Area Forecast Discussion Issued by NWS Pittsburgh, PA
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000
FXUS61 KPBZ 170331 AAA
AFDPBZ
Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
1131 PM EDT Sat Mar 16 2024
.SYNOPSIS...
The first in a series of cold fronts will cross the region
tonight into Sunday morning, creating a line of mainly light
rain showers. Additional cold fronts and upper disturbances
will create periodic precipitation chances again Sunday night
through Tuesday morning that may lead to limited snowfall
accumulation.
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.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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KEY MESSAGES:
- A cold front arrives tonight with gusty wind, rain showers
and introduction of a cooler air mass.
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Update...
Dry air was in place in the lower levels based on recent surface
obs, and upper air analysis. A low level jet was also across OH
and western PA, with 850 mb wind speeds around 45 kt. Some of
this wind is mixing to the ground on the leading edge of a band
of showers, as evaporation occurs. Updated the forecast to
include wind gusts up to 40 mph as the rain begins.
Previous...
The passage of an upper level trough and surface low into
Quebec will push a well-defined cold front southeast through
the region tonight. Rain showers ahead of the boundary are
likely to be light (most locations see less than 20% chance of
exceeding 0.25" total), with decreasing expected amounts from NE
to SW due to farther removal from stronger upper forcing.
Ensembles favor fairly rapid drying post-frontal passage as the
dry westerlies develop aloft with the main upper trough axis
hanging to the NW.-- End Changed Discussion --
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.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
KEY MESSAGES:
- Cold advection plus weak lake fetch will support isolated to
scattered showers favoring northwest PA and the higher
terrain.
- Precipitation type will be a mix of rain and snow during
daylight hours before switching to snow.
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In the post-frontal environment, the Upper Ohio River Valley
will be positioned within general westerly flow as the upper
trough axis remains over the Western Great Lakes. There is some
discrepancies among hi-res and global models on angle of the
boundary layer flow, which will play out in one of two scenarios
for the afternoon (forecast more closely tied with scenario 1).
Scenario 1: A more W-E to WSW-ENE orientation should maintain
dry slotting over the region and create little to no fetch of
lake moisture to support afternoon showers. Temperature will be
near to slightly above average, though gusty wind will keep
`feel-like` temperature down.
Scenario 2: A more WNW-ESE orientation would allow for some
lake moisture influx to the boundary layer, combining with broad
ascent to foster isolated/scattered afternoon showers. Cold
advection aloft would remain limited and thus still see a mix of
rain/snow with no accumulations. Temperature is closer to
average while wind remains gusty.
Overnight, a shift of the upper trough axis towards Lake Erie
will send a secondary cold front towards the region while
cooling 850mb temperature. A slight increase in boundary layer
moisture while maintain broad ascent (though losing diurnal
heating) will enable a continuation of isolated light snow
showers. Lack of deeper moisture and stronger forcing will
ensure any snowfall accumulations during this period will be
light (if any, given warmer grounds).
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Seasonably cool temperature favored through mid week and may
persist into the following weekend.
- Large variation in snowfall accumulation during early week
scattered snow showers.
- Uncertainty remains large for next synoptic pattern to end
week.
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The weather pattern through Tuesday favors persistent upper
troughing over the Great Lakes that will feature embedded
shortwaves crossing the Upper Ohio River Valley region. This
regime features below average temperature and waves of scattered
to potentially numerous showers, with the general thermal
profiles favoring snow (though a few locations may see rain mix
in during the warmer afternoon hours). The largest discrepancy
at this time appears to be moisture availability; while not
large, 24 hour QPF 75th/25th percentile spreads from ensemble
model data suggest range from nothing to 0.10". That shows
potential for either little falling snow or localized bands that
could see 1 to 2" of accumulation (without accounting for
ground impacts, etc.). Current forecast represents a blend of
options; at this time, it remains unlikely for much snowfall
impact even if higher- end moisture values develop.
Rising pressure heights should promote a drying and warming
trend mid-week, but once again, ensemble spread becomes large in
diagnosing the evolution of weak upper low leaving the Four
Corners region and depth/strength of the lower Canadian trough.
In general, two favored solutions which suggested either a
cooler, drier weekend pattern (deeper Canadian trough that
keeps southern wave farther south) or a warmer, wetter pattern
(flow becomes mixed and allows for some influx of moisture from
southern wave).
&&
.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
A cold front will approach from the Upper Great Lakes region
tonight. This front will cross the Upper Ohio Valley region
tonight around roughly 04Z - 06Z through Sunday morning 12Z,
with showers and MVFR restrictions expected. In addition, SW
wind gusts to 20-25kt are expected with mixing and a tightening
pressure gradient ahead of the front. A WSHFT to the NW, with
additional gusts to 20kt are expected after tonight`s FROPA.
There will be a period tonight before the approach of the front
where some LLWS will be present. Expect this to last through
03Z-04Z until the front brings the stronger winds to the
surface.
Conditions will be slow top improve heading through the day
tomorrow as northwest flow will continue to bring in scattered
to broken MVFR cigs through the day on Sunday. Scattered passing
showers/snow showers will also be the case on Sunday. Strong
northwest flow will continue and winds are still expected to be
gusting up to 20 knots at times during the day on Sunday. Most
snow shower/rain shower impacts will be confined to the north
and in the ridges to the east.
.Outlook...
Restrictions and scattered snow showers return Monday night and
Tuesday with a reinforcing cold front and subsequent upper
troughing. VFR returns Wednesday as a ridge of high pressure
builds in.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Frazier
NEAR TERM...WM/Frazier
SHORT TERM...Frazier
LONG TERM...Frazier
AVIATION...Shallenberger