CLE issues Area Forecast Discussion (AFD) at Dec 7, 12:55 AM EST304
FXUS61 KCLE 070555
AFDCLE
Area Forecast Discussion
National Weather Service Cleveland OH
1255 AM EST Sat Dec 7 2024
.SYNOPSIS...
High pressure builds eastward today. A weak low moves eastward
across the northern Great Lakes this afternoon into tonight with
a surface trough crossing the region tonight. A larger low
pressure system moves across the area on Monday followed by a
cold front on Tuesday.
&&
.NEAR TERM /THROUGH TODAY/...
10:00 PM Update:
We are finally beginning to see lake effect snow return to
northern Erie County after a several hour break. As a shortwave
moves east of the region into the overnight the low-level flow
is still expected to veer for a few hours over the lake,
pushing the band that's currently impacting western NY south
into Erie County and increasing shoreline convergence enough
along the far northeastern Ohio shoreline that some snow should
develop there as well overnight.
Still, the snow has been a bit slower to return to Erie County
than expected and has not yet shown signs of developing along
the Ohio lakeshore. Took a close look at the meteorological
set-up and made targeted/conservative changes to the forecast.
The overall assessment is that lake effect potential tonight is
a bit less impressive overall. While the band should sag into
Erie County and while convergence will increase along the
lakeshore as far west as Lake County, 1000-850mb mean RH is
currently less than 60%, which is rather dry. While low-level
RH is projected to increase overnight, inversion heights will
begin lowering as we get into some subsidence behind the trough
passage, to the point where forecast soundings and plan-view
model forecast outputs suggest the bulk of the moisture and lift
will be below the dendritic growth zone. In addition, the
boundary layer directional shear is on the high side for a
favorable lake-effect set-up. This all suggests that it will be
hard to see heavy snow accumulations across the area tonight.
Even when attempting to be conservative with forecast changes,
still ended up lowering amounts in northern Ashtabula County to
3" or less, with the greatest amounts near Conneaut. Amounts in
northern Erie County came down a bit too but are still higher,
generally in the 3 to 6 inch range in the northern half of the
county with a sharp drop-off to 1" or less along the Crawford
County line. Activity should shift offshore Saturday morning.
Given the continued downtrend in snow amounts in northern
Ashtabula County, canceled the warning early there. Will
maintain the warning for Erie County, as several inches of snow
is still possible. While rates won't be that impressive given
the negative factors described above, a long fetch and strong
shoreline convergence could support rates up to about 1" per
hour, assuming the band currently over western NY can push south
into northern Erie County tonight for a time.
Otherwise, raised low temperatures just a bit tonight given
winds staying up and fairly numerous clouds. Hourly temperatures
were running milder than the previous forecast. Also added some
low POPs from northeastern Ashtabula County into Northwest PA
for a few hours Saturday afternoon, as mid-level isentropic
lift may support some light synoptic snow with minimal to no
accumulation.
Previous Discussion:
High pressure and drier air continue to build over the region
tonight. Surface observations across northern Ohio and Northwest
Pennsylvania already show southwesterly winds areawide. This will
keep lingering lake effect snow confined to lakeshore sites across
Ashtabula County and Erie County PA. An upper level shortwave
will sink south across Lake Erie overnight tonight and supply an
additional push of moisture to allow for lake effect snow to
persist into daybreak Saturday. As such, have extended the end
time for the Lake Effect Snow Warning for Ashtabula County and
Erie County PA through 7 AM Saturday. An additional 3-6 inches
of snowfall along the lakeshore in Ashtabula County with up to
6-10 inches of additional snowfall is expected across Erie
County PA through Saturday morning. Given the placement of the
lake effect snow band and sharp QPF gradient, opted to cancel
the Lake Effect Snow Warning for Crawford County PA as any
additional snowfall will be light with minimal accumulation.
High pressure settles south of the forecast area by Saturday which
will bring a window of quiet weather and increasing temperatures.
One more chilly night tonight with lows dipping into the low 20s.
Afternoon highs on Saturday will rise into the mid to upper 30s with
low to mid 30s across the Snowbelt.
&&
.SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/...
A warming trend accompanied by some rain will be the story heading
into early next week. An upper level split flow pattern will develop
with upper level ridging building overhead on Sunday ahead of a
trough lifting out of the Four Corners Region. Southerly flow
returns with a warm front lifting north on Sunday night. As the
airmass moderates Sunday night, we will also see rain developing
along the front. Dewpoints climb above the freezing mark
and will remain there for about 48 hours. Above normal
temperatures are expected Monday and Tuesday as low pressure
passes north of the Great Lakes Region placing our forecast area on
the warm side of the system. High temperatures Monday into Tuesday
will tend to be in the mid 40s in the snowbelt while portions of
northwest Ohio reach the low 50s. Have lowered highs slightly for
eastern areas during this time frame as the cold snow will still
have an impact. The warmth and moist conditions will lead to
extensive melting of the snowpack in the snowbelt region. Initially
the round of rain Sunday night into Monday will likely be
absorbed into the snowpack as the snowpack ripens and starts to
melt. Another lighter round of rain is possible Tuesday into Tuesday
night. The estimated water content within the deep snowpack is
roughly 2.0-4.0 inches with expected rain of a quarter inch to
three quarters inch. This is expected to occur over a two to three
day window. Conditions will certainly get soggy and we will be
monitoring for the potential for localized flooding. Residents can
help by clearing drains of snow so that water can get to appropriate
drainage system. Some minor flooding of low lying and poor drainage
areas is possible but we are glad that forecast rainfall amounts
are not higher.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
The above mentioned low pressure system will pull a cold front east
across the area Tuesday night. Temperatures on Wednesday will
drop back into the 30s with a secondary push of colder air
arriving Wednesday night as a stronger trough dives south out
of Canada and swings across the Great Lakes Region. This leads to a
period of westerly flow on Lake Erie with temperatures cooling
enough to support lake effect snow. Will carry high pops along
the lakeshore and to a lesser extent across the remainder of the
snowbelt as accumulating snow looks possible Wednesday night into
Thursday. Will need to get a better handle on wind
direction and mesoscale parameters before having a
handle on accumulations. Temperatures will below normal on Thursday
but will start to warm by Friday as the trough shifts east across
New England.
&&
.AVIATION /06Z Saturday THROUGH Wednesday/...
Lake effect snow continues in mainly Northwest Pennsylvania
through a good chunk of the morning hours, although with less
intensity than previously expected. Have only 4SM snow showers
at KERI with MVFR ceilings through the rest of the morning
before it dissipates.
Otherwise, expect VFR to prevail at all other TAF sites through
the TAF period with some mid-level clouds (as low as 4,000 to
6,000 feet) drifting through at times this morning and maybe
into the early afternoon hours.
Southwest winds will persist at 8-12 knots this morning. Winds
gradually strengthen this afternoon and tonight, peaking at
around 15-18 knots tonight with gusts up to ~25 knots. A strong
southwesterly low-level jet paired with a temperature inversion
will lead to low-level wind shear after 00Z this evening. Most
model guidance has varying winds speeds of around 50 to 60 knots
at 2kft.
Outlook...Periods of non-VFR are expected late Sunday night
through Tuesday as low pressure brings rain to the region. A
cold front will cross Tuesday night, potentially bringing some
rain showers and non-VFR with the front followed by lingering
lake effect snow in Northeast Ohio and Northwest Pennsylvania on
Wednesday.
&&
.MARINE...
A trough remains over the eastern Great Lakes while high pressure
builds over the Ohio Valley. This is maintaining a brisk westerly
wind of 15 to 25 knots for tonight. A Small Craft Advisory remains
in effect for the nearshore waters east of the Lake Erie Islands
through Sunday night. While there is not currently a Small Craft
Advisory west of the Islands, one will likely be needed again for
Saturday night. In addition, southwest to westerly winds increase to
near Gale Force on the eastern half of Lake Erie for Saturday night.
A Gale Watch has been issued from approximately Cleveland eastward
as an area of low pressure moves across the Upper Great Lakes. Waves
will remain elevated on the east half of the lake through Sunday as
winds start to decrease.
Southwest winds will continue early next week, but will veer to
northwesterly with the passage of a cold front on Tuesday Night.
This will likely result in another window of Small Craft conditions
as waves increase behind the front for the mid-week period.
Water levels are hovering near, but just above, the critical
mark for save navigation across the western basin this evening.
Water levels are expected to bounce around near to just above
the critical mark through Saturday. Will closely monitor that.
There is greater potential for water levels to fall below the
critical mark Saturday night as southwest winds pick up, and a
Low Water Advisory will likely be needed in future updates.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...Lake Effect Snow Warning until 7 AM EST this morning for
PAZ001-002.
MARINE...Small Craft Advisory until 4 AM EST early this morning for
LEZ143-144.
Small Craft Advisory until 7 AM EST Monday for LEZ145-146.
Small Craft Advisory until 4 PM EST this afternoon for
LEZ147>149.
Gale Watch from this afternoon through Sunday morning for
LEZ147>149-166>169.
&&
$$
SYNOPSIS...Iverson
NEAR TERM...Iverson/Sullivan
SHORT TERM...KEC
LONG TERM...KEC
AVIATION...Saunders
MARINE...KEC
Source:
CLE issues Area Forecast Discussion (AFD) at Dec 7, 12:55 AM EST---------------
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