Area Forecast Discussion Issued by NWS Pittsburgh, PA
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000
FXUS61 KPBZ 161528
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
1128 AM EDT Sat Mar 16 2024
.SYNOPSIS...
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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.-- End Changed Discussion --
&&
.NEAR TERM /THROUGH TONIGHT/...
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KEY MESSAGES:
- Warm advection and insolation will raise area temperature
about 10 degrees above the daily average.
- A cold front arrives late tonight with mainly light rain
showers and introduction of a cooler air mass.
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Dry advection aloft plus subsidence ahead of the next upper
level trough is aiding rapid stratocu erosion across western PA
and northern WV approaching the noon area. With clearing skies
and weak warm advection, area temperature is expected to remain
approximately 10 degrees above the daily average.
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 /SUNDAY THROUGH SUNDAY NIGHT/...
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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).-- End Changed Discussion --
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.LONG TERM /MONDAY THROUGH FRIDAY/...
KEY MESSAGES:
- Cold temperatures are expected to linger through Tuesday
- Lake enhanced snow is expected Sunday night into Tuesday.
- Wind chill values will be abnormally cold early Tuesday (teens
in the lower elevations/single digits to below zero in the
higher terrain).
- Above average temperatures return mid-week.
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Long range ensemble models continue to favor a cold pattern
across the Ohio River Valley late Sunday into Tuesday across
the Great Lakes. Arctic air will drive high and low temperatures
to be below average by 5 to 10 degrees Monday and Tuesday.
Probability of low temperatures below 25F Tuesday morning is
55% or higher near I-80 and in the ridges.
As a large upper-lvl low pivots out of the Great Lakes and
enters New England, flow off of Lake Erie will shift from the
west to northwest. Therefore, snow shower potential will drift
further south of I-80 Monday afternoon into Tuesday. Probability
of one inch of snow for both days ranges between 50% to 70%
north of I-80/eastern Tucker County. Probability of >= 0.1
inches of snow is elevated (above 90%) within the ridges due to
upsloping and confided along I-80 (in close proximity to the
lake). Accumulation will likely be focused during the overnight
time period, when sfc temperature fall near or below freezing.
With a strong gradient wind associated with the low and cold
advection, expected wind chill values to be abnormally cold
early Tuesday. Teens in the lower terrain, single digits to
below freezing in the ridges of PA/WV.
Increase fetch over the lake with a new shortwave may keep snow
showers in the region into Wednesday. However, accumulation will
likely be very little given a building ridge to the west.
Near to above average temperatures are expected to mid-week into
Friday. However, precipitation chances may return as a trough
advances across the Southeast and tracks north along the East
Coast.
&&
.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
A bit of patchy fog and low stratus will finally dissipate by
14Z or 15Z at the latest under high pressure.
Mid and high level clouds are expected to increase later today
as a cold front approaches from the Upper Great Lakes region.
This front will cross the Upper Ohio Valley region tonight
through early Sunday, with showers and MVFR restrictions
expected. In addition, SW wind gusts to 20kt 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 the late Saturday night FROPA.
.Outlook...
Gusty NW wind is expected Sunday behind the exiting cold front.
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...Frazier
SHORT TERM...Frazier
LONG TERM...Hefferan
AVIATION...WM/Shallenberger