Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 090150
Area Forecast Discussion
National Weather Service Louisville KY
950 PM EDT THU OCT 8 2015
Issued at 950 PM EDT Thu Oct 8 2015
Have a nice line of storms forming out ahead of the cold front
headed our way. Support for this line however should wane before it
reaches our area, but cannot rule out some showers making into our
southern Indiana counties before daybreak. Still looks like the best
focus for storms will be Friday late morning and into the afternoon
in our east and southeast forecast area. Forecast is pretty much on
track and only did a grid update to match obs.
.SHORT TERM (Now through Friday Night)...
Issued at 325 PM EDT Thu Oct 8 2015
The synoptic pattern this afternoon features split flow aloft, with
a strong cutoff low across the Desert Southwest and a PV anomaly
within the northern stream over the Northern Plains. This PV
anomaly will be the main focus of the long term as it will help
enhance precipitation chances across the region.
For this afternoon, expect mainly dry conditions to persist.
However, a weak PV anomaly is trekking across IL and southern IN this
afternoon into this evening. In response, weak isentropic lift and
surface moisture advection has enveloped portions of the TN Valley
which has caused a few showers to pop up. Some of this activity may
try to build northward into southern KY late this afternoon into
this evening, but do not expect coverage of measurable precipitation
to exceed 15%. Therefore, will continue with a dry forecast but do
not be surprised to see a few stray showers around.
For tonight, attention will turn northwest toward a cold front which
is currently draped across portions of Iowa. This front will
quickly drop southeast tonight entering the region by daybreak
Friday. The trend in guidance has been quicker with the frontal
passage. This is significant because this will keep the front out
ahead of the deeper ascent associated with the incoming PV anomaly
and associated jet streak. Therefore, coverage along the front in
the morning will be isolated to scattered given the lack of upper-
level forcing. However, the forcing should begin to overspread the
front by the early afternoon hours, which should increase shower and
thunderstorm coverage along the front by the early afternoon, mainly
across the southeastern part of the forecast area. Given the
quicker frontal progression outrunning the better forcing, have
lowered pops a bit for the northern part of the forecast area
(southern IN and northern KY). If the front continues to trend
quicker through the region, then even the southeastern CWA (Lake
Cumberland region) may miss out on the more widespread coverage of
showers/storms. This is a trend that will be monitored in coming
Given the quicker fropa, instability will struggle to build across
much of the area expect perhaps the southeastern CWA where anywhere
from 500-1000 J/kg will be present. This instability coupled with
the arrival of the deeper forcing should promote isolated to widely
scattered storm coverage by the early to mid afternoon hours over
south-central and east-central KY. Given only marginal deep-layer
shear values (30 knots) and the lack of more robust instability,
severe weather is not expected. However, a strong storm with gusty
winds is not completely out of the question especially if the front
is slower than is currently forecast.
Otherwise, the front will bring cooler and drier weather into the
region Friday night. After lows tonight in the 60s and highs
tomorrow in the mid 70s (perhaps near 80 in the southeastern CWA),
lows Friday night will dip into the upper 40s and lower 50s.
.LONG TERM (Saturday through Thursday)...
Issued at 245 PM EDT Thu Oct 8 2015
We`ll start the long term with a departing front and upper trough
Sat morning leaving behind low clouds. Low clouds will gradually
clear the region from NW to SE on Sat. The cooler airmass behind the
front combined with low clouds should limit high temps to the mid to
Sfc high pressure will dominate the region Sat night/Sun with upper
level ridging nudging in from the west. This will result in mostly
clear skies. With light winds and good rad cooling Sat night, lows
should drop into the 40s Sat night. Temps do look to recover Sunday
afternoon into the lower 70s.
A quick moving, moisture starved cold front and upper trough will
move through the region Mon/Monday night bringing mainly showers to
the area. At this point, coverage does not look great with models
disagreeing on exact timing so will go with 20-30% coverage Mon/Mon
night. Highs on Mon should recover well into the mid to upper 70s.
Another shot of seasonably cool air will arrive behind the front for
Tues causing highs to fall back into the upper 60s/lower 70s. We
should be dry for Tues/Wed with mostly clear skies.
.AVIATION (00Z TAF Update)...
Issued at 730 PM EDT Thu Oct 8 2015
Still cannot rule out a light shower this evening along and east of
a KBWG/KFFT line, as one upper-level impulse pushes east. Chance too
low though to put in the TAF. A cold front still on track to move
across the region at mid morninng for KSDF/KBWG and a couple hours
later for KLEX. Enough of the guidance is calling for a widely
scattered line of showers near KSDF around daybreak, so kept in the
previous vicinity wording for a couple of hours there. Expect more
development with just a little bit of heating over the KBWG/KLEX
corridor, so went with a longer period of vicinity showers there. A
rumble of thunder cannot be ruled out for those sites either, but
probabilities are in the slight chance range, so left them as