Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 210133
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
933 PM EDT Thu Jul 20 2017

.SYNOPSIS...
A frontal boundary will slowly sag south across the region
through the weekend. This will combine with a warm and humid
airmass to produce occasional thunderstorms through the rest of
the week and into the weekend.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
The 00Z KILN sounding tonight came in notably more unstable than
the balloon launch from last night, but the end result is
roughly the same, with no activity of note anywhere in the
forecast area. There seems to be no large-scale support for
ascent over the region at the moment, with some subsidence
likely behind the MCV which moved through the CWA (as a
weakening MCS) several hours ago. Some models (recent HRRR/RAP
runs / 18Z NAM) are essentially convecting at will over the
western ILN CWA or upstream over Indiana, and real life has yet
to play this scenario out -- not a huge surprise given the lack
of convergence in the low-levels or any sort of shortwave
support in the mid levels. PoPs have been limited overnight from
the previous forecast, though not entirely removed -- a few
showers or storms will continue to be possible in the unstable
air mass, though the chance for anything larger-scale or
organized is waning considerably.

Surface dewpoints seem to be slightly outperforming a model
consensus, which has forced some slight increases in both T/Td
forecasts through the overnight period. Will still be watching
for potential low cloud development across the northern third of
the CWA overnight, but this scenario was covered well in the
previous forecast, with no updates needed.

Previous discussion >
Remnants of a MCS were moving across the CWA early this
afternoon. We have also seen separate scattered convective
development across portions of eastern OH.

MCS will likely continue to weaken and then dissipate as it
moves across southern OH through mid afternoon. Expect a
relative lull in convective activity after that due to some
subsidence and lingering clouds behind this system.

Most high resolution models then suggest that after this lull
there will be renewed convection across the CWA sometime this
evening, likely aided by sufficient instability (CAPE) and
also an increase in shear particularly across the northern
portion of the CWA. There is still uncertainty with the exact
location/coverage of convection, and therefore have kept pops
in the low chance category. Some of guidance also indicates
convection making it pretty far south toward the Ohio River late
at night. Can`t completely rule out this solution, but favored
highest pops near/north of Interstate 70 where it looked more
favorable for convection into the night. Any storms will be
capable of producing locally strong/damaging wind gusts and also
heavy rainfall that could lead to localized flash flooding.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
A hot and humid air mass will continue to reside over the CWA on
Friday. There is general agreement that the morning will be dry.
There may be some clouds to start to day, but with sufficient
insolation maxima have the potential to be just as warm if not
1-2F higher than Thursday. Combining this with lower to mid 70s
dewpoints brings heat index values into Heat Advisory criteria
(100-104F) for a few hours Friday afternoon across portions of
southeast IN, southern OH and northern Kentucky. As such, a
Heat Advisory has been issued for these areas. Upper 90s heat
index values are forecast further north.

Uncertainty continues regarding convection Friday afternoon into
Friday night. A cold front will likely sag down into central
IN/OH which can serve as one focus for convection, but think
that mesoscale influences may be more important and those
details are not well known at this time. Followed continuity
with chance of convection increasing in the afternoon/evening,
and kept chance pops into the night especially across the
northern CWA given the boundary in place and also potential for
a new MCS to approach late at night.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Active weather pattern will continue into Saturday. Frontal boundary
may move slightly northeast as a warm front, but its effective push
will be dependent on where exactly another potential MCS moves. For
now, an embedded disturbance in the northwest flow aloft to produce
such an MCS is forecast to affect our northern zones where the
highest PoPs have been placed. Chances for showers and thunderstorms
then decrease as one heads toward the Tri-State. Potential for
severe storms will be there due to adequate4 instability and deep
layered shear. Heavy rain due to high pwats and potential flash
flooding will also exist. Again, temperatures will be dependent on
convection and convective debris clouds but should make the
mid/upper 80s far north to the lower 90s south. Some heat indices
may touch 100 briefly in the south on Saturday afternoon.

For Saturday night, looks like another disturbance and perhaps a low
level jet will generate another round of showers/storms with the
northern zones again having the highest threat.

On Sunday, models suggest that a weak boundary/trough axis may move
east of the region by afternoon. As such, highest chances of
showers/storms will be in our southeast with the lowest in the west.

For Sunday night into Monday night, mid level trough axis will
traverse the Great Lakes and Ohio Valley. This will be associated
with a cold front that will move slowly southeast through the
region. Will continue with a chance of showers/storms Sunday night,
with decreasing chances of precipitation occurring as the front
passes through. We should be dry for the most part by Monday night.

Under northwest flow in the wake of the mid level trough, surface
high pressure will build into the region Tuesday. The high will
continue to extend and influence our weather into Wednesday. Dry
weather and highs in the lower to mid 80s are expected.

The next weather system may begin to affect the area by Thursday as
return flow between departing high and an approaching cold front
bring the next threat for showers and thunderstorms.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected at least in the near term, with all
TAF sites currently in an area with scattered clouds and no
precipitation. As the next few hours progress, some showers and
thunderstorms are expected to develop over Indiana. As this
occurs, some of this activity may eventually move toward the TAF
sites, but with a low probability of impact to any individual
airport. Will continue to use a VCSH tonight to account for
this.

Later in the overnight hours, some MVFR visibilities and lower
clouds (possibly MVFR/IFR ceilings) are likely to develop in
northern Ohio. As some of this will likely drift southward into
Columbus, some reduced aviation conditions are in the forecast
near daybreak for KCMH/KLCK. There is a lower probability that
IFR ceilings could form and move into the area, possibly
affecting KDAY as well.

Any chances for precipitation tomorrow appear marginal and
disorganized, so they will not be included in the TAFs this far
away. Aside from this possibility, VFR conditions are expected.

OUTLOOK...Thunderstorms will be possible at times from Friday
through Monday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Heat Advisory from noon to 7 PM EDT Friday for OHZ077>082-088.
KY...Heat Advisory from noon to 7 PM EDT Friday for KYZ089>100.
IN...Heat Advisory from noon to 7 PM EDT Friday for INZ073>075-080.

&&

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


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