Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 121623

Area Forecast Discussion
National Weather Service Louisville KY
1223 PM EDT MON OCT 12 2015

...Forecast Update...
Issued at 1222 PM EDT Mon Oct 12 2015

Early afternoon satellite imagery reveals mostly sunny skies across
the district.  Temperatures continued to warm into the upper 60s and
lower 70s region wide.  With decent insolation expected,
temperatures are likely to top out in the upper 70s to the lower 80s
this afternoon.

Surface cold front out to the west will continue to move eastward
this afternoon and evening.  Latest model runs continue to generate
a band of convection along the cold front as it heads through the
Ohio Valley.  Overall, the pattern is one of those split type
patterns where better moisture remains south of the region and
stronger dynamic support reside to the north.  Current thinking is
that we`ll likely see convection develop in the 21-22Z time frame
and then slide eastward this evening.  A narrow window of
opportunity exists for some stronger thunderstorms, mainly capable
of producing small hail and gusty winds.  Highest threat area would
be generally south of I-64 and along and east of I-65.

The current forecast has this covered fairly well.  We did make some
minor adjustments to the forecast elements, specifically in refining
the convective timing this afternoon.  In general, this resulted in
reduced PoP coverage early this afternoon with a ramp up in the 21-
22Z time frame through about 02Z tonight.

.SHORT TERM (Now through Tuesday)...
Issued at 310 AM EDT Mon Oct 12 2015

A pool of 850-700hPa moisture over the middle Mississippi Valley
early this morning, revealing itself in a patch of clouds visible on
satellite loops, will expand and advect eastward into the Tennessee
and Ohio valleys today. Meanwhile, a cold front curving from
Wisconsin to the Texas panhandle this morning will push eastward,
crossing southern Indiana and central Kentucky this evening. As the
front impinges upon the pool of low/mid level moisture, convection
will begin to break out.

It looks like a broken band of showers and thunderstorms will
develop around 21Z in a NNE-SSW orientation from southeastern
Indiana through or near the Louisville metro to the Bowling Green
region. Soundings show a layer of dry air aloft as well as dry sub-
cloud air from the surface to 850hPa. 0-6km bulk shear briefly peaks
around 30-35kt just ahead of the front and DCAPE peaks around 1500
J/kg. So, if convection can get going, gusty winds look to be a
threat with the stronger storms. Wet bulb zeroes are progged to be
fairly high, but with the aforementioned zones of dry air helping to
slow down the melt rate of any stones, some pea sized hail at the
surface can`t be entirely ruled out under the more robust updrafts.

The main negative to convection developing is instability. We should
have a good amount of cloudiness through the day, limiting
instability potential. Models are progging only weak LI and CAPE
values. So, for now, it looks like SPC`s outlook of just general
thunder is probably the safe way to go. If we end up getting more
sun than expected, though, then perhaps some stronger storms could
develop this evening, especially from between Louisville and
Lexington south to between Bowling Green and Lake Cumberland.

As for temperatures, we`re getting into the time of year when cloud
cover makes a big difference on how high the mercury can climb in
the afternoon. Southwest winds will become brisk and somewhat gusty
(to around 20-25mph at times) ahead of the approaching front, but
expected cloudiness will limit warming. Will aim for highs generally
in the 75-80 degree range.

Any showers and storms that develop along the front will be gone by
midnight as the front exits. Skies will clear quickly and
temperatrues will fall to around 50.

Tuesday looks very nice as high pressure noses in from the Red River
Valley. We should see lots of sunshine and afternoon temperatures
peaking around 70.

.LONG TERM (Tuesday Night through Sunday)...
Issued at 255 AM EDT Mon Oct 12 2015 Columbus Day Edition

Tuesday Night through Monday...

Well...this upcoming week is characterized by high zonal flow aloft
with mainly dry frontal systems pushing thru every 36 to 48 hours.
For next weekend an anomalously strong area of Canadian high
pressure and cooler low level temps builds into the region bringing
the coolest autumn air to date and potential frost across the Nrn

Tue night thru Thu...

Surface high pressure will build in from the northwest bringing a
very pleasant fall airmass to the Ohio Valley. This will bring
mostly sunny days with good afternoon mixing taking place and mostly
clear nights.

Temperature wise, expect highs 68 to 77 across the region. The
warmest readings would generally be confined to areas across
southern KY with the coolest readings along/north of I-64. Overnight
lows look to cool into the 40s through the period.

Thu Night into Fri AM...

Short wave energy moving across the Great Lakes will help push a
cold front through the area Thursday night.  This will bring an
increase in clouds especially in areas wnw of I-65. The question is
will there be any precip with the system? The extended Blender came
in with paltry POPS for 15 to 22% across the northern CWA.  The ECM
showed a smidgen of moisture so for now 4 1/2 days out will keep it
dry. This was coordinated with ILN, IND, and JKL.

Temps Thu night ahead of the approaching front will be a tad milder.
Latest guidance here suggests lows only cooling to around 50.

Fri PM thru Monday...

Drier, cooler weather will continue Saturday and into Monday.
Surface high pressure will build in from the northwest again, but
this time there is more cold air aloft with H8 temps of 0C to +2C
along and north of I 64. As the high moves overhead late Saturday
night into Sunday morning, a decent signal from the models suggests
good radiational cooling setting up which looks to produce at least
a scattered frost. There could be some patchy frost Saturday
morning, but winds may be mixed enough to preclude this.

Not all areas will see a frost Sunday morning, but areas from
southern Indiana into the Bluegrass region of central Kentucky
currently stand the best shot at frost. Previous day shift forecast
grids reflect this nicely.

Highs Friday will top out in the mid-upper 60s, lows Saturday
morning will dip into the upper 30s to the lower 40s across the
region. Highs Saturday will mainly be in the 50s, except lower 60s
along and w-sw of I-65. Lows Saturday night will likely drop into
the 33-37 range in the northeastern sections with upper 30s
elsewhere.  Highs on Sunday look to rebound into the mid 60s.


.AVIATION (12Z TAF Update)...
Issued at 644 AM EDT Mon Oct 12 2015

Clouds have begun to develop this morning over the Ohio and
Tennessee Valleys and will spread through Kentucky during the
morning hours, but will remain well VFR.

A cold front will sweep through the region this evening and will
bring a broken line of showers and storms with it. Too early for
enough confidence to include VCTS, but went ahead with a PROB30 to
give a heads-up. LEX stands the best shot at convection. Recent
model data have initiated storms a little later and little farther
west than data used for the 06Z TAF package, so have delayed
convection about an hour in this package versus the earlier package.

Winds today will come in from the southwest and may gust to around
20 knots at times.

The front will depart quickly this evening and leave mostly clear
skies in its wake.


.LMK Watches/Warnings/Advisories...


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Long Term......JDG
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