Scientific Forecaster Discussion
fxus63 klmk 232146
Area forecast discussion
National Weather Service Louisville Kentucky
546 PM EDT Tue may 23 2017
Issued at 546 PM EDT Tue may 23 2017
Breaks in the cirrus/ac have allowed instability to increase over
southeastern portions of central Kentucky ahead of surface low
pressure east of Nashville. A corridor of slightly negative Li and
SBCAPE near 1000 east of I-65, combined with some deep moisture
convergence and a weak pool of slightly cooler temperatures aloft,
has led to thunderstorm development west of Lake Cumberland. The
storms will move to the northeast and should begin to weaken as the
sun continues to lower.
Grids and related products have been updated for the thunderstorms.
Short term (now through wednesday)...
issued at 330 PM EDT Tue may 23 2017
..much cooler and rainy overnight and Wednesday...
A deepening upper low over Iowa will dive south to Missouri
overnight. Meanwhile, the southern stream shortwave that brought a
few light showers to the Lake Cumberland region this morning will
continue exiting to the northeast. Still can't rule out an isolated
light shower over the southeast County Warning Area this evening. Otherwise, the vast
majority of folks will stay dry this evening under partly to mostly
Steady pressure falls continue across the area this afternoon as a
broad area of low pressure develops. Scattered showers and a few
thunderstorms have developed along a weak cold front from Illinois down
into MO. East of the Mississippi, this activity will track to the
In addition to the upper low dropping south, a vigorous shortwave
currently over the Red River valley is forecast to swing around the
base of the trough to Dixie by 12z. This wave then swings due north
into the Ohio Valley tomorrow as it wraps into parent circulation.
The result will be rapid pressure falls and widespread rain over
central Kentucky and southern in very late tonight through Wednesday
morning. Some of the latest hi-res guidance would suggest we could
see an mesoscale convective vortex develop and track north through east-central KY, with an
associated threat for localized gusty winds. Isolated storms will be
possible, especially by mid to late morning. Another risk is minor
flooding, particularly in areas that received heavy rainfall over
the weekend (washington and Scott counties in indiana).
Model thicknesses and widespread rain suggest highs remaining in the
60s for Wednesday. Rain will likely become more scattered by late
afternoon or the evening, but isolated to scattered showers will
continue overnight. Lows will fall into the low to mid 50s.
Long term (wednesday night through monday)...
issued at 345 PM EDT Tue may 23 2017
..chilly weather Thu...
..Warmer for the Memorial Day weekend with mesoscale convective system activity...
As the upper low spins overhead, a shot of wrap-around moisture will
bring more widespread showers once again Thursday morning. Shower
activity could remain more scattered across the southwest.
Temperatures will remain well below normal with highs in the mid 60s
to low 70s. Instability will be limited, but much cooler air aloft
could result in some graupel or pea-size hail.
Friday is a brief warmup as shortwave ridging crosses the region
with thicknesses supporting upper 70s to low 80s with sunshine.
Clouds will be moving in late in the day though.
A warm front will lift out of Arkansas/OK and move to near ind-cvg by Sat
morning. Depending on where this sets up is critical to the pops.
Mid-level waves ejecting through west-southwest flow aloft along this boundary
should lead to mesoscale convective system development for the Holiday weekend, but the
precise location of the boundary will change the rain and
temperature forecast significantly. Blended guidance remains below
the likely range for rain and thunderstorms over the weekend, so
will maintain current forecast.
Aviation (18z taf update)...
issued at 120 PM EDT Tue may 23 2017
Pressures areawide are steadily dropping this hour as a broad upper
low approaches the region. The gradient is very loose across the
region however, and that is leading to more light and variable
winds. We really shouldn't see any focus in direction until during
the day Wednesday, as a meso-low develops...but confidence in
exactly where that develops is too low to put in the tafs at this
time. We do have confidence in increasing rain chances and poorer
flying conditions during the morning hours, where low-end MVFR
conditions are expected, if not IFR. These conditions will persist
to the end of the period.