Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 170557

Area Forecast Discussion
National Weather Service Louisville KY
157 AM EDT Sat Mar 17 2018

...Updated Aviation Discussion...

.Forecast Update...
Issued at 855 PM EDT Fri Mar 16 2018

A weakening surface low was spinning over eastern Kansas this
evening, with an arc of showers and thunderstorms along the occluded
front in eastern Missouri. Dry, easterly flow prevailed north of the
warm front draped across Tennessee. This dry air will keep the rain
at bay until 06z. That warm front is still forecast to lift north
overnight. The band of showers and likely a few thunderstorms will
push west to east across central KY/southern IN between 06-11z.
Latest RAP soundings do show 200-300 J/kg MUCAPE for a 2-hour window
for most locations. A low-level inversion will keep any storms


.Short Term...(This evening through Saturday night)
Issued at 315 PM EDT Fri Mar 16 2018

Afternoon satellite imagery shows a large arcing band of cloudiness
from the upper Midwest through the Ohio Valley.  Skies across the
region were partly to mostly cloudy.  Temperatures ranged from the
lower 40s over far NE KY to the lower 60s across far SW KY. Overall,
there was about a 10 degree gradient across our forecast area.  For
the remainder of the afternoon, we expect cloudiness to persist and
thicken as the afternoon wears on.  Highs will top out in the next
hour or two with lower-mid 40s over the Bluegrass region and mid-
upper 50s over our southwest sections.  While there are some returns
on area radars, antecedent dry air in place will likely keep any
precipitation falling from reaching the ground through the early
evening hours.

For tonight, surface boundary to the south of the region will drift
back northward in the form of a warm front.  Combination of
isentropic lift along with some height falls aloft should result in
more widespread precipitation development.  Overall model solutions
have been trending a little slower with precipitation development on
this cycle.  However, our thinking is that precipitation should
start to increase after 17/00Z and then spread eastward toward the I-
65 corridor toward midnight.  This activity should spread eastward
through the rest of the forecast area overnight.  Model proximity
soundings do not show a lot of surface instability.  However, there
could be some pockets of elevated instability which may lead to a
rumble of thunder as the showers move through the region.  Lows
tonight will range from the mid-upper 30s over the northern
Bluegrass to the lower 50s over our southwestern sections.

For Saturday and Saturday night, we`ll see the surface warm front
nudge northward throughout the day.  Current thinking is that it
will likely reach as far north as the Ohio River by late morning to
mid-afternoon, leading to a strong temperature gradient across the
region.  Highs may range from the lower 40s across our far northern
southern IN counties to near 70 down along the KY/TN border region.
A surface low and upper level wave will move eastward across the
region during the day.  Some instability will develop during the
afternoon hours and a line, or several lines of broken convection
will likely develop and move southeast across the region.  The best
chances for thunderstorms on Saturday would be generally along and
southeast of a line from Leitchfield to Lexington.  This activity
will rapidly move off to the southeast and clear the region by early-
mid Saturday evening.  Skies are forecast to clear out from
northwest to southeast overnight.  Lows will range from the lower
30s over southern Indiana to the lower 40s over far southern KY.

.Long Term...(Sunday through Friday)
Issued at 338 PM EDT Fri Mar 16 2018

Sunday through Monday Night...

A period of weak upper level ridging will be seen on Sunday across
the region. This should result in a short dry period of weather on
Sunday with highs in the 54 to 59 degree range.  Clouds will be on
the increase Sunday night as another weather system approaches from
the southwest.  Best chances of precipitation late Sunday night will
be across our far southwest and southern areas.  Lows will range
from the upper 30s across southern IN to the upper 30s to the lower
40s across southern KY.

By Monday afternoon, compact but nearly vertically stacked surface
and upper level low will roll eastward through the region.  This
feature will bring widespread precipitation to the region.  A tight
thermal gradient may be seen once again as temperatures will range
from the mid-upper 50s in the north to the upper 60s across the
south.  Model soundings do show some potential for some surface
based instability to develop across southern KY Monday afternoon, so
some thunderstorms will be possible as this feature moves through
the region.  Some wrap around precipitation is likely to linger
Monday night with temperatures falling into the mid 30s in the north
and in the lower-mid 40s across the south.  If some colder air were
to work in, we could see a bit of a rain/snow mix across southern IN
and far northern KY by Tuesday morning.  Something to watch in
future forecasts.

Tuesday through Friday...

Active and progressive upper level pattern is forecast to persist
across much of North America through the long term period.  This
will result in episodic bouts of inclement weather and colder than
normal temperatures for the period.

The upper level pattern will feature a ridge in the western US with
a trough in the east.  A few disturbances will roll through the
upper trough and may result in several storm systems affecting the
eastern US coast through the period.  A rather strong perturbation
looks to move through the region late Tuesday and into Wednesday.
This will bring a period cold rain to the region.  However, colder
air wrapping into the system may result in snows developing across
the area late Tuesday and into Wednesday morning.  The Euro is a bit
more progressive here keeping the highest threat of snowfall across
southeastern KY.  The GFS is a bit more amped up and produces more
widespread snows across the area.  For now, have used a general
blend of the Euro and GFS here which results in rain and snow for
the forecast Tuesday night into Wednesday.

By late Wednesday, we`ll see the progressive pattern continue and we
should see ridging building in from the west which will yield a
drier, but continued cool pattern for Thursday.  Inclement weather
looks to return by Friday as the next weather system pushes eastward
into the region.

As for temps, warmest period will be on Tuesday with highs in the
upper 40s to the lower 50s.  Highs Wednesday are dependent on
aforementioned storm track.  The blend yields highs in upper 30s to
the lower 40s, though highs may end up being a little colder than
that.  Temps will rebound slightly on Thursday and Friday with temps
warming back into the 40s and 50s. Overnight lows look to be in the
upper 20s to the lower 30s.


.Aviation...(06Z TAF Issuance)
Issued at 150 AM EDT Sat Mar 17 2018

Early this morning, the first TAF concerns will be LLWS at
SDF/LEX/BWG and t-storm chances at BWG.  A strong LLJ and line of
convection ahead of an approaching low pressure system will move
through the region during the pre-dawn hours.  BWG looks to be most
affected with LLWS and a t-storm chance, but the LLJ could be decent
at SDF/LEX as well early this morning.  Winds at 2 kft look to be
from the SW at 35-38 kts with sfc winds east-southeast between 5-8
kts.  T-storms at BWG could reduce flight conditions to MVFR/IFR if
strength is maintained as they progress east from western KY. Will
need to monitor.

After this line of convection passes through this morning, expect
VCSH throughout the rest of the morning hours.  Also a warm front
will slowly move north through central KY today settling somewhere
over north central KY this afternoon.  Along and north of the front
at SDF/LEX/HNB, expect showery conditions, light/vrb winds, and IFR-
MVFR conditions throughout the day.  This afternoon SDF/LEX stand
the best chance at a few t-storms as a sfc low passes through. At
BWG, a few t-storms will also be possible this afternoon along with
gusty southwest winds.

Convection should end late tonight after passage of the low pressure
with conditions returning to VFR.




Short Term...MJ
Long Term....MJ
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