Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 270516
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
116 AM EDT Mon Mar 27 2017

...Updated Aviation Discussion...

...Forecast Update...
Issued at 745 PM EDT Sun Mar 26 2017

Bulk of precip threat now east of the region. Still have a few light
showers showing up near Louisville, so later this evening will issue
an update to remove precip wording. Otherwise made some minor
adjustments to morning precip chances. These did not change the
overall rain chances for the daytime period, so no zone update is
needed.

.Short Term (Now through Monday Night)...
Issued at 330 PM EDT Sun Mar 26 2017

One more round of showers and a few storms is expected through the
mid part of the afternoon into the early evening, just ahead of a
cool front extending from the low pressure system moving into the
Great Lakes. With steeper low to mid level lapse rates, just enough
instability may exist for a slightly stronger updraft capable of
producing gusty winds and perhaps some pea sized hail due to
freezing levels less than 9 K feet. Overall tops shouldn`t get much
past 15-20K feet, so they should mainly just be showers.

Otherwise, we dry out through the overnight as progressive shortwave
ridging briefly builds overhead. Given partial clearing and some
lighter surface winds, combined with recent rainfall think we could
see some patchy fog. Will downplay this notion for now given
uncertainty in cloud cover and mixy near surface winds. Most lows
are expected to drop into the low or mid 50s overnight, depending on
location.

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

As we move into Monday and Monday evening, another progressive
shortwave enters the mid Mississippi River Valley. A weak surface
low will accompany this feature and travel up the Wabash and Ohio
River Valleys. Data has been fairly consistent in showing moderate
instability developing ahead of this feature later Monday afternoon
into the evening, although it is not a slam dunk given the degree of
expected cloud cover during the day. Could see some warm advection
showers or storms by late morning into early afternoon, however the
higher resolution convection allowing models key in on our bigger
threat later in the afternoon into the evening. Arrival of the
potent shortwave should trigger storms to our west. Given favorable
shear profiles, some initial discrete storms are possible and will
likely congeal into organized line segments as they approach our
CWA. Our main severe threat would be damaging winds, and possibly
hail if some isolated cells remain. In addition, cannot rule out a
non-zero tornado threat as surface low in our area may be able to
locally back the surface winds and ultimately increase low level
helicity for any storm able to take advantage. Our western CWA
appears to be the main severe threat focus for this round of storms
as it should weaken the further east and removed from daylight we
get on Monday evening.

.Long Term (Tuesday through Sunday)...
Issued at 330 PM EDT Sun Mar 26 2017

Tuesday - Wednesday Evening...

Shortwave trough axis pushes east Tuesday morning, with progressive
shortwave ridge axis building overhead through Wednesday. After some
lingering light rain showers in the morning, a weak frontal boundary
will stall over our region the rest of Tuesday and could provide a
very isolated rain chance. Will keep any mentionable pops in the 10-
20% range. In reality, the bulk of Tuesday and Tuesday night will be
dry. Highs should top out in the mid and upper 60s, and touching 70
in our SE. Lows should be in the upper 40s and low 50s.

Frontal boundary lingers in the area on Wednesday, however the lack
of moisture and enough focusing along the weak front will keep
mentionable pops out of the forecast. Expect another day in the
upper 60s to near 70 for highs.

Wednesday Night - Friday Evening...

The upper ridge axis pushes east Wednesday night, and the stalled
frontal boundary begins to slowly lift back north as a warm front
ahead of the next weather maker. A deep low pressure system moves
out of the southern Plains and into the Great Lakes by Friday,
bringing a combo of Pacific and Gulf moisture with it. Scattered
showers on Thursday morning should give way to more widespread
showers and a few thunderstorms Thursday afternoon into Thursday
night. Coverage should then reduce from west to east as we move
through the day on Friday. Will continue with Pops in the high
likely range later Thursday into early Friday, with scattered
coverage on either side. Surface low associated with the system does
look to track just north of our area so we will stay on the milder
side with temps mostly in the mid to upper 60s. A few low 70s are
likely on Thursday afternoon before precipitation really ramps up.
Will also continue mention of a slight chance of thunder during this
time as some instability looks to materialize.

Friday Night - Sunday...

Overall higher confidence in this time frame than what was observed
24 hours ago. Looks like a repeat of the early to mid week process
as the shortwave trough axis pushes east Friday night, followed by a
shortwave ridge axis Saturday through most of Sunday. Another
shortwave then arrives later Sunday in the continuous train of
anomalies pushing through the progressive flow. Sensible weather
should feature lingering light rain showers ending Friday night,
followed by a dry Saturday, Saturday night, and at least the first
half of Sunday. Some rain chance will likely be needed later Sunday
afternoon into Sunday night if consensus on the timing is accurate.
Look for highs mostly in the mid to upper 60s with lows in the mid
to upper 40s. These temps reflect at or just above the expected
climo for this time of year.

&&

.Aviation (06Z TAF Update)...
Issued at 1255 AM EDT Mon Mar 27 2017

Shortwave ridging in between two upper impulses has quieted down the
weather across Kentucky, with VFR conditions and light winds. Will
carry a few hrs of MVFR visibilities in BWG just either side of
daybreak, as the fog climo there still seems to trump the potential
mid-level ceiling. Otherwise moderate to high confidence that
conditions will remain VFR through at least mid-afternoon on Monday.

Strato-cu deck comes in late morning in response to warm
advection/weak isentropic lift. However, looks like it stays just
barely VFR, if it is actually enough for a ceiling. Will carry VCSH
during this time period as well, with the best shot initially at
BWG, then trending toward SDF and possibly LEX later in the
afternoon.

A more solid band of showers and storms comes in during the evening,
and will warrant prevailing SHRA, with just VCTS/CB. Fairly
confident in MVFR prevailing visibilities, but can`t rule out brief
IFR periods in the stronger cells. Less confident in the ceiling, as
none of the model guidance is hitting any restrictions hard at all
and we haven`t seen ceilings go down and stay down the last couple
days. Will keep ceilings VFR.

&&

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

$$

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



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