CLE issues Area Forecast Discussion (AFD) at Nov 26, 4:45 PM EST096
FXUS61 KCLE 262224
AFDCLE
Area Forecast Discussion
National Weather Service Cleveland OH
445 PM EST Tue Nov 26 2024
.SYNOPSIS...
High pressure slides through the Ohio Valley tonight before exiting
east on Wednesday. Low pressure tracks through the Ohio Valley
Wednesday night into Thursday. Cold air flows in behind this low
pressure beginning Thursday night and into the weekend.
&&
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
Quiet weather tonight into Wednesday morning as weak high pressure
slides through the Ohio Valley. Lows tonight generally in the upper
20s and lower 30s, warmer along the eastern lakeshore. We are
finally seeing a nice window of clearer skies and sunshine this
afternoon, though high clouds will begin to build in and lower
tonight into Wednesday morning.
Weak low pressure will track through the Ohio Valley Wednesday night
into Thursday morning before shifting towards the East Coast on
Thursday. Some light rain showers are possible Wednesday afternoon
within some mid-level warm air advection/isentropic lift ahead of
the approaching shortwave and developing low pressure. However,
greater precip potential is evident beginning Wednesday evening and
into Wednesday night as we get into an expanding shield of light to
moderate precipitation on the northwest side of the developing low
pressure in the Ohio Valley. Models still slightly disagree on how
consolidated pieces of vorticity within the shortwave trough will
be, leading to some disagreement over how strong the low will be, how
intense lift is within the shield of precipitation and how far
northwest the precipitation gets. The difference is evident between
runs such as the 12z ARW/HRRR and 18z NAM, which offer the stronger
solution, and the 12z NAM/RGEM, which offer the relatively weaker
solution. The 12z European model and 18z HRRR offer a bit of a
middle ground solution and are closest to the current forecast.
In terms of what this all means, there's fairly high-confidence that
much of the area will see a period of light to moderate cold rain
mixed with wet snow late Wednesday through early Thursday. Daytime
highs Wednesday will be in the low to mid 40s, with lows Wednesday
night ranging from the lower to upper 30s, right on the fence of
rain vs snow. Confidence in seeing any precipitation does begin to
lower into the Toledo area. The weaker solution would keep QPF
amounts under 0.25" area-wide, while the stronger option could
yield up to a few tenths of an inch of QPF, especially across our
southern and southeastern counties where the greatest overall QPF is
expected. Models that depict the stronger system depict a band of
mid-level frontogenesis getting into our southern counties, which
could lead to a narrow corridor of banded precipitation. The weaker
solution would generally lead to a lighter precip shield with a
sharper northwest edge to the precip somewhere west of I-71.
In terms of precip type specifics and any snow amounts/impacts,
generally expect snow to be of lower-impact though the forecast
does have some complexity. Surface temperatures will start well-
above freezing and may not get to freezing outside of the highest
terrain. However, 925mb temperatures will fall below 0C 3-6z, with
a bit of room for surface temperatures to wet-bulb as steadier
precip arrives (though dew points won't be extremely low, so this
won't be dramatic). This generally gets us to a point where steadier
precip should allow locations above 1000 feet in elevation could see
snow mix in starting 3-6z and then through the night...however,
lower elevation locations seeing any snow and hillier locations
seeing any accumulation would depend on seeing enough banded precip
to get stronger dynamic cooling and greater precipitation rates.
Models such as the 18z NAM and 12z HRRR/ARW, with more amplified
solutions, would support a 1 to 3 inch type accumulation in the
higher terrain of interior Ohio and northwestern Pennsylvania, with
little to no accumulation in the lower terrain (but likely flakes
for most of the area). Weaker solutions, such as the 12z NAM/RGEM,
would probably bring snow flakes to hillier locations but with
little to no accumulation, with the lower elevations staying mainly
or all rain. While one solution is slightly more exciting than the
other for fans of winter weather, neither solution is a huge impact
or accumulation. Given that just slight differences in the handling
of the shortwave energy are what is causing the differing model
solutions, our forecast offers a middle ground that leans on the
conservative side, showing accumulations of up to 1" in the higher
terrain and a rain/snow mix with little to no accumulation below
about 1000 feet in elevation. Trends in upcoming suites of guidance
will be monitored for continued tweaks.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
W'erly flow aloft is expected on Thanksgiving. Within this flow, a
prominent shortwave trough is still expected to advance E'ward
through our CWA during the morning through early afternoon, which
will allow the attendant and deepening surface low to shift NE'ward
from the Mid-Atlantic region toward Cape Cod between daybreak and
nightfall as an occluded front slides E'ward through our region and
ushers-in a much colder air mass, albeit gradually at first.
Widespread precip associated with frontogenetical forcing for ascent
within the low pressure system's TROWAL and moist isentropic ascent
ahead of the shortwave trough's axis will exit E'ward during the
morning through early afternoon. A relatively-deep surface-based
melting layer will allow precip to fall mainly as rain, but a few
wet snowflakes may mix-in, especially during the early morning and
early evening. No snow accumulation is expected. In addition, a
sufficiently-cold/moist mean low-level flow over/downwind of ~10C
Lake Erie is expected to back from N'erly to NW'erly and allow lake-
effect precip to impact most of our CWA. Daytime highs are expected
to reach the upper 30's to mid 40's.
Behind the aforementioned, prominent shortwave trough, a deep
mid/upper-level longwave trough associated with an unusually-cold
air mass becomes established over eastern Canada and the eastern
United States Thanksgiving night through Friday night, which will
allow cyclonic W'erly to NW'erly flow aloft and additional, embedded
shortwave disturbances to affect the eastern Great Lakes and Upper
OH Valley. At the surface, a trough lingers over/near our region.
Low-level CAA will occur in earnest and allow 850 mb temperatures
initially near -7C to drop to near -10C to -13C over ~10C Lake Erie
and our CWA as low-level moisture remains abundant and deep. Lake-
induced CAPE is expected to increase to at least moderate
magnitudes. Given the aforementioned CAA and wet-bulb effect, lake-
effect precip, mainly in the form of snow, is expected in/near the
snowbelt of NE OH and NW PA as mean low-level flow backs from
NW'erly to W'erly Thursday night and then varies between primarily
WSW'erly and WNW'erly on Friday through Friday night, which will
allow the LES to become focused in/near the primary snowbelt. The
aforementioned shortwave disturbances traversing our area will cause
the mean low-level flow direction to fluctuate. Given the expected
thermodynamics, a projected cloudy DGZ of about 1 km thick, and
expectation for strong/maximized ascent at a lake-effect cloud
temp of ~-10C per model soundings in BUFKIT, efficient snow
production and periods of steady to heavy snow are expected. At
least several inches of snow accumulation are expected where
the heaviest/most-persistent LES occurs, which will likely be
in/near the primary snowbelt. Moist isentropic ascent preceding
shortwave trough axes will allow periods of lighter snow with minor
snow accumulations to occur outside the LES. Stay tuned for forecast
updates, including eventual winter WX alerts. Overnight lows are
expected to reach mainly the mid 20's to lower 30's around daybreak
Friday and be followed by Friday afternoon highs in mainly the lower
to mid 30's. Overnight lows should reach mainly the 15F to 25F range
around daybreak Saturday.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
The deep mid/upper-level longwave trough is expected to persist over
eastern Canada and the eastern United States through the long-term
period. This will allow cyclonic W'erly to NW'erly flow aloft and
embedded shortwave disturbances to continue to affect our CWA as an
unusually-cold air mass remains entrenched across the Great Lakes
and OH Valley. At the surface, a trough lingers over/near the Great
Lakes, including our CWA. Daily afternoon high temperatures are
expected to reach roughly the 25F to 35F range and daily low
temperatures are expected to range from the mid teens to upper 20's
around daybreak Sunday, Monday, and Tuesday, respectively.
Temperatures at 850 mb near -9C to -13C over/downwind of ~10C Lake
Erie, abundant/deep low-level moisture on the synoptic scale, and
sizable lake-induced CAPE are expected to allow LES, steady to heavy
at times, to persist over/downwind of Lake Erie. Based on the latest
projected evolution of relevant shortwave disturbances, mean low-
level flow should vary between W'erly and SW'erly on Saturday into
the first-half of Sunday. Later on Sunday through Monday night, mean
low-level flow should vary between W'erly and NW'erly before
potentially backing to SW'erly on Tuesday. Periods of steady to
heavy LES are expected to impact the snowbelt of NE OH/NW PA and
vicinity when mean low-level flow is W'erly or NW'erly. Significant
and impactful snow accumulations are possible, but exact snowfall
totals remain uncertain. Stay tuned for forecast updates. Moist
isentropic ascent preceding shortwave trough axes will allow periods
of lighter snow with minor snow accumulations to occur outside the
LES.
&&
.AVIATION /18Z Tuesday THROUGH Sunday/...
Still a mix of VFR and MVFR at 18z, with all sites expected to
continue to trend to VFR through the afternoon as high pressure
and drier air building in leads to clouds continue to slowly
rise and scatter out. High clouds will start streaming in
tonight, but expect ceilings to remain well-above even 5000 feet
through the end of the TAF period.
West-southwest winds 12 to 18 knots with gusts 20 to 30 knots
early this afternoon will generally ease to 3 to 8 knots
tonight, though ERI will stay a bit windier. West-southwest
winds remain relatively light Wednesday morning.
Outlook...Non-VFR likely in rain and/or snow Wednesday night
through Thursday and with a transition to lake effect snow
Thursday night through Saturday.
&&
.MARINE...
Gale Warning in effect until 10 PM this evening for all U.S. waters
from Conneaut to Buffalo. Small Craft Advisory in effect until 1 AM
Wednesday from Maumee Bay to Vermilion; until 7 AM Wednesday from
Vermilion to Avon Point; until 10 AM EST Wednesday from Avon Point
to Conneaut.
A low meanders near James Bay through tonight as a ridge builds over
Lake Erie from the Lower OH Valley. The interaction between the low
and ridge will allow W'erly winds as strong as 25 to 35 knots
through this early evening to ease to 10 to nearly 20 knots and
become SW'erly to W'erly by daybreak Wednesday. Waves as large as 4
feet in the western basin and as large as 7 to 14 feet farther east
will subside gradually so that by daybreak Wednesday, waves are
expected to subside to 2 feet or less in the western basin and 6
feet or less farther east.
The aforementioned low will weaken and meander near James Bay
through Saturday before drifting E'ward on Sunday. Otherwise, the
aforementioned ridge will exit gradually E'ward on Wednesday through
Wednesday night as a separate low moves from the south-central U.S.
toward the Mid-Atlantic states and strengthens. S'erly to W'erly
winds around 5 to 15 knots on Wednesday are expected to become
variable around 5 to 10 knots Wednesday night as the southern low
begins to extend a weak trough over the Lake Erie region. Waves are
expected to subside to 3 feet or less by sunset Wednesday evening.
An occluded front will sweep E'ward across Lake Erie on Thanksgiving
as the southern low moves NE'ward from the Mid-Atlantic states to
the Canadian Maritimes and deepens further by daybreak Friday.
Behind the occluded front, a trough lingers over Lake Erie through
this Sunday. As the occluded front moves E'ward across Lake Erie on
Thanksgiving, variable winds around 5 to 10 knots ahead of the front
become NW'erly to N'erly around 10 to nearly 20 knots. Waves are
forecast to remain primarily 3 feet or less, but occasional 4
footers are possible in the central basin, where fetch will be
greater. Winds are expected to be primarily WNW'erly to WSW'erly and
around 15 to 25 knots Thursday night through Friday, although winds
are forecast to reach 30 knots at times on Friday. Waves are
expected to build as large as 3 to 6 feet Thursday night and as
large as 5 to 10 feet on Friday through Sunday, especially in the
central and eastern basins. Another Small Craft Advisory will likely
be needed.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
MARINE...Small Craft Advisory until 1 AM EST Wednesday for LEZ142>144.
Small Craft Advisory until 7 AM EST Wednesday for LEZ145.
Small Craft Advisory until 10 AM EST Wednesday for LEZ146>148.
Gale Warning until 10 PM EST this evening for LEZ149-169.
&&
$$
SYNOPSIS...Sullivan
NEAR TERM...Sullivan
SHORT TERM...Jaszka
LONG TERM...Jaszka
AVIATION...Sullivan
MARINE...Jaszka
Source:
CLE issues Area Forecast Discussion (AFD) at Nov 26, 4:45 PM EST---------------
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