Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 260437
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1237 AM EDT Tue May 26 2015

...Updated Aviation Discussion...

...Forecast Update...
Updated 940 PM EDT Mon May 25 2015

Precip that carried into the late afternoon has dissipated as it
moved into eastern Kentucky this evening. Looks like much of the
overnight period will be dry, even though it wouldn`t be surprising
to see a stray shower somewhere in this juicy air mass.

Forecast confidence is somewhat limited as high-resolution models
all seem to be too slow with the convection pushing out of the Red
River Valley and into Arkansas. Still believe the upper disturbance
associated with this convection will be the main player in shower
and T-storm chances ramping back up over the Ohio Valley. Will keep
much of the overnight dry, but precip chances will return after
about 08-09Z in the west. Given due north movement and what we saw
earlier this morning, still not ready to trust that batch of rain
over eastern Tennessee. Therefore the counties closest to the
Cumberland Escarpment will hold on to a 20 POP for most of the
night.

Products have been updated to better capture the details of precip
timing.

.SHORT TERM (Now through Tuesday Night)...
Issued at 330 PM EDT Mon May 25 2015

Mostly cloudy conditions were noted across the forecast area this
afternoon.  A mid-level wave was riding northeastward along the
western periphery of a mid-level ridge axis centered well to our
east.  Area radars show a large area of rain extending from near
Bowling Green northeastward to near Frankfort.  This area of rain
will continue to move off to the east/northeast during the remainder
of the afternoon.  Areas west of I-65 in IN and KY are expected to
see drier conditions as we head into the evening hours.
Temperatures have remained on the cool side of the guidance envelope
in the west/central due to ongoing cloudiness.  Afternoon readings
ranged from the upper 70s to near 80 in the I-75 corridor with upper
60s to the lower 70s in area out from I-65 and points west.  There
may be a little bit of temp recovery in our central/west sections as
the rain shield shifts eastward.

For tonight, mid-level wave over us now will continue to trek off to
the northeast. This should result in a decrease in precipitation
this evening and into the overnight hours.  A persistent southerly
flow will keep temperatures warm though, with overnight lows in the
mid-upper 60s.  Mid-level wave currently over TX will lift
northeastward late tonight and into the Mid-Mississippi Valley
toward morning.  This may result in some additional shower develop
late tonight over our far west/southwest sections.  However, much of
the region looks to remain generally dry overnight.

For Tuesday, upper level wave will approach the region from the
southwest.  This should allow precipitation to spread into western
KY during the morning hours...especially in areas west of I-65.  As
this system approaches, model forecast soundings for tomorrow
afternoon show a moderately unstable atmosphere with mixed layer
CAPE values in the 1700-2600 J/KG range.  Wind profiles remain
rather strong (especially with strong speed shear in the mid-levels)
though not much low level speed/directional shear is forecast.  With
the wave approaching, atmosphere looks to be a bit more favorable
for organized strong/severe convection tomorrow afternoon.  Initial
thinking is that multi-cellular and multi-line convection will
likely develop in the afternoon in/around the I-65 corridor and then
push eastward.  Overall profiles suggest a damaging wind threat with
these storms...especially in areas along/east of I-65.  In addition
to the wind threat, heavy rainfall will be possible with any of the
storms.

Confidence in the development of severe convection is still a little
below average here due to the possibility of morning convection
disrupting the destabilization process for the afternoon.  The
cloudiness also will make forecasting high temperatures a challenge
as well.  Have leaned heavily on the multi-model consensus here with
highs in the low 80s in the east and upper 70s in the west.

Bulk of the convection is likely to push off to the east tomorrow
evening, but some additional scattered convection will be possible
overnight Tuesday/into Wednesday.  Lows tomorrow night look to cool
into the mid-upper 60s.

.LONG TERM (Wednesday through Monday)...
Issued at 315 PM EDT Mon May 25 2015

Wednesday - Wednesday Night...

SW flow through a deep layer will be in place on Wednesday, with
scattered showers/storms ongoing across our eastern CWA on Wednesday
morning. This precipitation will be ahead of a disturbance embedded
within the flow, and will leave a subsident airmass in their wake as
they diminish by late morning/midday. Expect a fairly quite early
and mid afternoon as the stable airmass then tries to destabilize
under increasingly less cloudy skies across the west. There is a
possibility of more scattered showers/storms then working into our
NW CWA late afternoon ahead of a weak cool front trailing from a
system moving into SE Ontario. So in summary, expect scattered
convective coverage generally in our east in the morning, and
focused across our NW in the late afternoon. The NW should see more
sun through much of the day so will go with low 80s there, and upper
70s east.

The weak cool front will wash out over our CWA on Wednesday night
with scattered showers/storms slowly diminishing across the center
part of our CWA. Expect lows in the mid 60s.

Thursday - Friday Night...

Expecting less in the way of storm coverage Thursday through Friday
night as a SE CONUS upper ridge becomes more established over the
Ohio River Valley, and pushes the stronger westerlies north. This
will set the stage for an "early summer-like" pattern where moderate
afternoon instability will give way to isolated to widely scattered
storms. Expect week flow through the atmospheric column, so nothing
organized during this time. Highs should be warmer given more peaks
at the sun, so calling for mid and upper 80s. Lows each night should
mostly range in the 65-70 range.

Saturday - Monday...

A stronger shortwave will move across the northern Great Lakes to
eastern Quebec on Saturday, helping to suppress the SE CONUS ridge
over our region. This will allow the trailing cold front from the
aforementioned system to work into our CWA and should provide
slightly better focus for convection. Main focus should be across
our NW where Sct-Num coverage should exist. More widely scattered
coverage is expected east. Saturday won`t be a washout as it will
take until the afternoon to kick off precipitation. So, expecting
temps to reach the mid 80s for highs.

The frontal boundary will still be in the region through the weekend
and into the first part of next week. Meanwhile, weak forcing for
ascent is anticipated ahead of a slowly ejecting southern Plains
disturbance. So, will keep mainly diurnally driven chances going
during this period. This won`t be a wash out, however several
chances for precip should present themselves mainly each
afternoon/evening and with any subtle disturbance causing local
mesoscale convergence sufficient to kick of showers/storms. Temps
will be dependent on position/orientation of the frontal boundary,
but should generally be in the upper 70s or lower 80s dependent on
which side you are on.

Overall, the threat for severe is expected to be pretty low through
the long term, although not zero. Early in the weak, instability
will be more plentiful so can`t rule out a pulse storm or two. Later
in the weekend and into Monday, better (still marginal) deep layer
flow will be in place with less in the way of instability. Some
places may accumulate decent rainfall amounts if they see repeated
t-storm activity.

&&

.AVIATION (06Z TAF Update)...
Updated 1230 AM EDT Tue May 26 2015

Plan on scattered/broken high clouds early this morning with
light south/southwest flow. Any breaks could result in a brief
period of fog at BWG/LEX. Surrounding obs have bounced in the 1-2 sm
range but as more clouds across TN move in, this should keep fog
potential and duration to a minimum.

Tightening pressure gradient later this morning and this afternoon
will result in south gusts 20-25 kts. An approaching weather system,
combined with a moist/unstable airmass, could bring a round of
thunderstorms through central KY. Current timing would be from
17-18z to 22-23z.

There are some suggestions that a weaker, more subtle wave could
linger through this evening and tonight, keeping isolated/scattered
showers around. Confidence isn`t high enough at this time to include
in the TAF.

Forecast Confidence
======================
Ceilings:   High
Visibility: Medium
Winds:      High
T-storm:    Medium

&&

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

$$

Update.........RAS
Short Term.....MJ
Long Term......BJS
Aviation.......ZT






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