CLE issues Area Forecast Discussion (AFD) at Dec 31, 10:03 AM EST840
FXUS61 KCLE 311503
AFDCLE
Area Forecast Discussion
National Weather Service Cleveland OH
1003 AM EST Tue Dec 31 2024
.SYNOPSIS...
A low pressure system will cross the area today and extend a cold
front across the region tonight. A trough will set up over Lake Erie
behind the low for Wednesday and remain through the weekend.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
930 am update...
The next weather system is already moving into northern Ohio
this morning and will bring another round of soaking rainfall
to the entire area today into this evening. There is a large
area of moderate to heavier rain showers that is quickly
advancing northeastward from western/central Ohio this morning.
This wave of steadier rain will impact the Cleveland metro
through lunchtime with an ETA moving into the CLE around 11 am.
One interesting note to mention is that the KCLE radar over the
past couple of hours has shown a classsic bright banding
signature because of wet snow flakes and melting snow aloft just
a couple thousand feet off the surface. The only minor
adjustment we made with this late morning forecast update was
adding a very slight chance of thunder during a 3 hour window
from midday to early afternoon. Otherwise it will be just a
cold, soggy rest of the day into this evening for our region.
The rest of the forecast is on track with no other changes
needed at this time.
Previous discussion...
The weather pattern timing within the forecast period is quite
poetic to the calendar with a warm and generally rainy synoptic
system expected for the last day of 2024. The first day of 2025
will then feature the start of a prolonged cold and snowy
period for the region, as lake effect snow warnings have been
issued for the first two days of January.
For today, a low pressure system spins over central Illinois
coincident with an upper level shortwave digging through the
Great Lakes region. This system has been somewhat delayed in the
timing of rain into the forecast area this morning as the
initial bands of rain spiraling around the low are losing out
to dry air overhead and radar returns have struggled to
materialize to the surface. However, these returns are
indicative of a mid-level cloud deck across the region, which
is abating the dry air aloft and will eventually allow a band of
steady rainfall to cascade across the region later this morning
into the early afternoon. Have continued to mention a 100
percent chance of rain across the area, but have narrowed the
window to reflect a more certain band of rain that is currently
pacing its way northeast through Indiana. As the center of the
low moves through the region, rain will become a bit more
diffuse as there is some drier air on the southern side of the
system that will allow for some brief breaks in rain before the
cold front starts moving through the area. While this could be
described as a period of more "scattered" rain showers across
the area, have maintained generally higher PoPs mostly in the
likely range. As the cold front drifts through the region this
afternoon through tonight, there will be a transition from rain
to wet snow and have forced snow to start a bit earlier in
Northwest Ohio, as temperatures are generally going to struggle
today and the Toledo area will struggle to get into the warm
advection region of the high, so there will be an easier
tendency for snow before the ball drop tonight and have some
light accumulations, mainly for grassy and elevated surfaces.
The cold front will move across the region tonight into
Wednesday and all rain will transition to snow with a strong
surge of cold air with the front. There could be a wet half inch
to inch of snow with the transition late tonight into Wednesday,
although this may only be realized on grassy and elevated
surfaces and not area roadways. The event will then transition
to a lake enhanced snow event. The onset of the event will be
largely driven by the passing cold front and upper trough
supporting snow across Northeast Ohio and Northwest
Pennsylvania. However, cold air advection and a unified
northwest flow across the region will eventually allow for lake
effect processes to become more efficient and the driving force
behind heavy snow squalls in the region. These bands of heavy
snow will be further helped by upslope flow in the higher
elevation areas of NE OH/NW PA, specifically Geauga County, OH
and Erie and Crawford Counties, PA. These areas will also get
some assistance from upstream clouds and moisture from off Lakes
Michigan and St. Clair, and perhaps even Lake Huron.
With that, have upgraded the Winter Storm Watch to a Lake
Effect Snow Warning for Geauga County, OH and Erie and Crawford
Counties, PA. For Geauga County, have ended the warning at 7 PM
Thursday, as the flow becomes more westerly and slightly
disrupted, where any snow bands should lift north out of the
county and the area should have a pronounced break before the
weekend. For NW PA, have run the warning clear through Sunday.
More is described in the below sections on the lake effect
characteristics but overall, any lull will be brief. For the
remainder of the Winter Storm Watch, the snow event for
Wednesday and Thursday remains conditional for the end snowfall
totals and impacts. This event will be tied to the upslope of
higher elevations to compensate for some lack of cold air aloft.
In addition, final band placement will also dictate totals and
slight movements north or south could have large implications,
as just pieces of the remaining watch zones remain the most
favorable for this event (e.g. - areas east of I-271 in
Cuyahoga County, areas along and south of I-90 in Lake County,
and areas south of I-90 and above the Grand River Valley in
Ashtabula County). However, can say that there will be a break
in Ohio from the snow and have truncated the Winter Storm Watch
to match the Geauga County warning for now (and discussed more
below). Will allow for another forecast cycle to help with
clarity on any upgrades to these zones for total snowfall and
eventual impacts.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As we head from Wednesday into Wednesday night we will transition to
lake effect snow as synoptic moisture, lift, and snow exit to the
east-northeast. Lake effect snow will continue through much of
Thursday on a west or slightly north of due west flow, targeting
the primary snowbelt from northern/eastern Cuyahoga County points
east. Lake effect will likely lift towards the lakeshore and may
briefly shut off completely in Ohio and Crawford County PA late
Thursday and Thursday night as flow backs ahead of a shortwave
rippling through the region. Some light synoptic snow or snow
showers are possible with this feature Thursday night into Friday
morning with modest accumulations possible outside of the lake
effect. Lake effect becomes re-established in a west-northwest flow
Friday and Friday night as colder air flows in behind the shortwave.
As mentioned in the near term section above, we upgraded Erie and
Crawford Counties in PA and Geauga County in OH to a Lake Effect
Snow Warning beginning on Wednesday. Confidence in the initial leg
of the event (the synoptic/lake-enhanced component through Wednesday
afternoon followed by the lake effect Wednesday evening through
Thursday afternoon) producing warning-level amounts and impacts is
highest in these counties. The warning for the PA counties runs
through Sunday, as little break in the action is expected there and
there's decent confidence in the additional snow Friday into the
weekend also reaching warning-level amounts and impacts at times.
We've made some adjustments to the timing of the Ohio headlines.
While it is very likely we will need additional headlines (and quite
possibly warnings for some) for Friday and into the weekend, there
will be a decent break in the action late Thursday into Thursday
night. There's also lower confidence in Cuyahoga, Lake, and
Ashtabula reaching warning-level amounts and impacts with the first
phase of the event. So, we ended the Geauga County warning Thursday
evening and truncated the end time of the Ohio watches to match that
timing. This is largely semantics but helps us better message the
more immediate snow starting Wednesday, and will give us greater
opportunity to access any break in the snow and what headlines may
be needed for Friday and into the weekend after the break.
A reasonably conducive setup for lake effect snow is anticipated
Wednesday evening through early Thursday. Conditions gradually
become a bit more marginal during the day Thursday. Mean boundary-
layer flow is expected to start off slightly north of due west
Wednesday night (280 degrees give or take) before gradually backing
to a more westerly direction (260 degrees give or take) through
Thursday. This should initially focus a band of more organized snow
from northern Cuyahoga County towards Geauga County/southern Lake
County Wednesday night, with a secondary area of greater snow likely
across interior portions of Erie County and northern Crawford County
PA. The western band should gradually become more focused closer to
the lakeshore in Lake, northern Geauga, and northern Ashtabula
County through the day Thursday while snow in PA gradually shifts
out of Crawford County and becomes focused on Erie County, with snow
likely focusing on the northern half of the county through the
afternoon. Other parts of the primary snowbelt will see some snow
between these bands, but it won't be as organized or heavy outside
of the bands. Inversion heights over the lake rise to 8-9k feet
Wednesday night with moisture depth to close to a similar level,
with upstream moisture connections to Lakes Michigan and St Clair
consistently hinted at. The flow will be a bit strong over the lake
at 20-30 knots, though shear won't be too strong and the flow does
ease a bit on Thursday. Instability won't be extreme with lake to
850mb temperature differentials near 15C, though the profile is
sufficient for decent snow within bands, especially considering
improving snow ratios starting Wednesday night as cold air flows in
and lowers the dendritic growth zone into the lake effect clouds.
Inversion heights and moisture depth do gradually lower through
Thursday, though accumulating snow should continue within the couple
of organized bands expected to be drifting around. Overall, there
should be enough juice for snow rates frequently 0.5 to 1.0" per
hour within the organized bands through Thursday morning, with
isolated peak rates of 1.0-1.5" per hour possible. Rates likely
decrease some Thursday afternoon. With the flow fairly steady for
most of Wednesday night before gradually backing on Thursday, bands
will likely be slow-moving/persistent enough over the areas they
impact to bring peak totals of 6-12" (locally higher not impossible
over the higher terrain in Erie County PA) in the Wednesday night-
Thursday timeframe, with lighter amounts elsewhere.
A shortwave and associated low-level trough axis will work through
the area Thursday night and early Friday. Have a chance for snow
showers mentioned area-wide. It will be plenty cold enough for snow
to stick to all surfaces into Friday morning, so while snow amounts
will be light (<1") there could be some impacts to the Friday
morning commute where snow showers occur with the shortwave passage.
Lake effect will largely focus just offshore or near the lakeshore
from Lake County OH points northeast late Thursday afternoon through
early Friday as the shortwave passes through, with highest
confidence in accumulations in this window in parts of Erie County.
Conditions will only be marginally conducive for lake effect snow in
this time with modest amounts of instability, inversion heights in
the 5-7k foot range, and somewhat dry profiles. So while some
accumulations likely will continue beneath lake effect bands it
should be at a gradual rate. Winds turn much more west-northwest
(280-300 degrees) Friday and Friday night behind the shortwave as
colder air pours in (850mb temperatures falling to -15C to -17C).
This will allow lake effect to spread back into interior portions of
the primary snowbelt, and could bring activity into the secondary
snowbelt and places like the Akron/Ravenna/Youngstown areas as well.
Flow over the lake will be a bit lighter (and fairly well-aligned)
in this window, with temperature profiles suggesting very efficient
and fluffy snow and stronger instability. Inversion heights will
likely climb to 8-10k feet behind the shortwave with some spokes of
synoptic moisture working through the region through at least Friday
night. This suggests another round of impactful lake effect snow
setting up Friday and Friday night, with snow rates potentially
greater than 1" per hour in more organized bands and renewed
accumulations almost certainly requiring headlines, both in our PA
counties where warnings are already in effect and back into Ohio.
With a somewhat shorter fetch, periods of greater synoptic moisture
and upstream connections, along with terrain/upslope enhancement,
will come into play in determining where heavier snow occurs.
Outside of locations downwind of Lake Erie, the cold cyclonic flow
and flow off of the upper Great Lakes should keep flurries and some
snow showers going (with minimal accumulation) behind the shortwave
passage through Friday and likely into Friday night.
Highs Thursday will generally be in the upper 20s and lower 30s,
with highs knocked back slightly into the 20s Friday. Lows Wednesday
and Thursday nights will be well into the 20s with some 10s coming
into play for Friday night. Winds will be brisk with gusts 20-30 MPH
at times through the period.
&&
.LONG TERM /SATURDAY THROUGH MONDAY/...
Lake effect will be ongoing to start the weekend and a decent setup
should allow for impactful accumulations for at least the first half
of the weekend. The general trend will be for activity to gradually
lose intensity from southwest to northeast the second half of the
weekend as surface ridging tries nosing in. Guidance disagrees on
how quickly this happens. Confidence in accumulating lake effect
continuing does start decreasing by Saturday night and especially
Sunday, particularly farther west into the Ohio snowbelt counties.
Additional impactful accumulations are likely into the weekend where
the lake effect sets up and new headlines that will likely begin on
Friday for this "second phase" of this lake effect event will
continue into the weekend (and already do so in PA). The weekend
should be mainly dry and cold outside of the lake effect.
A narrow ridge axis (both surface and aloft) should move overhead
Sunday or Sunday night, finally ending the lake effect once that
happens. This break in the snow may be short-lived, as guidance is
in good agreement that a potent shortwave will eject into the
central U.S. and spawn a "Panhandle Hook" low pressure Sunday that
will work towards our region to start next week. The pattern as this
occurs is expected to feature a robust -NAO block near Greenland
with a classic 50/50 low near Newfoundland, with a +PNA ridge along
the US west coast. This strongly suggests we'll remain cold and that
any precipitation this system brings should be in the form of snow.
The main uncertainty is whether there's actually too much blocking,
as that could cause the storm to weaken as it heads into the Ohio
Valley and keep most of the snow south of our area. Per the National
Blend of Models, the odds of over 2" of snow across the forecast
area through Tuesday morning with this system generally range from
30-50%, with odds of over 6" of snow in the 10-20% range. So
expectations should be kept in check for now, though there is room
for a more widespread synoptic snow if the stronger solution pans
out. Either way, colder air and likely more lake effect snow should
flow back in beyond the end of the long term forecast period.
&&
.AVIATION /12Z Tuesday THROUGH Saturday/...
VFR conditions maintain across the region this morning with just
mid-level clouds overhead ahead of a low pressure system that is
moving toward the airspace. The first band of rain is
approaching from the southwest and will start to bring
conditions further down the VFR scale and eventually to MVFR.
Despite the expansive rain on the northern side of the low
pressure system, upstream observations show that non-VFR has
been difficult to develop and particularly IFR or lower
conditions. Therefore, have bucked model guidance slightly and
held off on the timing for IFR across the terminals to be more
focused on when heavier rain is expected for when rain will
start changing over to wet snow. Eventually, IFR will be the
expect ceiling across the region on the back side of the low
pressure system and cold front with snow moving across the
region through the end of the TAF period. Winds will be variable
with the passing low. Winds will be easterly to start and veer a
touch to the southeast ahead of the low with some gusts
expected. Winds will shift quickly with the low and cold frontal
passage to the northwest tonight and gusts will increase with
values to 30 kt expected.
Outlook...Non-VFR expected with lake effect clouds and snow
across the region through the weekend.
&&
.MARINE...
Low pressure will approach from the west today, tracking near the
southern Lake Erie shoreline this evening and tonight. Behind the
low pressure, cold cyclonic flow will arrive Wednesday night and
persist through at least early Sunday. This will lead to a prolonged
period of unsettled marine conditions.
Northeast winds will increase to 15-25 knots ahead of the low today,
prompting Small Craft Advisories beginning at 10 AM for the western
nearshore waters. Flow turns more north-northwest into tonight
behind the passage of the low and increases to 20-30 knots, for
which Small Craft Advisories kick in farther east. Generally west-
northwest flow will continue over the lake through the weekend, at
20-30 knots through Thursday before slackening slightly to 15-25
knots. We won't be too far off from a gale at times Wednesday and
Thursday, though would like to see a bit more flow aloft to increase
the concern for it. The overall impression is that odds for a gale
in that window are in the 10-30% range, mainly over the central and
eastern basins. High pressure will try to provide at least
temporary improvement at the end of the weekend into early next
week. Small Craft Advisories expire Thursday morning in the western
nearshore waters and run through Sunday to the east.
Some ice growth is likely beginning Friday night, especially across
the western basin. Moderate freezing spray is possible Friday night
into the weekend, though the impression is that the air temperature
and wind combination should be relatively far off from headline-
worthy (i.e. "heavy") freezing spray.
&&
.CLE WATCHES/WARNINGS/ADVISORIES...
OH...Winter Storm Watch from Wednesday morning through Thursday
evening for OHZ011-012-014-089.
Lake Effect Snow Warning from 7 AM Wednesday to 7 PM EST
Thursday for OHZ013.
PA...Lake Effect Snow Warning from 7 AM Wednesday to 7 PM EST
Sunday for PAZ001>003.
MARINE...Small Craft Advisory until 10 AM EST Thursday for LEZ142>144.
Small Craft Advisory from 4 PM this afternoon to 4 PM EST
Sunday for LEZ145>148.
Small Craft Advisory from 1 AM Wednesday to 4 PM EST Sunday
for LEZ149.
&&
$$
SYNOPSIS...Sefcovic
NEAR TERM...Griffin/Sefcovic
SHORT TERM...Sullivan
LONG TERM...Sullivan
AVIATION...Sefcovic
MARINE...Sullivan
Source:
CLE issues Area Forecast Discussion (AFD) at Dec 31, 10:03 AM EST---------------
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