Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 280238
Area Forecast Discussion
National Weather Service Louisville KY
1038 PM EDT WED JUL 27 2016
Issued at 1039 PM EDT Wed Jul 27 2016
...Flash Flood Watch Now In Effect...
Went ahead and started the Flash Flood Watch a few hours early as
flash flood threat continues to increase across our western portions
of the Watch area. Very high PWAT airmass (2.2-2.4) combined with a
slight uptick in 850 mb moisture transport has resulted in an
increase in coverage and impressive rainfall rates moving into our
western counties. Some of these areas have already picked up
impressive amounts over the last 24 hours so will be monitoring
closely for possible Flash Flood Warnings through the overnight.
Issued at 756 PM EDT Wed Jul 27 2016
...Flash Flood Threat Increasing Across our Western CWA...
Main focus for heavy rainfall will now shift toward complex coming
into our western CWA near Ohio County. Given previous heavy
rainfall, will be quick on the trigger for Flash Flood Warnings if
current radar presentation/rates hold together. Taking a quick look
at the environment, a 2.4-2.5 inch PWAT airmass is nosing up into
our region ahead of a weak upper low, with a slight uptick in low
level jetting likely adding to the deeper layer moisture convergence
into the area. Bottom line, is that latest mesoanalysis points
toward an increasing Flash Flood threat across western portions of
our CWA early this evening, likely extending northeastward through
the overnight. Like the plaecement of the current Flash Flood Watch,
although am a bit concerned that it could be a tier of counties
further northward. Keep an eye out for possible extensions northward
if data/radar trends allow for this.
.SHORT TERM (Now through Thursday Night)...
Issued at 310 PM EDT Wed Jul 27 2016
Earlier convection that dropped around 3 inches of rain in parts of
Ohio County this morning has left behind boundaries across central
Kentucky. These boundaries are serving as a focus for isolated to
scattered convection for the remainder of this afternoon, with
torrential rainfall and localized flooding as the main threat. Heat
of the afternoon will also provide just enough instability that
locally gusty winds are also possible, but expect most if not all
convection to remain sub-severe.
While some of the convection will die down this evning with the loss
of heating, the better moisture feed over the Pennyrile region will
likely keep storms going. After midnight, expect precip to spread
northeast, warranting likely POPs across most of the area by
daybreak. The upper trofiness will hold strong Thursday and Thursday
night, and with the very moist air mass still in place, as well as
the nearly stationary boundary parallel to the flow aloft, we`ll
have repeated showers and thunderstorms. Not necessarily expecting
an all-day rain, but will see enough intervals of moderate to heavy
rain to support likely/categorical POPs. High precipitation
efficiency will result in locally very intense rainfall rates at
time, with 2-3 inches in an hour or two not out of the question.
Localized flash flooding is a good enough bet to warrant a Flash
Flood Watch late tonight through Thursday night, generally along and
south of the Western Kentucky and Bluegrass Parkways. Localized
flooding is still a possibility anywhere in the CWA, but the
probabilities do diminish as you head north. Widespread QPF through
Friday is 2-3 inches in the watch area, with lesser amounts to the
.LONG TERM (Friday through Wednesday)...
Issued at 320 PM EDT Wed Jul 27 2016
High chance/low likely POPs will continue into Friday as the broad
upper trof remains in control for most of the eastern CONUS. Will
continue with warm and humid conditions and scattered, mostly
diurnal convection for much of the weekend. By Sunday/Monday, the
trof axis shifts just far enough to the east to get rid of some of
the deeper moisture, resulting in more isolated POPs as we head into
next week. Western CONUS ridge tries to build into the Ohio Valley
heading into the middle of the work week, but can`t really take out
POPs or push temps too high given the difficulty in amplifying the
pattern this season. No day looks like a washout, but it`s also
difficult to zero in on any dry day. Temps will run near seasonal
normals by day, and a bit above by night.
.AVIATION (00Z TAF Update)...
Issued at 734 PM EDT Wed Jul 27 2016
Low confidence forecast for this evening as thunderstorm evolution
is tough to pin down. Expect current convective activity over SDF to
diminish by the time this new cycle takes effect at 00z, so will
start out with a period of VFR and dry at all TAF sites. Winds
should be variable through the evening hours as remnant outflow
boundaries continue to float around.
Focus will then be from around midnight and into the pre-dawn hours
as several signs point to an increase in deep moisture ahead of a
weak upper low. Already seeing signs of an increase in t-storm
coverage over the lower Ohio River Valley and expect this could
project into our region overnight. Tried to hint at the best timing
with some VC wording, but not confident enough to pull the trigger
on prevailing TSRA at this time. Most likely spots for any TSRA
would be at BWG/SDF in the 03 to 10 z time frame, but again not
confident enough to to nail it down at this time. Main impacts would
be torrential rainfall, gusty winds, and a vis restrictions.
Some vis restrictions could be around for sunrise, but the focus
shifts to numerous showers and t-storms through the day.
KY...Flash Flood Watch through Friday morning for KYZ026>028-039>043-