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000
FXUS61 KILN 210735
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
335 AM EDT Mon Aug 21 2017

.SYNOPSIS...
Above normal temperatures will persist across the Ohio Valley
through Monday ahead of a cold front. The cold front will bring
showers and thunderstorms on Tuesday, then drier and cooler air
moves in for the rest of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Ongoing convection out in Indiana has continued to weaken as it
pushes east into a more stable air mass. The HRRR and RAP push
the convection east with the upper level disturbance and slowly
weaken it as the convection moves into a more unfavorable
environment. This afternoon the shortwave from this morning will
be exiting east with another shortwave move east from Iowa into
Illinois. At the same time a weak 850/700 mb jet will be
nudging into the area from the west. As this happens the GFS,
NAM, and CMC all generate QPF across our northwest starting late
this morning into afternoon. Taking a look at forecast
soundings reveals the GFS showing extensive cirrus debris across
the area with only weak destabilization (CAPE ~ 700 J/kg). The
NAM on the other hand does not show much cirrus debris and
starts to destabilize (k index of 40 at KDAY by 21z). By later
in the afternoon the ongoing complex of thunderstorms over Iowa
will be approaching the area from the west. CAPE values
drastically decrease across central and southern Indiana, and
Ohio so am expecting the complex to fall apart. Still though,
there will likely be a large amount of cloud debris today near
eclipse time (esp. towards Dayton and areas northwest).
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
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This evening, convection or decaying showers from the afternoon
will start to come to an end as daytime heating is lost. Tonight
a potent upper level system over the Hudson Bay will begin to
wrap up into an upper level low and head south. Mid and upper
level flow will quickly start to amplify as the newly formed low
pushes southeast.

Ahead of the main upper level system a wedge of PV will swing
east helping to get showers and thunderstorms going Tuesday
afternoon. SFC to 6 km bulk shear values at this time are around
40 kts (slightly higher on the NAM and slightly lower on the
GFS). ML CAPE values on the GFS are only around 700 J/kg while
the NAM has values approaching 2000 J/kg. Looking more in depth
at forecast soundings reveals why. The GFS clearly shows a
cirrus shield inhibiting the area from fully destabilizing. Also
at this time the cold front has yet to enter our CWA. Therefore
convection will be dependent on destabilization as surface
convergence from the front will come later. Not surprisingly SPC
has therefore kept the area in a slight risk given supportive
bulk shear vectors and questionable instability. The primary
threat still looks to be damaging winds (possibly some type of
broken line forming).
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&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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Showers and thunderstorms will linger into Tuesday evening,
especially across southeast portions of our forecast area. However,
as the cold front pushes off to our southeast and drier air begins
to filter in behind the front, expect pcpn to taper off from the
northwest as we head into Tuesday night.

Surface high pressure will build down across the Great Lakes through
the rest of the week. This will lead to mainly dry and cooler
conditions. However, some mid and upper level short wave energy
dropping down across the Great lakes on Thursday could lead to a few
showers, especially across northeast portions of our area.
Temperatures through the end of the week will be several degrees
below normal with highs in the 70s and overnight lows in the 50s. We
will start to get into some return flow through the weekend, leading
to a slight warmup by the end of the long term period.
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&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
Surface high pressure was centered off to our southeast this
morning with convection ongoing in Indiana. This convection is
in response to a shortwave that is pushing east across northern
Illinois. More stable air exists over Ohio though so am
thinking convection will weaken before making it to the TAF
sites.

This afternoon high res models then indicate showers and
thunderstorms possibly forming across our northwestern zones
along the nose of a weak LLJ. The RAP, HRRR, WRF DART, and NMM
show convection in some form or fashion while the NSSL WRF and
NAM 3 km are dry. For now have just added a VCSH for KDAY due to
uncertainty in formation.

OUTLOOK...Thunderstorms are likely Tuesday into Tuesday
evening.

&&

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

&&

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