776
FXUS61 KCLE 220313
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
1013 PM EST Thu Nov 21 2024

.SYNOPSIS...
Low pressure over the Great Lakes will merge with a low off the New
England Coast tonight into Friday, leaving a surface trough
lingering through Saturday. High pressure will nudge across the area
on Sunday before another low pressure system impacts the region on
Monday.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
Lake and Cuyahoga Counties were upgraded to a Lake Effect Snow
Warning as reports started to trickle in of 4-7". While the
band has started to finally push south, snowfall remains heavy
with 1"+ per hour snowfall rates. Much of the metro area will
receive 1-3" of snow before pushing south into the secondary
snow belt. The trough has been slower to push south than
previously expected, maintaining a cooler southwest wind and
piling up the snow in the eastern suburbs. In the wake of the
trough, winds will shift around to the north with a break in
precipitation. Temperatures are still forecast to trend up into
the mid to upper 30s in the warning area overnight with a warmer
flow coming in off Lake Erie and weak warm advection in the low
levels.

Coverage of precipitation will increase again heading into
Friday morning as moisture wraps around the back side of the
upper low. Northwest winds increase on Friday with a
strengthening pressure gradient and surface low pressure
retrograding west across New York.

Previous discussion...As an occluded low continues to impact
the region into tonight, scattered snow showers are expected to
continue. Given near freezing surface temperatures and a push of
colder air this evening, would not be surprised if some areas
saw up to 0.5", especially in higher elevations.

More notably is the band of lake effect snow that is currently
residing over Lake Erie. As the aforementioned low begins to
merge with a low pressure off the New England Coast, winds
across the area will gradually shift to a more west-
northwesterly pattern. When this happens (expected sometimes
between 21-23Z this evening) the aforementioned band of lake
effect is expected to push inland. There is high model agreement
amongst hi-res guidance for heavy snow to occur across portions
of western Cuyahoga and Geauga Counties. The timing of this
band is important to note as it will likely coincide with the
evening rush hour and increase the likelihood of impacts. Given
the warmer antecedent conditions, expect the first bit of snow
to melt on contact before accumulating. However, with heavy
rates of up to 1"/hr, visibilities will rapidly diminish and
motorists should use caution and allow for extra time when
traveling. As a result of the accumulating snow potential and
the possible impacts, a Winter Weather Advisory has been issued
until 12PM for the aforementioned counties.

Digging more into the nuanced aspects of this forecast through
midnight tonight, there are multiple factors that could shift the
forecast one way or another. To start off, models are consistent
with strong omega forcing, a convergent boundary developing on
the southern edge of Lake Erie, and very cold 850mb temperatures
of -5 to -7C pushing south which are all very conducive for
lake effect showers, leaving much of the nuances to
temperatures. Along the immediate lakeshore, much of the
precipitation will remain as rain or a rain/snow mix as warm air
advects south off of the lake, but how far south this warming
goes is a bit uncertain. Opted to decrease rain/increase snow
potential along the higher terrain with colder temperatures
expected. In addition, models suggest that there is a potential
for more of a graupel/snow mix inland, although impacts will
likely remain the same. To summarize, there is high confidence
in an impactful lake effect band during the evening rush hour,
but less confidence in snowfall totals associated with the band.


Tonight, precipitation chance should become isolated to the eastern
portion of the CWA as the low merges in New England and leaves a
surface trough over the area. With the occluded nature of the low,
warmer air is actually expected to wrap around the center and result
in warmer 850mb temperatures throughout the surface trough. As a
result, precipitation should gradually change from snow to rain from
north to south, ultimately becoming only rain by Friday morning.
Although warmer, these 850mb temperatures coupled with a
convergent boundary will result in a full transition to lake
effect on Friday. The wind forecast will be critical in the
placement of these showers. Currently, winds are expected to
become more northerly throughout Friday, which has the potential
to result in a Lake Huron connection and areas along and east
of I77 being impacted by widespread rain into Friday night. As
the trough gradually shifts east Friday night, showers will
follow suit and should shift to impacting primarily the snowbelt
by Saturday morning.

Overnight lows tonight will drop into the upper 20s to low 30s,
gradually increasing into the mid 30s Friday morning. Highs on
Friday will climb into the low to mid 40s, remain nearly steady
Friday night.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
One more shortwave trough will rotate through the mean mid/upper
longwave trough Friday night into Saturday morning as the closed low
near New York City finally starts to drift into the Atlantic. Mid-
level PVA and enhanced low-level convergence as the trough crosses
Lake Erie combined with continued NW flow across Lakes Huron and
Erie will once again increase the coverage of lake-effect/lake
enhanced showers Friday night into Saturday. H85 temps will have
modified significantly by that time, with values of 0-2 C, and this
will reduce the instability and prevent anything overly heavy.
However, given the at least conditional instability, deep synoptic
moisture, and enhanced lift, kept likely to categorical PoPs over NE
Ohio and NW PA through midday Saturday. The lake-effect showers will
very gradually taper off Saturday afternoon through Sunday morning
over NE Ohio and NW PA as the flow backs southwesterly and drier air
and a lowering inversion work in from the west in response to
shortwave ridging slowly building across the Ohio Valley and
southern Great Lakes. Lake-effect precip is almost always slower to
end than guidance suggests, and there are hints at a final weak
shortwave dropping through the exiting trough Saturday night, so
maintained chance PoPs through Sunday. No snow is expected for the
weekend as boundary layer temps will be too warm. The shortwave
ridging combined with weak surface high pressure nosing into the
Ohio Valley will finally bring dry conditions Sunday afternoon, but
this won`t last long before shower chances slowly return from west
to east Sunday night as isentropic ascent ramps up ahead of the
next system. More on that in the Long Term section.

Highs will range from the mid 40s to around 50 Saturday, warming
slightly into the mid 40s to low 50s Sunday. Lows Saturday night
will dip into the mid/upper 30s, with mid 30s to low 40s Sunday
night.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As mentioned above, another system will quickly follow for early
next week since a very active pattern has finally developed after a
quiet Fall. Quasi-zonal flow across the CONUS and mid/upper
shortwave ridging over the southern Great Lakes Monday will somewhat
break down to allow a fast moving mid/upper trough to cross the
Great Lakes Monday night and Tuesday. This trough will deepen/dig
slightly into the eastern Great Lakes by Wednesday, bringing another
quick shot of cold air to the region. It will not be as cold as the
previous airmass, with H85 temps averaging a marginal -5 C for lake-
effect, but it will lead to lake-effect rain/snow showers once again
downwind of the lake. Expect widespread rain showers Monday as the
cold front approaches and interacts with a 100-110 knot H3 jet, and
this will transition to lake-effect rain and snow behind the front
Monday night and Tuesday in the cold air advection. Wind direction
and boundary layer moisture/shear are uncertain this many days out,
but current indications are for a W to WNW flow, so placed the
highest PoPs in the primary snowbelt of NE Ohio and NW PA. The lake-
effect precip will gradually taper off Tuesday night and Wednesday
as the trough lifts out. Too early to think accumulations, but
again, thermodynamics are marginal, so it would probably be hard to
see much more than light accumulations on grassy surfaces Tuesday
into Wednesday, mainly at night and away from the lakeshore.

For Thursday into next weekend, deterministic and ensemble guidance
continue to support a chunk of true arctic air moving into the
northern Plains and Upper Midwest and eventually across the Great
Lakes. This is in response to a blocking ridge developing over the
North Pacific and Alaska which could bring more sustained cold
through early December. Guidance has been suggesting a wave of low
pressure to develop on the cold front Thursday or Friday, which
would make sense given the dynamics, but track and strength are
impossible to pinpoint 7 days out. At this time, brought in broad
chance to likely PoPs Wednesday night into Thursday. The main
message is that a rainy and windy system is possible around
Thanksgiving followed by a cold weekend that could include some lake-
effect snow, depending on how everything aligns. Stay tuned!

&&

.AVIATION /00Z Friday THROUGH Tuesday/...
Heavy snow has been ongoing over Lake Erie and into the eastern
Cleveland suburbs as a trough has been nearly stationary over
Lake Erie. This trough is expected to push south of the lake
through 03Z and push this west to east band of snow south across
the metro area. Still expecting this band to bring moderate to
brief heavy snow to CLE for up to an hour which could lead to a
quick inch of snow. Snow is also likely to reach CAK/YNG with
IFR possible but more in the 1-2 mile visibility range. ERI has
been warmer and could see brief snow or a rain snow mix. Behind
the trough, winds will shift to the north off warmer Lake Erie
and temperatures are expected to climb bringing a transition
back to rain working north to south overnight. An increase in
precipitation is also expected overnight into Friday at eastern
terminals. Ceilings will tend to lower to IFR during the day on
Friday as low pressure over eastern New York retrogrades
westward. In NW Ohio brief snow showers are possible but will
tend to be light with MVFR visibilities, mainly at TOL.

Winds are starting off at southwesterly at less than 10 knots
but will veer to northwesterly and increase through the day on
Friday. Most sites will see winds gusting to around 25 knots on
Friday with locally up to 30 knots or higher at CLE and ERI
where stronger flow is expected off Lake Erie.

Outlook...Non-VFR conditions will be possible Friday through
Saturday in scattered lake effect rain showers, possibly mixed
with snow showers at times early on Friday. Gusty winds from the
north and northwest up to 35 knots will also be possible Friday
through Saturday, especially areas closer to the lakeshore as
as well NEOH and NWPA.

&&

.MARINE...
The lake will remain active over the next 5 days, typical for late
November. A surface trough crossing the lake tonight as the upper
low drifts southward will shift winds to the NW along with an
increase in speeds to 20-30 knots late tonight and Friday. This will
build waves to 6-10 feet before NW winds gradually taper to 15-25
knots Friday night and Saturday while backing more westerly by
Saturday night. Issued Small Craft headlines for the entire lake
from tonight into the weekend, especially the central and eastern
basins which will see higher winds and waves through midday Sunday.
This is high confidence. However, there could be a marginal Gale (34
knots) late tonight through Friday morning. This is low confidence
since there is not much of an 850 mb jet compared to classic events.
If it occurs, it would probably be due to the pressure gradient
briefly tightening, but confidence was too low to issue a warning,
so kept a Gale Watch at this time. As mentioned, it will definitely
be a high end Small Craft Advisory.

Winds will back to SW and briefly decrease to 5-15 knots Sunday into
early Monday before WSW winds increase to 20-30 knots again late
Monday into Tuesday, so additional headlines are likely at that
time.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...Lake Effect Snow Warning until 2 AM EST Friday for OHZ011-012.
     Winter Weather Advisory until 2 AM EST Friday for OHZ013.
PA...None.
MARINE...Small Craft Advisory from 1 AM Friday to 10 AM EST Saturday
     for LEZ142.
     Small Craft Advisory from 1 AM Friday to 7 PM EST Saturday for
     LEZ143.
     Small Craft Advisory until 10 AM EST Friday for LEZ144>147.
     Gale Watch from Friday morning through late Friday night for
     LEZ144>147-164>167.
     Small Craft Advisory from 1 AM Friday to 10 AM EST Sunday for
     LEZ148-149.

&&

$$

SYNOPSIS...Campbell
NEAR TERM...Campbell/KEC
SHORT TERM...Garuckas
LONG TERM...Garuckas
AVIATION...KEC
MARINE...Garuckas