Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 261054
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
654 AM EDT Sat Jul 26 2014

...Updated Aviation Discussion...

.SHORT TERM (Now through Sunday)...
Issued at 355 AM EDT Sat Jul 26 2014

...Increasing confidence for severe threat tonight through Sunday...

Saturday:

During the day today, the weather is expected to be relatively
benign for much of the forecast area with clouds cluttering the
skies as afternoon heating kicks in. Have kept much of the area dry
with precip chances increasing as the evening hours approach.
Southwesterly winds will also increase today as high pressure exits
the region and allows for a tightening pressure gradient, thanks to
a surface low pushing its way in behind it. Throughout the day, look
for increasing warm, moist air to advect into the region, charging
the atmosphere up for what`s to come tonight. Expect highs to be
much warmer than Friday, near or slightly above 90 degrees with
higher dewpoints.

Saturday night:

As the headline indicates, severe potential for tonight appears to
be likely over southern IN and northern KY. The primary question
will be the timing of this well-advertised MCS. Hi-res models are in
general agreement of it entering the far western counties around 02Z
and plowing its way across the forecast area, affecting the
Louisville and possibly Lexington metro areas, before exiting
sometime after 06Z. The secondary question is how far east the
severe threat will reach but it appears as though the MCS will begin
its decay after it gets through the Louisville metro as it loses
some of its support. PWATs increasing to around 2 inches, increasing
low- to mid-level shear, 2000+ J/kg of MUCAPE, and steep lapse rates
will all combine to create a damaging wind threat along with heavy
rainfall. These parameters look to be their highest along and north
of the I-64 corridor and west of I-65 in southern IN. A few models
are hinting at multiple rounds of weather even after the MCS has
paid a visit so have left mentionable PoPs through early Sunday but
this activity, if it occurs, should remain below severe criteria.

Temperatures will likely remain steady through the overnight period,
only dropping down into the low to mid 70s.

Sunday:

The severe threat continues into Sunday with the focus shifting to
the southern and eastern counties as a cold front approaches from
the north. However, uncertainty remains in the details of how things
will pan out as it will largely depend on early morning convection.
If the MCS does come through earlier in the evening on Saturday and
no other development occurs, then model soundings are indicating
that the damaging wind threat, heavy rainfall, and additionally hail
will be a major concern. Classic inverted V soundings can be seen in
the latest run of the GFS (00Z), especially in southern KY where the
airmass will likely not be worked over. Stay tuned for more details
as this time approaches.

Highs on Sunday are currently forecast to be a degree or two cooler
than Saturday but still reaching the upper 80s and low 90s,
especially in the south. Even with cloud cover potentially lingering
around from overnight convection, the WAA ahead of the front will be
in high gear and should push up those temps regardless. Dewpoints
will also continue to be on the high side - into the 70s.

.LONG TERM (Sunday night through Friday)...
Issued at 320 AM EDT Sat Jul 26 2014

Showers and storms should be exiting south central and east central
KY Sun evening at the beginning of the long term period.  Some of
these storms could be strong to severe in nature Sun evening
although it looks like the cold front will move through during the
evening hours so any stronger storms should be moving out fairly
quickly Sun night.  A massive upper level trough will overtake the
Midwest bringing another round of cool air.  We`ll see one more
chance at some light rain showers over the area as energy along a
secondary front pushes through the area Monday.

Tues/Wed/Thurs will be dry and pleasant as cool Canadian high
pressure drifts south into the Midwest.  Under mostly sunny skies,
high temps will range from the mid 70s to the lower 80s with lows in
the upper 50s and lower 60s.

Shower/storm chances will arrive once again for Friday and through
the weekend as the upper trough hangs over the Midwest with ridging
over the western CONUS.  A split flow pattern will try to develop
during the weekend possibly resulting in an upper low becoming cut
off over the Midwest.  Should this pattern pan out, several rain
chances will be in store with unseasonably cool temps for next
weekend.

&&

.AVIATION (12Z TAF Update)...
Issued at 652 AM EDT Sat Jul 26 2014

VFR conditions are expected to continue to prevail now through this
evening but then becomes more questionable as an MCS is expected to
develop and directly impact southern IN and northern KY. Have
continued to carry VCTS in this update for SDF given confidence in
thunderstorm activity in and around the terminal. Additionally, have
introduced VCTS mention in the LEX TAF to account for the MCS to
track into the Bluegrass region. However, less confidence exists for
the exact timing as these systems have a tendency to accelerate
beyond what the models are able to capture. For this update, have
bumped up the time frame by an hour, putting SDF in the 03Z-07Z
range and LEX in the 05Z-09Z time frame. BWG should escape direct
impact from this MCS but could still see some concerns to aviation
interests as it brushes past to the north.

By midday Saturday, the pressure gradient will tighten over the Ohio
Valley as a surface low vies to move right on in behind an exiting
high pressure, approaching the southern Great Lakes from the Plains
by the end of this TAF period. Winds for much of Saturday are
expected to be greater than 10 knots and from the southwest, gusty
at times. Winds could briefly die down as the sun sets at SDF but
are anticipated to pick back up with the approaching MCS.

&&

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

$$

Short Term........lg
Long Term.........AMS
Aviation..........lg




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