NWS Area Weather Forecast Discussion
Louisville, KY

FXUS63 KLMK 200653

Area Forecast Discussion
National Weather Service Louisville KY
253 AM EDT Mon Aug 20 2018

.Short Term...(Today and tonight)
Issued at 253 AM EDT Mon Aug 20 2018

Closed ULL was evident on water vapor imagery this morning, spinning
toward MCI. Deep, moist convergence was analyzed in an arc on the
leading edge of the system`s dry slot and strongest low-level
moisture transport. Regional radar featured a band of showers with
embedded thunder stretching from STL down into Arkansas. Skies were
partly to mostly clear across our CWA early this morning, with the
leading edge of the cloud shield pushing across western Kentucky.
Cloud cover will quickly ramp up this morning as the system`s warm
front lifts NE toward the area. Until then, patchy fog is likely in
the eastern valleys. Dense fog looks unlikely with gradually
increasing wind fields in the BL.

The nearly-stacked cyclone is forecast to spin eastward across
northern Missouri today. Warm frontal moisture/lift will bring
decent rain chances to the southwest forecast area around 12z,
reaching Louisville/Etown/Bardstown by late morning/midday. Lift
diminishes with time today, and a potential broken/widespread line
of showers and elevated storms this morning near Bowling Green
should become more scattered further north and east by 16-18z. Even
an elevated storm this morning could produce heavy rainfall and
brief gusty winds, however. Behind this first wave, sfc winds are
forecast to become breezy out of the SSW in the warm sector. Precip
coverage will feature a relative lull from mid-afternoon through
late evening. Widely scattered storms are expected, a few of which
will likely be fairly strong. Very moist low levels will support
quick destabilization during the second half of the day, but thicker
mid level clouds will put a lid on surface heating.

Stronger destabilization is likely off to our south and west, where
initiation is likely along the cold front this afternoon and
evening. Possible severe storms to our west may threaten zones
west of I-65 between 00-06z this evening. The upper level trough
will move across Illinois overnight, allowing a 35-40 kt LLJ to
develop over the lower Ohio Valley. Scattered strong storms will
continue to be possible after 06z as the cold front pushes east, but
waning BL instability will limit the damaging wind potential.

The main risk with this system today and tonight is torrential
rainfall and localized flash flooding. Given heavy rains over the
past 3-5 days, rainfall rates and local FFG will need to be
monitored closely. PWATs are currently exceeding 2.1 inches in
portions of eastern Missouri. Flood waters could quickly become life
threatening with high rates falling onto already soggy areas. But
with deep layer shear increasing to around 35 kts overnight,
isolated damaging winds are a secondary threat.


.Long Term...(Tuesday through Sunday)
Issued at 245 AM EDT Mon Aug 20 2018

Tuesday looks to be a day of transition, with the low-level jet and
moisture plume already off to our east, but the upper trof axis yet
to swing through the Ohio Valley. Will hold on to lingering shower
and storm chances, mainly in the morning. Temps will be solidly
under climo, especially during the day, but the dewpoints will stay
up until the secondary front pushes through Tuesday night.

NW winds setting up on Wednesday will bring a shot of early fall
weather as Canadian high pressure builds in. Temps and dewpoints
Wednesday through Thu night will be more typical of mid or late

By late Friday the surface high slips to our east, opening up low-
level return flow, and the pattern becomes more unsettled under a
more SW upper flow ahead of a progressive trof moving into the Upper
Midwest. Fairly low-confidence forecast as far as POPs go, as it
remains in question whether the moisture feed and/or dynamical
support will come together over the Ohio Valley. Low chance POPs on
Saturday, with just a slight chance on Sunday as the upper ridging
starts to win out. Either way, temps look to rebound to the high
side of climo both day and night.


.Aviation...(06Z TAF Issuance)
Issued at 156 AM EDT Mon Aug 20 2018

Partly cloudy to mostly clear conditions were observed across
central Kentucky and southern Indiana early this morning. Satellite
imagery shows just a narrow cirrus band moving over LEX this hour
with scattered mid-level clouds further west. LEX/BWG have the best
chance at seeing some brief MVFR fog toward sunrise, but increasing
winds just off the surface will limit dense fog potential. Thicker
mid/high clouds are steadily spreading eastward over western KY,
however. These clouds are the leading edge of a broad cloud shield
associated with a low pressure system centered over MCI. Deep
moisture/lift associated with warm advection has resulted in
widespread showers with embedded storms in an arc from near STL down
into Arkansas.

This warm front is forecast to lift NE across the area this morning
into early afternoon. Wouldn`t expect more than isolated to
scattered thunderstorms by the time the main band reaches BWG toward
12z. But showers will be more likely at BWG from 12-15z, SDF from 14-
17z, HNB from 13-16z, and LEX after 17-18z. Behind this initial
wave, we`ll be in the warm sector of the system with more isolated
to widely scattered shower/storm activity this afternoon and
evening. SSW winds will increase to 10-15 kts after 15z. Any storm
later in the day could be strong with very heavy rainfall and brief
gusty winds. But given lower coverage, should be a relative lull in
the rains for multiple terminals. Higher rain and storm chances will
return late tonight as the system`s cold front pushes through.




Short Term...EBW
Long Term...RAS

Forecast Discussion from:
Script developed by: El Dorado Weather
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