Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 242316
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
716 PM EDT Fri Apr 24 2015

...Updated Aviation Discussion...

.SHORT TERM (Now through Saturday Night)...
Issued at 325 PM EDT Fri Apr 24 2015

...Severe Weather Possible Saturday Afternoon and Evening...

Severe weather still looks to be a good bet for Saturday afternoon
as a mid level wave and its attendant surface low move through the
lower Ohio Valley. For tonight moisture will be on the increase as a
warm front moves in from the south. Some light showers will be
possible before midnight in association with a weak wave moving
through. However, the better chance for showers and possibly a few
thunderstorms will be after midnight through mid morning as the warm
front pushes north. These thunderstorms are not expected to be
severe at this time but could produce brief heavy rainfall.

The warm front will stall out across central Kentucky tomorrow
as the surface low drops southeast towards the area. Models continue
to indicate we should have a dry slot punching in south of the
front. This could lead to some clearing with temperatures warming
into the mid to upper 70s. In addition, moisture will continue to
pool south of the front with dewpoints rising into the lower 60s.
Through the afternoon the atmosphere will become unstable south of
the front with CAPE values rising to 1000-1500+ J/kg. Strong mid
level winds will result in effective shear of 50-60 knots. In
addition, helicity values will rise to 250+ m2/s2, with higher
values near the stalled front.

All in all, supercells will be the preferred storm mode with this
system. Very large hail and damaging winds could be present with any
supercell. Some of the storms could produce tornadoes as well,
particularly in the vicinity of the front. There is still some
uncertainty as to where exactly this front will end up. Currently
the NAM is the outlier and furthest to the south, so am leaning away
from its solution slightly. Currently it looks like the highest
threat for strong severe storms will be along and south of the I-64
corridor. However, a few strong to severe storms cannot be ruled out
north of there. These storms look to begin to develop around 3-4 pm
EDT and continue through around 10-11 pm.

In addition to the severe threat, there is some concern with heavy
rainfall potentially leading to some flash flooding. This would be
particularly a concern along the front and just to the north of it
where we could have some training of cells. The best chance for this
would be across southern IN and north central KY. This area has been
the wettest so far this month, so this will bear watching carefully
tomorrow as well.

.LONG TERM (Sunday through Friday)...
Issued at 315 PM EDT Fri Apr 24 2015

High impact weather is expected to be well south and east of the
region by Sunday morning.  However, a trailing mid-level wave and
cold front will swing through the region and bring an end to the
rainy weather.  It appears that the previous forecast remains on
track with precipitation ending by midday Sunday with high pressure
building into the region.  High pressure at the surface combined
with a northwesterly flow aloft will provide cool and dry weather
for the early part of next week.  Rather deep troughing is expected
to remain over the far eastern US as a series of upper level waves
rotate within a larger gyre aloft.  This closed upper low will
eventually move off to the east by midweek or so.  Temperatures
early next week will remain below seasonal normals with highs in the
upper 50s to the lower 60s.  Overnight lows will cool into the upper
30s to the lower 40s.

Around midweek, closed low coming out of the southern stream will
weaken and become an open wave as it gets into the southern Plains.
As this southern wave move eastward, a stronger northern stream wave
will continue to dive south rather sharply and may phase with that
southern stream system.  Should this occur, we would see rather
cloudy and showery conditions from Wednesday into early Thursday
before ridging builds back in from the west.  As we get into the
latter half of the week, the global ensemble guidance suggest that
ridging will build in from the west as a deep closed low moves off
the US east coast.  This will keep the Ohio Valley in a dry NW flow
with temperatures starting off cool but slowly moderating through
the end of the week.  Unseasonably cool temperatures will be the
rule on Wednesday with highs in the low-mid 60s, but we should see
near normal temps (upper 60s to lower 70s) return by Thursday and
continue into Friday.  Overnight lows look to be generally in the
mid-upper 40s.

&&

.AVIATION (00Z TAF Update)...
Updated at 715 PM EDT Fri Apr 24 2015

VFR conditions are expected at the terminals in the first six hours
of the TAF period.  A warm frontal boundary will lift northward
toward the region late tonight.  Widespread showers with some
embedded thunderstorms will be possible mainly after 25/06Z at KBWG
and after 25/07-08Z at KSDF and KLEX.  Surface winds will remain out
of the southeast this evening and into the overnight hours.  With
the frontal boundary and precipitation approaching, ceilings will
drop into the MVFR levels late tonight as well.  Current thinking is
that we should stay above IFR thresholds late tonight and through
early Saturday morning.  However, there is a slight chance that we
could see brief drops to IFR levels.

We expect shower and thunderstorm activity to diminish and move
northward and should generally clear the terminals after noon EDT
Saturday.  A temporary break in the precipitation looks likely with
ceilings scouring out in the afternoon.  Best shots of VFR look to
be down in the KBWG area Saturday afternoon, but we could have MVFR
ceilings hang in around KSDF and KLEX.  Surface winds Saturday
afternoon will be stout out of the SW with sustained speeds of
10-15kts with gusts to 20kts being possible.

Additional thunderstorms are expected to develop Saturday afternoon
as a low pressure system pushes in from the NW.  This will likely
bring a round of strong/severe storms to the terminals in the 25/21Z
through 26/03Z time frame.

00Z TAF Forecaster Confidence
=============================
Ceilings    : Medium
Visibilities: Medium
Winds       : High
=============================

&&

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

$$

Short Term........EER
Long Term.........MJ
Aviation..........MJ




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