091
FXUS61 KCLE 272003
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
403 PM EDT Thu Jun 27 2024

.SYNOPSIS...
High pressure will persist over the area through Friday before
moving off the Northeast Coast Friday evening. A low pressure
system will impact the Great Lakes region on Saturday and
Saturday night before high pressure builds back in Sunday
through Tuesday.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
Scattered to broken cumulus field across the area gradually
dissipates this evening as we lose boundary layer mixing with
sunset. High pressure continues to build in tonight with patchy
fog in parts of eastern Ohio and inland Northwest Pennsylvania
before this high moves off to the east Friday and Friday night.
Temperatures increase on the backside of the departing high with
temperatures into the 80s by Friday afternoon. Approaching
trough from the west will result in increasing southwest
moisture advection and showers and thunderstorms Friday night.
PoPs start off around 20% Friday evening increasing to 60% by
late Friday night.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Saturday continues to look like an active day with both severe storm
potential as well as heavy rainfall and resultant flash flooding.
However, confidence is greater for heavy rainfall than severe
weather. See details below.

A mid/upper shortwave trough will track from the Upper Midwest
through the central and eastern Great Lakes Saturday through Sunday.
An associated surface low will track from the Lake Superior/Upper
Michigan vicinity Saturday morning into Quebec by late Sunday,
dragging a cold front southeast across the region Saturday night
into Sunday morning. The warm front looks to lift out of NE Ohio and
NW PA rather quickly Saturday morning placing the entire region in
the warm sector. Deep west-southwesterly flow and resultant warm air
advection will tap into a broad heat dome over the central
Mississippi and Tennessee Valleys with 850 mb temps rising to around
+18 C along with rich low-level moisture advection bringing dew
points into the low to mid 70s. This pattern could support very
oppressive conditions with temperatures around 90F, but extensive
cloud cover and areas of showers will likely hold temperatures down
in the low to mid 80s in most areas Saturday afternoon. This makes
the degree of the severe threat highly uncertain as the cold front
approaches Saturday evening. NAM forecast soundings and plan views
are suggesting a saturated, cloudy profile holding MLCAPE values
below 1000 J/Kg in most of the region Saturday afternoon with only
around 1500 J/Kg at the surface. This combined with flat mid-level
lapse rates of 5 to 5.5 C/Km could make it tough to sustain deep
updrafts. Overcast skies and scattered showers Saturday morning into
the afternoon are the result of decaying convection expected to move
in from the NW Friday night, so there will likely be outflow
boundaries and differential heating boundaries over the region for
the afternoon. This makes the convective initiation messy, and it is
likely that numerous showers and thunderstorms will redevelop on
these boundaries in the warm sector Saturday afternoon and evening
well ahead of the cold front. For this reason, went with categorical
PoPs. There is plenty of shear for damaging winds and a few
tornadoes given 45-50 knots of westerly 500 mb flow yielding 30-40
knots of effective bulk shear, with 25-30 knots of low-level shear.
This leads to low-level SRH values of 100-200 m2/s2, especially in
NE Ohio and NW PA. With these shear values and the overall synoptic
forcing near the base of the progressive shortwave trough, feel that
there will be a few severe storms, but how widespread and organized
they will be is uncertain due to the potential for the instability
to stay weak as mentioned above. If greater heating can be realized,
then the severe potential could increase. The SWODY3 slight risk
still looks reasonable at this point, but CSU Machine Learning
probabilities have come down from previous runs and now suggest a
marginal potential for severe weather, so it seems to be keying on
the lack of instability.

We are much more confident on heavy rainfall rates from
thunderstorms Saturday afternoon and evening. PWAT values look to
rise to 2 to 2.25 inches which is around the climatological max for
the date. Forecast soundings suggest deep warm cloud layers too and
LCL heights below 1000 m which will limit evaporation. This all
points to highly efficient rainfall rates. The aforementioned mid-
level flow and shear will keep convection moving, but with numerous
boundaries in place, there could be repeat rounds in some areas.
Drought has been expanding across the region, so rainfall is greatly
needed, but high rates could still cause some flash flooding in
urban areas, as well as low-lying and poor drainage areas. The WPC
Day 3 Marginal risk for excessive rainfall has been expanded
westward to account for this potential.

Showers and thunderstorms will end from NW to SE Saturday night,
with all areas expected to be dry behind the front by Sunday morning
as Canadian high pressure builds in from the Upper Midwest. This
high will slide overhead Sunday and Sunday night, and this combined
with fairly deep mid/upper troughing over the eastern Great Lakes
and New England will lead to a sunny, pleasantly cool day. Expect
highs Sunday to stay in the mid/upper 70s with much lower humidity.
Lows Sunday night will fall into the low/mid 50s.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Mid/upper troughing and Canadian high pressure will remain across
the eastern Great Lakes to start the week. This will maintain the
mostly sunny and pleasant weather for Monday with highs in the
mid/upper 70s. The high will slide off the Mid Atlantic coast
Tuesday and Wednesday as a large mid/upper ridge over the southern
Plains and Mississippi Valley expands northeastward into the Great
Lakes ahead of a broad mid/upper trough progressing through the
northern Rockies and northern Plains. This will bring heat and
humidity back into the region with highs returning to the mid 80s
Tuesday and potentially low 90s Wednesday. The southern Great Lakes
region will be near the northern edge of the associated thermal
ridging (heat dome, so there will likely be a frontal boundary
nearby to focus ridge riding convection and potential MCS activity.
Ensemble guidance is keying in on Wednesday and Thursday to have
some potential for organized severe weather due to a shortwave
crossing the Great Lakes and starting to flatten the ridge, and the
CSU Machine Learning severe weather probabilities suggest a marginal
risk areawide those days. The front may push southward Thursday, so
slightly cooler conditions are expected with mid/upper 80s, but
still humid. Due to uncertainty on convective features this far out,
kept broad chance PoPs Tuesday night through Thursday.

&&

.AVIATION /18Z Thursday THROUGH Tuesday/...
Scattered cumulus field remains over the area through late this
afternoon. Clear skies with scattered high cirrus expected
through the rest of the TAF period as high pressure builds in.
Patchy low visibility is possible late tonight into early
tomorrow morning for valleys in far eastern Ohio and inland
Northwest Pennsylvania. Light winds out of the north become
light and variable tonight before become south to southeast
during the day Friday.

Outlook...Non-VFR possible in showers and thunderstorms on
Saturday.

&&

.MARINE...
Quiet conditions are expected on the lake the next few days. Light
and variable winds tonight will become E at 10-15 knots Friday
before turning S and increasing to 15-20 knots late Friday night and
Saturday morning behind a warm front. Winds then veer a bit SW
Saturday afternoon while staying in the 15-20 knot range. Winds will
turn NNW behind a cold front by Sunday morning while staying 15-20
knots, and this will build wave heights to 3 to 4 feet in the
central and eastern basins, so Small Craft headlines are likely to
be needed Sunday. N winds of 10-15 knots Sunday night will diminish
to 5-10 knots Monday while turning E then SE by Tuesday.

Locally higher winds and waves are possible in and near
thunderstorms Friday night and Saturday.

&&

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

&&

$$

SYNOPSIS...Saunders
NEAR TERM...Saunders
SHORT TERM...Garuckas
LONG TERM...Garuckas
AVIATION...Saunders
MARINE...Garuckas