Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 281243

843 AM EDT Thu May 28 2015

...Forecast Update...
Updated 840 AM EDT Thu May 28 2015

Complicated forecast for today as multiple factors will affect if we
get storms. On radar now are some light rain showers over the Lake
Cumberland area extending south into TN. These are ahead of a
slow-moving shortwave over the TN Valley. In addition we have a weak
front located near the Ohio River, with a theta-e ridge axis ahead
of it. There are no showers associated with this feature, instead we
have low clouds. These clouds and some patches of fog should limit
destabilization. Thus have trimmed back pops for the morning hours
along the Ohio River , but kept values in the 30-40 range for south
central KY.

This afternoon`s development will depend on how quick the clouds
erode. Still think the best shot will be with the slow-moving
shortwave, so have continued the focus in the southern part of the
area. Though any clearing up north could lead to isolated storm
development. Storm motion should be fairly slow given forecast
soundings with little flow in the low levels. Not worried about any
kind of flood issues with the slow flow however as precipitable
waters are not too high. Also, we should not have any issues with
severe weather.

Updated 650 AM EDT Thu May 28 2015

Convection has remained limited to south central KY this morning so
will remove POPs elsewhere before 12Z.  Still think we`ll see an up
tick in shower/storm activity by mid to late morning as the upper
level disturbance moves in from the south.  Patchy fog with some
locally dense patches have been observed.  Visibilities have varied
greatly this morning with isld reports of dense fog.  Therefore will
issue an SPS for patchy dense fog for the next few hours.  Fog
should improve fairly quickly this morning.

.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

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

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

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 (12Z TAF Update)...
Updated 650 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 day.  With plentiful
sfc moisture from recent rains and very light or calm sfc winds, fog
and low stratus have developed across the region but overall don`t
appear to be affecting the TAF sites as bad as previously thought.
IFR conditions will continue at SDF through the next few hours.
BWG/LEX may go down to MVFR levels briefly 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 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.




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