000
FXUS63 KLMK 151048
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
648 AM EDT WED MAY 15 2013

...Updated Aviation Discussion...

.Short Term (Today - Thursday)...
Issued at 300 AM EDT Wed May 15 2013

Expect mostly sunny skies today with gusty southwest winds as we
remain in a tight sfc pressure gradient between systems.  The main
forecast challenge for today will be temperatures and exactly how
warm we`ll get.  According to the latest model guidance, h85 temps
should be around 16-17 degrees C which would translate to temps in
the mid to upper 80s at the sfc using dry adiabats.  Based on
observed temps for Tues, think that this sounds reasonable.  As a
reference though in case temps over achieve, here are record highs
for May 15th:

SDF  92, 1900
BWG  92, 1962 & previous years
LEX  89, 1962
FFT  91, 1962 & previous years

Forecast highs for today are about 4-5 degrees below these records.

Late this afternoon we`ll see convection light up along a warm front
located over central IL/IN.  As we get into the evening hours, some
models indicate that this convection will work southward into our
southern IN and northern KY counties between 0-6Z.  This would most
likely be due to either the boundary sagging a bit farther south
and/or convection re-firing on outflow boundaries of initial storms
moving south into our area.  Either way, as convection becomes
farther displaced southward from the boundary and a nocturnal stable
layer starts to develop, think that showers/t-storms should become
elevated as they enter our area Wed night.  Perhaps a few could
contain gusty winds or small hail, but nothing near severe limits is
anticipated.

Late tonight, a weakening upper low pushing eastward out of the
southern Plains will spread vorticity into our region producing more
elevated showers/t-storms for the area late tonight into Thurs
morning.  This convection will move from WSW to ENE throughout the
morning hours Thurs.  By the time they exit southwest IN and north
central KY early in the afternoon, a few may once again be
able to become sfc based with some gusty winds or small hail
possible.  However, the overall wind column is not supportive of
strong storms.  With morning showers/storms spreading cloud cover
over most of the area, think that Thurs afternoon chances are less
than previously anticipated so have lowered POPs to 20-35% over most
areas Thurs afternoon into the evening hours.  However, it should be
noted that this is a complicated situation to follow so POPs may
need to be adjust Thurs afternoon based on the evolution of Thurs
morning`s convection.

With clouds/convection over the area tonight and Thurs, expect a
lower diurnal range of temps.  Lows tonight should remain in the low
to mid 60s for the most part.  Highs on Thurs will be highly
dependent on the exact timing of convection and whether or not we
get some breaks in the clouds Thurs afternoon.  For now, will base
temps on a mostly cloudy afternoon and go on the conservative side
with forecast highs in the upper 70s to around 80.

.Long Term (Thursday Night - Tuesday)...
Issued at 314 AM EDT Wed May 15 2013

Thursday Night - Friday Night...

A frontal boundary will remain draped across central Indiana and
southern Ohio as we end the work week. Meanwhile, shallow and weak
northwest flow will hold aloft. There are a few subtle shortwaves
forecast to traverse the area, most notably Thursday night and again
on Friday afternoon. Will continue the trend of putting the most
focus for coverage (scattered) of showers and storms across the
northeastern CWA close to the frontal boundary through this period.
South of I-64, coverage should be more isolated to widely scattered,
however enough moisture and modest instability will warrant pops
mainly from a diurnal convection standpoint. The overnight periods
should be mostly dry, but will still carry low pops. Expect lows
each night mainly in the lower 60s, and highs on Friday around 80.

Saturday - Sunday...

Upper level flow will begin to amplify across the CONUS over the
weekend as upper level ridging begins to develop over the east and
upstream troughing develops to the west. The Ohio Valley will find
itself to the northeast of the ridge axis on Saturday, with a moist
and more unstable airmass to work with. There is also some data
supporting a weak upper level disturbance traversing the region.
This will provide focus for better coverage of thunderstorms.
Forecast soundings offered by the GFS would suggest a heavy rain
threat as a tall and skinny CAPE profile combines with PWATs up
around 1.8 inches. Adding to the threat of heavy rain will be
generally weak flow through the column. Convection may linger into
Saturday night. Sunday becomes a little less certain as focus shifts
upstream to a developing system over the central Plains. Will leave
scattered showers and storms in the forecast to account for the
unstable and uncapped environment, although it is tough to really
place a triggering mechanism at this point due to difference in
model solutions. Overall, highs on Saturday and Sunday should be in
the low 80s, with mild overnight lows in the mid 60s.

Sunday Night - Tuesday...

As we head into early next week, upper level blocking ridge axis
will be east of the CWA, with an upstream trough across the central
Plains. A baroclinic zone will set up between these two features,
with the bulk of precipitation to our northwest on Sunday night and
Monday. As we head into Tuesday and Wednesday, it appears the
front will slowly slide eastward over the Ohio Valley, which
could provide a prolonged period of scattered to numerous showers
and storms as upstream blocking keeps the boundary from progressing
east too quickly. Better deep layer flow, along with instability may
lend to a stronger storm threat. Highs are expected to be in the low
80s, with lows in the mid 60s.

&&

.Aviation (12Z TAF Issuance)...
Issued at 645 AM EDT Wed May 15 2013

VFR conditions will prevail through the TAF period.  An area of
surface high pressure to the south across the northern Gulf of
Mexico and an area of low pressure passing across the Great Lakes
has placed the Ohio Valley within a fairly tight pressure gradient.
This gradient will promote southwesterly winds throughout the day
today, becoming gusty especially during the afternoon hours during
peak mixing (expected gusts between 20-25 knots). Despite a few
passing high clouds, skies will remain generally clear for much of
the day.  By this evening, convection along a warm front will light
up over central IL/IN.  As the night wares on, convection is
expected to enter all three terminals as a result of the boundary
sagging southward, possible outflows from evening storms, and added
vorticity from an upper level trough pushing into the region from
the west.  Have gone with VCSH for now although t-storms are
certainly possible.  Just not confident enough with the evolution of
storms tonight to nail down t-storm chances yet.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
KY...NONE.
$$


Short Term.......AMS
Long Term........BJS
Aviation.........AMS