102
FXUS61 KPBZ 091721
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
121 PM EDT FRI OCT 9 2026
WHAT HAS CHANGED
THERE IS LITTLE CHANGE TO THE MESSAGING FOR THE INCOMING
REMNANTS OF HURRICANE ISAIAS.
KEY MESSAGES
1) RAIN CHANCES AND GUSTY WINDS RETURN LATE SATURDAY NIGHT INTO
SUNDAY AS THE REMNANTS OF ISAIAS TRACK NORTH.
DISCUSSION
KEY MESSAGE 1...
CONFIDENCE REMAINS HIGH THAT QUIET AND DRY CONDITIONS WILL
PERSIST THROUGH LATE SATURDAY UNDER HIGH PRESSURE.
HURRICANE ISAIAS IS FAVORED TO WEAKEN BUT MAINTAIN A CLOSED
SURFACE TO MID-LEVEL CLOSED LOW STRUCTURE AS IT LIFTS NORTHWARD
THROUGH THE TENNESSEE RIVER VALLEY SATURDAY BEFORE ADVANCING
EAST NORTHEAST ACROSS THE UPPER OHIO RIVER VALLEY TO MID
ATLANTIC REGIONS SUNDAY. TROUGH AND LOW PRESSURE ASCENT
COMBINED WITH A TROPICAL AIRMASS (WHICH PUSHES PWAT VALUES
BETWEEN THE 90TH AND 100TH PERCENTILES) RESULTS IN WIDESPREAD
RAIN ENVELOPING THE REGION OVERNIGHT SATURDAY THROUGH EARLY
MONDAY MORNING, WITH ENSEMBLE MEAN RAINFALL TOTALS GENERALLY
RANGING BETWEEN 1 TO 1.5 INCHES.
THE FIRST CONCERN RELATES TO FLOODING RISKS WHERE LOCALIZED JET
DYNAMICS CREATE NARROW CORRIDORS OF ENHANCED RAINFALL RATES
THAT PUSH TOTALS INTO THE 2-3" RANGE. LATEST GUIDANCE FAVORS
SUCH CORRIDOR DEVELOPING ALONG A SSW-NNE AXIS FROM ROUGHLY NOBLE
COUNTY, OH TOWARDS MERCER COUNTY, PA (THOUGH VARIANCE REMAINS
IN BOTH ITS DEVELOPMENT AND EAST-WEST POSITIONING). IF MOST OF
THIS RAIN CAN OCCUR WITHIN A 6-HR PERIOD (PROBABILITY IS LESS
THAN 10% FOR SUCH TO OCCUR) AND/OR WIND-AIDED DEBRIS (LIKE
LEAVES, TWIGS, ETC.) CLOGS STORM SEWER WATER MITIGATION SYSTEMS,
THEN LOCALIZED FLOODING COULD OCCUR. HOWEVER, THE PRECEDING DRY
ANTECEDENT CONDITIONS COMBINED WITH LOW PROBABILITIES FOR HIGH
RAINFALL RATES (DUE TO LIMITED BUOYANCY) AND/OR ACCUMULATIONS
(6-HR FFG FOR MOST AREAS IS ABOVE 2") MEANS THE LIKELIHOOD OF
ITS DEVELOPMENT IS LOW.
THE OTHER CONCERN RELATES TO THE LIKELY DEVELOPMENT OF A
STRONGER LOW-LEVEL SOUTHEASTERLY JET LATE SATURDAY INTO SUNDAY
EARLY AFTERNOON THAT RESULTS IN GUSTY WINDS THAT APPROACH WIND
ADVISORY CRITERIA IN THE HIGHER TERRAIN. THIS 850MB JET, AS
DEPICTED BY THE 12Z RRFS MODEL, SITS BETWEEN 40-55 KTS AND
PEAKS SUNDAY MORNING BEFORE WANING, OFFERING A CHANCE FOR GUSTS
IF ANY MIXING CAN OCCUR. THOUGH THIS IS UNLIKELY FOR THE LOWER
ELEVATION LOCATIONS (WHERE PROB OF GUSTS EXCEEDING 40MPH ARE
LESS THAN 10%), THE HIGHER TERRAIN OFFERS BETTER CHANCES PURELY
DUE TO CLOSER PROXIMITY TO THIS JET SUCH THAT PROBABILITIES OF
EXCEEDING 40MPH AR AROUND 50-80% BUT ONLY 20-40% FOR EXCEEDING
45MPH. IF CONFIDENCE INCREASES THAT GUSTS COULD MEET/EXCEED
WIND ADVISORY CRITERIA (46 MPH), THEN A WIND ADVISORY FOR THOSE
HIGHER TERRAIN AREAS WOULD BE ISSUED.
ALL IMPACTS WANE SUNDAY NIGHT AS THE SYSTEM EXITS EAST, THOUGH
LINGERING RAIN MAY CONTINUE THROUGH MONDAY FOR THE HIGHER
TERRAIN. THE NEXT CHANCE FOR RAIN ARRIVES WITH A POTENTIAL COLD
FRONT TUESDAY AFTERNOON/EVENING FAVORING NORTHWEST PA.
AVIATION /18Z FRIDAY THROUGH WEDNESDAY/
VFR CONDITIONS CONTINUE TO BE FORECAST WITH HIGH CONFIDENCE OVER
THE NEXT 24 HOURS. THE FIRST CIRRUS CLOUDS AHEAD OF ISAIAS WILL
BUILD IN FROM THE SOUTH DURING THE AFTERNOON AND EVENING, AND
WILL BEGIN TO SLOWLY THICKEN AND LOWER LATER TONIGHT AND THROUGH
SATURDAY. WEST WIND AROUND 10 KNOTS THIS AFTERNOON WILL BECOME
LIGHT AND VARIABLE TONIGHT, AND THE SETTLE TO EAST/SOUTHEASTERLY
DIRECTION AROUND 10 KNOTS BY LATE MORNING TOMORROW.
OUTLOOK...
RESTRICTIONS, INCLUDING WIND SHEAR, ARE LIKELY STARTING
SATURDAY NIGHT AND CONTINUING INTO SUNDAY AS THE REMNANTS OF
ISAIAS TRACK NORTH.
BRIEF IMPROVEMENT TO VFR MONDAY MAY BE FOLLOWED BY MORE
RESTRICTIONS FROM THE NEXT DISTURBANCE TUESDAY.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
DISCUSSION...FRAZIER
AVIATION...CL
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