHTS AN AREA OF
WEAK CONVERGENCE NEAR THE OH/WV BORDER CURRENTLY THAT WILL SHIFT
NE THROUGH TONIGHT.
FLOODING REMAINS THE HIGHEST RISK FACTOR DUE TO: 1) PWAT VALUES
APPROACHING 1.7" OR AROUND 90TH PERCENTILE AMOUNTS (DRY SLOTTING
AROUND UPPER LOW AS REDUCED AMOUNTS COMPARED TO 12Z SOUNDING);
2) WARM CLOUD LAYER AIDING WARM RAIN PROCESSES (13.5KFT FREEZING
HEIGHT); 3) STORM MOTION NOT TOO FAR OFF PARALLEL FROM SURFACE
BOUNDARY POTENTIALLY ALLOWING FOR STORM TRAINING; AND 4)
POTENTIAL SURFACE HEATING WITHIN CLOUD BREAKS TO IMPROVE
BUOYANCY AND HELP RAINFALL RATES (ONGOING STORMS SUGGESTS
2-3"/HR RATES POSSIBLE, HIGHER CAN'T BE RULED OUT). THE MOST
SUSCEPTIBLE AREAS ARE THOSE PREVIOUSLY RECEIVING RAIN,
SPECIFICALLY A NARROW SWATH FROM NORTH CENTRAL GREENE COUNTY
(PA) THROUGH CENTRAL ALLEGHENY COUNTY (PA) THAT SAW ANYWHERE
FROM 1-2.5" ALREADY TODAY. THE BIGGEST UNCERTAINTY LIES IN
WHETHER ENOUGH BUOYANCY AND CONVERGENCE DEVELOP TO RESULT IN
MORE ISOLATED VS. MORE WIDESPREAD STORM COVERAGE.
OTHER HAZARDS TO MONITOR BUT ARE OF LOWER PROBABILITY IS
DAMAGING WIND AND TORNADOES. FOR DAMAGING WIND, THE THREAT IS
TIED TO DEEP ENOUGH CONVECTION TO TAP INTO A LAYER OF DRIER AIR
BETWEEN 600-400MB THAT MAY BE ENOUGH FOR DOWNBURST POTENTIAL;
HOWEVER, LATEST ACARS A MORE BEARISH ON THIS DRY LAYER WHICH
SUGGESTS THE LIMITED THREAT IS EVEN LOWER. FOR TORNADOES, 0-3KM
HODOGRAPH CURVATURE INSINUATES POTENTIAL FOR RIGHT-MOVERS (THINK
MOTION NE AT 45 DEGREES) TO MAXIMIZE SFC VORTICITY AND CREATE
GENERALLY ISOLATED, WEAK TORNADOES. HI-RES GUIDANCE SUGGESTS ANY
SUCH OCCURRENCE IS FAVORED SE OF PITTSBURGH WHERE LOW-LEVEL
CURVATURE AND AFTERNOON HEATING MAY BE BEST MAXIMIZED PRIOR TO
THE CONVERGENT LINE ARRIVING.
LOSS OF HEATING PLUS EASTWARD MOVEMENT OF THE UPPER TROUGH
FAVORS DOWNWARD TRENDS OF CONVECTIVE ACTIVITY AFTER 10PM WITH
ALL RISKS ENDING BY MIDNIGHT (IF NOT, SOONER).
KEY MESSAGE 2...
SHORTWAVE RIDGING AND SURFACE HIGH PRESSURE FAVORS A DRYING
TREND MONDAY INTO TUESDAY, THOUGH ENOUGH MOISTURE MAY LINGER TO
OFFER LOW PROBABILITY AFTERNOON THUNDERSTORMS THAT DEVELOP AT
PEAK DIURNAL HEATING.
LONG-RANGE PATTERN FAVORS RENEWED SHORTWAVE TROUGH MOVEMENT
THROUGH THE OHIO RIVER VALLEY BUT WITH VARYING DEPTHS AND
TIMING. IF THE PATTERN FEATURES A WEAKER TROUGH FARTHER NORTH,
NEAR DAILY PRECIPITATION CHANCES MAY BETTER BE ACCOMPANIED BY
SEVERE/FLOOD HAZARDS DUE TO BETTER MOISTURE INFLUX AND LIMITED
AIRMASS CHANGING. A DEEPER TROUGH PATTERN WOULD RESULT IN LESS
FREQUENT PRECIPITATION CHANCES THAT LIMITS THE DAYS OF POTENTIAL
IMPACTS. IT REMAINS BEST TO MONITOR FORECAST TRENDS FOR
WEDNESDAY INTO NEXT WEEKEND TO BETTER UNDERSTAND POTENTIAL STORM
TIMING AND THEIR ASSOCIATED RISKS.
AVIATION /18Z SUNDAY THROUGH FRIDAY/
HIGH CONFIDENCE OF IFR CIGS OVERNIGHT INTO MONDAY MORNING AND
WITH ANY STORM THAT IMPACTS AN AIRPORT.
NUMEROUS SHOWERS AND STORMS ARE EXPECTED THROUGH EARLY EVENING.
THESE WILL CONTAIN HEAVY RAIN THAT WILL DROP THE VIS BELOW 3SM
IN NEARLY EVERY STORM THAT IMPACTS A TERMINAL. THE ACTIVITY
MOVES EAST THIS EVENING OWING TO WIDESPREAD IFR STRATUS BY 6Z.
ONE OF THE FORECAST CHALLENGES IS WHEN WILL THE CIGS GO ABOVE
1KFT? GIVEN UPSTREAM CONDITIONS, ELECTED TO HOLD ONTO IFR CLOUDS
THROUGH MIDDAY MONDAY THEN LIFT TO MVFR AT THE EVERY END OF THE
FORECAST.
WIND WILL BE LIGHT FROM THE SOUTH THEN CALM OVERNIGHT THEN
NORTHERLY MONDAY.
OUTLOOK... BRIEF IFR VIS RESTRICTION ARE POSSIBLE THE LATTER
PART OF THIS WEEK WITH AN UPPER LEVEL TROUGH OVERHEAD. SHOWERS
AND STORMS WILL BE SCATTERED MAINLY DURING THE AFTERNOON AND
EVENING, SO NOT AN ALL DAY EVENT.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR PAZ007>009-013>016-
020>022-029-031-073>078.
OH...FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR OHZ040-041-050.
WV...FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR WVZ001>004-012-021-
509>514.
DISCUSSION...FRAZIER
AVIATION...MCMULLEN
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