Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 210724

Area Forecast Discussion
National Weather Service Louisville KY
324 AM EDT Mon Aug 21 2017

.Short Term...(Today through Tuesday)
Issued at 310 AM EDT Mon Aug 21 2017

Solar Eclipse Weather Today...

Solar eclipse day has finally arrived. A dry weather day is expected
across central KY and south-central IN for this historic event. The
main concern centers on the amount of cloud cover as the eclipse
passes across our area. Currently, there is a an area of high clouds
over MO and southern IL. High res models suggest these clouds will
move eastward today with at least some high cirrus over central KY,
although the clouds should thin with time. Meanwhile, a mesoscale
convective system (MCS) over IA at this time should expand and
propagate east-southeast through the morning hours. This will spread
high-level convective debris clouds east-southeast into IL,
eventually IN, and possibly into KY by late this morning or early
afternoon. Also, scattered diurnal cumulus clouds should begin
developing just before the period of eclipse totality. Bottom line,
expect scattered lower clouds and scattered high clouds that could
potentially have a slight negative effect on the eclipse, but should
still permit ample viewing under a partly to mostly sunny sky. We
will continue to evaluate cloud cover trends through the morning and
early afternoon today.

Temperatures will rise quickly this morning, but fall a few degrees
just before and during the max eclipse period early this afternoon,
especially in our far southwest counties where totality occurs (less
effect farther northeast). Temperatures will then rebound and top
out in the lower 90s in most areas by late in the day. With expected
humidity levels, heat indices should rise into the mid to perhaps
upper 90s right before the eclipse in our southwest counties near
the zone of totality, then fall back a few degrees, before reaching
the mid to upper 90s again late afternoon. Elsewhere, expect max
heat indices in the mid 90s late this afternoon. Expect a south to
southwest wind of 5-10 mph. Use caution when outside today due to
the heat and humidity. Will continue to issue a Special Weather
Statement to highlight this.

High res models suggest that scattered convection could develop late
this afternoon over parts of central/srn IL into central IN from
outflow from the current MCS over IA. However, these are expected to
remain just north and west of our area.

Tonight and Tuesday...

Skies should be mostly clear/partly cloudy tonight. However, as a
shortwave trough aloft moves eastward across the Plains and into the
mid MS Valley, convection is likely to develop to our north and west
with convective debris clouds increasing by Tuesday morning over our
northern counties. Lows should be around 70 or lower 70s in most
areas, except mid 70s in Louisville.

As the trough pushes eastward on Tuesday, a surface cold front will
settle southeast. The air mass should become moderately unstable
ahead of this feature. While deep-layer shear values should only be
modest, forcing should be sufficient for numerous showers and
thunderstorms Tuesday afternoon over south-central IN and then
central KY into the evening within the right entrance region of a
modest jet streak aloft. This favors convective evolution into a
couple lines, with a few of the strongest cells capable of producing
isolated wind damage due to small-scale convective cold pool surges.
Brief heavy rain is likely as well given an expected moist air mass
and efficient rainfall production processes. Highs Tuesday will
depend on how soon convection develops, but mid 80s to around 90 is
expected for now.


.Long Term...(Tuesday night through Sunday)
Issued at 315 AM EDT Mon Aug 21 2017

As the cold front moves across central KY Tuesday night, showers and
storms will occur across southern and eastern counties before
exiting to the south and east by Wednesday morning. The front will
usher in dry pleasant late summer weather across the Ohio Valley
starting Wednesday through the end of the week, as relatively cool
refreshing surface high pressure takes control across the Great
Lakes states. Expect high temperatures in the upper 70s to lower 80s
Wednesday though Saturday with nighttime lows in the 50s in many
parts of south-central IN and central KY. Humidity values will be
low as well.

By late next weekend, a weather system could approach from the west
with a slight chance of showers late Sunday for a part of central
KY, with a better chance next Monday.


.Aviation...(06Z TAF Issuance)
Issued at 120 AM EDT Mon Aug 21 2017

VFR is expected at the TAF sites this forecast cycle.  With upper
level clouds expected to continue on and off through the overnight
hours, feel any fog formation will be very limited so went more
optimistic with vsbys in the TAFs.  A few cu around 5-6 kft will
likely develop this afternoon in addition to some upper level

Otherwise, expect light and variable or calm winds overnight. Winds
will pick up out of the south-southwest between 5 and 10 mph by mid




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