Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 250714
Area Forecast Discussion
National Weather Service Louisville KY
314 AM EDT MON JUL 25 2016
.SHORT TERM (Now through Tuesday)...
Issued at 301 AM EDT Mon Jul 25 2016
The synoptic pattern early this morning features a strong ridge
aloft holding on across much of the south-central CONUS, with a
piece of that ridge centered over the mid-Atlantic region. A trough
moving through the Great Lakes and southern Canada this morning will
knock the ridge down just enough to bring better chances for
thunderstorms through the period.
We continue to watch a decaying MCS to our north early this morning.
Satellite trends have shown substantial cloud top warming with this
convection over the past hour or two, with its appearance on radar
also becoming more ragged. An outflow boundary has raced out of
this convection and is currently located across southwestern IN,
arcing northeast into central IN.
There will be a couple of potential foci for convective development
today. One could occur as early as this morning. It is once again
not a banner day for model guidance as many members, including the
CAMs, are not handling ongoing convection well. That being said,
NSSL-WRF seemed to be doing fairly well this morning and largely
trended the forecast towards its solution. This solution, which has
support from the HRRR, breaks some isolated/scattered convection out
across the Ohio Valley this morning aided by the approaching outflow
boundary and perhaps a weak vort lobe rounding the Mid-Atlantic
ridge. Therefore, will up pops a bit this morning and continue to
watch trends over the next couple of hours. The main outflow
boundary will continue to sag along and to the south of the Ohio
River this afternoon, serving as a convective focus across central
and south-central KY. A weak synoptic front, currently located
across northern IL, will sag into southern IN and northern KY late
this afternoon and early this evening, perhaps serving as an
additional focus for convection in these regions assuming they can
destabilize sufficiently behind the approaching outflow boundary
(and under some convective debris) from the decaying MCS this
morning. Will keep pops just under the likely range today, but once
these boundaries` locations are fine-tuned, likely pops may be
needed in future updates. Weak tropospheric flow will persist
today, thus the storms will be slow-moving and pulse-like in nature.
However, wet microbursts will be possible in the deeper cores, and
localized flash flooding will also be possible given the expected
slow storm motions.
Outside of thunderstorms, heat will once again build today. With
moisture pooling ahead of the sagging boundaries, dewpoints will
likely hold in the mid to even upper 70s this afternoon. The
thought is that developing convection and cloud cover should help
keep highs confined to the low 90s, but some isolated locations
could push the mid 90s which would push heat index values above Heat
Advisory criteria (105) for a time this afternoon. If these areas
appear as if they will become more widespread through the morning
hours, a short-fused Heat Advisory may not be out of the question
for portions of the region.
Convection will diurnally wane tonight. However, the synoptic
boundary will likely stall over the region through Tuesday, which
will keep showers and thunderstorms in the forecast tomorrow. Given
the northerly bias in guidance the past few weeks with respect to
effective boundary placement, have favored a more southerly solution
for pops tomorrow which puts the highest values in central and south-
.LONG TERM (Tuesday Night through Sunday)...
Issued at 310 AM EDT Mon Jul 25 2016
The synoptic pattern at the start of the long term period will
feature a weakening subtropical ridge, which will allow more of a
weak trough aloft to build into the Ohio Valley through the period.
This will bring cooler, but continued unsettled weather to the
region through the end of the week.
Synoptically, it appears the best chances for precipitation in the
long term period will come Thursday and perhaps into Friday as a
trough slides through the lower Great Lakes and Ohio Valley region.
This trough may be amplified enough to push a stalled front through
the region late Saturday into Sunday, which should help dry things
out (at least the northern CWA) by the second half of the weekend.
Will trend the forecast in that direction with this package.
Otherwise, given the expected convection, temperatures will be a bit
cooler late this week into this weekend with highs only expected in
the mid 80s Thursday through the upcoming weekend.
.AVIATION (06Z TAF Update)...
Issued at 125 AM EDT Sun Jul 25 2016
VFR conditions are expected for much of the overnight at the TAF
sites. Probably will see a little bit of haze develop at KSDF
between 25/10-13Z. Cu field will redevelop after 25/15Z and a front
will continue to push down from the north. Convective allowing
models show scattered storms developing around 25/18Z and lasting
through about 26/00-01Z. So we will keep the PROB30 groups going in
the TAFs. Surface winds will be light and variable overnight with a
southwest flow expected this afternoon.