Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 260741
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
341 AM EDT Wed Apr 26 2017

.SYNOPSIS...
Southerly flow will result in warm and dry weather today.
A cold front will push across the region on Thursday with high
pressure briefly building in behind the front. Conditions will
become unsettled over the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Our area will remain between two systems today. A building mid
level ridge across the region this morning will shift off to the
east while a cold front moves toward the western Great Lakes
and middle/lower Mississippi River Valley. Subsidence will
result in only few to scattered cirrus. Southerly flow will
increase with locally breezy conditions expected, especially
over the Whitewater/Miami Valleys and west central Ohio.
Temperatures will be much above normal, warming into the lower
to mid 80s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Embedded s/wv in the flow will eject from the southern Plains
to the middle Mississippi River Valley tonight. As this occurs,
low pressure will ripple along the cold front, eventually
lifting north into the western Great Lakes. This will allow the
cold front to approach the region tonight. Skies will start out
mostly clear this evening/early morning with clouds increasing
from the west. Low level moisture convergence in the form of a
strong 850 mb low level jet will bring showers and embedded
thunderstorms to our western CWFA between 09Z and 12Z.

On Thursday, embedded s/wv will move into the western Great
Lakes while the cold front advances east across the forecast
area. Instability will have waned by Thursday morning, and not
a lot of uptick in instability is expected as clouds increase
and the front moves into the eastern forecast area by 18Z.
Although a strong low level jet will exist initially, the low
level 0-3 km shear vector is mainly parallel to the forecast
orientation of the precipitation. This does not bode well for
much in the way of bowing segments. Finally, with the s/wv
passing north by afternoon, convection will become more
scattered as it advances into our eastern CWFA. Thus, the
threat for severe storms will remain marginal/isolated as in
agreement with SPC SWODY2. After a warm start in the lower to
mid 60s, temperatures will have a muted warming trend given some
CAA by afternoon and cloud cover. Highs will range from the
upper 60s west to the mid 70s east.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
A shortwave and cold front will be pulling northeast of the region
on Thursday evening, leading to gradually (though partially)
clearing skies. With this front and shortwave glancing through the
region, rather than ushering in a major change in air mass,
temperature recovery in southerly flow on Friday should be strong --
and in fact, it could end up warmer than Thursday due to the lack of
rain.

As height rises occur on Friday into Saturday, with ridging becoming
established across the southeastern states, another big wave in the
pattern will begin to develop over the central plains. As this
occurs, 00Z models have been more insistent on a strengthening and
re-positioning of the old frontal boundary, leading to significant
frontogenesis over the Ohio Valley on Saturday. With a tightening
theta-e gradient across the region, this front will likely act as a
focus for shower and thunderstorm development -- perhaps as soon as
Friday afternoon, but especially going into Friday night and
Saturday. Most of the precipitation is expected to be focused along
and north of the front, where surface-based instability will be
limited, but elevated instability will allow for convection. Where
model solutions begin to diverge is on potential drying south of the
boundary in the warm sector, as well as on specific timing or
magnitude of any waves of showers/storms during this time frame.

There remains strong agreement in the general pattern for Sunday
into Sunday night, with deepening low pressure at the surface and
aloft ejecting from the plains into the Great Lakes, driving a
strong cold front through the Ohio Valley. It looks mostly certain
that the ILN CWA will end up completely in the warm sector within a
regime of deep and strengthening southerly flow, before
precipitation becomes more likely in the second half of the day. Of
concern is the inconsistency with which the placement and strength
of the upper low has been handled -- both from model to model and
even within the GEFS solutions, which diverge most significantly
from Sunday morning onward. For this reason, no attempt at a
specific forecast for hazards will be made at this juncture. With
that said, depending on how the pattern ends up working out, some
threat for heavy rain and severe weather could occur. With flow
looking mostly-meridional, that could certainly be one limiting
factor for a severe threat, but the magnitude of the flow will
offset that to a degree.

Behind this front, as opposed to the Thursday system, there will be
a notable change in air mass -- and strong cold advection that will
likely lead to wind gusts in the 30-40 MPH range. Something to add
to the HWO once this gets a little closer in the forecast cycle.

Temperatures appear likely to remain above normal through the
weekend, though the very sharp temperature gradient currently
forecast for Saturday results in lower-than-normal confidence there.
Sunday could be very warm, especially if the drier warm sector
solutions verify, and most notably in the southeastern ILN CWA --
with mid 80s in the forecast and possibly some room for that to
move. Behind the front on Monday, there will be a significant drop
in temperatures -- a difference of around 20 degrees from Sunday.
This forecast will continue to undercut the general model blend,
coming closer to raw GFS/ECMWF numbers for Monday.

No signs of significant weather on Tuesday or Wednesday, with some
gradual warming expected in pseudo-zonal flow.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Mid level ridge will continue to build northward into the middle
Ohio Valley through sunrise. Only some scattered cirrus is
expected. Any mist/fog should be isolated.

For today, mid level ridge shifts east while a cold front moves
east into the western Great Lakes and middle/lower Mississippi
River Valley. Again, only some FEW-SCT cirrus is expected.
Southerly winds will increase between 15Z and 18Z will become
locally gusty between 20 and 25 knots.

For tonight, an embedded disturbance will eject from the
southern Plains into the middle Mississippi River Valley. This
will perturb an area of low pressure on the cold front to our
west which will begin to make inroads east as the low ripples
northward toward the western Great Lakes. Showers and embedded
thunderstorms are expected along and ahead of the front in an
axis of low level moisture convergence and upper level support.
These showers and embedded storms will move toward the western
terminals toward 12Z. Winds will stay locally gusty overnight as
the pressure gradient tightens.

OUTLOOK...MVFR ceilings and visibilities along with a chance of
thunderstorms on Thursday. MVFR ceilings and visibilities with
a chanced of thunderstorms again Friday night through Sunday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.

&&

$$
SYNOPSIS...Hickman
NEAR TERM...Hickman
SHORT TERM...Hickman
LONG TERM...Hatzos
AVIATION...Hickman



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