Area Forecast Discussion
Issued by NWS Cleveland, OH

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FXUS61 KCLE 171503
AFDCLE

Area Forecast Discussion
National Weather Service Cleveland OH
1103 AM EDT Thu Aug 17 2017

.SYNOPSIS...
Low pressure over the upper midwest will cross the northern Great
Lakes today and tonight, then slide across eastern Canada. A weak
warm front will lift north across the area today followed by a cold
front late tonight and Friday morning. A short wave trough aloft
will cross the eastern Great Lakes on Saturday. High pressure will
build across the area by Sunday.

&&

.NEAR TERM /THROUGH FRIDAY/...
Showers have been limited in coverage this morning although
moisture continues to advect into the region. Dewpoints are
increasing with values in the low 70s already across much of
western Ohio. Visible satellite shows breaks in the clouds
across southern Ohio with an expanding cu field. Also to note is
a band of showers and thunderstorms approaching from Indiana.
The atmosphere is starting off weakly capped, but instability
will increase ahead of this line with storms intensifying as
they move into western portions of our forecast area this
afternoon. The Storm Prediction Center has expanded both the
slight risk of severe thunderstorms and the 5 percent tornado
outlook to include most areas west of Interstate 71. ML Cape
progged to increase to around 1200 J/kg with cloud cover
limiting values from getting much higher. Backed low level flow
relative to the stronger 40-50 knots of southwesterly flow aloft
does create a concern for rotating storms this afternoon. LCLs
will also be low given the moist environment so a tornado or two
is possible. Thunderstorms will be heavy rain producers but
hopefully storm motion to the northeast of 30-40 mph will
prevent flooding from being too much of a concern. Main time
frame for strong storms today will be 1-8PM.

Original "NEAR TERM" discussion...
A relatively strong surface low pressure and short wave energy
will track across the Great Lakes with a broad area of
warm/moisture advection ahead of the system. Coverage of showers
and storms will increase across the midwest and spread into
northwest Ohio early this morning. The eastward movement will
fight the dry atmosphere and downslope flow for a while this
morning and it may take until afternoon to get the activity to
extreme NE Oh and northwest PA.

Once the atmosphere has moistened up, additional thunderstorms will
develop as the trough approaches. Wind fields aloft will be
strong for this time of year. These storms should have both
shear and cape available but mid level lapse rates are progged
to be weak. Drying aloft is progged to increase from the west
this afternoon which will steepen lapse rates but may
ultimately cap the development. I suspect there will be a sweet
spot where severe storms develop and it could be in northwest or
north central OH during the mid/late afternoon. Will include
the threat in the Hazardous Weather Outlook.

Forecast high temperatures today will be on the high end of
guidance since the showers and thunderstorms will likely not be
persistent and the air mass is warm.

Unsure how far east the stronger storms will push this evening as
the sweet spot gets pinched off. Will keep higher pops across
northeast OH and northwest PA the first part of tonight. The
showers and storms could reach a point tonight across extreme NE
OH and NW PA where there is redevelopment with the potential
for heavy rain for a while. PW is progged to remain above 2
inches across extreme NE OH and NW PA through the evening.

The weak cold front may take until late tonight or Friday morning to
push across the forecast area. Model soundings suggest that the
drying aloft and subsidence will increase Friday as the leading
shortwave lifts out. Will keep a small pop across extreme northeast
OH and northwest PA through midday Friday since there may be just
enough upward motion and convergence to pop a shower a two until the
front is through. Cooler tomorrow as cold advection will be steady
through the day behind the front. High temps not too far from
normal.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
Shortwave energy enhancing the upper trough across the Ohio Valley
for Saturday will likely be enough to produce a few scattered
showers/thunderstorms across the area. Hopefully that this threat
will push east of the area by evening with the bulk of the trough
through, but there is the possibility that a few showers linger into
the evening across the far east. High pressure overspreads the area
for Sunday.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
The high shifts east for Monday. We will have a touch of good
summer heat Monday with highs in the mid and upper 80s with
subtle ridging overhead and H8 temperatures getting close to
+20C. For now leaned toward the warmer ECMWF guidance, but it is
possible a few locations could touch 90.

We return back to a longwave western U.S. ridge/eastern U.S.
trough by midweek. The warm and muggy airmass for Monday night
and into Tuesday will be replaced with highs in the 70s and a
more comfortable night for Wednesday night with lows back into
the 50s. Showers and thunderstorms look to be a good bet
sometime on Tuesday, but have limited precip chances to 50/50
until the timing is more firmly set. Right now the major
shortwave player across the northern Plains phases quickly with
more minor impulses across the southern Plains which may not
hold. Behind this frontal system, high pressure builds southward
from south- central Canada/upper Midwest for mid week.

&&

.AVIATION /12Z Thursday THROUGH Monday/...
A 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 continue to spread
across northwest and north central OH this morning with a few
embedded storms. It will likely take until afternoon to reach
KYNG and KERI. This first round of showers/storms will moisten
up the atmosphere and MVFR ceilings will develop, especially in
the vicinity of showers. Additional showers and storms will
develop this afternoon although the specific timing and location
becomes more difficult to pin down. The afternoon storms across
northwest and north central OH could become severe with strong
winds. 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...
A warm front will be pushing northeast across the lake today into
this evening bringing the east-southeast winds around to the south-
southwest.  The cold front will follow late tonight with winds
shifting to the west.  The winds in the warm sector today/this
evening will be brisk, but with the offshore flow will likely not
need a small craft advisory just yet.  For Friday, though, a small
craft advisory looks to be a good bet with the west flow east of the
Islands. Thunderstorms that develop this afternoon primarily across
the western basin may be strong to severe.

Winds diminish with time Saturday backing and then veering as a weak
upper disturbance moves a trough across the lake. Winds settle
further as high pressure passes over the lake Sunday, shifting east
of the lake for Monday.

&&

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

&&

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


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