817
FXUS61 KPBZ 291741
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
141 PM EDT WED APR 29 2026
WHAT HAS CHANGED
THE POTENTIAL FOR ROTATING SHOWERS/THUNDERSTORMS THIS AFTERNOON,
AS WELL AS FOR A COUPLE OF RESULTING TORNADOES, HAS INCREASED A
BIT SINCE THIS MORNING. THE AVIATION DISCUSSION HAS ALSO BEEN
UPDATED.
KEY MESSAGES
1) SHOWERS AND THUNDERSTORMS ARE EXPECTED AHEAD OF A COLD FRONTAL
PASSAGE. THERE IS CONCERN THAT A FEW LOW-TOPPED STORMS MAY ROTATE
AND PRODUCE TORNADOES.
2) BELOW-AVERAGE TEMPERATURES AND FROST/FREEZE CONDITIONS
POSSIBLE FRIDAY AND THROUGH THE WEEKEND.
DISCUSSION
KEY MESSAGE 1...
IN THE WAKE OF MORNING SHOWERS AND THUNDERSTORMS, A NARROW WARM
SECTOR IS TRYING TO DEVELOP EAST OF PITTSBURGH AND SOUTH OF
I-80, DESPITE ONGOING LIGHT RAIN. THIS IS AHEAD OF A COLD FRONT
THAT WILL MOVE EAST ACROSS THE REGION THIS AFTERNOON, WITH WEAK
SURFACE LOW PRESSURE RIDING NORTHEAST ALONG IT. ADDITIONAL
CONVECTION IS EXPECTED TO FIRE ALONG AND AHEAD OF THE BOUNDARY,
WHERE 500-1000 J/KG OF SURFACE- BASED CAPE IS FORECAST TO
DEVELOP BY RAP/HREF PROGS. WITH THESE STORMS, HAIL AND STRAIGHT-
LINE WIND CONCERNS APPEAR TO BE QUITE MARGINAL GIVEN THE
TALL/SKINNY CAPE PROFILES, RELATIVELY WEAK FLOW, AND LACK OF DRY
AIR ALOFT/DCAPE.
HOWEVER, WE ARE CONCERNED ABOUT THE POTENTIAL FOR LOW-TOPPED STORMS
TO PRODUCE ROTATION AND POTENTIALLY A FEW TORNADOES. TODAY'S
ENVIRONMENT IS SHOWING SOME SIMILARITIES TO THE SETUP OF MAY 17,
2024, A DAY WHEN LOW-TOPPED SUPERCELLS PRODUCED FIVE TORNADOES IN
OUR FORECAST AREA. THE 12Z SOUNDING IS ALSO EERILY SIMILAR TO THE
SOUNDING FROM THAT MORNING. BOTH FEATURE DECENT LOW-LEVEL HODOGRAPH
CURVATURE, GOOD POTENTIAL FOR 100+ J/KG OF 0-3KM CAPE, AND VERY LOW
LCLS. GIVEN THE SHORT, COMPACT NATURE OF THE STORMS, IT MAY TAKE
LESS THAN THE TYPICAL 30 KNOTS OF ROTATIONAL VELOCITY TO PRODUCE A
TORNADO. ON THAT DAY NEARLY TWO YEARS AGO, RADAR-BASED ROTATIONAL
VELOCITIES OF LESS THAN 20 KNOTS WERE NOTED IN A FEW OF THE BRIEF
TORNADOES THAT OCCURRED.
THE SPECIAL 17Z SOUNDING WE LAUNCHED DOES SHOW A FAVORABLE LOW-LEVEL
WIND FIELD, WITH A SICKLE SHAPE IN THE LOWEST 0.75KM OR SO. HOWEVER,
ABUNDANT CLOUD COVER AND ONGOING LIGHT PRECIPITATION IS KEEPING THE
LOWER LEVELS STABLE ACROSS MUCH OF THE AREA. AT LEAST A MODEST
AMOUNT OF HEATING WILL BE NEEDED TO GET ENOUGH 0-3KM CAPE TO SUPPORT
STRETCHING OF UPDRAFTS FOR ANY TORNADOGENESIS. THIS CURRENTLY SEEMS
MOST LIKELY TO THE EAST AND SOUTH OF PITTSBURGH, WHERE CLOUDS ARE A
BIT THINNER AND WHERE SOME TEMPERATURES HAVE REACHED THE MID 60S.
THE RAP SUPPORTS THIS THINKING, PEGGING THIS REGION AS THE MOST
LIKELY TO ACHIEVE 100 J/KG OF 3CAPE. ANY CELL THAT GETS SUFFICIENTLY
TALL (AROUND 15KFT OR SO) MAY POTENTIALLY SPIN IN THIS
ENVIRONMENT, AND GIVEN THE LOW LCLS AND DEWPOINTS AROUND 60, IT
WILL NOT TAKE MUCH TO GET ROTATION TO THE GROUND. THIS IS LIKELY
A DAY ON WHICH THE MOST LIKELY SEVERE THREAT IS TORNADO, AS
THIS SOUNDING CONTINUES TO SUPPORT THE NOTION THAT STRAIGHT-LINE
WIND DAMAGE AND SEVERE HAIL ARE QUITE LOW IN PROBABILITY. THE
TIMING WINDOW FOR THIS POTENTIAL RUNS FROM NOW UNTIL 22 OR 23Z,
WHEN THE COLD FRONT COMPLETES ITS PASSAGE.
PRECIPITATION CHANCES LARGELY END BY SUNSET, ALTHOUGH CLOUDS
WILL LINGER THROUGH THE NIGHT. A COOLER AND DRIER AIRMASS WILL
THEN POUR INTO THE REGION.
KEY MESSAGE 2...
BEHIND THE FRONT, THERE IS HIGH CONFIDENCE IN THE DEVELOPMENT
OF A MID-LEVEL TROUGHING PATTERN OVER THE NORTHEAST CONUS
STARTING THURSDAY AND CONTINUING AT LEAST THROUGH THE WEEKEND. A
FEW CHANCES OF LIGHT SHOWERS ARE FORECAST THROUGH THE PERIOD AS
INDIVIDUAL SHORTWAVE ROTATE AROUND AN EASTERN CANADIAN UPPER
LOW. OVERALL, THIS PRECIPITATION IS EXPECTED TO HAVE LOW IMPACT.
THE MAIN STORY WILL BE THE BELOW-NORMAL TEMPERATURES THAT WILL
BECOME ESTABLISHED, WITH FORECASTED HIGHS/LOWS IN THE NEIGHBORHOOD
OF 10 TO 15 DEGREES BELOW NORMAL FROM THURSDAY THROUGH AT LEAST
SUNDAY. LOW TEMPERATURES IN THE 30S ARE EXPECTED FOR MOST OF THE
AREA FRIDAY, SATURDAY, AND SUNDAY MORNINGS. PROBABILITIES FOR
TEMPERATURES LESS THAN 37F PEAK AT 80% TO 90% FOR MOST LOCATIONS
NORTH OF PITTSBURGH AND IN EASTERN OHIO SATURDAY MORNING, BUT REMAIN
GENERALLY ABOVE 45% IN MOST LOCATIONS OUTSIDE OF MAJOR RIVER
VALLEYS. FROST/FREEZE HEADLINES WILL LIKELY BE NEEDED FRIDAY THROUGH
SUNDAY.
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
A MIXED BAG OF RESTRICTIONS IN THUNDER, CIGS, AND VIS ARE
EXPECTED TODAY AS A SURFACE LOW PASSES OVERHEAD. SHOWERS
CONTINUE TO FILL IN OVERHEAD, WHICH WILL OVERSPREAD THE AREA
INTO THE AFTERNOON, LOWERING CIGS WITH A >80% CHANCE OF AT LEAST
MVFR AREA-WIDE THROUGH ROUGHLY TOMORROW MORNING. CELLS MAY
BECOME MORE SCATTER, BUT INTENSE AS THE ENVIRONMENT TAPS INTO
THE BEST INSTABILITY.
IN THE MID-AFTERNOON (ROUGHLY 18Z TO 00Z), A LINE OF MORE
ROBUST SHOWERS IS EXPECTED TO DEVELOP ON A COLD FRONT AND PASS
FROM WEST TO EAST. IF THE AREA IS ABLE TO GARNER ENOUGH
INSTABILITY, SOME STORMS MAY BE POSSIBLE, MOST LIKELY FOR
SOUTHEASTERN PORTS (MAINTAINED PROB30S NOTED FOR NOW). I NEAR
TERM UPGRADE OR DOWNGRADE FROM PROB30 MAY BE NECESSARY. LOW
LEVEL SHEAR MAY HAVE A LOW-END TORNADO THREAT TOWARDS
LBE/AGC/MGW.
THESE SHOWERS MAY ALSO TEMPORARILY DROP CIGS/VIS TO IFR/LIFR
WHERE THE LINE IS MORE INTENSE. BEHIND THE HEAVIER SHOWERS AND
RAIN WILL BE A WIND SHIFT, WITH WINDS TRANSITIONING MORE
NORTHWEST BEHIND THE LINE. SOME GUSTS UP TO 20MPH AND CIGS
BORDERLINE MVFR/IFR ARE POSSIBLE THEREAFTER AND INTO THE
OVERNIGHT HOURS.
TONIGHT, THERE IS INCREASED CERTAINTY IN BROKEN IFR CIGS
(PATCHY LIFR), BUT EVEN WITH THIS, LOW MOISTURE MAY BE PREVALENT
ENOUGH FOR PATCHY IFR VIS AS WELL IN FOG. TEMPO 1SM TO 1/2SM
BR/FG WAS NOTED AT THE MOST SUSCEPTIBLE PORTS. SCATTERING AND
LIFTING IS FORECAST INTO THE DAYLIGHT HOURS ON THURSDAY.
OUTLOOK...
ISOLATED SHOWER ACTIVITY IS EXPECTED THURS AFTERNOON. CIGS WILL
LIKELY CLIMB BACK TO VFR AFTER SUNRISE WITH MIXING OF DRY AIR
FROM THE NORTHWEST.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
DISCUSSION...CL
AVIATION...MILCAREK
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