Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 160712

Area Forecast Discussion
National Weather Service Louisville KY
312 AM EDT Sun May 16 2021

.Short Term...(Today and tonight)
Issued at 300 AM EDT Sun May 16 2021

Latest WPC analysis places a quasi-stationary sfc front from
southern Kansas across the Ozarks and well into Tennessee, but it`s
fairly difficult to pick up in the obs this far east. Deep
convection is occurring north of the front in Kansas, but none of
the models exactly have a good handle on any of the very widely
scattered light rain showers east of the Mississippi. Most precip
over the Ohio Valley is being lost to evaporation, but a few
sprinkles have been hitting the ground.

Main challenge in the next 24 hrs is precip potential and timing,
and confidence is somewhat limited. Mid-level clouds have us off to
our mildest start in nearly two weeks, but will also severely limit
diurnal warming especially as they thicken along the northward
moving warm front. Think there is an opportunity for precip, mainly
as light rain, from mid-morning into early afternoon. Rain chances
today will be mainly focused south of the Western Kentucky and
Bluegrass Parkways, with about a 50/50 chance of measurable precip.
With next to no instability and weak dynamics, there`s a low
probability for embedded thunder and no expectation of severe wx.

Better rain chances will be after midnight tonight, as the shortwave
ridging aloft progresses far enough east to let the sfc warm front
get a stronger northward push. We`ll ramp POPs up to likely roughly
along and north of the I-64 corridor. Will also include a chance for
embedded thunder, but again not expecting any organization or
intensity. QPF is still modest, around a quarter inch where the best
rain chances will be.


.Long Term...(Monday through Saturday)
Issued at 255 AM EDT Sun May 16 2021

The long term period continues to look unsettled for Monday and
Tuesday as an oscillating quasi-stationary sfc boundary extends from
the central Plains and cuts across the Ohio Valley. After a stretch
of unseasonably cool temperatures last week, we look to transition
to a warmer pattern later in the upcoming week as the amplified flow
aloft develops a broad ridge across the eastern third of the US.

For Monday, the sfc boundary should be located just to our north. A
southerly low level jet core will be off to our west, but enough
Gulf moisture advection overrunning the boundary will pose an
increased precip prob for areas along and north of I-64. Forecast
sounding profiles reveal a lack of shear, but do carry sufficient
instability in the neighborhood of 1200 J/kg of SBCAPE. This will
pose more of a brief heavy rain type of convection. Favorable
environmental parameters for flash flooding concerns are not quite
met, with the warm cloud layer expected to be around 8k ft (greater
than 10k ft is favorable), and PW of 1.2" will be slightly lower
than the 75th percentile from BNA sounding climo, but we will be
near 80% RH in the low/mid levels. Southerly winds will not only
bring additional moisture to the region, but will also bring
seasonal temps back to the forecast, with mid-upper 70s expected.

On Tuesday, the upper level pattern will begin to amplify as a
stacked low sits over the Mountain West and upper ridging takes
place over the eastern third of the CONUS. However, at the sfc,
expect to see continued PoPs as waves eject out of the central
Plains and ride along the wavy frontal boundary. The sfc boundary
will eventually shift northward by Tuesday night, bringing drier wx
to the region. QPF for Monday to Tuesday is focused primarily along
our southern IN counties, which could see up to 0.5-0.75". For areas
along the I-64 corridor, around a quarter of an inch is possible for

For Wednesday and beyond, strong meridional flow sets up across the
US. The stacked low once over the west will track northward along
the southern stream ridge and eventually open. Upper level ridging
looks to anchor itself across the eastern US, placing sfc high
pressure over the East Coast and deep southerly flow along the
Mississippi/Ohio River valleys for mid to late week. With possibly
the warmest days of the year thus far, we could see temps reach the
mid-upper 80s for Wed-Sun.


.Aviation...(06Z TAF Issuance)
Issued at 115 AM EDT Sun May 16 2021

IMPACTS:  VFR conditions overnight. MVFR in light rain roughly
daybreak through early afternoon.

DISCUSSION: Light winds and mid-level ceilings will prevail
overnight, perhaps building down to FL060 by daybreak. Light rain
will break out around daybreak, and even if some terminals remain
dry expect MVFR ceilings. Will recover to VFR late afternoon, with
SDF and HNB deteriorating late evening as another round of rain
arrives. Either could eventually build down to IFR but expect that
will be beyond the valid time of these TAFs.

CONFIDENCE: Medium confidence on all forecast elements.




Short Term...RAS
Long Term...CJP
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