-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 181031
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
631 AM EDT Tue Jul 18 2017

.SYNOPSIS...
An upper level ridge of high pressure will build into the mid
Ohio Valley through the end of the work week, leading to a
gradual warming trend. There will also be an increasing chance
of thunderstorms as we head toward the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A scattered to occasionally broken sc field has developed
across the region this morning and this will likely linger
through mid morning. As we begin to destabilize through late morning
and into this afternoon, this should transition to more of a cu
field. The mid level ridge will nose eastward into the area
through this afternoon and this should help limit shower and
thunderstorm development. However, several of the higher res
models as well as the NAM are suggesting the possibility of a
few pop up showers and thunderstorms while the GFS looks like it
keeps just a strong enough cap in place to prevent any
development. Thus, it looks like pcpn chances will be rather low
with the best chance for anything popping up likely being
across our northern areas where some weak low level convergence
will be present this afternoon. As a result, will go ahead and
hang on to a slight chance of pops across mainly the north for
this afternoon. 850 temps and low level thicknesses are fairly
close to what we saw on Monday, perhaps bumping up a tad through
late afternoon. This should allow for highs generally in 85 to
90 degree range today.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Once again, would expect any isolated shower/thunderstorm
activity to dissipate heading into this evening as we lose the
daytime heating. Lows tonight will be in the upper 60s to lower
70s.

Heights will nudge up a bit more through the day on Wednesday
which should allow for highs a degree or two warmer, into the
upper 80s to possibly lower 90s. This will combine with dewpoints
in the upper 60s to push heat indices into the mid to possibly
upper 90s through the afternoon hours. Meanwhile, the GFS and
ECMWF have some weak short wave energy pushing east southeast
across the southern Great Lakes on Wednesday while the NAM
brings the energy more southeast toward our area. Will trend
toward the more northern solutions but will allow for a slight
chance of pcpn across our northwest through the afternoon to
account for some of the uncertainty.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Upper level ridging will be centered over the central United States
Wednesday night with an upper level low located over North Carolina.
Simultaneously a long wave trough axis will located over eastern
Canada. Models have struggled over the last couple of days of how
the long wave trough, upper level low, and mid level ridge will
interact. On Thursday models have been in fairly good agreement with
the mid level ridge remaining over the central United States with
the upper level low remaining quasi-stationary. The ILN forecast
area remains on the edge of the mid level ridge with only the CVG
GFS forecast sounding showing any hint of mid level ridging. Overall
though forecast soundings do destabilize Thursday afternoon. ML CAPE
values on the GFS average around 1500 J/kg with the greatest
instability across the northwestern zones. A weak upper level
disturbance is also expected to track across Michigan Thursday
afternoon. Given this have the chance of precipitation increasing
Thursday afternoon with the highest chance of rain to the north. Due
to the forecast areas close proximity to the ridge, 850 mb
temperatures also climb to just above 20 degrees C. This combined
with dewpoints in the lower 70s will push heat indicies into the mid
to upper 90s (approaching 100 across the southwest).

Friday afternoon mid level ridging begins to slowly break down as
the upper level low that was over North Carolina retrogrades west
underneath the ridge. Some weak upper level disturbances will likely
continue to rotate around the ridge, but the main contributor to the
higher chance of precipitation will be the collapse of the mid level
ridge. GFS forecast soundings completely destabilize Friday
afternoon with PWATs around 1.70" (at the 90th percentile for this
time of year). Have gone ahead and nudged PoPs up Friday afternoon
and kept towards a more diurnal component for Thursday evening into
Friday afternoon. The other concern for Friday will be the heat.
Highs will likely be around 90 degrees across the southwest and with
dewpoints in the lower 70s heat indicies will be near 100 (mid to
upper 90s for rest of the CWA). Due to the above have kept the
mention of high heat index values in the HWO for Wednesday through
Saturday).

Friday night into Saturday models have changed their tune with the
upper level low that was supposed to stay nearly stationary over the
Hudson Bay now more progressive with a surface cold front well
further north and east of the region. Due to this the track of the
heavier precipitation maximum (or potential MCS) with the embedded
short wave is now further north. Still though, with the mid level
heights falls, anomalously high PWATs, and instability rain will
remain in the forecast.

Sunday a short wave will dive southeast towards Michigan dragging a
surface cold front with it. Models quickly diverge here on
solutions. The GFS has the short wave heading east with the
retrograding upper level low finally being caught back up in the
main group velocity of the east coast long wave trough. This means
the front stalls across the area Monday with a surface low tracking
across the baroclinic zone Tuesday morning. The front then slowly
sags south Tuesday into Wednesday. The ECMWF is similar except the
upper level low disperses over southeast Texas. This allows the cold
front to clear the forecast area early Tuesday morning. For now have
leaned towards the GFS solution.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
Areas of MVFR fog have developed this morning with some patchy
IFR and lower vsbys in the river valleys, especially in the lower
Scioto Valley. This fog should dissipate within the first hour
or so of the TAF period with sct cu then developing through
late morning and into this afternoon. As we destabilize through
the day, it will be tough to rule out an isolated pop up shower
or thunderstorm. However, the chance appears low enough to
leave a mention out of the TAFs. Any pcpn should quickly
dissipate this evening, leaving mainly clear skies through the
overnight.

OUTLOOK...Thunderstorms are possible Friday and Saturday.
-- End Changed Discussion --

&&

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

&&

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