PBZ issues Area Forecast Discussion (AFD) at Sep 17, 7:51 PM EDT048
FXUS61 KPBZ 172351
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
751 PM EDT Thu Sep 17 2026
.WHAT HAS CHANGED...
Today's flood threat continues to fall as probabilities for the
axis of heavier rain shifts southwest of the region. The long
range outlook is fairly unchanged with variability on specific
daily details limiting threat analysis. Updated for the 18z TAF
issuance.
&&
.KEY MESSAGES...
1) Flash flood risk will continue to wane through Friday morning
as axis of heavier rain favors SE of the region.
2) Active weather returns starting Saturday into next week that
could portend to increased flood risks.
&&
.DISCUSSION...
KEY MESSAGE 1...
Latest analysis showers the main axis of low-level warm
advection (around the 925mb height) that has been the focus for
heavy rain shower and thunderstorm development NE of it is
struggling to advance farther east than the IN/OH border. Add in
generally mostly cloudy skies for the region that limits the
degree of destabilization, the risk for flash flooding is
lowering as the next wave is more likely to produce light to
moderate rain showers mainly W of I-79 and south of I-80. The
threat remains non-zero given prior morning rain that saturated
various localities and the continued presence of 95th+
percentile PWATs, but the inability to foster additional
development while maximizing their rainfall rates favors the
lack of additional flooding concerns.
Surface high pressure behind the shortwave driving the OH
convection currently will continue to shift north of the region
through Friday morning. This will push the nominal surface
boundary southward and offer slightly cooler plus drier air for
the rest of the day Friday.
KEY MESSAGE 2...
The reprieve in active weather will be short-lived as there is
high confidence for more rounds of showers and thunderstorms
starting Saturday into early next week. This is due to the
region generally sitting on the NE periphery of a lower
Mississippi to Tennessee River Valley high while a series of
shortwaves traverse the ridge top. Additionally, warm, moist
advection favors a return of the humid airmass characterized by
anomalously high PWAT values ranging from 1.4"-1.9", all of
which is above the 90th percentile. Though finer details vary
model-to-model and day-to-day (some discussed momentarily), the
broader messaging of this pattern lends to likely periods
featuring showers/thunderstorm that carry an increased risk for
flash flooding and, pending other environmental aspects, severe
weather.
One component that can be expounded on more is the flash flood
risk for the Saturday night to Sunday night 24-hour period. For
reference, global models (notoriously weak on convective element
depictions) suggest a setup that sees an MCS exiting the western
Great Lakes towards the Upper Ohio River Valley producing a
large swath of rain. Current ensemble mean rainfall total values
over this 24-hour period range from 0.75"-1.5" with the axis
favoring the I-80 corridor. Pending the potential north/south
re-positioning of this axis, high-end scenarios could see totals
in the heaviest axis in the 2-3" range; any additional
convective element boost theoretically could push that higher.
Entering this period, the region already is fairly saturated
with lowered flash flood guidance; any rain that develops AFTER
this initial window likely does with almost fully saturated
grounds that sees a high percentage of rainfall translate to
run-off (increasing flash flood likelihood). If confidence in
these outcomes increase, Flood Watches may be issued in the
coming days.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Rainfall is expected to dissipate this evening which will
leaves us with clearing, light winds and a very moist surface.
These conditions are favorable for mist and fog development.
Models seem to favor low stratus paired with mist versus fog at
this time. MVFR restrictions seem likely with drops to IFR and
LIFR certainly possible.
Expect a gradual lifting of fog/stratus following sunrise
tomorrow morning. VFR conditions are likely Friday under high
pressure with northerly wind between 5-10 knots.
Outlook...
Restrictions are likely to return Saturday night into Sunday
morning with an increased chance for showers and thunderstorms
associated with an approaching disturbance.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
DISCUSSION...Frazier
AVIATION...Lupo/AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Sep 17, 7:51 PM EDT---------------
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