Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 220500
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
100 AM EDT Sat Apr 22 2017

...Updated Aviation Discussion...

...Forecast Update...
Issued at 525 PM EDT Fri Apr 21 2017

Two separate areas of precip nearing central KY/south central IN
this hour.  One, more stable in nature is along our western border
with PAH`s forecast area. An occasional lightning strike has been
noted in this region over southern KY. The second, more active area,
is across middle TN, and slowly lifting northward. Despite some good
heating over central KY this afternoon, RAP model forecast soundings
show this has not been enough to overcome an inversion around 800
mb, and consequently not even seeing much in the way of cumulus
development. So any rain chances look to come as these two waves of
precip move into our region. The more stable one looks like it will
get here faster, though our Lake Cumberland area still may see a few
stronger storms...there is an area of new development just over
southern Pickett county in TN.

Have trended the forecast toward the models that are handling the
present situation the best. A third system out over southern
MO/northern AR looks to move in with another wave of rain late
tonight. Rainfall totals by daybreak could get up to an inch across
portions of southern KY.

.Short Term (Now through Saturday Night)...
Issued at 300 PM EDT Fri Apr 21 2017

Early this afternoon, a cold front was draped from SW TN into far
southeastern Kentucky.  North of the front, precipitation had
diminished and clouds have started to scour out.  In the near term,
it appears that several hours of mainly dry weather are expected
along with some clearing skies.  This will result in temperatures
rising with some late day highs in the upper 60s to the lower 70s.

For this evening and overnight, the lull in convection is not
expected to hold across the region.  With the afternoon sun, we
should see some pockets of instability developing.  Convection has
already begun to develop along the I-40 corridor in TN in the weakly
capped airmass down that way.  Decent bulk shear values (>30kts)
have been helping convection become strong at times.  The latest
short term mesoscale models lift this line of convection northward
into southern KY later this evening (23-01Z) and then into central
KY toward midnight.  We may see a secondary lull in convection until
the upper wave arrives overnight brining the main slug of convection
to the region.  Given the good agreement in the models, have gone
ahead and bumped up PoPs for the tonight period.  Lows tonight will
range from the mid-upper 40s across southern IN and northern KY to
the lower 50s in southern KY.

For Saturday, cloudy skies with periods of showers and a few
thunderstorms are expected.  The best chance of storms would be most
concentrated across our southern counties.  A strengthening pressure
gradient will result in breezy/brisk conditions throughout the day.
Sustained winds of 15-20 MPH with gusts up to 30 MPH will be
possible at times.  It will be rather raw with highs only warming
into the lower 50s across southern IN and northern KY. Some warmer
temperatures with lower-mid 60s are possible down across southern KY.

For Saturday night, bulk of heavier rainfall will shift into eastern
Kentucky.  For much of southern IN and north-central KY, low
cloudiness along with some light rain showers are expected to
continue into the overnight hours.   It will remain a breezy and a
rather raw evening with lows cool into the upper 40s with overnight
lows dropping into the lower-mid 40s in most spots.  The only
exception will be Lake Cumberland region where upper 40s to around
50 will be possible.

In terms of rainfall, a general 1 to 2.5 inches of rainfall is
expected through the short term period.  Antecedent conditions are
relatively dry across much of west-central KY.  Current rivers are
not running high.  Some FFG values are lower across our Bluegrass
region.  However, 24hr FFG values are slightly over 3 inches in many
places.  So while heavy rainfall will be possible during the period,
it appears that the threat of widespread hydrologic issues remains
low, but we`ll continue to monitor things closely.

.Long Term (Sunday through Friday)...
Issued at 305 PM EDT Fri Apr 21 2017

Upper level low will slowly move across the region on Sunday.  This
will result in mostly cloudy conditions with some scattered light
showers around.  Skies will likely take time to clear out Sunday
evening.  Highs will warm into the lower 60s where we clear out
first (our NW areas).  In areas that stay socked in, highs will
likely top out in the mid-upper 50s.  Lows Sunday night will cool
into the mid-upper 40s.

Ridging will build into the region for Monday and Tuesday resulting
in dry conditions.  Daytime highs will warm into the 70s with
overnight lows in the 50s.

The models are in agreement that the next front will come into the
region on Wednesday bring showers and a few thunderstorms.  As we`ve
seen in previous systems of late, it appears that the front will sag
southward and stall out across TN late Wednesday into Thursday
before lifting back as a warm front on Thursday.  Model differences
crop up by Friday as the models are trying to resolve when the next
weather system comes in from the west.  That system could be a
decent severe weather maker to our west next week and could bring
unsettled weather to our area by next weekend.

Highs on Wed/Thu will be in the upper 70s to the lower 80s, with
highs solidly in the lower 80s by Friday.  Overnight lows will
generally cool into the upper 50s to the lower 60s.

&&

.Aviation (06Z TAF Update)...
Issued at 100 AM EDT Sat Apr 22 2017

Complicated weather this TAF period as a couple of surface lows pass
by to our south and an upper low advances from eastern Kansas to
western Kentucky.

MVFR sub-fuel alternate ceilings will continue during the pre-dawn
hours. SDF carried a ceiling around 900 feet earlier and regional
obs show additional ceilings around that height just upstream, so
will have to account for the possibility of an IFR ceiling returning
to SDF early in the TAF period.

A wave of showers over Missouri overnight will push through the
terminals during the daylight morning hours. There may be a brief
break late this morning, and then the next wave of showers, currently
over Kansas, is expected to push through. Ceilings should be MVFR
throughout the day.

Winds will come in from the northeast and may gust into the 20-25kt
range, especially this afternoon.

Though widely scattered showers will still be possible, this
afternoon and tonight should be drier than this morning. MVFR
ceilings will continue, though, until around 06Z tonight before
rising to VFR.

&&

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

$$

Update.........RJS
Short Term.....MJ
Long Term......MJ
Aviation.......13



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