Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 290506
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
106 AM EDT Wed Jul 29 2015

...Updated Aviation Discussion...

...Forecast Update...
Issued at 830 PM EDT Tue Jul 28 2015

Issued another update to remove the pre-first period wording and to
expand fog coverage. Soupy airmass in place along with winds
expected to become light and variable soon should lead to at least
areas of fog overnight. Quite the complex has formed to our west
this evening, and the residual upper level disturbance may lead to
an enhancement of showers storms toward daybreak, mainly west of the
I-65 corridor. Thus will keep in the slight chances of storms we
have there overnight.

Issued at 545 PM EDT Tue Jul 28 2015

Did a grid update earlier this hour to account for current radar
trends. Latest HRRR finally getting a handle on precip this
afternoon, and it shows this precip decaying with sunset. Previous
runs had the cells over central Illinois decaying immediately after
model initialization, which has not occurred yet. Latest CIMSS
NearCast does show the central part of our county warning area being
a less likely place for storm development, and despite stronger
outflows moving through that region, we only are seeing weak storms.
Latest AMDAR data from a flight into SDF confirms this thinking,
with a fairly strong cap above 600 mb that is limiting how tall the
storms near SDF are getting.

Despite that cap, the presence of these boundaries as well as a
muggy airmass should keep non-severe storms forming over the next
few hours until we can get the sun to set. Latest NAM still trying
to show a wave of decaying storms coming in to our western forecast
area toward daybreak. These would be from the cells now over Iowa as
they round the top of the ridge over the mid MS valley. Made no
changes to the daybreak period for now.

.SHORT TERM (Now through Wednesday Night)...
Issued at 325 PM EDT Tue Jul 28 2015

Scattered storms were ongoing across the area as of 19Z.  Some
storms were strong with lots of lightning, torrential rainfall, and
gusty winds up to around 40 mph.  Expect convection to continue
through the evening hours as an upper level shortwave dropping SE
out of IL keeps storms going or even enhances development this
evening.  With ample instability in place as well as DCAPE, high
precipitable water values, and weak boundaries for storms to train
along, a strong wind threat and localized flooding threat will
continue through the evening hours.  Storms should diminish through
the late evening hours with the area becoming completely dry after
midnight.  Expect low temps in the low to mid 70s with some patchy
fog/haze developing after midnight as it has done the past few
mornings.

For Wednesday, we`ll start the day with a dying complex of storms
entering areas west of I-65.  This morning batch should fizzle out
or become just isld showers by mid morning.  Some breaks in the
clouds are expected during the morning and early afternoon hours
allowing some instability to build.  A cold front will approach the
area Wed afternoon causing more convection to fire.  Although
morning clouds/precip may inhibit the environment somewhat and the
front is pretty weak, we should still have enough forcing and
instability to produce strong to marginally severe storms with
strong winds, small hail, and torrential rainfall.  Storms should
persist through the evening before diminishing by late evening with
the cold front passage.  Highs for Wed should range through the
upper 80s to lower 90s with heat index values in the lower 100s
mainly west of I-65.  The good news is any precip should provide
relief from the heat tomorrow and there is a good chance for precip
to occur 40-50%.   Wed night low temps should range through upper
60s/lower 70s.

.LONG TERM (Thursday through Tuesday)...
Issued at 245 PM EDT Tue Jul 28 2015

The main forecast concern in the long term is temperatures as much
of the extended forecast looks dry across the lower Ohio Valley. The
start of the period /Thursday morning/ will feature a cold front
bisecting the forecast area. A pool of high moisture along and ahead
of the front combined with weak lift will support the chance of
showers/storms during the morning hours across south-central
Kentucky. The front then quickly drops into TN by 18z and in its
wake, much drier and more pleasant conditions will build into the
region.

Plan on low humidity and more pleasant summer conditions Thursday
afternoon through Friday as highs top out right around normal /mid
to upper 80s/ and overnight lows will be in the low to mid 60s.
Outside of scattered afternoon cumulus, skies look to be mostly
sunny to sunny.

A weak front approaches from the northwest on Saturday but will
likely wash out before making it to the Ohio River. Humidity will
slowly increase this weekend as dewpoints creep back up into the
mid/upper 60s. Look for afternoon highs to gradually warm as well,
approaching 90 degrees by Sunday.

Going into next week, will continue to advertise a dry forecast as
approaching fronts wash out or stall to the northwest. Some signals
that a stronger front may make a push through the area mid to late
week but model uncertainty is high.

&&

.AVIATION (06Z TAF Update)...
Updated 100 AM EDT Tue Jul 28 2015

Steamy conditions will persist overnight, with fog potential being
the biggest near-term question. Rainfall Tue afternoon/evening was
fairly unimpressive near the terminals, and visibilities didn`t drop
too hard in the morning anyway. Temp/dewpoint spreads remain
slightly wider than advertised by models, so it seems that MVFR
should cover the visibilities around daybreak. Best chance of any
IFR restriction seems to be in LEX, as cirrus should keep any fog at
BWG in check.

Next challenge is timing and impact of any convection as a cold
front moves in late in the day. Morning should be high and dry as
the storms over Iowa and northern Missouri struggle to organize into
any kind of MCS that could dive at us early in the day. Hi-res
models all point to mid/late afternoon for any T-storms, and there
remains a hint that some of the are could get gapped. If a storm
does directly affect an airport, there will be MVFR vis in rain, if
not briefly IFR. Will carry a PROB30 group for that into early
evening.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

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




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