Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 180049
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
848 PM EDT MON JUN 17 2013
Issued at 848 PM EDT Mon Jun 17 2013
Activity continues to wane this evening, as surface temperatures
have cooled resulting in diminishing surface instability. However,
a wave of isentropic ascent in advance of the approaching shortwave
trough continues to slide northeast across Kentucky, which should
keep showers and a few thunderstorms going for the next several
hours across portions of Kentucky and southern Indiana.
Southern Kentucky is enjoying a break for now, but additional
showers and isolated thunderstorms will continue to develop
northeast of a surface low progged to slide through TN. It remains
unclear just how widespread this activity will be, but a low-level
jet of 25-35 knots should help keep coverage up enough to warrant
50-60 pops across southern KY. Forecast soundings do show some
slight warming aloft, and with the loss of any surface-based
instability, think thunder overnight will remain rather isolated,
thus have kept only isolated thunder in the grids.
.SHORT TERM (Tonight through Tuesday night)...
Issued at 340 PM EDT Mon Jun 17 2013
Broadly cyclonic upper flow over the eastern CONUS will carry a
couple disturbances over the Ohio Valley through Tuesday night.
Moist and unstable low levels will fuel convection, but forecast
confidence is low due to uncertainty in timing of upper features,
and how convection will change the atmosphere for the next
Boundary extending from near Brandenburg to between Danville and
Somerset is serving as a focus for convection. Slow-moving storms
will mostly be heavy rain producers, but FTK has gotten 42 mph gusts
and pea-sized hail out of an isolated cell in the last 30 min. Will
highlight heavy rain and pulse wind potential from storms this
afternoon, but organized SVR is not likely.
Will ramp POPs up south of the boundary to account for activity that
may spread in from western KY/TN as we head into the evening. The
main shortwave will come through after midnight, so will expand POPs
northward for that. Likely POP south of the Parkways, but low-end
chance over southern Indiana as most of the forcing aloft looks to
remain over the Tennessee Valley.
Precip chances continue into Tuesday, especially in east central
Kentucky, in closer proximity to the boundary and surface reflection
of the upper disturbance. Slightly drier NE flow will serve as a
limiting factor, so will taper to lower POPs and warmer afternoon
temps west of I-65.
Upper shortwave trof currently diving out of the Upper Midwest will
finally kick this moisture out by midnight Tuesday night. This is a
slower progression than previously advertised, but there is good
agreement among the synoptic scale models. Therefore have introduced
a chance POP for Tuesday evening, albeit a low-QPF scenario. After
midnight the high over the Great Lakes should be able to build south
in earnest, resulting in a drying trend with below-normal temps and
.LONG TERM (Wednesday through Monday)...
Issued at 220 PM EDT Mon Jun 17 2013
This period mostly should be quiet. High pressure at the surface
will start off centered over the eastern Great Lakes. Precipitable
waters will fall to under an inch. By week`s end ridging aloft
should allow temperatures to warm back into the 90s, at least at
SDF, but drier surface dewpoints should make this heat wave a little
more bearable than the one last week. The ridge aloft will be
centered over the mid Mississippi river valley Sunday and Monday,
which despite increasing precipitable waters, should keep rain
chances low. Best chance, still slight, should be across our east.
.AVIATION (00Z TAF Update)...
Issued at 622 PM EDT Mon Jun 17 2013
Rather low-confidence forecast this evening, as several complexes of
thunderstorms have erupted across KY. Latest radar imagery shows a
feature moving through southern KY, which continues to push
northeast. This is likely a wave of isentropic ascent ahead of the
approaching system, which will continue to push northeast into KSDF
and KLEX over the next few hours, keeping the threat for
thunderstorms going there. Once this moves through, there may be a
brief break in the activity late this evening as instability wanes.
However, as the main shortwave trough and surface low approach
overnight, showers and thunderstorms will once again move into KY.
The best coverage overnight looks to be near KBWG, closest to the
surface low. Will carry MVFR restrictions for all of this activity,
but brief IFR conditions will be possible in the heaviest storms
early this evening and again overnight.
The storm system will push east by Tuesday afternoon, allowing for
improving conditions. Could be a stray shower or thunderstorm
developing tomorrow afternoon across mainly KBWG or KLEX, but
confidence is too low to include at this time. With the surface low
passing south of all terminals, winds will go from NE to more N
through the overnight hours into Tuesday morning, but should remain
rather light except in the heavier thunderstorms.