Area Forecast Discussion
Issued by NWS Cleveland, OH

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FXUS61 KCLE 161755

Area Forecast Discussion
National Weather Service Cleveland OH
155 PM EDT Wed Aug 16 2017

High pressure will build east across the Great Lakes region today. A
warm front will lift north toward the region tonight, lifting
through the area on Thursday as low pressure deepens and tracks into
the Great Lakes. A cold front will push east through the region on
Friday, with high pressure building in behind the front through the


Cumulus has been building in an area of weak convergence from
Findlay southeast to near Delaware. A few showers have started
to develop and expect this area to slowly drift north this
afternoon. Raised pops to around 30 percent in our southern tier
of counties. It will be hard to get any thunderstorms given the
warm air in the mid-levels. Showers that do develop will be
fairly brief.

Original discussion... Surface high pressure will dominate the
area today, with little weather concerns through early afternoon
across the area, aside from some early morning patchy fog.
Expanded slight chance pops across the southwest CWA a bit this
afternoon, as guidance continues to indicated isolated
convection focused along a 925mb theta-e gradient. Went a couple
degrees warmer with highs today compared to previous forecast,
in line with the warmest MOS guidance.

Surface warm front near the Ohio River will lift north toward the
area tonight, as upper trough/cutoff low and attendant deepening
surface cyclone over the northern Plains tracks east towards the
Great Lakes. Precip chances will slowly increase from the west
tonight as low level jet inches towards the region and pieces of
energy eject east/northeast out of the upstream trough. Have slowed
the arrival of pops from previous forecast considerably, with chance
pops not arriving across the western part of the area until 09Z.
This may need to be slowed even further over the next forecast cycle,
with most of the area possibly remaining dry through 12Z Thursday.

Pops will increase through the day Thursday as the warm front lifts
north through the area and the low tracks into the western Lakes.
Again, have slowed down the pop trend from previous forecast, with
likely pops not arriving until 15-18Z west, and expanding across the
entire area by 22-00Z. Models have trended a little deeper/slower
with the low and the attendant cold front, so the forecast may be
too fast yet. Dewpoints will surge into the low 70s in the warm
sector Thursday, with highs in the mid 80s. 1000-2500 j/kg of SBCAPE
possible across the area, with deep layer bulk shear 35-40 kts may
be enough to sustain organized convection late in the afternoon with
damaging wind gusts the primary threat. Instability is likely
overdone a bit in the models, with convective debris limiting
overall isolation. Concur with the SPC Day 2 outlook with a
widespread marginal risk.


Most of the models show what is essentially a dry slot sweeping
across the lower Great Lakes Thursday night with increasingly dry
air aloft and some subsidence. Will start out with "likely" pops
Thursday evening and then lower the forecast probabilities from west
to east Thursday night. The front will arrive late, probably early
Friday morning, and cannot rule out enough low level convergence and
upward motion to generate a scattered to broken line of showers or
thunderstorms but it does not appear worthy of more than a "slight
chance/chance" pop Friday, mainly in the morning.

The models have been consistent with a nice trailing short wave on
Saturday. The better upward motion and precipitation will gravitate
toward the better instability which will be well south of the area
but the actual short wave may track across the lower Great Lakes and
there would seem to be at least a chance or slight chance of a
shower or perhaps a thunderstorm. The warm waters of Lake Erie could
contribute some instability. Not sure whether Saturday may end up
being mostly cloudy or partly cloudy. Will forecast high
temperatures near guidance from the mid 70s to around 80.


The pattern will become more amplified next week. Surface high
pressure should build across the Great Lakes by Sunday and heights
will rebound. The air mass will warm above normal early next week
ahead of the next cold front which looks on track for sometime later


.AVIATION /18Z Wednesday THROUGH Monday/...
Diurnal cumulus will expand this afternoon, especially from
FDY-MFD. Can not rule out a brief shower at either location but
chances are below 20 percent so did not include in these

Otherwise a brief decrease in cloud cover expected this evening
before high clouds increase from the west overnight. These
clouds will lower with time as moisture increases ahead of low
pressure approaching from the midwest. Expecting showers to
expand late tonight and move northeast across the area into
Thursday morning. Although thunderstorms are possible with this
first round, the coverage is expected to be low so did not
include thunder prior to 18Z. Did include a few prob groups in
the western terminals where showers could be a little heavier
and drop visibilities to MVFR. Showers and thunderstorms
expected to expand across NW Ohio after 19Z and spread eastward
ahead of an upper level trough. Winds will be out of the
north and east most sites through tonight before shifting around
to the south on Thursday.

OUTLOOK...Areas of Non-VFR possible Thursday through Thursday
night with scattered storms.


High pressure will slide across Ontario and Quebec today and
the flow on the lake will remain northeast veering more easterly
by tonight. As pressure falls to the west, the winds will pick
up on the lake also enhanced by the onshore component this
afternoon. Winds and waves will stay below small craft criteria
but the lake will get a but choppy by late this afternoon and
tonight, especially the west half of the lake.

A deepening low pressure system will track across the northern Great
Lakes Thursday into Friday. A warm font will cross Lake Erie o
Thursday followed by a cold front Friday morning. The wind field
will increase with this system as well as the threat for showers and
thunderstorms. The southwest flow will become west and northwest on
Friday and a small craft advisory may be needed. High pressure will
quickly build east across the Great Lakes this weekend and winds and
waves will settle down.




NEAR TERM...KEC/Greenawalt
SHORT TERM...Kosarik
LONG TERM...Kosarik
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