Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 280707
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
307 AM EDT Thu May 28 2015

.SHORT TERM (Now through Friday)...
Issued at 245 AM EDT Thu May 28 2015

Early this morning a weak sfc front was just to our NW while an
upper level impulse was approaching from the southern states.  While
we sit in between these features during the pre-dawn hours, patchy
fog is expected to develop.  Plentiful low level moisture and very
light or calm winds will help fog formation, however, a thick upper
level cloud deck should work to prevent fog from becoming dense in
nature.

As the sfc front and upper level impulse move into the Ohio Valley,
shower/storms will begin to fire over our region around sunrise.
Isld to sct convection will stick with us throughout the day as we
remain in a moist, unstable environment.  Weak trigger mechanisms
and overall wind profiles suggest that convection should remain
below severe limits today.  Still some strong storms with small hail
and strong wind gusts may occur especially this afternoon when CAPE
levels and lapse rates are more favorable.  With slightly less
coverage of precip compared to yesterday, temps should warm into the
low to mid 80s.

Tonight models indicate convection will diminish after sunset with a
dry period expected during the overnight hours.  Models indicate a
weak impulse may bring renewed convection to the area just before
sunset.  Still others would suggest that partial clearing combined
with light winds and moist low levels would again be good for light
patchy fog formation.  Low temps tonight should range through the
60s.

More isld-scattered storms are expected Friday as a weak impulse
pushes through the region.  Again no organized severe weather threat
is expected.  High temps for Fri should be in the lower 80s.

.LONG TERM (Friday Night through Wednesday)...
Issued at 300 AM EDT Thu May 28 2015

Latest 00z GFS and ECMWF models are in reasonable agreement with
synoptic pattern in extended forecast, indicating unsettled weather
with periodic showers and thunderstorms. General mid-level troughing
over the central Plains on Friday is forecast to evolve into a
slow-moving cutoff low over the mid-to-lower Mississippi Valley late
this weekend and through the early and mid parts of next week. Ahead
of this feature will be a persistent feed of low-level moist
southerly air over much of the Ohio and Tennessee Valleys, including
central Kentucky and south-central Indiana.

As the mid-level low closes off to our west, it will induce a weak
surface low to our west along a cold front which will sag slowly
southeast into the lower Ohio Valley including Kentucky over the
weekend and early next week. Scattered showers Friday night will
transition to more numerous showers and thunderstorms Saturday
afternoon through Sunday night. Difficult to pinpoint where greatest
coverage of rainfall will be over the weekend, but along and north
of the front is favored at night, and along and south of the front
is favored during the day within greater low-level instability. This
includes much of central Kentucky and southern Indiana.

At this time, wind fields/system dynamics do not support much severe
weather, but a few strong pulse storms are possible from time to
time especially over central Kentucky south of the front during the
afternoons. However, persistent precipitable water values of 1.5-1.8
inches, deep warm cloud depths, moist model soundings, and moisture
replenishment courtesy of continued low-level inflow suggest periods
of heavy rainfall from many of the storms over the weekend.

During the early and mid parts of next week, the surface front is
forecast to move back north and/or become more ill-defined. With a
persistent moist atmosphere and the mid-level low/trough still to
our south and/or west, more showers and thunderstorms are expected
but overall coverage should diminish with the activity becoming more
diurnally-driven, i.e., a relative max in activity in the afternoon
and early evening, with spotty showers overnight. In this regime,
there could be patchy fog during the overnight periods as well. By
late next week, the evolution of the low/trough becomes tenuous, so
expect lower chances of precip. Overall, there will be a chance of
precip every day of the extended but it won`t rain everywhere
everyday.

Temperatures over the weekend will be dependent on the frontal
position, as there should be a decent difference north to south
across it. Temperatures will also be modulated by where precip is
most prevalent. Next week, daytime temperatures should be seasonal
in general with values modulated by several opportunities for precip
and ample cloud cover. Temperatures at night should remain mild in
most areas.

&&

.AVIATION (06Z TAF Update)...
Updated 115 AM EDT Thu May 28 2015

The main TAF challenges for this issuance will include low cigs/fog
early this morning and timing the next round of showers/storms
through the region later today.  Currently a sfc front was
approaching from the NW with an upper level impulse pushing north
from TN.  Our region remains in between these features attm, but
each will infringe upon the area throughout the TAF period.  With
plentiful moisture from rains early today and sfc winds expected to
turn light or calm during the pre-dawn hours, fog and low stratus is
expected to drop flight conditions to at least MVFR/IFR and possibly
lower.  Flight restrictions will be most severe between 10-13Z this
morning.  Conditions should improve after sunrise, but convection
looks to fire along the aforementioned synoptic features and result
in isld-sct coverage of showers/storms mainly from just after
sunrise through late afternoon.  It`s a little difficult to pinpoint
an exact window of opportunity for the TAF sites to receive a
t-storm today so will stick with VCTS and see how convection evolves
throughout the day.  Although flight conditions could be reduced to
MVFR/IFR in any t-storm, prevailing flight conditions should
generally return to VFR after sunrise this morning.  Winds will be
ENE at BWG/SDF and more SSE at LEX during the daylight hours today.

&&

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

$$

Short Term........AMS
Long Term.........TWF
Aviation..........AMS





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