757
FXUS61 KPBZ 200621
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
221 AM EDT WED MAY 20 2026
WHAT HAS CHANGED
THE MARGINAL RISK AREA FOR SEVERE STORMS TODAY HAS EXPANDED
BACK NORTHWEST SLIGHTLY, BUT STILL REMAINS WELL SOUTH OF
PITTSBURGH. CONFIDENCE IN A QUITE WET MEMORIAL DAY WEEKEND
CONTINUES TO INCREASE.
KEY MESSAGES
1) A CONDITIONAL THREAT OF ISOLATED SEVERE THUNDERSTORMS WITH
DAMAGING WIND GUSTS EXISTS SOUTHEAST OF PITTSBURGH THIS
AFTERNOON.
2) CONFIDENCE IN SOAKING RAINFALL DURING THE MEMORIAL DAY
WEEKEND CONTINUES TO INCREASE.
DISCUSSION
KEY MESSAGE 1...
SOME SCATTERED SHOWERS CONTINUE ACROSS THE REGION DURING THE
EARLY MORNING HOURS IN A MOIST ENVIRONMENT WITH LINGERING
OUTFLOW BOUNDARIES. MORE CONCENTRATED SHOWERS AND THUNDERSTORMS
ARE EXPECTED TO ARRIVE AFTER SUNRISE AS A WEAK SHORTWAVE RIDES
NORTHEASTWARD AHEAD OF A COLD FRONT THAT IS SLATED TO CROSS
TODAY.
THE FRONT SHOULD BE DRAPED ACROSS THE NORTHWESTERN PORTION OF
THE CWA AT 12Z, AND SHOULD CROSS THROUGH THE PITTSBURGH AREA
AROUND MIDDAY. ONGOING RAIN AND CLOUD COVER AHEAD OF THE
BOUNDARY LEND SOME UNCERTAINTY TO THE AMOUNT OF DESTABILIZATION
THAT WILL BE ABLE TO OCCUR OVER OUR SOUTHEASTERN COUNTIES THIS
AFTERNOON. REFS GUIDANCE SUGGESTS 500-1000 J/KG OF SURFACE-BASED
CAPE BY 18Z IN THIS AREA, WHILE THE HREF GOES A LITTLE HIGHER
IN PRESTON/TUCKER COUNTIES, FURTHEST AHEAD OF THE FRONT. SHEAR
IN THE 0-6KM LAYER IN THIS AREA IS NOT TOO IMPRESSIVE, REMAINING
UNDER 30 KNOTS AHEAD OF THE FRONT, WHICH WILL LIMIT STORM
ORGANIZATION. STILL, THERE MAY BE A RELATIVELY BRIEF WINDOW
DURING THE MID-TO-LATE AFTERNOON FOR TALL STORMS TO TAKE
ADVANTAGE OF MARGINAL DCAPE TO PRODUCE ISOLATED STRONG TO
DAMAGING GUSTS. HAIL APPEARS TO BE A SECONDARY THREAT DUE TO
GENERALLY POOR MID-LEVEL LAPSE RATES AND THE LIMITED SHEAR. SPC
HAS ISSUED A MARGINAL (LEVEL 1 OF 5) RISK FOR AREAS SOUTHEAST OF
A ROUGH LINE FROM CONNELLSVILLE PA TO NEW MARTINSVILLE WV. THE
PASSAGE OF THE FRONT SHOULD END ANY SEVERE THREAT BY 00Z.
SOME VERY LOCALIZED INSTANCES OF HEAVY RAINFALL ARE ALSO POSSIBLE
WITH THESE STORMS. CLOUD-LAYER FLOW WILL BE LARGELY PARALLEL TO THE
FRONT, WHICH COULD ENCOURAGE STORM TRAINING. ALSO, EXPECTED
PRECIPITABLE WATER VALUES OF 1.5 TO 1.6 INCHES IS AT THE VERY TOP OF
CLIMATOLOGY. HREF/REFS MAX PRECIP POTENTIAL SUGGEST LOCALIZED 1.5-
1.75 INCH TOTALS ARE NOT OUT OF THE QUESTION IN NORTHERN WEST
VIRGINIA. STILL, 3-HOUR FFG VALUES ARE GENERALLY NEAR OR JUST ABOVE
2 INCHES IN THIS AREA, AND THUS ANYTHING MORE THAN AN ISOLATED WATER
ISSUE OR TWO IS NOT EXPECTED.
KEY MESSAGE 2...
THE FRONT MAY WAVER NEAR THE SOUTHERN REACHES OF THE CWA THROUGH
THURSDAY NIGHT, KEEPING OCCASIONAL RAIN CHANCES IN THE FORECAST,
ESPECIALLY SOUTH OF I-70. THE ENVIRONMENT FAVORABLE FOR STRONG
CONVECTION AND HEAVY RAINFALL WILL HAVE DEPARTED THOUGH, AND NO
MAJOR IMPACT FROM THIS ACTIVITY IS EXPECTED.
MEMORIAL DAY WEEKEND CONTINUES TO LOOK QUITE WET OVERALL. SURFACE
LOW PRESSURE LIFTS NORTHEASTWARD INTO THE LOWER OHIO VALLEY TO
OUR WEST FRIDAY INTO SATURDAY, BRINGING THE BOUNDARY BACK NORTH
AS A WARM FRONT AND PUSHING A BROAD INVERTED TROUGH INTO OUR
REGION. THIS SHOULD RETURN ANOMALOUSLY HIGH PRECIPITABLE WATER
VALUES BACK NORTH, ACCOMPANIED BY BROAD ISENTROPIC LIFT. ALSO DURING
THIS TIME, SURFACE HIGH PRESSURE IS FORECAST TO BE CENTERED
OVER THE UPPER GREAT LAKES AND NEW ENGLAND STATES. THIS SETUP IS
SIMILAR TO PAST EVENTS THAT HAVE GENERATED 2+ INCHES OF
RAINFALL ACROSS THE LOCAL AREA, THOUGH IT SHOULD BE NOTED THAT
MINOR DEVIATIONS (E.G., EAST-WEST POSITIONING OF THE LOW OR
STRENGTH OF THE RIDGE) COULD RESULT IN THE AXIS OF HEAVIEST
RAINFALL SHIFTING AROUND (OR AWAY FROM) THE LOCAL AREA.
NEVERTHELESS, THE NBM CONTINUES TO ILLUSTRATE A 60-80% CHANCE
FOR AT LEAST AN INCH OF 24-HR RAINFALL ACCUMULATION FRIDAY INTO
SATURDAY, AND A 20-50% CHANCE FOR 2+ INCHES.
A SECOND WAVE OF RAIN IS THEN FORECAST SUNDAY INTO MONDAY THOUGH
THAT ONE APPEARS A BIT MORE PROGRESSIVE IN NATURE THANKS TO A
POTENTIAL GREAT LAKES SHORTWAVE THAT HAS SOME FORWARD MOMENTUM.
NBM PROBABILITIES FOR AN INCH TOP OUT IN THE 20-30 PERCENT
RANGE BETWEEN 12Z SUNDAY AND 12Z MONDAY. WHEN LOOKING AT THE
TOTAL 72-HOUR PERIOD FROM 12Z FRIDAY TO 12Z MONDAY, THE NBM HAS
A 50 TO 65 PERCENT CHANCE FOR 2 INCHES OR MORE OF RAIN ACROSS
THE MAJORITY OF THE FORECAST AREA. EXTENDED MACHINE-LEARNING
GUIDANCE SUGGESTS SEVERE WEATHER CHANCES REMAIN QUITE LOW
THROUGH THIS PERIOD, SO THAT ASPECT IS OF LESSER CONCERN.
HOWEVER, MMEFS RIVER GUIDANCE DOES SUGGEST SOME POTENTIAL IMPACT
ON AREA RIVERS BY EARLY NEXT WEEK IN HIGHER-END PRECIPITATION
SCENARIOS, WITH A NUMBER OF FORECAST POINTS ON THE LARGER RIVERS
POTENTIALLY REACHING ACTION STAGE. THIS ALSO SUGGESTS THAT
FLOODING ISSUES ON SMALLER STREAMS AND CREEKS MAY BECOME AN
ISSUE IN TIME. IT IS TOO EARLY TO DISCUSS SPECIFICS AND FORECAST
DETAILS ARE YET TO BE SOLIDIFIED, BUT THIS SIGNAL WILL WARRANT
MONITORING THROUGH THE WEEK.
AVIATION /06Z WEDNESDAY THROUGH SUNDAY/
SHOWERS AND A FEW THUNDERSTORMS HAVE CONTINUED TO DIMINISH FOR
MOST AREAS TONIGHT AS THESE HAVE OUTRUN THE MORE FAVORABLE
INSTABILITY, LOOKING AT THE LATEST MESOANALYSIS AND 00Z
INSTABILITY CHARTS. A COLD FRONT WILL CONTINUE TO APPROACH THE
AREA THROUGH MORNING, WITH ADDITIONAL SHOWERS CROSSING THE AREA.
MVFR RESTRICTIONS ARE ALSO EXPECTED TO DEVELOP WITH INCREASING
LOW LEVEL MOISTURE ASSOCIATED WITH THE FRONT.
A GRADUAL DECREASE TO IFR IS EXPECTED FOR MOST PORTS AFTER FROPA
FROM MID MORNING INTO THE AFTERNOON. AREAS FROM HLG TO MGW WILL
SEE A POTENTIAL FOR A THUNDERSTORM WITH DIURNAL INSTABILITY
BUILDING AHEAD OF THE LATER FROPA. INCLUDED A PROB30 AT HLG,
WITH A TEMPO AT MGW WHERE THERE IS A HIGHER POTENTIAL FOR
THUNDERSTORMS FROM MID TO LATE AFTERNOON. A WIND SHIFT TO THE
NW, AND EVENTUALLY N, IS ALSO EXPECTED AFTER THE PASSAGE OF THE
FRONT. SOME IMPROVEMENT BACK TO MVFR IS EXPECTED BY EVENING,
THOUGH A CROSSING WAVE ALONG THE FRONT COULD SPREAD A FEW MORE
SHOWERS ACROSS THE REGION.
OUTLOOK...
RESTRICTIONS WILL LIKELY CONTINUE INTO TONIGHT WITH THE CROSSING
WAVE ALONG THE FRONT. VFR SHOULD RETURN TO MOST AIRPORTS ON
THURSDAY AS HIGH PRESSURE BRIEFLY BUILDS IN FROM THE N, THOUGH
MGW COULD SEE RESTRICTIONS CONTINUE THROUGH LATE MORNING.
WIDESPREAD RESTRICTIONS IN RAIN ARE EXPECTED TO OVERSPREAD THE
REGION FROM S-N FRIDAY INTO SATURDAY WITH A WARM FRONT. SOME
IMPROVEMENT IS POSSIBLE SUNDAY UNTIL A COLD FRONT APPROACHES
LATER IN THE DAY.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
DISCUSSION...CL/CERMAK
AVIATION...WM
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