Area Forecast Discussion
Issued by NWS Wilmington, OH

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000
FXUS61 KILN 190136
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
936 PM EDT Sun Aug 18 2019

.SYNOPSIS...
A disturbance will move across the region tonight bringing a
round of thunderstorms. Additional storms will be possible from
time to time from Monday through Wednesday until a cold front
moves through the region. Cooler and less humid conditions will
work into the area Thursday and Friday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Convective line is pushing east across western portions of our
fa. This is associated with a mid level short wave that will
progress east through the early morning hours. For the most
part, the convective line has been weakening as it has moved
into our area with the strongest activity now to our north in
an area of slightly better forcing/shear. The airmass across our
east is still unstable though so it may take a few hours for
the convective line across our area to completely wind down.
Have nudged up pops across about the northern two thirds of our
fa through the rest of this evening to account for this.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Guidance suggests that a weak boundary will be in the area which
will be a focus for slightly enhanced moisture. With heating
this will be a zone of higher instability. With weak
disturbances moving across the area, there will be a chance of
additional storms Monday afternoon. Cannot rule out the
possibility of isolated activity continuing into Monday night.
With no change in airmass, expect highs and low to be near
persistence.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Quasi-zonal/west-northwest midlevel flow will remain entrenched
across the lower Great Lakes region through the first part of the
workweek, with a quasi-stationary/oscillating front stretching
across the heart of the Ohio Valley for Tuesday into Wednesday. The
front will gain a bit of southward momentum Monday night as heights
fall aloft and surface high pressure builds east through the heart
of the Great Lakes region by Monday night. However, the front will
become somewhat washed out across the area by early Tuesday, with
southwesterly surface flow resuming area-wide by Tuesday afternoon.
And with the remnant synoptic-scale boundary (and potentially
several convection-induced mesoscale boundaries) lingering about the
area on Tuesday, will maintain a chance PoP across most of the ILN
FA -- especially during the diurnally-favorable time frame of
afternoon/early evening. Although the deep-layer flow fields appear
to be rather weak in nature -- generally 20kts or less through the
bottom 30kft of the column -- the moderate to high instability could
be enough to initiate some slow-moving convective re-initiation
during the afternoon/early evening -- especially in the presence of
the aforementioned boundary(ies). Although the best chance for this
isolated to scattered development appears to be centered across the
middle of the ILN FA, identification of the subtle boundaries which
will provide the ultimate focus for such activity is very difficult
at these time ranges -- lending itself to lower confidence on
exactly what areas may be favored for afternoon thunderstorms on
Tuesday.

The hottest day of the extended period will likely be Tuesday
ahead/south of the aforementioned E-W oriented front across the
northern/central Ohio Valley -- with heat index values in the upper
90s possible mainly south of the I-70 corridor. This being said,
confidence on these values being met is rather low given the
aforementioned uncertainties in cloud/convective coverage during
peak heating hours. By Wednesday, mid/upper level troughing across
the Great Lakes region will become more pronounced as a
stronger/better push of cooler/drier air arrives late Wednesday
night into Thursday with the passage of a cold front. The arrival
and subsequent progression of the cold front through the region
later Wednesday will likely bring with it the best chance for
widespread showers and storms Wednesday afternoon/evening than will
be the case at any other point during the entire long term period.
While the specifics of the this system and the corresponding impacts
on the sensible weather locally are still a bit uncertain, feel
confident in maintaining high chance PoPs Wednesday into Wednesday
night.

And although cooler and drier air will be filtering in Wednesday
night -- especially near/north of the I-70 corridor, the front/s
progression south may be slowed somewhat as it nears the Ohio River
as more S/W energy ejects east from the mid-Missouri Valley into the
western Tennessee Valley. This may act to stall /or at the very
least slow/ the front/s progression southward Thursday morning
through Thursday evening before it finally begins to definitively
push south of the ILN FA Thursday night. The slowed progression
early Thursday may may allow for continued PoPs mainly along/south
of the Ohio River before drier conditions return area-wide by
Thursday night.

Much cooler and less humid air will build into the region for Friday
and Saturday as high pressure returns to the area. Confidence
remains fairly high in seasonable temperatures and dry conditions
for the final part of the week.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Thunderstorms have continued to develop across Indiana early
this evening and have begun to organize into more of a line
across central Indiana. Hi res models are showing this
continuing to push east into our area through mid to late
evening with some possible development along the southern edge.
They are also indicating an overall weakening trend as the
storms move into our area. We are still fairly unstable across
our area though so there is some uncertainty as to just how fast
they will begin to weaken. KDAY appears to have the best
chance for seeing thunderstorms through the evening hours and
will try to time those in with a tempo tsra. With less certainty
at the remaining TAF sites, will cover with just a VCTS for a
few hour period.

These storms are at least partially associated with a mid level
short wave that will move east across the region tonight. As we
get on the back side of this and continue to lose the diurnal
heating, expect pcpn to taper off through the overnight hours.
Some mainly valley fog will be possible later tonight,
especially in the southern valleys. Otherwise, expect VFR
conditions through the remainder of the TAF period.

OUTLOOK...Thunderstorms possible Tuesday and Wednesday.

&&

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

&&

$$
SYNOPSIS...
NEAR TERM...JGL
SHORT TERM...
LONG TERM...KC
AVIATION...JGL


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