Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 261457
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1057 AM EDT Sun Mar 26 2017

.Forecast Update...
Issued at 1055 AM EDT Sun Mar 26 2017

The morning showers are persisting across our eastern CWA, but will
continue to lift out of the area over the next couple of hours. Back
to the west, we are seeing a lull in activity as mid level dry punch
is working in. This does not mean the end of the showers, however as
low to mid level lapse rates will remain steep ahead of the next
vort max rotating around the parent upper low near the Quad Cities.

Latest mesoanalysis does show a small amount of instability
developing back to the west where precipitation has ended, and data
continues to suggest that up to 500 J/KG of CAPE will develop by
midday into the afternoon. Model guidance depicts the development of
scatted to numerous showers and a few storms by early to mid
afternoon, especially across southern IN. Given the steep low and
mid level lapse rates, there should be enough instability for some
thunderstorms and the potential for gusty winds (~30-40 mph) to
accompany them. In addition, a small hail threat isn`t out of the
question given low freezing levels around 8 K feet, although storm
tops will likely be capped at around 15K feet given strong mid level
subsidence. Also think it is worth mentioning that the vertical wind
profile below the equilibrium level would be supportive of a few
organized updrafts, if instability ends up being sufficient. In this
case, a few stronger organized storms are possible where higher wind
gusts (likely in the SPS range) might be possible. Will have to
monitor early afternoon trends.

&&

.Short Term...(This afternoon through Monday evening)
Issued at 300 AM EDT Sun Mar 26 2017

...Strong to Severe Storms Possible Monday...

Stacked low pressure was centered over northeast Missouri early this
morning, with a long band of showers stretching from the Gulf Coast
to the Ohio Valley. The showers are located just ahead of the
negatively-tilted trough, which will continue to swing into the
region this morning. Closest lightning activity was in western TN,
near the surface boundary and under more of an influence from cold
pool aloft. Lightning does not look likely early this morning with
minimal instability and moist-adiabatic lapse rates. Ongoing steady
band of light to moderate showers will gradually lift northeast of
the forecast area by 12z.

After sunrise, activity looks to be more scattered in nature with
some potential for isolated thunder. Instability is still quite
marginal, but can`t rule out lightning completely as temps aloft
cool. Without widespread showers during the daytime, highs in most
places should recover into the upper 60s to around 70 degrees. A
brief period of dry weather is expected late this evening into early
Monday. Very brief shortwave ridging will push through the Ohio
Valley ahead of a low pressure system in the Plains. Lows tonight
will be in the upper 40s to mid 50s.

A progressive shortwave trough swings into the Ohio Valley on
Monday. There is medium-high forecast confidence in a surface low
moving from NW Arkansas at 12z Mon to Indiana by late Monday
evening. A 35 kt SW LLJ noses through the forecast area during the
afternoon and evening hours. Latest forecast soundings suggest
moderate buoyancy will develop with a capping inversion in place
through 18z or so. Dewpoints are forecast to rise into the mid and
upper 50s. 0-6 km shear looks to be around 35-40 kts. There is also
a fair amount of shear (25 kts) in the lowest 1 km, and effective
SRH peaks around 200 m2/s2 during the afternoon and evening. Strong
to severe storms are possible with this environment, including
damaging wind gusts, hail, heavy rain, and an isolated tornado.

&&

.Long Term...(After midnight Monday night through Saturday)
Issued at 340 PM EDT Sat Mar 25 2017

Showers could linger east of I-65 Tuesday morning as low pressure
departs to the east. In general, upper level ridging will keep
central KY and southern IN mostly dry Tuesday and Wednesday. Highs
Tuesday and Wednesday will be in the mid 60s to low 70s. Morning
lows are expected to be in the mid 40s to low 50s.

The weather turns active once again late this week. Showers and
thunderstorms appear most likely Thu, Thu night, and Friday as a
deep upper level trough moves into the region. Forecast confidence
regarding the detailed evolution of this low pressure system remains
low. The latest ECMWF features an evolution that is most consistent
with the recent pattern, with ridging across the NE US and a surface
track to the north of the forecast area. However, the latest GFS
suppresses the system further south, right through the Ohio Valley.
For now, will feature likely rain chances, a slight chance for
thunder, and highs generally in the 60s to around 70 degrees.

The weekend looks pretty quiet with high pressure and drier air
returning to the Ohio Valley. Blended guidance suggests highs in the
60s, with Sunday warmer than Saturday.

&&

.Aviation...(12Z TAF Issuance)
Issued at 635 AM EDT Sun Mar 26 2017

Shield of widespread rain currently affecting SDF and LEX, with LEX
so far remaining VFR while SDF is trying to break out of fuel-
alternate MVFR. A modest dry slot is trying to punch up through
south central Kentucky, but BWG is still seeing intermittent
showers.

Will most likely initialize LEX with prevailing -SHRA but will keep
VFR conditions. Worst case seems to be MVFR but above fuel-
alternate, given trends in the upstream observations. BWG and SDF
will be issuance time decisions.

By late morning the widespread rain should be to our north and east,
but scattered showers will almost certainly warrant a couple hours
of VCSH. Winds will be picking up out of the south, or perhaps SSW,
with gusts just shy of 20 kt. As the afternoon progresses, expect
precip chances to diminish below any mention-worthy probabilities,
and ceilings to go solidly VFR.

Winds should die down this evening, and after a brief mid-level
ceiling expect enough clearing to consider some fog potential
heading toward Monday morning. Will keep vis MVFR or better for now,
with any ceilings staying VFR.

&&

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

$$

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



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