Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 201718

Area Forecast Discussion
National Weather Service Louisville KY
118 PM EDT Thu Oct 20 2016

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1130 AM EDT Thu Oct 20 2016

Western band mentioned below has gotten wider, with some stronger
cells embedded. Surface-based instability does look limited though,
as we have not had more than roughly 30 mph wind gusts come out of
these cells, with no hail reports. The latter doesn`t mean there is
no hail, as the cells are going over less populated areas.  A
stronger cell developed on the north side of an outflow boundary and
now has moved into Crawford county Indiana. That cell spiked up over
PAH`s area, but has since weakened. Peak gust from that one for EVV
was ~35 mph.

There is a narrow areas of more sunshine now entering our southwest
forecast area. This area should be narrow enough to prevent too much
heating, so the threat for severe winds is lessening. Still dynamics
aloft could make for some stronger elevated cells with hail,
especially along and east of the I-65 corridor this afternoon.

Issued at 805 AM EDT Thu Oct 20 2016

Currently have two main bands of precip across the region, one
oriented from Madison, IN southwest to Hartford, KY and the other
running from Franklin to Stanford, KY. The first line is expanding
in coverage, with satellite imagery showing cooling cloud tops,
whereas the second line is just maintaining itself with lower
clouds. Have trended hourly pops to account for these bands, but the
overall forecast for high pops today hasn`t changed much. This new
band may actually help to limit severe chances later in the day.

High-res guidance was showing a band of instability east of I-65
coinciding with the best shear as the main trough axis gets through
here. Even with less surface-based instability, dynamically we`ll
have some lift in the right rear quadrant of a jet crossing the
Midwest. So widespread showers and scattered thunderstorms are in
order, but the threat for severe weather is still in question. Have
added gusty winds and small hail wording to the zones for the

.SHORT TERM (Now through Friday)...
Issued at 302 AM EDT Thu Oct 20 2016

...Strong to Severe Storms Possible Today...
...Much Cooler Starting Tonight...

An active weather day is expected as a surface low pressure
system and cold front track across the lower Ohio Valley.

As of 3 am, a stalled front lies along and just north of the Ohio
River while a weak area of low pressure was analyzed over southwest
Kentucky. The upper levels featured extensive southwest flow from
Texas to New York while a shortwave trough was across the central
Plains. Regional radar showed a large shield of showers and
thunderstorms from near St Louis through Indianapolis and northwest
Ohio. Southern Indiana and central Kentucky were mainly dry at the

Increasing height falls associated with the advancing and amplifying
shortwave trough later this morning and this afternoon combined with
the surface low tracking toward Ohio will bring widespread showers
and thunderstorms to the area. Beginning this morning, a pre-frontal
shield of showers may develop and spread into the Lake Cumberland
and Bluegrass regions, as seen in the past few runs of the HRRR.

By early afternoon, the surface low is expected to be near
Cincinnati with its trailing cold front extending southwest through
parts of the area. The environment along and ahead of the front is
expected to be characterized by SBCAPE of 1000 to perhaps 1500 J/kg.
Winds aloft will also be on the increase helping to increase the
deep layer shear to 35 to 40 kts. This combination should allow
convection to uptick and grow, and support marginally severe storms
capable of producing damaging winds and large hail. The anomalously
high PWATs will make for heavy rain producing storms as well though
antecedent conditions plus a progressive storm motion precludes a
higher flood risk. The highest risk for severe storms will near and
east of the I-65 from early/mid afternoon through early evening.

Temperatures today will be complicated depending on frontal passage
timing and precipitation. 70s are likely out in the warm sector
across south-central KY to the southern Bluegrass regions, and if
there are more breaks in the clouds than expected, then mid/upper
70s are not out of the question. Back across southwest/southern
Indiana, showers and an earlier frontal passage may hold readings in
the 60s, or even falling temperatures by afternoon.

Precipitation will end west to east tonight as the upper trough axis
swings across the lower Ohio Valley. Soundings show a fair amount of
moisture trapped within the low-level inversion and low clouds are
expected in the wake of the front. Drizzle or even a light shower or
two is possible overnight. Much colder air will pour into the region
with lows expected to range from the mid 40s across southern Indiana
to near 50 toward the Lake Cumberland region.

For Friday, plan on a swing to much cooler temperatures along with
brisk north to northwest winds. It will certainly feel and look more
like fall. Across the Bluegrass, morning showers may still be
possible. The best chance for an extensive strato-cu cloud deck is
across the northern and eastern half of the area where low-level
moisture is likely to be still around. After experiencing mid 80s to
near 90 degrees earlier this week, highs on Friday will only reach
the mid to upper 50s!

.LONG TERM (Friday Night through Wednesday)...
Issued at 307 AM EDT Thu Oct 20 2016

Friday night the upper trough axis will be east across the
Appalachians while cool Canadian high pressure will be dropping into
the mid-Mississippi River Valley. Plenty of cold air advection will
put lows Saturday morning in the upper 30s to low 40s. The coldest
readings will be found across southwest Indiana where winds are
expected to be lightest, and also in the typical colder spots that
are more sheltered. In either of these places, patchy frost isn`t
out of the question. Stubborn strato-cu slow to exit and a more
mixed boundary layer could hold readings slightly higher than some
of the colder raw guidance suggests, and leaned more toward the
ECMWF solution for lows Saturday morning.

High pressure will dominate the weather Saturday and Sunday,
bringing mostly sunny skies and pleasant October fall weather. Plan
on highs Saturday to top out around 60, and in the upper 60s to
around 70 on Sunday. West winds will become gusty Sunday afternoon
15 to 25 mph.

Another front crosses the region Monday but is expected to do so
dry. Plan on seasonable temperatures for the remainder of the long
term period with highs in the upper 60s to low 70s, and morning
lows in the mid 40s to low 50s.


.AVIATION (18Z TAF Update)...
Issued at 117 PM EDT Thu Oct 20 2016

First batch of convection is currently moving through the I-75
corridor and will continue to move off through the coalfields of
east KY this afternoon.  Second batch of showers is lifting through
the Pennyrile region of western KY and will pass through the I-65
corridor in the next several hours and then through the I-75
corridor later this afternoon and evening.  Flight conditions will
generally be low end MVFR to high end IFR this afternoon.  Ceilings
are expected to be between 600-1500 ft AGL this afternoon and
continue through the overnight hours.  Winds will start off out of
the south and shift to the west/northwest this afternoon at KSDF and
KBWG and then at KLEX by early evening.  Winds this evening will be
out of the northwest and gusty with sustained speeds of 10-12kt and
gusts up to 20kts at times.

Ceilings overnight look to remain IFR at all the sites.  Some light
rain and mist will be possible at all the terminals.  Ceilings will
likely start to rise a bit after dawn on Friday...most likely after




Short Term.....ZT
Long Term......ZT
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