Area Forecast Discussion
Issued by NWS Cleveland, OH

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FXUS61 KCLE 100229

Area Forecast Discussion
National Weather Service Cleveland OH
929 PM EST Sat Dec 9 2017

An upper level trough will remain across the eastern United States
for much of the week. At the surface, broad low pressure over the
Central Great Lakes will pull away to southern Quebec by Sunday
morning. A secondary trough will slide south across the Eastern
Great Lakes Sunday night, followed by yet another area of low
pressure crossing the Great Lakes region on Monday night.


The filling of the upper level low is occurring much faster
than expected with much of the snow decreasing in coverage.
Still seeing some heavier bursts of snow along the frontal
boundary that is sagging slowly southeastward across Lake Erie.
Locations from Cleveland to Erie will see the best chances of
seeing light accumulations through the remainder of the night.
Best timing for the bursts of heavier snow off the lake look to
be now (930 pm) through about midnight then trying to pick back
up again 2-3 am through sunrise. Best chances of seeing more
than 2 inches will be across NW PA. However the higher terrain
of eastern Cuyahoga County into Geauga County could see amounts
around 2 inches.

Previous Discussion...
Upper level vortex can be seen on water vapor imagery this
afternoon sliding southeast from the western Great Lakes towards
the Ohio Valley. At the surface, a broad area of low pressure
is located across the central Great Lakes. Light snow is
expected to continue to spread east this evening ahead of the
trough axis although is fighting low level dry air with
dewpoints that are slow to climb. Dewpoints in the east remain
in the lower teens and this has reduced the potential for a
widespread light coating of snow across the area. Outside of the
snowbelt, most areas will see little to no accumulation. With
that said, lake enhanced snow has been energetic off the
upstream lakes and this will be the focus for the forecast

Lake Erie remains quiet this afternoon but snow showers will develop
this evening as the low level trough swings east across the
lake with increasing low level convergence. We will transition
to pure lake effect snow behind the trough as the west northwest
flow sets up for the overnight hours. The initial burst of snow
accompanying the trough does not look as good as previous
forecasts and have backed off slightly on accumulations across
the snowbelt. Despite this, steep lapse rates expected to
develop with good moisture through 10K feet. Unfortunately the
airmass is just a little too warm such that the the best lift
is below the dendritic growth zone in the column. Accumulations
will range from less than an inch to 1 to 3 inches for the
favored upslope locations. Best snowfall expected in Erie County
PA where some enhancement possible off Lake Huron for a few

Have gone ahead and issued a Winter Weather Advisory for Erie County
PA as this is just the first of several rounds of snow expected over
the next 36 hours. Accumulations through midday on Sunday will range
from 2 to locally 5 inches, with the highest inland. Drier air over
the lake on Sunday may work to create a break in the activity before
a west to east band tries to develop during the afternoon as
convergence increases with the backing flow. There is uncertainty on
where this band will develop and how slow it will be to move
offshore. This band expected to eventually intensify offshore with
the heaviest snow focused down the lake into New York, before
crashing back onshore Sunday night. Adjustments may be needed to
the forecast in the Advisory area, either to account for a
prolonged break in snow on Sunday, or to account for higher
snowfall if this band is stronger when it pushes back south.
Generally expecting another 2 to 5 inches Sunday night. Westerly
winds will be a little more brisk on Sunday and wind chills
will not get out of the teens.


The active pattern continues through the first part of the work
week. A clipper rounding the Midwest/western Great Lakes Monday will
bring increasing chances of a light general warm advective snow to
the region by mid to late afternoon. Fairly early Monday the flow
will have backed enough to push any remaining lake effect offshore
of Erie PA. Highs will be close to freezing. A second low develops
just east of the lakes as a stronger shortwave dives south out of
Canada. This will strengthen the cold front crossing the area early
Tuesday morning. So most will see a general light snow Monday night
with lake enhancement for the snowbelt occurring Tuesday.
Temperatures may fall through the day Tuesday. Late Tuesday through
Wednesday morning synoptic moisture increases with a shortwave
rounding the primary trough parked across the eastern lakes. This
may enhance/expand the area of snow for Tuesday and have kept the
likely/categorical precip chances for north central through northeast
OH and nw PA going through Tuesday night. The northwest flow
continues into Wednesday and so will the snow showers. Temperatures
will bottom out Tuesday night with lows in the teens.


Weak high pressure will move up the Oh Valley Wed night and help to
weaken and shift the lake effect snow band further to the northeast.
The models show some light snow in the south half of Oh Wed night
but with the surface high will hold this threat to only a slight

Another clipper type low will move across the region later Thu into
early Fri trying to spread another batch of widespread light snow
around the area with maybe a little lake effect to follow later Fri
into Fri night.

High pressure shoots up the OH valley Fri night and should bring the
lake effect to an end. However, any break from snow will be short-
lived as the models show a band of warm advection cloudiness and
possible snow developing over the north part of the cwa for late Fri
night and Sat.

Temps will continue to run below normal into Fri night then should
moderate closer to normal by Sat aftn.


.AVIATION /00Z Sunday THROUGH Thursday/...
Cold front is moving across Lake Erie and NW Ohio with the
enhanced convergence likely causing some heavier bursts of snow.
TAF sites from the Central Highlands to NW PA will be impacted.
Greatest impacts with the lake effect snow will be from KCLE to
KERI with IFR conditions a definite as winds shift around to
the northwest. Winds will become gusty with the northwesterly
flow with 20 to 25 knots possible. Expect to see MVFR and brief
IFR at all inland locations. Ceilings will attempt to lift in
the wake of the 2 to 4 hour period of snow for inland locations.
Some low end VFR is possible across northwest Ohio overnight.
This trend of lifting ceilings will occur across all inland
sites on SUnday. However lake effect snow will be close to the
lakeshore from KCLE to KERI with KERI being impacted through the
day on Sunday.

OUTLOOK...Non-VFR likely Sunday night, Monday night, and
Tuesday night area wide. Non-VFR continuing across northeast
OH/northwest PA for most of the time through Wednesday night.


The small craft advisory east of Vermilion starts later this evening
and will run through early Monday morning. Winds will shift to the
west-northwest and increase in the wake of a cold front this
evening. Winds back to the southwest fairly quickly Sunday as
another clipper will round the Great Lakes. It will be marginally
strong and the western basin may need a small craft advisory for a
short time Sunday. West-northwest winds again follow for Sunday
night through Monday at which point they begin to diminish. Yet
another clipper arrives for Monday night with a similar response
from the winds. The northwest flow Tuesday looks to last through mid
week. Lake effect will taper off on Wednesday as winds begin to
back again ahead of the next clipper. It will remain cold and
will forecast highs only from around 20 to the mid 20s


PA...Winter Weather Advisory until 7 AM EST Monday for PAZ001-002.
MARINE...Small Craft Advisory until 4 AM EST Monday for LEZ145>149.


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