Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 292322
Area Forecast Discussion
National Weather Service Louisville KY
722 PM EDT FRI APR 29 2016
...Updated Aviation Discussion...
.SHORT TERM (Now through Saturday Night)...
Issued at 320 PM EDT Fri Apr 29 2016
The synoptic pattern this afternoon features a potent trough across
the Southern Plains. This trough will take on more of a negative
tilt as it ejects northeast into the Midwest, bringing chances for
showers/thunderstorms through the period.
An MCS continues to churn across portions of Dixie Alley early this
afternoon. The stratiform rain shield continues to slowly progress
ENE into portions of western KY, but is fighting increasingly dry
low-level air. Do think this shield of rain will get into portions
of south-central KY (with even a few lightning strikes possible),
but think it`ll struggle once it nears the I-64 corridor where the
drier air is more established.
As the aforementioned trough ejects into the Midwest, isentropic
lift will commence in response late tonight on the nose of a 55-knot
low-level jet. This will result in light shower activity initially
late tonight as the column saturates, but moisture advection will
markedly increase by mid/late morning Saturday as the low-level jet
veers into the Ohio Valley atop a surface warm front lifting north.
This will result in a swath of showers and thunderstorms, with the
best coverage expected along/west of I-65 in the late morning hours,
shifting northeast through the early afternoon. Can`t rule out some
small hail with this activity given the elevated instability, but no
severe weather is expected.
Just how fast we are able to clear out the precipitation Saturday
afternoon will set the stage for thunderstorm potential late
Saturday afternoon into Saturday night. As it looks now, areas
along and west of I-65 will get into the eastern edge of the best
instability axis. Convection should develop along the MS River
Valley in the afternoon beneath the exit region of an upper-level
jet streak, spreading east towards the region in the early evening
hours. The best threat for severe with this activity does appear to
be off to the west, but can`t rule out a few stronger storms getting
into the western LMK CWA tomorrow evening. Again, this threat will
likely be more fine-tuned once we see how the morning convection
plays out and where the eastern edge of the better instability sets
Showers and thunderstorms will become less numerous late Saturday
night after 06Z, but with the main upper-level forcing nosing in
during this time, still could see some showers/storms continuing
thus will continue with 40-60 pops.
.LONG TERM (Sunday through Friday)...
Issued at 335 PM EDT Fri Apr 29 2016
Low pressure will move up the Ohio Valley Sunday, dragging its cold
front through southern Indiana and central Kentucky Sunday evening.
At 5H a compact vort max will cross the Midwest with an associated
speed max taking a path from Missouri to Indiana. Added support for
storms will be provided by a 100kt jet streaming from the Desert
Southwest to New England. Shear will be strong and surface dew
points will climb into the lower 60s -- about 15 degrees above
climatology for the first day of May. Convective temperatures in the
mid 70s should be attainable, though widespread clouds and possible
morning showers may help to tamp down surface-based instability. If
storms can get going, then hail looks like the primary threat thanks
to WBZ heights around 8k feet.
Showers and storms will push off to the east Sunday night. The
forecast for the work week is something of a mess given significant
disagreement among models. GFS is more or less a compromise among
the GFS/EC/GEM, but cannot make any big changes to the forecast at
this time given lack of strong support for any particular outcome.
There has, though, been a consistent signal of deep upper troffing
digging into the eastern United States for the second half of the
upcoming week, providing us with cool temperatures. We`ll see lows
in some spots down into the 40s each morning Tuesday through Friday.
.AVIATION (00Z TAF Update)...
Updated at 722 PM EDT Fri Apr 29 2016
Complex low pressure advancing from the Red River Valley to the mid
Mississippi Valley will throw several rounds of showers and
thunderstorms at us through much of the TAF period, likely beginning
during the pre-dawn hours Saturday. Timing each round is a tricky
deal, and for now will broadbrush with -SHRA and VCTS. As individual
disturbances become more clear, timing and conditions will be fine-
tuned in the forecast.