Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 212332

Area Forecast Discussion
National Weather Service Wilmington OH
732 PM EDT Fri Oct 21 2016

A drier and cooler airmass will filter into the region tonight
into Saturday.


The upper level trough is continuing to push off to the east this
afternoon. The back edge of the pcpn is now about to the Scioto
River Valley and it should continue to taper off across our far
east through late afternoon.

The forecast concern for tonight will be the potential for any
frost to form. We are only running in the upper 40s to lower 50s
at the moment and low level CAA is forecast to continue into the
overnight hours. However, there are a couple of factors (namely
clouds and wind) resulting in some uncertainty for just how far
temps will drop and whether or not we will actually get frost

The western edge of the more stratiform clouds has become more
cumuliform looking and this will likely erode away as we head
into this evening. However, across eastern portions of our area,
the clouds look more stratiform so would expect them to linger a
little longer into the night there. Meanwhile, the low level flow
will back a little through the night and this should allow for
some of the lake effect clouds coming off of Lake Michigan to work
their way eastward into at least western parts of our area later
tonight. With this in mind, will generally keep at least partly
cloudy skies going through the night across our area. Meanwhile,
surface high pressure over the mid Mississippi Valley will begin
to build eastward into the Tennessee Valley overnight. This will
allow for a gradual decreasing pressure gradient through the
night, but expect it to still stay strong enough to keep at least
a little wind going overnight.

Given the continued CAA, think temps will fall into the mid to
upper 30s across much of our area. However, given the uncertainty
of the clouds and the wind possibly staying up, think the best way
to handle this situation is to hold off on a frost advisory. Since
there is a chance some areas could clear off for awhile and
decoupling could possibly occur in some low lying areas, will
still go ahead and include patchy frost wording in the
grids/forecast for later tonight into Saturday morning. Will also
issue an SPS to highlight the possible frost threat and


The upper level trough will pivot up across the northeastern
United States through the weekend with the flow across our region
becoming less amplified. Surface high pressure will build
eastward across the Tennessee Valley through the day on Saturday.
This will keep us dry but cool on Saturday with highs only in the
low to mid 50s. Some short wave energy will drop down across the
eastern Great Lakes Sunday into Sunday night. However, the best
forcing will remain off to our northeast and the airmass is fairly
dry so will maintain a dry forecast through the end of the short
term period. Temperatures will modify some on Sunday with expected
highs in the mid to upper 60s.


The long term will open up Monday with a shortwave diving
southeast around a rotating upper level low over Quebec. As the
shortwave dives southeast this will help to build the upper level
trough axis back west allowing more cold air to spill into the
Northeast United States. More recent model runs have tried to
trend the shortwave further west and seem to have agreed on the
shortwave moving southeast over Michigan. Overall the upper level
trough axis will setup east of the area allowing the heart of the
cold air to spill east of the Ohio Valley. The associated cold
front will push through the region Monday afternoon pushing
temperatures back down to near or slightly below normal values. As
has been the case the last couple of days the frontal passage
appears dry. PWATs ahead of the front only go up to about 0.75"
and the area remains on the convergent side of the trough axis.
Almost all of the positive vorticity advection is also east of the
area. Tuesday morning surface high pressure will move in from the
north allowing winds to go mostly calm . Some high clouds may be
moving in from the west, but chances seem to be growing that frost
may be possible.

During the day Tuesday a shortwave will move over the midwest and
head east. At the same, the upper level trough axis over New England
will pull east. In response to the shortwave, a surface low will
form near the Nebraska/ Iowa border. During the day Wednesday the
shortwave will strengthen and start to wrap up. Both the GFS and
ECMWF are in pretty good agreement with this and have the shortwave
wrapping up into a low over Wisconsin Wednesday evening. Across
southwest Ohio low level flow will continue to increase ahead of the
low with strong upper level divergence. Divergence will come from
the RRQ of the upper level jet streak along with upper level
diffluence from the splitting of 250 mb winds. Instability at this
time looks limited but shear profiles are impressive (SFC-1km ~35kts
via GFS forecast soundings). Any change in the placement of the low
will easily change the values and orientation of the bulk shear
vectors though. Future model runs will help to continue to refine
this. Thursday afternoon into Friday the shortwave will push east
but the ECMWF and GFS differ on how the shortwave ejects. The ECMWF
picks up the shortwave in the main flow moving a cold front through
the area. The GFS on the other hand washes the shortwave out and
slowly pushes it southeast. The CMC has the shortwave diving into
southeast Texas and appears to be the outlier. For now have kept the
forecast trended towards ECMWF.


Upper trough axis is now east of TAF sites. Low level moisture
persists in the northwesterly flow ahead of surface high pressure.
This will keep ceilings in the MVFR range at ILN CMH and LCK for
a few more hours before ceilings lift above 3000 ft later tonight.
Ceilings at western sites DAY CVG and LUK have already reached

As the upper trough continues east and the center of the surface
shifts to the southeast, VFR will persist, and skies will become
mainly clear at all sites by the end of the forecast. Winds of 10
knots or so will keep BR from forming.

OUTLOOK...No significant weather expected.




LONG TERM...Haines
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