Area Forecast Discussion
Issued by NWS Cleveland, OH

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FXUS61 KCLE 170559
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
159 AM EDT Thu Aug 17 2017

.SYNOPSIS...
Low pressure over the midwest will move to northern Michigan by
Thursday evening, then slowly continue northeast into Canada. A weak
cold front will move east across the area Thursday night with cooler
air arriving with a secondary trough Friday night. High pressure
will build northeast up the Ohio Valley on Saturday.

&&

.NEAR TERM /THROUGH TODAY/...
No major changes with this update. Some shower and thunderstorm
activity is trying to develop across southwest Ohio and more
lighter stuff over eastern Indiana. This activity will gradually
move east toward the area overnight.

PREVIOUS DISCUSSION...
A few showers are sneaking into the southern counties late this
afternoon focused in a region of weak surface convergence. Weak
instability along with warm air in the mid levels above 700mb is
limiting vertical growth with storms struggling to get much above 15-
20k feet. Will leave an isolated shower or thunderstorm in the
forecast for the southern counties through about 8 PM. After
that skies will tend to clear this evening before high cloud
arrives overnight. Clouds will tend to thicken and lower with
time so expecting lows to occur during the overnight hours
before warming late. Increasing humidity at the western
terminals will keep lows closer to 70 while eastern sites taper
down to near 60 in NW PA.

For Thursday we turn our attention to the trough approaching from
the plains. Low pressure over Iowa will track northeast towards
Upper Michigan on Thursday. Moisture advection occurs overnight in
advance of the trough although the low level jet energy we saw a
couple days ago has backed off. Model sounding show sufficient
moistening of the column aloft that expect to see showers expanding
into NW Ohio during the morning. Conditions will be fairly stable
with this first round so mainly expecting showers with a few
scattered thunderstorms around.

After the initial push of moisture, breaks in the showers are likely
before starting to fill back in with daytime heating. PW values will
be near 2" so thunderstorms will produce locally heavy rain.
Expecting fairly cloudy conditions to have some limiting effect on
temperatures so forecast highs are only in the low to mid 80s. Any
breaks will allow for a quick jump in both temperatures and
instability. Otherwise expecting showers and thunderstorms to fill
in during the afternoon as weak front arrives from the west with
large scale lift increasing with the arrival of a mid-level dry
slot. Best forcing is focused across NW Ohio where the Storm
Prediction Center has brought a slight risk of severe thunderstorms
into NW Ohio. ML Cape only expected around 1000 J/kg during the
afternoon so that will be a limiting factor. AS the front moves east
Thursday night, storms will be tracking northeast along the frontal
boundary which could lead to some training and heavy rainfall. Rain
will taper off from west to east during the overnight as the drier
air spreads in from the west.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
Some lingering showers in the East to start of Friday morning
but they should move east by the afternoon. Models continue in
good agreement moving an upper level short wave across the
forecast area on Saturday. For now will just keep chance pops
going.

Short wave moves east of the forecast area Saturday night.  Sunday
should remain dry with ridge of surface high pressure lingering over
the Eastern lakes.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
High pressure will drift east of the region Sunday night with
southerly winds returning for Monday. Expect to see some afternoon
cumulus develop across inland locations. The next storm system will
dig into the Western Great Lakes early Tuesday then drift eastward
through the day. Thunderstorm chances increase Tuesday afternoon
through the overnight. For now have only gone with high end chance
POP`s which means scattered thunderstorms. However if the models
remain consistent over the next few days we will be able to nudge
POP`s higher. A cold front will cross the region at some point
Wednesday morning into the afternoon. We then will monitor for some
lake effect showers for Wednesday night.

Monday will be the warmest day of the long term with highs in the
mid to upper 80s. Slightly cooler Tuesday with the extra cloud cover
and showers around but still in the 80s. Cooler Wednesday with highs
dipping back into the 70s for most locations.

&&

.AVIATION /06Z Thursday THROUGH Monday/...
South becoming southwest low level jet will spread across the
area this morning with deep Gulf moisture and increasing upward
motion. Showers and thunderstorms will increase in coverage with
MVFR visibility in showers. The first round of showers/storms
will moisten up the atmosphere this morning across northwest and
north central OH and MVFR ceilings will develop, especially in
the vicinity of showers by mid/late morning. Additional showers
and storms will develop this afternoon although the timing and
location becomes more difficult to pin down. By this evening,
the majority of showers/storms should have ended across NW OH
with activity continuing across NE OH and NW PA.

OUTLOOK...Areas of Non-VFR possible Saturday.

&&

.MARINE...
The flow will turn to the south overnight ahead of next system.
Models in reasonable agreement with low tracking across the Northern
Lakes Thursday night dragging a cold front across Lake Erie. Choppy
conditions develop on the lake as the winds turn to the North to
Northwest behind the front.   For now will continue with 10 to 15
knots and 2 to 4 foot waves...but marginal small craft advisory is
not out of the question in the East.   High pressure builds quickly
over the lake on Saturday.

&&

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

&&

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


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