-- Discussion containing changed information from previous version are highlighted. --
602
FXUS61 KCLE 180556
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
156 AM EDT Sat May 18 2024

.SYNOPSIS...
Weak low pressure aloft will slowly push a cold front across the
region tonight and Saturday. The front will wash out over the
Appalachians late Saturday followed by high pressure building in
Saturday night. The high will remain in control through Tuesday
before low pressure and a cold front approach by Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
10:19 PM EDT Update...

At time of writing, a broken line of showers/thunderstorms is
continuing to persist E`ward across portions of NW PA, NE OH,
and Mid-OH as the collective downshear outflow boundary
interacts favorably with ambient, albeit weak, low-level
vertical wind shear amidst sufficient boundary layer moisture
and instability. Expect this convection to dissipate and/or exit
our CWA by midnight tonight as mean mid-level flow remains
W`erly and the boundary layer continues to stabilize via
nocturnal cooling. A diffuse low-level convergence zone
associated with a weak surface trough axis persists near a
roughly Findlay to Mansfield to Meadville, PA line this late
evening. This weak surface trough axis is expected to drift
SE`ward and exit the rest of our CWA during the predawn hours of
Saturday morning. Given continued boundary layer stabilization
via nocturnal cooling through daybreak Saturday morning, the
potential for additional convection to blossom along this
trough axis is limited, but non-zero. A cluster of showers
and thunderstorms is persisting generally S`ward over
southeastern Lower MI, but expect this convection to dissipate
before reaching our CWA due to aforementioned nocturnal boundary
layer stabilization. However, will continue to watch this
convection closely. Behind the weak surface trough, a weak and
stabilizing surface ridge builds from the west and north through
Saturday night, which is expected to allow fair weather to
grace our entire CWA. Updated POP`s and sensible WX grids
accordingly.

The other concern through most of Saturday morning is fog.
Nocturnal cooling amidst lingering low-level moisture,
including that from recent rainfall, and a weak synoptic MSLP
gradient will continue to permit the development/downward
expansion of widespread stratus and radiation fog development
the rest of this evening and especially early Saturday morning.
Also expect limited nocturnal cooling/resulting reduction in
surface dew point depressions to allow at least patchy
advection fog to develop over Lake Erie overnight tonight,
especially east of roughly Avon Point, OH. Issued a Dense Fog
Advisory where forecast confidence is greatest in the
development of at least areas of dense fog by daybreak. The
advisory is in effect from 12 AM to 10 AM EDT Saturday. Any fog
should dissipate by late Saturday morning, once diurnal
convective mixing of the boundary layer commences and taps into
drier air aloft. However, some NWP models suggest at least
patchy advection fog over Lake Erie may linger well into
Saturday. The rest of the forecast remains valid. Please see
discussion below for further details.

Previous Discussion from 3:55 PM EDT...

A weak but broad mid/upper trough remains across the Great Lakes and
Ohio Valley this afternoon, with associated weak surface low
pressure just south of James Bay extending a cold front through
Lower Michigan and Indiana. Synoptic forcing and deep layer wind
profiles are very weak, but upper-level diffluence and the right
entrance region of a 75-85 knot H3 jet streak lifting through
the southern Great Lakes generated widespread shower activity
this morning since plenty of low-level moisture is in place. The
steadiest showers are currently exiting far eastern Ohio and
western PA coincident with the aforementioned jet streak lifting
out of the region, but breaks in the cloud cover are generating
weak to moderate instability characterized by SBCAPE of
1000-1500 J/Kg in NW and north central Ohio. This combined with
continued low-level moisture (dew points low/mid 60s) and upper
diffluence and low-level confluence ahead of the cold front is
supporting the development of diurnal convection. Doppler radar
and visible satellite loops show most of this developing from
north central Ohio through the central highlands at the time,
but development is also taking place in Lower Michigan away from
the lakes. With all of this in mind, all areas could see
passing showers or thundershowers this afternoon and evening,
but the greatest potential is over the southern and eastern
counties from roughly Mt. Vernon to Youngstown, so put the
highest PoPs there through the evening. Since the flow aloft is
weak, deep layer shear values will only be 10-15 knots, so
severe weather is not expected. The only concern with the
convection will be locally heavy rainfall that could lead to
localized, nuisance flooding. PWATs remain in the 1.3 to 1.5
inch range in much of the area which is around the 90th
percentile of daily climatology for the date, and RAP forecast
soundings show fairly tall, skinny CAPE with freezing levels a
little above 700 mb. This combined with the weak flow profile
and the flow parallel to the front will allow for some slow
moving convective cells with efficient rainfall rates of 1-2
inches per hour. Any issues would likely be if convection can
train.

The weak mid/upper trough axis will further weaken and move east of
the region tonight and Saturday allowing shortwave ridging and broad
surface high pressure to nudge in from the west by Saturday night,
but it looks to be a slow process since two northern and southern
stream weak troughs are pretty separated from the main jets aloft.
This will cause the weak cold front to slowly progress east and
southeast across the region tonight and Saturday before washing out
near the Appalachians. Most areas will dry out tonight, but with the
front and associated low-level moisture taking their time exiting on
Saturday, diurnally driven convection will develop again from late
morning through the afternoon, mainly east of I-77. Coverage should
however be less than today, but locally heavy downpours could occur.
All areas will dry out Saturday night as the high builds in.

Lows tonight will range from the upper 50s to around 60, with highs
Saturday in the upper 70s/low 80s in NW and north central Ohio where
more sunshine occurs, but mid 70s in NE Ohio and NW PA. Lows
Saturday night will fall into the mid/upper 50s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
The weather pattern will shift to a hotter and more summer like for
later this weekend into early next week. An upper level ridge of
high pressure will develop and expand over the Ohio Valley region
Sunday and Monday. The main storm track will shift northward into
the Upper Midwest and Upper Great Lakes region for a few days. With
high pressure in control, we will expect fair weather conditions
with mostly sunny to partly cloudy skies. High temperatures on
Sunday afternoon will range from the lower to middle 80s. There
could be a light lake breeze Sunday afternoon closer to the
lakeshore that may keep temperatures in the upper 70s. We will add
another degree or two for Monday afternoon with high temperatures
ranging from the lower to upper 80s. We should stay dry Sunday
through Monday.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
High pressure will continue to remain in control of our weather on
Tuesday keeping us very warm and dry. Temperatures will be once
again in the middle to upper 80s. By Tuesday night, the upper level
ridge of high pressure will begin to break down and a series of
shortwave troughs will swing through the Great Lakes region by the
middle of next week. A slow moving cold front will start to slide
into the Lower Great Lakes region and Ohio Valley region late
Tuesday night through late Wednesday night. Showers and
thunderstorms will become likely by the middle of next week.
Temperatures will also be slightly cooler with the rain chances in
the area Wednesday through early Thursday.

&&

.AVIATION /06Z Saturday THROUGH Wednesday/...
-- Changed Discussion --
Light winds, low-level moisture, and radiational cooling are
anticipated over the area tonight. Scattered non-VFR conditions
are expected within low stratus and patchy to areas of fog
tonight into Saturday morning. While all TAF sites have a chance
of IFR and briefly LIFR visibilities and ceilings primarily
between ~09Z and 14Z, KCLE/KYNG/KERI and maybe KTOL have the
best shot at prolonged IFR and LIFR conditions. Conditions
should quickly improve to VFR once diurnal mixing kicks in by
mid morning. Can`t rule out some isolated showers south of KFDY
to KCAK during the afternoon, but precipitation chances are too
low to include any showers in TAFs at this time.

Winds will be variable and 5 knots or less through the entire
TAF period.

Outlook...Non-VFR possible with periodic showers and
thunderstorms Tuesday and Wednesday.
-- End Changed Discussion --

&&

.MARINE...
Overall the weather forecast for Lake Erie will remain quiet this
weekend into early next week. High pressure will return over the
lake this weekend with a light northeast flow under 10 knots for the
weekend. A warm front will lift across the lake Monday with a return
of southeast flow over the lake. Southerly flow will continue to
increase up to 15 knots Tuesday and Wednesday ahead of a low
pressure system that will move through the Upper Great Lakes for the
middle of the week. No marine headlines are expected at this
time.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
OH...Dense Fog Advisory until 10 AM EDT this morning for OHZ009>014-
     019>023-089.
PA...Dense Fog Advisory until 10 AM EDT this morning for PAZ001>003.
NY...None.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...Garuckas
NEAR TERM...Garuckas/Jaszka
SHORT TERM...Griffin
LONG TERM...Griffin
AVIATION...Maines
MARINE...Griffin