PBZ issues Area Forecast Discussion (AFD) at Jan 31, 9:06 PM EST127
FXUS61 KPBZ 010206
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
906 PM EST Fri Jan 31 2025
.SYNOPSIS...
Flooding concerns remain in ice jams within the watch area
through tomorrow morning. Above average temperatures with
intermittent rain chances are expected into next week. Another,
higher-QPF, system is possible by mid-to-late week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
KEY MESSAGES:
- Light rain showers with cold frontal passage, mixing
with/changing to snow before ending
- Patchy freezing drizzle possible, mainly north and east of
Pittsburgh
- Temperatures falling into the 20s overnight
----------------------------------------------------------------
The cold front continues to sink across central OH/southwest PA
at this time, with the system dry slot retreating east. Low-
level moisture, and a mid-level shortwave trough crossing the
Upper Ohio Valley, will continue to create scattered to numerous showers
into the overnight hours. Precipitation is forecast to
potentially mix with/change to snow before ending in most areas
by sunrise, with a very minor ridge accumulation possible. Warm
ground temperatures should prevent meaningful accumulation in
most other cases. Additional liquid rainfall should generally
remain below 0.20 inch in most cases. Despite this, ongoing
runoff and the continued potential for ice jams on the Cheat
and Youghiogheny Rivers led to the continuation of the ongoing
Flood Watch through the night.
Deeper moisture aloft is departing the region rapidly, evidenced
by water vapor loops and the 00Z PBZ sounding. As a result, the
presence of -10C cloud tops/ice nuclei will be called into
question. As a result, precipitation may taper to drizzle, and
potentially freezing drizzle as temperatures fall below freezing
into the 20s overnight. While patches of freezing drizzle may
occur north of Pittsburgh late tonight, the best potential for
freezing drizzle/fog producing a glaze on elevated surfaces lies
on the higher ridges into tomorrow morning. Another factor to
consider: ss road chemicals may have been washed off roads by
the rain, some icy spots may develop on currently wet roads as
well as the temperatures drop.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
KEY MESSAGES:
- Dry weather returns Saturday
- Increasing warmth again Sunday
--------------------------------------------------------------------
Much of the eastern-CONUS weather over the coming days will be
driven by the development, strengthening and amplification of a
H5 closed low off the coast of the Pacific Northwest, and
downstream of a sharpening ridge into Alaska. How this system
evolves will dictate the downstream flow effects.
Uncertainties with this system, as are typical in closed lows,
revolve around the amplitude and timing of the low axis. There
remains very-high confidence in its overall closed nature thru
at least Day 4-5, but the uncertainty in timing its eventual
phasing and forecast amplitude lend some question to impacts
downstream as downstream ridging could become more amplified
than ensemble mean heights might suggest.
The other impact to this low closing off will be its impact on
shortwave troughs revolving around the broader longwave troughing
that will linger downstream of the Alaska ridge over ern Canada
and Greenland.
The net result for this weekend will be a rapid ejection of the
ongoing trough in the ern Great Lakes region and rapid building
of a sfc ridge. A deformation band to the low's north may graze
the I-80 corridor on Sat as the system departs, but ice nuclei
will disappear rapidly, which could spell a brief period of
freezing drizzle in the I-80 corridor on Sat. If this occurs,
little impact is expected, as ground temperature has warmed
considerably.
Otherwise, building high pressure and attendant cold-air
advection may be offset by strong insolation on Sat, returning
daytime temps to near average.
A clipper system with varying potential strengths among ensemble
forecasts could graze the region on Sun/Mon. At a minimum,
increasing warmth is likely on Sun as low-level flow strengthens
out of the southwest in response to this system. Light
precipitation in this warm-advection regime is featured with
high confidence late in the day on Sun.
Irrespective of the system's strength, it will be past the
region by Mon, with the associated cold front impinging on the
Upper Ohio Valley, returning temps toward seasonal normal and
posing a slight chance of rain.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
KEY MESSAGES:
- Rain and snow chances return Wednesday with low pressure
-------------------------------------------------------------------
The medium range will feature a mid-level atmospheric battle
between the nrn jet stream around the above-mentioned Greenland
low and the srn jet stream around the closed low in the Pacific
Northwest.
Based on ensemble clustering, there appears to be relatively
high confidence in ridging developing downstream of the closed
low, with uncertainty for the ern CONUS related mainly to the
height field downwind of the ridge axis interacting with the nrn
jet stream across the nern CONUS.
Eventually, the ridge axis is likely to begin an ewd jaunt as
the Pacific Northwest closed low opens and phases into the
broader flow. Timing uncertainties dominate the cluster analysis
in this period, as a strong shortwave trough moves into south-
central Canada and attempts to sync with the opening nwrn-CONUS
low.
This system is most likely to affect the Upper Ohio Valley in
the Wed-Thu timeframe given the timing uncertainties mentioned
above. It will pose the greatest probability for precipitation
over the week, but looks to draw warm air nwd sufficient to
maintain predominantly a liquid mode, with the possibility of a
few flakes on the back side on Fri as cooler air filters in.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Minus LBE/MGW, a majority of light rain has been reduced to
light drizzle or no precip across the region. Brief periods of
VFR/MVFR have been noted with warm advection for sites south of
BVI. However, cold air is projected to advance over the next 4
to 6 hours and return IFR restrictions with lingering moisture.
The cold front is just south of CLE.
The potential for fog north of PIT will likely decrease between
00Z to 03Z with advancing cold air.
Cig improvements are projected as between 10Z to 15Z Saturday
with increase low and mid-lvl subsidence. VFR cigs is likely
after 13Z low-lvl mixing.
Outlook...
Weak shortwave movement in zonal flow to the north may lead to
a period of MVFR cigs (40-60% probability of occurrence) and
light rain/drizzle Sunday that favors northwest PA.
Periods of gusty wind may also develop as low pressure system
cross north of the region through early next week.
&&
.HYDROLOGY...
Updated forecasts for the Upper Monongahela and Cheat Rivers
this evening raised a few points slightly higher. Forecast
points are still not forecast to reach flood stage, but several
action stages are still expected, with crests during the
daytime hours on Saturday for the Cheat, and during the
afternoon and evening hours of Saturday for the Youghiogheny and
Monongahela Rivers.
Allegheny and Muskingum Basins:
Observed/forecast rain totals, river rises, areal ice coverage
and reaming snow pack are similar across these basins and their
reactions to these conditions are expected to be similar. Rises
in these basins are expected to be on the order of 1-3 feet. A
reduction in the risk for ice jams DOES NOT mean that risk is
eliminated and forecast crests in these basins could still
disturb areal ice and cause localized ice jam flooding. At this
time no points in either basin are expected to reach action
stage, but the risk for ice jam flooding still exists.
Upper Monongahela, Cheat and Youghiogheny Basins:
Forecasted rain amounts, observed snow pack and ice coverage are
similar across these basins. Most of the forecast crests for these
rivers have dropped several feet.
Several points on the Upper Mon, as well as Rowlesburg and
Albright on the Cheat, are still forecast to reach action
stage. Rises on the order of 6 to 12 feet are still forecast.
Earlier brief ice jamming on the Cheat at Parsons and Rowlesburg
has eased, with ice and water flowing down river freely at this
time. Still, localized ice jam flooding remains a possibility
downstream. At this time no points are forecast to reach minor
flood.
Forecast rises on the Yough are expected to be on the order of 3-6
feet which will be sufficient to disturb more plentiful and thicker
ice coverage found here. At this time no points along the Yough are
forecast to hit action stage, but ice jam flooding can occur.
Lower Monongahela Basin:
Rises on the order of 6-12 feet are still expected. These rises
are still expected to put several points to action stage. At
this time no forecast points are expected to reach minor flood.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch through Saturday afternoon for PAZ073>076.
OH...None.
WV...Flood Watch through Saturday afternoon for WVZ509>514.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...CL/Milcarek
SHORT TERM...Kramar/WM/22
LONG TERM...Kramar/WM/Milcarek
AVIATION...Hefferan
HYDROLOGY...CL/AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Jan 31, 9:06 PM EST---------------
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