004
FXUS61 KPBZ 010811
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
411 AM EDT MON SEP 1 2025
SYNOPSIS
SEASONABLE AND MOSTLY DRY CONDITIONS PREVAIL THROUGH TUESDAY.
RAIN CHANCES RETURN WEDNESDAY AND THURSDAY WITH THE APPROACH AND
PASSAGE OF A COLD FRONT. THE FRONT PASSAGE IS MOST LIKELY
THURSDAY AFTERNOON WITH GUSTS OF 30MPH TO 40MPH POSSIBLE. COOLER
AND RELATIVELY DRIER WEATHER RETURNS LATE-WEEK.
NEAR TERM /UNTIL 6 PM THIS EVENING/
KEY MESSAGES:
- VALLEY FOG POSSIBLE IN THE MORNING.
- MORE SEASONABLE AND DRY CONDITIONS.
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ANY VALLEY FOG WILL ERODE READILY WITH CLEAR SKIES AND MIXING
THIS MORNING. A CLOSED MID-LEVEL LOW FROM THE ATLANTIC WILL
RETROGRADE NORTHWEST THROUGH THE DAY, EVENTUALLY REJOINING THE
FLOW. WITH A BIT MORE LOW LEVEL MOISTURE COMING IN FROM THE
ATLANTIC IN WEAK EASTERLY FLOW, WE CAN EXPECT A FAIR WEATHER
CUMULUS DECK TO DEVELOP IN THE AFTERNOON AND TAPER INTO THE
EVENING. HIGH PRESSURE AND SUBSIDENCE ALOFT WILL KEEP DAYTIME
CUMULUS SHALLOW, WITH ONLY A SLIGHT UPTICK IN SURFACE DEW
POINTS. THE RESULT? ANOTHER DRY AND PICTURE PERFECT DAY WITH
TEMPERATURES NEAR SEASONAL NORMALS AND HUMIDITY STAYING LOW,
MAKING CONDITIONS COMFORTABLE FOR THE LABOR DAY HOLIDAY.
SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/
KEY MESSAGES:
- VALLEY FOG CHANCES IN THE MORNING WITH SEASONABLE TEMPERATURES.
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ANY CUMULUS DECKS WILL LIKELY ERODE BEYOND SUNSET AGAIN WITH A
LOSS OF MIXING. CLAM AND CLEAR CONDITIONS WILL PROMOTE EFFICIENT
COOLING AND LOWS 5 TO 10 DEGREES BELOW NORMAL. THERMAL CONTRAST
BETWEEN THE AIR AND WATER MAY ALLOW FOR PATCHY RIVER VALLEY FOG,
PRIMARILY IN THE ALLEGHENY HEAD-WATERS.
TUESDAY WILL REMAIN QUITE SIMILAR TO THE DAY PRIOR WITH A
DEVELOPMENT OF AFTERNOON DAYTIME CUMULUS AND HIGH TEMPERATURES
NEAR SEASONAL NORMALS UNDER HIGH PRESSURE. LIGHT SURFACE
EASTERLY FLOW WILL KEEP LOW-LEVEL MOISTURE FROM ADVECTING IN
FROM THE SOUTHWEST, LEAVING FOR ANOTHER PLEASANT, LOW-HUMIDITY
DAY.
TUESDAY NIGHT, THE UPPER LOW THAT HAS ALLOWED STAGNANT
CONDITIONS TO THE NORTH WILL GRADUALLY PULL INTO THE CANADIAN
MARITIMES, AND A NORTHEAST-SOUTHWEST PRESSURE GRADIENT WILL
BEGIN TO ESTABLISH WITH A LIGHT SOUTHERLY WIND OVERNIGHT, AND A
TAD MORE MOISTURE THAN NIGHTS PRIOR. THIS MAY KEEP LOWS A
COUPLE DEGREES WARMER THAN THE NIGHT PRIOR (BUT STILL BELOW
AVERAGE) WITH SOME LOW CLOUD POTENTIAL, PARTICULARLY SOUTH OF
I-70.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
KEY MESSAGES:
- LOW RAIN CHANCES WEDNESDAY WITH SEASONABLE WEATHER.
- A COLD FRONT PASSAGE MOST LIKELY THURSDAY, ACCOMPANIED MY A
COOLDOWN AND THE POTENTIAL FOR SOME GUSTIER WINDS.
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A WEAK LOW-LEVEL SHORTWAVE TROUGH PASSAGE IS EXPECTED ON
WEDNESDAY WHICH WILL ALLOW FOR SOME LOW-LEVEL LIFT, BUT IN THE
LAST 24 HOURS, IT APPEARS MORE LIKELY THAT THE AFOREMENTIONED
MOISTURE FROM THE SOUTHERN APPALACHIANS WILL STRUGGLE TO ADVECT
IN IN TIME TO CONTRIBUTE TO MUCH IN THE WAY FOR PRECIPITATION
CHANCES. NBM ONLY HAS UP TO A 25% CHANCE, MOST LIKELY SOUTH OF
I-70. BECAUSE OF THIS DOWNTREND IN PRECIPITATION CHANCES AND
WIDESPREAD CLOUD COVER, THE FORECAST IS MORE CONFIDENT IN NEAR-
NORMAL TEMPERATURES WEDNESDAY. WHAT THIS WOULD MEAN FOR MOST IS
ANOTHER PLEASANT DAY WITH A FAIR WEATHER CUMULUS DECK. IN THE
LOWER PROBABILITY EVENT THAT MOISTURE ARRIVES SOUTH OF I-70,
TEMPERATURES AMY BE SLIGHTLY COOLER WITH RAIN AND MORE CLOUDS.
RAIN, SHOULD IT OCCUR, SEEMS TO BE UN-IMPACTFUL: YOU'D HAVE TO
EXCEED THE 90TH PERCENTILE TO START SEEING TOTALS >0.25" WITH A
LOCALIZED ABSOLUTE MAXIMA OF <1". AS THE PRESSURE GRADIENT
INTENSIFIES AHEAD OF THE APPROACHING TROUGH THURSDAY, YOU COULD
SEE SOME AFTERNOON/EVENING WIND GUSTS UP TO 20MPH TO 30MPH AT
MOST.
MORE PROLIFIC MOISTURE ESTABLISHES WEDNESDAY NIGHT INTO
THURSDAY AS SOUTHWEST FLOW ACCELERATES WITH THE APPROACH OF THE
UPPER TROUGH AND MEAN PWATS GO FROM ~1" WEDNESDAY AFTERNOON TO
~1.3" TO 1.5" BY THURSDAY AFTERNOON. THE INITIAL PUSH OVERNIGHT
WEDNESDAY WILL ALLOW INCREASING CLOUDS AND PRECIPITATION
CHANCES AS THE PUSH RIDES OVER COMPARATIVELY COOLER AND DRIER
AIR WITH WEAK MID- LEVEL PVA. BUT CHANCES REMAIN LOW AND RAIN
LIGHT WITH ANY INITIAL ONSET. THIS, COMBINED WITH INCREASED
WINDS, WILL KEEP LOWS NEAR NORMAL FOR THE FIRST TIME IN A WHILE.
HERE'S WHERE WE START TO SEE SOME VARIABILITY IN ENSEMBLE
CLUSTERING. 53% OF GUIDANCE HAS THE TROUGH DECOUPLING FROM THE
UPPER FLOW OVER LAKE SUPERIOR THURSDAY, THE REST HAVE IT
FARTHER NORTH OVER ONTARIO. A MORE SOUTHERN TRACK OVER SUPERIOR
MAY GENERALLY MEAN HIGHER RAIN TOTALS, BUT THE SAME MAY ALSO BE
TRUE FOR A NORTHERN TRACK WHERE THE LOW IS STRONGER DUE TO THE
DEGREE OF LIFT AND STRENGTH OF MOISTURE ADVECTION FROM THE
SOUTHWEST. FOR AN IDEA OF THE RANGE OF VARIABILITY FOR THESE TWO
SCENARIOS, THINK OF THE "WEAKER, NORTH" SCENARIO AS REFLECTING
TOTALS OF 0.25" TO 0.5" AREA-WIDE, WHILE A "STRONGER, SOUTH"
SOLUTION MIGHT EQUATE TO 0.75" TO 1.25" AREA-WIDE. WITH EQUALLY
SPLIT CLUSTERING IT IS HARD TO SAY EXACTLY WHICH WILL WIN OUT.
THE MOST ENSEMBLE TEMPERATURE SPREAD IS BETWEEN 11AM THURSDAY
AND 8PM THURSDAY, SHOWING AN AFTERNOON COLD FRONT PASSAGE IS
MOST LIKELY, WITH SOME TIMING UNCERTAINTY. WITH STOUT FORCING
AND FRONTAL MOTION, COMBINED WITH DEEPER MIXING AND A 500MB 50KT
JET, WINDS MAY GUST UP TO 30MPH TO 40MPH IN THE AFTERNOON AHEAD
OF AND ALONG THE FRONTAL PASSAGE (NBM MAX WIND DISTRIBUTION FOR
PIT).
FRIDAY, THE CLOSED LOW MAY WOBBLE AROUND WITH SOME SOLUTIONS
PLACING THE LOW OVER ONTARIO, AND OTHER ALONG THE SOUTHERN SHORE
OF THE HUDSON BAY. AGAIN, A MORE SOUTHERLY AND/OR STRONGER
POSITION WOULD MEAN COOLER TEMPERATURES, GENERALLY MORE CLOUDS
(OR EVEN SHOWERS) CHANCES ON SHORTWAVE SPOKES, AND GENERALLY
GUSTIER WINDS. A MORE NORTHERN AND WEAKER TRACK WOULD MEAN THE
OPPOSITE. THIS KEEPS NEXT WEEKENDS TEMPERATURE SPREAD ANYWHERE
FROM THE UPPER 60S TO MID 70S FOR HIGHS, DAYTIME WIND SPREAD
ANYWHERE FROM 25MPH TO 35MPH MAXIMUM GUSTS, AND RAIN CHANCES
ANYWHERE FROM 0% TO 30%.
MOST ENSEMBLES SEE A WARMING TREND BACK TO NEAR NORMAL
TEMPERATURES AS WE HEAD INTO THE MIDDLE OF NEXT WEEK, WITH ONLY
THE EXACT TIMING OF THE WARMUP THE MAIN AXIS OF UNCERTAINTY
DEPENDING ON THE DEPARTURE OF THE EASTERN TROUGH.
AVIATION /08Z MONDAY THROUGH FRIDAY/
HIGH CONFIDENCE THAT VFR CONDITIONS WILL CONTINUE THROUGH THE
TAF PERIOD. HIGH RESOLUTION MODELS DEPICT A WEAK SIGNAL FOR
RIVER VALLEY FOG EARLY THIS MORNING; FKL MAY OR MAY NOT
EXPERIENCE VIS RESTRICTIONS BETWEEN 10Z TO 12Z. OTHERWISE, A FEW
FAIR WEATHER CU MAY DEVELOP AFTER SUNRISE WITH DIURNAL HEATING.
THERE IS A LOW CHANCE OF PRECIPITATION TUESDAY INTO WEDNESDAY,
VFR CONDITIONS ARE LIKELY UNDER HIGH PRESSURE. HOWEVER, CAN'T
RULE OUT RIVER VALLEY FOG DURING EARLY MORNING HOURS, BETWEEN
09Z TO 12Z.
OUTLOOK.
THURSDAY INTO FRIDAY, THE PASSAGE OF A COLD FRONT WILL BRING
RAIN WITH THE POSSIBILITY OF ISOLATED THUNDERSTORMS. THE
BOUNDARY IS ALSO FORECAST TO BRING A STRONG VERTICAL WIND
PROFILE, WHICH INCREASES THE CHANCE FOR LOW-LEVEL WIND SHEAR
AND/OR WIND GUSTS.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...MILCAREK
NEAR TERM...MILCAREK
SHORT TERM...MILCAREK
LONG TERM...MILCAREK
AVIATION...HEFFERAN
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