PBZ issues Area Forecast Discussion (AFD) at Jan 30, 9:03 PM EST747
FXUS61 KPBZ 310203
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
903 PM EST Thu Jan 30 2025
.SYNOPSIS...
Widespread precipitation chances increase after midnight with a
passing low pressure system. The highest chances of >1" of rain
are south of I-70. River rises expected, though no flooding if
forecast apart from any that may result from ice jams. A period
of above average temperatures with intermittent rain chances
expected next week.
&&
.NEAR TERM /THROUGH FRIDAY/...
KEY MESSAGES:
- Mid and upper-lvl clouds will continue to increase before
midnight as a low pressure system approaches
- Rain chances increase after midnight (above 50%)
- Fog potential north of Pittsburgh
- Heaviest rainfall amounts are expected south of I-70 between
8am and 1pm Friday
- Flood Watch in effect for areas south and east of Pittsburgh
Friday
----------------------------------------------------------------
9PM update:
A shield of light rain is currently track through portions of
Ohio this evening as a low pressure system start to enter the
Ohio River Valley. Heavier amounts are noted within central and
western Kentucky, flooding is currently occurring (2 to 4 inches
have been measured).
Between 10pm to midnight, precip is expected to be in the
vicinity of eastern Ohio. With lingering dry air, 00Z PIT
sounding depict mostly dry conditions below 15kft, rainfall
intensity will likely stay less than 0.05"/hr.
Adjustments that have been made to the forecast: Fog has been
added to areas north of Pittsburgh early Friday into the
afternoon hours. Hi-Res model ensembles are noting a strong
signal of fog development due to light precip, light winds,
lingering snow pack, and high low- lvl saturation. A Dense Fog
Advisory or a Special Weather Statement may be necessary.
Previous Discussion:
Overnight, the dominant surface low will drop back under the
upper low and occlude. This will lead to a fairly elongated
area of rain as moisture overrides the surface boundary and is
lifted along the warm and occluded front. QPF will be maximized
immediately north of the front. For now, the highest
probability scenario (75% chance) is that this warm frontal
boundary ahead of the triple point lingers in central West
Virginia where up to 3" of rain is possible. For northern West
Virginia, this would equate to 1" to 1.5" for higher elevations
and 0.5" to 1" for the lowlands. In the last 24 hours, this axis
has shifted slightly to the south, making flooding concerns
slightly less likely for the Mon basin and upstream. That being
said, there is still a 10% to 25% chance this boundary pushes as
far north as northern West Virginia in the US-50 corridor which
would result in higher flooding concerns with 2" to 3" of rain
for Tucker County and the Cheat basin.
The maximized QPF with this event will likely be in the ridges
with orographically enhanced ascent and will mostly occur in the
convergence near the triple point before the clod/occluded
front passage Friday morning and early afternoon. With rain, dew
points into the 40s, and surface temperatures pushing 50 on
Friday for the mountains, snowmelt will also contribute to water
flowing into the rivers. While a complete melt may not be
possible for the highest snowpack (up to 10" of snow and 1.75"
of water equivalent in eastern Tucker COunty), it will certainly
notably reduce it, and nearly eliminate snowpack for parts of
the Laurels of Pennsylvania. With ice still observed on the
Yough and Cheat basin and rapid rises from snowmelt, some ice
jam concerns will be heightened despite no rivers currently
forecast to go to flooding based to QPF and snowmelt alone. This
has justified maintaining the flood watch.
For other parts of the region, there is high confidence that
maximized QPF will remain south, but there is still about 75%
confidence in widespread amounts at or around 0.5" what will
lead to river rises on other icy rivers; correspondingly, we
couldn't rule out ice jam concerns in other areas.
Precipitation chances decrease into Saturday night as the low
pulls away, though major stem river rises will continue into the
day on Saturday and Sunday.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
KEY MESSAGES:
- Flood watch for Laurel Highlands to nrn WV tonight through Sat
- Dry weather returns Saturday.
--------------------------------------------------------------------
River rises will continue into the day Saturday and Sunday with
additional ice jam concerns, particularly for the Yough and
Cheat basins. For more information, see the hydrology section.
Weather wise, for the day on Saturday and Sunday, weather will
remain mundane as high pressure fills in behind the cold
frontal passage. A brief period of freezing drizzle could not
be ruled out for the highest elevations late Friday night into
Saturday morning, but the main challenge to accretion will be
surface temperatures, as the period of low moisture and sub-
freezing air temperatures are expected to be brief and follow a
warm period.
Saturday will remain seasonable with clearing cloud cover and
lower precipitation chances thanks to an icy Lake Erie. Sunday
will feature a return to warm and moist southwest flow thanks to
an eastward migration of the high pressure, though a clipper
system may affect northeast zones with a brief bout of
precipitation late Sunday that is most likely rain with light
accumulations. This forecast if fairly high confidence given low
variability in ensemble clusters.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
KEY MESSAGES:
- Slight chance for rain with a Monday cold front
- Rain and snow chances return Wednesday with low pressure
-------------------------------------------------------------------
Model ensembles indicate a general zonal flow is expected across
the CONUS for much of the long term period, as a trough develops
off the Pacific NW coast. A weak cold front embedded in the flow
is progged to cross the Upper Ohio Valley region on Monday, with
only a slight chance of rain expected. Generally dry weather
returns on Tuesday as surface high pressure builds in.
Low pressure is expected to develop along a stalled surface
boundary across the Mississippi Valley region Tuesday night,
approaching the Ohio Valley region on Wednesday, though
clustered variability increases with this. Rain chances return
with the approach of the low. Some snow is also possible,
depending on the exact track of the low and where the surface
boundary sets up. Stayed close to the ensemble blend to smooth
out some of this uncertainty in the forecast. The more
concerning aspect with this secondary system is more potential
for higher QPF and additional river rises. Goal posts are
currently between 0.2" (10th percentile) and 2" (90th
percentile).
Temperatures are expected to average above seasonable levels
through most of the period, with Tuesday being the coldest day
after FROPA.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Confidence remains high that VFR conditions will prevail for all
sites before 04Z this evening. Lingering low and mid-lvl dry air
is noted on the 00Z PIT sounding (mostly below 15kft).
Restrictions are likely to progress from west to east with an
advancing low pressure system. Rapid saturation will likely
drop cigs into low IFR/LIFR with noted warm air aloft. Higher
rainfall intensity will likely remain focused south of PIT due
to jet dynamics. The mostly likely time period of heavy rainfall
will occur between 12Z to 18Z. Periods of fog can't be ruled
out due to high levels of surface saturation and light winds
between 11Z and 15Z. However, it may be spotty north of PIT and
may not prevail for long periods.
As the center of the low advances into western PA Friday
afternoon, expected LLWS to increase across the region (a range
between 30kt to 45kts is expected). Higher values are likely
southwest of PIT.
The surface cold front is expected to drive east between 19z-23z
Friday, creating a line of showers that could develop brief
gusty wind. Dry advection and increased mixing behind the front
suggests higher probabilities for lapses in rain and improved
restrictions at the end and just after the TAF period.
Outlook...
Lingering moisture and delay in the passage of the upper trough
may result in another period of IFR cigs with light rain/drizzle
late Friday night into early Saturday morning. High pressure and
dry advection in northwest flow will end precipitation by 12z
Saturday and aide gradual improvements to VFR by Saturday night
(near 100% probability).
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...
Rainfall amounts between 0.50-1.50 inches falling on a melting
snowpack could contribute to significant rises on area rivers,
especially in the Mon, Yough and Cheat basins. These rises will
certainly disturb areal river ice and could create ice jam
flooding. At this time multiple forecast points are forecast to
hit action stage but none are currently forecast to hit minor
flood stage.
Allegheny Basin:
Upcoming rainfall and current snowpack are lighter in the
Allegheny Basin than others. However, rain on rotting snow,
river ice and the heating induced snowmelt are likely to cause
rises this weekend of 1-2 feet. These rises could be enough to
disturb the current ice coverage on the river and lead to ice jam
flooding. At this time no points in the Allegheny Basin are
expected to reach action stage.
Monongahela, Youghiogheny and Cheat Basins:
These basins are grouped together because their anticipated rain
totals, snowpack and ice coverage are expected to create similar
issues.
Rises on the Upper Monongahela and Cheat rivers are expected between
6-12 feet. These rises will certainly disturb any river ice and can
exacerbate issues seen across these basins. At this time there are
several locations in these basins forecast to reach action stage.
Rises on the Lower Monongahela are expected to range between 10-20
feet. This is expected to take all forecast points on the Lower
Mon to action, but not to minor flood.
Rises on the Youghiogheny are expected to be on the order of 3-6 feet.
These rises will certainly disturb thick river ice observed along
the river. At this time no points are forecast to reach action
stage but issues due to ice jams can bring flood concerns anyway.
Ohio and Musk Basins:
Expected rainfall totals and observed snow depth is lesser across
these basins. However ice coverage is plentiful.
Rises on the Ohio are expected to be on the order of 5-10 feet.
At this time no points are forecast to move to action stage but
the disturbance of ice may cause issues.
Rises on the Beaver, Muskingum and Tuscarawas rivers are expected
to be on the order of 1-3 feet. At this time no points are
expected to move to action stage. However, these rises are
sufficient to disturb plentiful areal ice coverage and cause
issues.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Flood Watch from 1 AM EST Friday through Saturday afternoon
for PAZ073>076.
OH...None.
WV...Flood Watch from 1 AM EST Friday through Saturday afternoon
for WVZ509>514.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...Hefferan/Milcarek
SHORT TERM...Milcarek
LONG TERM...WM/Milcarek
AVIATION...Hefferan/Frazier
HYDROLOGY...AK
Source:
PBZ issues Area Forecast Discussion (AFD) at Jan 30, 9:03 PM EST---------------
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