Area Forecast Discussion
Issued by NWS Cleveland, OH

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727
FXUS61 KCLE 240545
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
145 AM EDT SUN JUL 24 2016

.SYNOPSIS...
Weak high pressure over the area will drift into the central
appalachians sunday as a weak cold front moves southeast through
the northern Great Lakes. The cold front will move southeast
across the region monday then high pressure will build over the region
for the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Updated the forecast to include more cloud cover overnight and
raise pops, mainly in the north, late tonight and Sunday. SPC
Mesoanalysis page indicates very unstable conditions are in place
across northern Illinois and Indiana with ML Cape of 2500-3500
J/kg and surface dewpoints in the upper 70s. Instability drops off
considerably to the north and east. The stronger development upstream
has been trending southward into the juicy airmass while storms in
Indiana continue to fall apart as they move eastward. Overnight we
expect to see storms eventually expand eastward across southern
lower Michigan as the trough approaches and low level jet feeds
into the back side of the system. Introduced a chanced of
thunderstorms in nw Ohio beginning after 2 am with better chances
of showers spreading east across Lake Erie and northern portions
of the forecast area through the day on Sunday.

The clouds and chances of precipitation raise a question about how
warm temperatures and how high heat index values will be on
Sunday. Raised mins a few degrees across most of the area tonight
and western areas may be starting off in the upper 70s to near 80
degrees. Temperatures may warm a little more slowly on Sunday than
previous days, but any breaks in the clouds will allow for a rapid
warm up. Humidity will also be up from today as dewpoints climb
back into the lower and possibly mid 70s in the west. Heat Index
values will likely be closer to the upper 90s than low 100s, but
given that this is the 3rd day of high temperatures, the heat is
likely starting to take a greater toll on people. Will let the
midnight shift take another look and make the final call on if the
Heat Advisory is needed tomorrow.

Previous discussion...
A quiet and sultry evening is in store for the region as weak high
pressure remains overhead. MLCAPE near 2000 j/kg is present but
with sufficient MLCIN to inhibit convection especially north of
Route US 30. The region should remain dry but can not rule out an
isolated shower south of US 30 but for now will keep the forecast
dry. Some drier air along with deeper mixing has lowered dew
points in inland nw PA and extreme ne Ohio. This will allow for
slightly cooler overnight lows in the mid 60s. Higher humidity
elsewhere will help keep temperatures from dropping out of the
70s. fair weather cumulus will dissipate toward sun set but high
clouds from distant west convection over WS and IL will likely
spread into the region.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/...
No changes are planned for the Heat advisory across the region
into Sunday evening as temperatures and humidity values will be
just high enough to support the advisory over the central and
western portion of the forecast area.

On Sunday the hot air mass will still be in place with 850 mb
temperature from 20-22c across the area. This could easily support
high temperatures in the mid 90s but there is some indication that
a weak impulse will be rippling east along the southern edge of
the westerlies just north of the region across Michigan and Lake
Erie and this may initiate showers and storms mainly in the
afternoon near Lake Erie. The increase in clouds and any
precipitation will help keep temperatures slight cooler than if an
adiabatic to supper adiabatic lapse rate were to develop in the
afternoon over the rather dry ground now in place.

A weak cold front will sag slowly south across the region late
Sunday and Monday and we can expect scattered showers and
thunderstorms to develop. The GFS is faster than the ECMWF and
brings the boundary across the region Monday morning which
diurnally is not a favorable time for convective development. The
Euro is slowly but appears to be even weaker with the front so
again the chances for rain are not overly high. 850 mb
temperatures are still be elevated but increased clouds and some
scattered showers should help keep temperatures down some.

The boundary will settle south of the region Monday night with
perhaps a lingering shower in the southeast counties early. Dry
conditions are expected through Tuesday with slight cooling to
only 17c at 850 mb.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
The zonal flow aloft is progged to evolve into a shallow trough
aloft as we transition back to a more seasonable weather pattern
toward the end of next week.

High pressure will slide off to the east on Wednesday.  The models
are in decent agreement with a warm front returning across the
midwest ahead of a cold front dropping across the Great Lakes by
Thursday.  Some of the models develop a surface low on the front on
Thursday and this could be from convective feedback and will keep
pops rather low on Thursday given the uncertainty. There is also
some disagreement on just when the cold front will drop across
the area. The ECMWF is a bit faster with the front by late Friday
while the other models prefer Saturday. The CMC develops a wave
on the front, again another potential result of convective
feedback. Will keep the forecast rather vague at this time with
a chance of showers/storms Thursday night into Saturday.

Temperatures will gradually trend toward normal with some
uncertainty each day depending on the amount of clouds and
potential showers/storms.

&&

.AVIATION /06Z Sunday THROUGH Thursday/...
High level cloud cover will continue to spill across the region
from the west as the MCS weakens over Michigan and Indiana. VFR
conditions are expected until some fog develops toward sunrise.
There could be some patchy IFR, especially at KCAK and maybe KMFD.
Warm temperatures and a lack of significant moisture at the middle
levels of the atmosphere will have impacts on the convective
development this afternoon. Unless an outflow boundary from this
mornings convection over Indiana can sneak into northern Ohio it
will be very difficult to see thunderstorm initiation. So with
that said we have kept the thunder from all the TAF sites through
the day. As a weak cold front approaches tonight into Monday
morning there could be some thunderstorms. Have placed a vicinity
thunder at KTOL around 05Z to cover this potential.

Winds will be mostly from the southwest this afternoon except for
along the lakeshore where some onshore flow is anticipated. The
lake breeze will likely only impact KCLE, KCGF and KERI.

OUTLOOK...Non-VFR possible late Sunday night into Monday in
thunderstorms. Non-VFR fog/mist possible each morning.

&&

.MARINE...
High pressure over the northern Great Lakes will move off to the
east. Winds will come around from the southeast and then southwest
by Sunday morning ahead of the next cold front. Winds will increase
from the southwest ahead of the front by Sunday night and from the
west behind the front on Monday. Winds and waves will approach small
craft advisory criteria but may stay just below. Thunderstorms will
probably spread across Lake Erie from later Sunday into Monday
morning and small craft operators will have to be alert.

High pressure will spread across the Great Lakes Monday and Tuesday
and shift east on Wednesday. The next cold front will sag across the
Great Lakes Wednesday and will approach Lake Erie Thursday.

&&

.CLE WATCHES/WARNINGS/ADVISORIES...
OH...Heat Advisory until 8 PM EDT this evening for OHZ003-006>011-
     017>021-027>031-036>038-047.
PA...None.
MARINE...None.

&&

$$
SYNOPSIS...LaPlante
NEAR TERM...KEC/LaPlante
SHORT TERM...LaPlante
LONG TERM...Kosarik
AVIATION...Mullen
MARINE...Kosarik



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