-- Discussion containing changed information from previous version are highlighted. --
619
FXUS61 KCLE 210102
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
902 PM EDT Fri Sep 20 2024

.SYNOPSIS...
High pressure exits gradually eastward as a trough enters from
the western Great Lakes region. The axis of this trough is
expected to drift eastward through northern Ohio and northwest
Pennsylvania during the early morning through early evening
hours of Saturday. Behind the trough axis, a very weak ridge
builds from the west through Saturday night. Another trough
accompanying a cold front begins to overspread our region from
the Upper Mississippi Valley and western Great Lakes by Sunday.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
-- Changed Discussion --
9:00 PM Update...
Very dry and stable air over our region allowed for showers and
thunderstorms along a weak trough to diminish as they entered
Northern Ohio earlier this evening. Fairly quiet night in store
with above normal overnight low temperatures settling in the
low to mid 60s.

Previous discussion...
A ridge at the surface and aloft exits E`ward through this early
evening. Behind the ridge, W`erly to WNW`erly flow aloft and
embedded shortwave disturbances affect our CWA through Saturday
as a weak trough, associated with a dissipated cold front,
overspreads our region from the western Great Lakes and
vicinity. The axis of this surface trough is expected to drift
E`ward across our region during the early morning through early
evening hours of Saturday. Lows are expected to reach mainly the
lower to mid 60`s around daybreak Saturday as an unusually-warm
air mass persists and intervals of cloud cover limit nocturnal
cooling. Daytime heating is expected to allow late afternoon
highs to reach the upper 70`s to near 80F in NW PA and mainly
the 80`s to near 90F in northern OH late Saturday afternoon.
Similar to today, a weak synoptic MSLP gradient and sufficient
daytime heating of surrounding land should allow a lake breeze
to occur over/within several miles of Lake Erie during the late
morning through early evening hours of tomorrow.

As of 3:45 PM EDT Friday, clusters of multicell showers and
thunderstorms were persisting generally E`ward over/near the
MI/IN/NW OH border. Expect this convection to weaken
considerably before reaching portions of our I-75 counties by
this late afternoon given weak boundary layer instability per
latest SPC mesoanalysis and the lack of cumuli in the
aforementioned area. Remnant/isolated showers should then
dissipate early this evening, west of I-71, as the pre-
convection boundary layer stabilizes via nocturnal cooling. As
mentioned before, the surface trough axis will drift E`ward
through our CWA during the early morning through early evening
hours of Saturday. A modest low-level return flow of warm/humid
air originating over the Gulf of Mexico, ahead of the
aforementioned surface trough axis, should allow
convergence/ascent along the trough axis to coincide with
sufficient low-level moisture and release at least weak boundary
layer instability for renewed development of isolated
showers/thunderstorms beginning after midnight tonight. Diurnal
heating of the relatively-moist boundary layer should yield
moderate MUCAPE and a somewhat greater chance for isolated
showers/thunderstorms along/ahead of the surface trough axis
Saturday afternoon through early evening, especially in far-NE
OH and NW PA, as deep layer bulk shear remains moderate. This is
where a few strong thunderstorms with small hail and strong
convective wind gusts are possible amidst sizable MUCAPE in the
hail growth zone, ambient atmospheric melting levels near
10.5kft AGL, steep low-level lapse rates, and moderate DCAPE
near 500 to 800 J/kg. Thus, cannot totally rule-out a few
instances of straight-line convective wind damage. In fact, SPC
has outlined a marginal risk of severe thunderstorms for much of
western PA and vicinity tomorrow, including southeastern
Crawford County.

Behind the surface trough axis, fair weather is expected through
Saturday night as a shortwave ridge aloft and attendant/weak
surface ridge build from the western Great Lakes area and the
ridge is accompanied by stabilizing subsidence. Partial clearing
associated with the subsidence and weak low-level dry air
advection behind the surface trough axis will permit greater
nocturnal cooling Saturday evening through daybreak Sunday
morning, when lows are expected to reach mainly the mid 50`s to
lower 60`s.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Entering a more active period with higher chances of precipitation
that will be welcome across the whole CWA. Upper level flow becomes
more zonal with a weak low pressure system/cold front tracks through
Sunday night/Monday with the boundary sinking just south of the CWA,
then pushing back into the CWA Monday night with the approach of a
secondary and stronger area of low pressure from the southwest. This
will bring waves of showers and storms entering the western zones
first around 21Z Sunday. Best forcing will occur when 500mb PVA
coincides with the surface system/low level f-gen from 00-03Z Monday
and then again at 06-12Z Tuesday and into the extended forecast time
frame. Should be a wetting rain for the region off and on during
this period, but still will take some time to make a significant
dent in the current drought status. That said, it should be a good
start heading into the long term. Cooler weather in this pattern as
500mb heights/850mb temperatures decrease along with rainfall for
Monday.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Diverging operational models into midweek once the cold front from
the secondary area of low pressure from the short term exits, and
the confidence in additional rainfall wanes, so will need a few more
forecast cycles to try and pin anything down here. The cooler trend
should continue through the period off the short term however, and
will carry low end POPs for now. Upper 60s to lower 70s expected by
Thursday.

&&

.AVIATION /00Z Saturday THROUGH Wednesday/...
Showers along a weak surface trough are slowly diminishing as
they enter a less favorable and drier airmass over Northern Ohio
while thunderstorms are developing to our southwest where a
more favorable airmass is in place. Not anticipating for showers
or thunderstorms to impact terminals through tonight. Can`t rule
out showers and thunderstorms redeveloping early Saturday
afternoon as the trough axis approaches Northeast Ohio/Northwest
Pennsylvania. For now, have -SHRA mention at KERI.

Generally easterly to southeasterly winds 5-8 knots ahead of
the trough will turn southwesterly through tonight while
remaining under 10 knots. Winds turn northwesterly behind the
trough during the day Saturday while increasing to 8-10 knots.

Outlook...Non-VFR possible with isolated to scattered showers
and thunderstorms Saturday afternoon through early evening and
again Sunday afternoon through Wednesday.

&&

.MARINE...
Briefly stronger ENE winds this evening could bring g 2ft waves in
the west central/western basin of Lake Erie, but varying wind
directions tonight through Saturday night will keep the lake
nearshore zones less than a foot, with only pockets of 1-2ft in the
open water zones. Offshore flow Sunday/Sunday night, but then back
to highly variable winds with shower/storm chances increasing with a
low pressure system approaching Monday and affecting the region into
mid week. Some chop should be expected during this time.

&&

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

&&

$$

SYNOPSIS...Jaszka
NEAR TERM...Iverson/Jaszka
SHORT TERM...26
LONG TERM...26
AVIATION...Iverson
MARINE...26