Area Forecast Discussion
Issued by NWS Louisville, KY

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159
FXUS63 KLMK 040512
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
112 AM EDT WED MAY 4 2016

...Updated Aviation Discussion...

...Forecast Update...
Issued at 725 PM EDT Tue May 3 2016

Still have some very weak radar returns in the northeast and have
trended the forecast to deal with those.  The chance of measurable
rainfall is very slight. Hi-res guidance continues to point to a
solid line of rain moving into the region Wednesday after the
morning rush. Ongoing forecast there looks good.

.SHORT TERM (Now through Wednesday Night)...
Issued at 305 PM EDT Tue May 3 2016

...Showery and Cooler Through Mid Week...

Late this afternoon, light rain showers were skirting across our
southeast Indiana/northern Bluegrass counties.  Could still see a
bit more development southward into more of southern Indiana and
northern KY through the evening hours, but shouldn`t be more than a
light sprinkle or shower at best.  Will continue 20-30% POPs for
this evening.

Showers should end toward late evening with mostly dry conditions
overnight.  Skies should become partly cloudy tonight behind this
wave.  Low temps look to bottom out in the upper 40s.

Look for a cold front and upper low to dive into our region for
tomorrow.  Showers and storms are expected to develop along the
front during the morning hours and move into our southern Indiana
counties around mid to late morning.  Convection is expected to
spread ESE through the rest of the forecast area during the day and
then diminish to isld-sct activity by tomorrow evening.  This is a
potent upper low with good forcing for ascent.  As the colder air
associated with it moves into our region and sfc heating takes
place, lapse rates will steepen sharply.  With modest 0-6 km bulk
shear of 25-35 kts and CAPE of 500-1000 j/kg, small to marginally
severe hail will be possible in low topped convection. The best time
for storms with hail would be during the late morning to early
evening hours.  Highs for tomorrow look to reach the upper 50s to
mid 60s with south central KY being the warmest under a longer
period of only partly cloudy skies in the morning/early afternoon.

Wed night/Thu we`ll see lingering shower activity on the NW side of
the upper low mainly focused east of I-65 on Thurs.  Temps will stay
on the cool side with Wed night/Thu night lows in the low to mid 40s
and Thu highs in the upper 50s to lower 60s.

.LONG TERM (Thursday through Tuesday)...
Issued at 105 AM EDT Wed May 4 2016

Thursday Night - Friday...

Highly amplified upper pattern features expansive closed lows over
the western and eastern coasts, with a blocking upper ridge over the
center part of the CONUS. The Ohio Valley will be in the deep
norhterly flow between eastern closed low and upper ridge to end the
week. With surface high pressure in place and a lack of moisture,
this will be a dry period with lows Thursday night in the mid 40s.
With rising heights/thicknesses on Friday, temps will rise to the
lower 70s.

Friday Night - Saturday...

The upper ridge begins to break down as we head into the weekend in
response to another shortwave diving through Ontario into the Great
Lakes. As this occurs, a frontal boundary will slide toward the Ohio
River by late on Saturday. With surface high pressure still holding
on, this should also be a mostly dry period. However, cannot rule
out a stray light rain shower Friday night. By late Saturday
afternoon and evening, scattered showers and an isolated
thunderstorm will be possible north of the Ohio River. At this
point, it looks like any precipitation activity should hold off in
the Louisville region until after 8 PM EDT.

Friday night lows will be milder than previous nights with readings
in the low to mid 50s. Saturday highs should be able to top out in
the low 80s before upper clouds arrive in the late afternoon and
evening.

Saturday Night - Tuesday...

A potentially showery period continues through the weekend and into
early next week as the aforementioned frontal boundary stalls over
the region, nearly parallel to the NW flow aloft. With the frontal
boundary serving as a mechanism for moisture convergence, expect
that isolated to scattered showers and storms will then be possible
mainly each afternoon and evening through Monday. A brief lull will
be possible on Monday night as a progressive upper ridge moves
through. Chances for showers or storms then return for Tuesday as
upper pattern transitions to a deep SW flow ahead of an approaching
trough. The associated low level response will help to lift the
aforementioned frontal boundary back north as a warm front, with
scattered showers and storms possible in the isentropic ascent
regime.

Saturday and Sunday night lows will be in the mid and upper 50s,
with lows by Monday night around 60. Highs in the mid and upper 70s
on Sunday will warm to near 80 on Monday and Tuesday. These readings
will be a bit tricky to nail down given a waffling frontal boundary
in the region.

&&

.AVIATION (00Z TAF Update)...
Updated at 105 AM EDT Wed May 4 2016

VFR through the night with intermittent mid-level ceilings in the
modest warm advection pattern. Front is on schedule diving into
northern Illinois, with a narrow rain shield just ahead of the
boundary.

Expect the rain shield to dive southeast into Kentucky by late
morning, but should be losing coverage as it is left behind by the
stronger upper forcing. Therefore will only carry prevailing SHRA in
SDF, with just VCSH in BWG and LEX. Ceilings will drop into high-end
MVFR, but we can`t rule out briefly going into fuel-alternate
conditions early/mid afternoon. Will reassess in the 12Z TAFs.

SW winds will pick up with the precip, with gusts just shy of 20 kt,
then shift to due west or WNW mid-afternoon. Will continue VCSH
behind the front as cold air aloft will support showery convection.
Can`t rule out isolated thunder or even small hail, but probability
too low to include in TAFs. Ceilings will lift and NW winds will lay
down around sunset.

&&

.LMK Watches/Warnings/Advisories...
KY...NONE.
IN...NONE.
&&

$$

Update.........RJS
Short Term.....AMS
Long Term......AMS
Aviation.......RAS



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