-- Discussion containing changed information from previous version are highlighted. --
961
FXUS61 KCLE 051840
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
240 PM EDT Wed Jun 5 2024

.SYNOPSIS...
A cold front will cross the area this evening. A surface trough
will build in on Thursday, lingering over the area through the
weekend.

&&

.NEAR TERM /THROUGH THURSDAY/...
-- Changed Discussion --
Clearing is occurring across the area and already seeing rapid
destabilization with SBCAPE values approaching 2000-2500 J/kg
just to the west of the area and MLCAPE values approaching
1000-1500 J/kg in the western half of the CWA. Multiple storm
complexes, including a cluster of storms to the southwest of the
CWA and a complex moving into NW OH, will move into the area
over the next couple of hours before tracking east later this
afternoon and into this evening. CAMs have generally
underestimated the amount of destabilization this afternoon and
most high res guidance has held off on stronger convection until
the cold front (currently over eastern IL) approaches from the
west late this afternoon into this evening. Uncertainty exists
in the severe weather potential late this afternoon into this
evening- will need to see how much this initial line holds
together as it moves into the CWA through early evening and how
much the atmosphere is worked over before the better forcing
from the front arrives from the west this evening.

Given the amount of moisture (PW values are over 1.5 inches
which is well above normal for this time of year),
buoyancy/CAPE, and effective bulk shear values to 20 to 25
knots, there may be isolated damaging wind gusts/downbursts. So
far there have only been a couple of instances of wind gusts
over 40 knots (still below severe limits), but the severe
weather risk should increase at least a little bit as clearing
and destabilization continue this afternoon. Heavy rain will be
a big concern since PW values are so high, CAPE profiles are
tall and skinny, and warm cloud layers are deep. Storm motion
may be a hair fast, but torrential rainfall rates and potential
for backbuilding could result in flooding primarily in low-
lying and urban areas. Can`t totally rule out isolated large
hail since instability is a bit higher than previously
anticipated, however the tornado threat remains low since shear
values are marginal. Long story short, isolated damaging wind
gusts and heavy rain/flooding are the main threats today.

Previous Discussion...
A deep upper-level trough digs down into the Upper Midwest this
morning, which is very apparent in water vapor imagery. A warm
front extending from a secondary low located over the northern
Great Lakes is moving northeastward across the forecast area
this morning. A few weak reflectivity returns are noted on radar
but have yet to see any weather stations report precipitation,
so there`s a good chance nothing is reaching the surface just
yet. However, CAMs do have rain showers becoming more developed
later this morning, especially along and east of I-77. These
showers could linger from Youngstown to Erie, PA (and vicinity)
through the early afternoon hours, something the HRRR has been
persistent on occurring with each run.

Moisture advection with increasing southerly winds today will
bring dew points into at least the mid to upper 60s, with some
pockets of around 70 by this afternoon/evening. A dry slot is
already observed within the warm sector across portions of
Illinois/Indiana, which will propagate into our western CWA
today. This should allow for a sizable break in cloud cover and
decent confidence in sufficient heating into the low to mid
80s, contributing to MLCAPE of 1000-1250 J/kg, mainly west of
I-77 and especially near the I-75 corridor. Lingering clouds and
showers may limit heating and instability east of I-77. As the
upper-level trough and associated belt of mid-level
southwesterly winds moves in, deep-layer shear of around 25-30
knots should be sufficient for organized convection and a low
chance of severe weather. For this reason, a marginal risk
(level 1 of 5) of severe thunderstorms is forecast for today.

A line of convection is observed on radar to our west extending
from the Chicago area southeastward down to Texas. This
convection will likely weaken some as it encounters a weakly
unstable environment this morning before becoming reinvigorated
(or redeveloping along its outflow boundary if it completely
dissipates) by this afternoon as instablilty increases ahead of
it. A linear storm mode is favored, though isolated
cells/clusters could develop out ahead of the main line (which
is hinted at by a few CAMs). Damaging winds is likely to be the
primary threat. The tornado threat has lowered substantially
from the previous forecasts as forecast low-level shear/helicity
has decreased quite a bit. Localized flooding with heavy rain
remains a possibility as just about every "flooding"
environmental parameter (PWAT, warm cloud layer, etc.) reveals
high water content throughout and expected efficient rainfall.
The likelihood of flooding would be especially possible if
storms could develop ahead of the "main line" of storms, or if
we observe backbuilding (Corfidi vectors this afternoon are
very favorable for flash flooding if this were to occur).
Limiting factors for flooding include dry antecedent conditions
and progressive nature of a linear system.

Convection is likely to exit the forecast area shortly after
midnight. The upper-level trough becomes a closed low as it
builds southeast into the Great Lakes region, with a secondary
cold front bringing isolated to scattered rain showers to the
area on Thursday. Cooler temperatures are expected with highs in
the upper 70s.
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&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
A cooler than normal and unsettled period of weather is still
expected to end the week and start the weekend thanks to an
unseasonably deep closed upper-level trough/low spinning over the
Great Lakes. Various smaller shortwaves and surface trough axes will
rotating through the larger trough, focusing occasional shower
chances. Daytime heating will also act to encourage an increase in
shower coverage each afternoon. At night, chilly air flowing over
the relatively milder Lake Erie waters may enhance showers east of
the lake...particularly late Thursday night into Friday morning and
again Friday night into early Saturday morning. Guidance is trying
to key on a couple of small shortwaves and associated surface
troughs dropping through between late Thursday night and Friday
evening. Agreement decreases farther out, though there are hints
that there will be another one or two shortwaves rotating through
between early Saturday morning and late Saturday night. We are not
looking at a washout for this forecast period though there will
likely be scattered to numerous showers around at times...especially
when subtle shortwaves work through and when and where lake
enhancement occurs in far Northeast OH and into Northwest PA. Can`t
rule out a bit of thunder each afternoon given cold air aloft aiding
in modest destabilization, though in general we`ll just see showers.
Overall QPF amounts will be light outside of lake enhancement, where
more frequent showers may add up a bit over a long period of time.

Highs will generally range from the mid 60s to mid 70s Friday and
Saturday (coolest far Northeast OH and Northwest PA, warmest along
the I-75 corridor) with overnight lows in the 50s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
We remain under the influence of the trough centered over the Great
Lakes/Northeast/southeastern Canada through Sunday night. The trough
should gradually shifting east Monday and Tuesday, though guidance
doesn`t agree on exactly how quickly that will happen. Our cool,
somewhat showery pattern will gradually moderate and dry out once
the trough decides to exit. Highs in the 70s and lows in the 50s
should generally rule the Sunday - Tuesday period, though with a
gradual moderating trend in afternoon highs starting by Tuesday.

&&

.AVIATION /18Z Wednesday THROUGH Monday/...
-- Changed Discussion --
Line of thunderstorms will move across the area this afternoon
into this evening as a cold front approaches from the west and
there will likely be periods of non-VFR visibilities within
thunderstorms. There may be brief gusts to 35+ knots in stronger
storms, best chance at western terminals (including KTOL/KFDY)
and generally expect storms to gradually weaken as they move
east this evening, hence slightly lower thunderstorm wind gusts
gusts at terminals east of KTOL/KFDY. Showers may linger into
late evening with MVFR ceilings likely primarily at eastern
terminals overnight into early Thursday morning. Some guidance
suggests potential for a period of IFR conditions at
KCAK/KYNG/KERI early Thursday morning, but confidence is low so
opted to maintain MVFR for the time being. Ceilings should
gradually improve from west to east towards the end of the
period, but can`t rule out widely scattered showers and isolated
thunderstorms as a trough pushes across the area during the day
Thursday.

Outside of thunderstorms, winds will be out of the
south/southwest at 10 to 15 knots with gusts to 20 to 25 knots
through early evening before diminishing to 5 to 10 knots
tonight. Winds become more westerly early Thursday morning and
will increase to 10 to 15 knots with gusts to 20 to 25 knots
likely towards the very end of the TAF period.

Outlook...Non-VFR will be possible with scattered rain showers
and isolated afternoon thunderstorms Thursday afternoon through
Monday.
-- End Changed Discussion --

&&

.MARINE...
A cold front will sweep across Lake Erie this evening and tonight.
Southerly winds to around 15 knots are expected ahead of the front.
Thunderstorms are likely over the lake this afternoon and evening,
with a few stronger storms possible. Winds shift west-southwest
behind the front tonight and more west-northwest Thursday night into
Friday, generally remaining west to northwest through early next
week. Winds will generally range from 10 to 20 knots through Sunday
before gradually relaxing into early next week. A couple of periods
of winds to around or slightly greater than 20 knots are possible...
mainly Thursday evening through early Friday behind a re-enforcing
trough axis and perhaps again at some point between Friday night and
early Sunday. Guidance still disagrees on the smaller trough
passages that will briefly enhance winds this weekend. Overall, the
lake will be somewhat agitated through the weekend with a couple
windows in which Small Craft Advisories / Beach Hazard Statements
could well be needed for the central/eastern nearshore zones.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...None.
PA...None.
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...Saunders
NEAR TERM...Maines/Saunders
SHORT TERM...Sullivan
LONG TERM...Sullivan
AVIATION...Maines
MARINE...Sullivan