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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 201957
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
357 PM EDT Mon Aug 20 2018

.SYNOPSIS...
Surface low pressure will track northeast from the mid Mississippi
Valley across the Great Lakes Tuesday. Showers and thunderstorms
will overspread the area ahead of an approaching warm front.
Precipitation will continue tonight and Tuesday as a cold
front sweeps east across the area. In the wake of the cold
front, a much cooler and more comfortable airmass will move into
the area, bringing dry weather through the remainder of the
work week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Mid level low evident on WV imagery over IA/MO border. This low
to open up and track into the Great Lakes overnight. Axis of
convection associated with warm advection arm/isentropic lift
pivoting into southwest Ohio. This arc of convection to pivot
northeast though ILN/s FA through early evening.

Boundary layer CAPE values of 1000-1500 j/kg feeding these
storms with bulk shear of 25 to 30 kts. DCAPE values around
1000 j/kg ahead of these storms. A few of the stronger updrafts
will have the potential to produce strong to severe winds mainly
over the western counties early. Models solutions continue to
highlight an axis of precipitable water values in excess of 2
inches. So along with wind, some of the storms will likely
contain heavy rainfall. HWO product accurately describes the
weather threats. Have increased pops to categorical to account
for this early convective band.

Expect a general lull (decrease in coverage) in convective
activity until favorable forcing re-develops late tonight when
a low level jet comes into play. By this time instability is
marginal with blyr instby of less than 1000 j/kg. Have pops
ramp back up late tonight to account for this enhanced forcing.

Expect mild lows from the upper 60s to around 70.


&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Low level jet with enhanced convergence ahead of initial
sfc front/trof will lead to a good chance for showers and
thunderstorms late tonight into Tuesday morning. Have likely
pops early. Linger these likely pops into Tuesday aftn over the
east, where airmass has a better chance to destabilize.

Even in the east cloud cover should limit instby to 1000-1500
J/kg. Better chance for severe east of ILN/s area but can not
rule out a damaging wind event or two in the far east. Highs
to range from the upper 70s northwest to the lower 80s
southeast.

Secondary front/trof to pivot through the area Tuesday evening.
This will keep the threat for showers and perhaps a thunderstorm
with marginal instby over the area. Drier air will begin to
advecting into the area but clouds will be slow to scatter out.
Expect lows from near 60 northwest to the mid 60s southeast.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
At the start of the extended forecast period on Wednesday morning, a
mid-level trough will be in place across much of the eastern half of
the CONUS, with surface high pressure beginning to move eastward
from the plains states. The trough will move east and allow for
broad ridging to build into the Ohio Valley by Thursday morning,
with the surface high entering the region. By Friday, ridging will
be more firmly established over the Appalachians, with the surface
high moving off the mid-Atlantic coast. This pattern supports a
typical gradual warming trend through the second half of the week,
with the air mass remaining relatively dry. It is a typical pattern
perhaps more likely to occur a month or so from now, but it will
provide a period of below-normal temperatures on Wednesday,
Thursday, and Friday. Starting out with highs in the lower to upper
70s on Wednesday, temperatures by Friday will have adjusted upward
only slightly -- upper 70s to lower 80s.

The weather pattern will continue to adjust over the weekend,
switching to more of a warm-advection and potentially stormy
scenario. On Saturday morning, there will be an increase in
southerly flow into the Ohio Valley, as a mid-level trough positions
itself just upstream of the region. This will support the
development of precipitation on Saturday -- right now appearing to
favor the early part of the day. Admittedly there is good agreement
in the last two runs of both the GFS/ECMWF on timing, but this is a
change from yesterday, so PoPs will be kept in the 20-30 percent
range until this solution gains a little more temporal continuity.
There is high confidence in a ridge settling into the southeastern
states through the rest of the weekend and into next week, with low
confidence in the timing and magnitude of any shortwaves moving
across the northern tier of states during this time frame. As such,
PoPs will be kept in the 20-percent range through the weekend, with
temperatures continuing to gradually warm into the middle to upper
80s by Sunday and Monday.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
Axis of thunderstorms developing across Indiana ahead of an
approaching warm front. These storms to pivot northeast through
the TAF sites this aftn into the early evening. VFR conditions
may drop down to IFR in thunderstorms for a brief period. Have
covered this threat with tempo groups for thunderstorms, IFR
visibilities and MVFR ceilings.

After these storms move through, expect a general lull in pcpn
activity through the remainder of the evening with VFR conditions.

Another enhanced chance for storms will occur late tonight when
a low level jet shifts northeast into the Ohio Valley. Instability
will be marginal at this time, so have covered this threat with
prevailing showers and VCTS. With the approach of a surface cold
front expect ceilings to drop to MVFR category late tonight into
Tuesday morning.

As surface winds shift to the southwest and then west on Tuesday
gusts of 20 to 25 kts will be possible.

OUTLOOK...Chance of thunderstorms into Tuesday evening.

&&

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

&&

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