Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 031749
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
149 PM EDT Fri Jul 3 2015

...Forecast Update...
Updated at 149 PM EDT Fri Jul 3 2015

Although coverage of convection is expected to decrease this
evening, the ground across much of the region is so well saturated
that any heavy downpours that do form will be capable of producing
flash flooding quickly and easily. So, after talking with JKL,
decided to extend the FFA for most of central Kentucky and southern
Indiana through the night. Would rather cancel it early than have
problems after expiration.

After consulting with ILN, though, will indeed let the headline for
Scott and Jefferson counties in Indiana and Trimble County KY expire
on time at 8pm EDT. Better chances for heavy rain will be south of
there, and those locations have had time to dry out today.

.SHORT TERM (Now through Saturday)...
Issued at 300 AM EDT Fri Jul 3 2015

...Flash Flood Potential Continues Through This Evening...

Main weather features are a nearly stationary front draped across
Kentucky, and yet another upper-level impulse swinging into the
mid-Mississippi Valley. Better instability has been suppressed
mainly into Tennessee, but expect that to change later today.

Expect shower and T-storm development again in the heat of the day,
with the greatest coverage and strongest storms south of the front
where instability is greater. Plenty of cloud cover to limit
heating, but with convective temps in the mid/upper 70s it won`t
take much at all. Tall/skinny CAPE, deep warm cloud layers, high
precipitable water, and slow storm motion on the order of 10 kt at
best, all support heavy rain as the main threat. And with 1-hr Flash
Flood Guidance running less than an inch in a few spots, even brief
heavy rainfall could create serious flash flood concerns. Thus the
Flood Watch will continue to fly into this evening, and while that
may or may not be long enough, confidence is too low to extend it at
this time.

By Saturday there should be enough NW flow and ridging to push the
moisture axis and forcing farther south and east. Still carrying
chance POPs mainly south of the Western Kentucky and Bluegrass
Parkways, tapering to a dry forecast over southern Indiana. Heavy
rainfall could again be a threat in south central Kentucky, but
we`ll refine that before we consider extending any headlines.

.LONG TERM (Saturday Night through Thursday)...
Issued at 303 AM EDT Fri Jul 3 2015

Saturday Night - Monday...

The main eastern CONUS troughing will be lifting out of New England
on Saturday night while surface high pressure builds in, however a
weak upper low will be left meanderaing around the central
Appalachian spine through Monday. This feature looks to kick just
enough moisture back toward our SE CWA to keep some Iso to widely
Sct (20-30%) mention Saturday/Sunday afternoon/evening. For the most
part, think that we`ll be able to keep the nights dry once evening
convection dies off. As a result, have mostly dry conditions for the
NW two-thirds of the CWA during this time. Can`t rule out a spotty
shower or storm back this far NW, but certainly won`t be to the
degree that we`ve seen over recent days. Will go with highs in the
mid 80s under the drier pattern, but wouldn`t be surprised to see a
few spots hit the upper 80s. Lows should be in the low and mid 60s
each night.

Monday Night - Thursday...

Upper ridging and meandering upper low will be shunted off to the
east through mid week as a shortwave moves from the northern Plains
through the Great Lakes. This will bring more zonal flow over the
Ohio River Valley, with a trailing cold front approaching and then
stalling out nearly parallel to the upper flow. As a result,
sensible weather will transition back to what looks like a wetter
pattern with temperatures dependent on where the boundary sets up
and each afternoon`s convection.

Scattered warm advection showers should arrive by dawn on Tuesday
mainly across our west, with better chances arriving later in the
day as the front approaches. Will then go with at least scattered
coverage (30-50%) through Thursday as the lingering boundary acts as
a trigger. Generally going with highs in the low and mid 80s, and
lows in the upper 60s and low 70s.

Overall, not too concerned about severe weather with the storms as
better deep layer shear values will be furthern north within the
stronger belt of westerlies. A few stronger storms may be able to
develop on instability, however would be more pulse in nature. Heavy
rain may become a concern as precipitable water values will be up
around 2 inches through the column.

&&

.AVIATION (18Z TAF Update)...
Issued at 114 PM EDT Fri Jul 3 2015

Showers and a few thunderstorms have begun to sprout across southern
Indiana and central Kentucky ahead of an approaching 5H shortwave
trof and along an east-west surface boundary. Thunderstorm coverage
is expected to increase this afternoon as instability increases.
Some training of storms will be possible, so, if a line of storms
sets up directly over an airport there could be an extended period
of time below VFR in heavy downpours.

Convection coverage will gradually decrease tonight. The decrease
may be rather gradual, and we may hold on to a few showers
throughout the night. Ceilings are expected to lower once again in
the very moist atmosphere, and some light vsby reductions will be
possible especially at BWG.

Stubborn upper troffing will remain overhead and the wavy surface
boundary will still be in the area, but both features will be weak
and there won`t be quite as much moisture in the column, resulting
in lower shower/storm coverage.

Winds will be chaotic throughout the TAF period, but will be on the
light side (outside of thunderstorms).

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...FLASH FLOOD WATCH until 8 PM EDT this evening FOR KYZ032.

     FLASH FLOOD WATCH through Saturday morning FOR KYZ023>031-
     033>043-045>049-053>057-061>067-070>078-081-082.

IN...FLASH FLOOD WATCH until 8 PM EDT this evening FOR INZ078-079.

     FLASH FLOOD WATCH through Saturday morning FOR INZ076-077-083-
     084-089>092.

&&

$$

Update.........13
Short Term.....RAS
Long Term......BJS
Aviation.......13





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