Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 202317
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
617 PM EST Tue Feb 20 2018

...Updated Aviation Discussion...

.Short Term...(This evening through Wednesday night)
Issued at 300 PM EST Tue Feb 20 2018

Afternoon temperatures across the region were generally in the
upper 70s to around 80 in most places.  A very late springlike day
across the Ohio Valley.  Louisville International has hit 82 in the
last hour which is the highest maximum February temperature at the
station.  South to southwest winds of 15-25 MPH were common with
occasional gusts to 35-40 MPH at times.  The warm and breezy
conditions will continue through the afternoon hours with the winds
slackening off toward sunset.  Look for temperatures to settle down
into the 70s this evening before cooling off into the 60s later in
the overnight period.

A cold front out to the west will begin to move eastward late
tonight.  Showers, with a few rumbles of thunder will enter the
region from the west/northwest late tonight.  Best chances of precip
will be west of the I-65 corridor.  In fact, the eastern edge of the
rains will should be reaching the I-65 corridor by 12Z Wed morning.

The front will push through the region on Wednesday with widespread
showers being seen across the region.  Temperatures will fall behind
the front with daytime highs on Wednesday likely occurring around
midnight tonight.  By late afternoon, temperatures should range from
the lower 40s in southern Indiana to the lower 60s around the Lake
Cumberland region.  Rainfall amounts from late tonight through
Wednesday afternoon should run around 0.50 to 1.00 inch west of I-65
with 0.25 to 0.50 east of I-65.  It does not appear that significant
runoff will occur with this activity.  However, this will just prime
the soil up for more runoff later this week.

Frontal boundary looks to slowly stall out to our southeast
Wednesday evening.  Moist southwest flow aloft will continue to
transport moisture into the region.  So widespread rain showers look
likely through much of Wednesday night.  Lows should exhibit a
gradient from south to north with lows in the upper 30s to the lower
40s across southern Indiana and upper 40s to the lower 50s across
the areas along the KY/TN border region.

.Long Term...(Thursday through Tuesday)
Issued at 300 PM EST Tue Feb 20 2018

...SIGNIFICANT LONG DURATION RAINFALL EVENT UNFOLDING FOR LATE THIS
WEEK AND INTO THE WEEKEND...

...FLOOD WATCH FOR ALL OF SOUTHERN INDIANA AND MUCH OF CENTRAL
KENTUCKY THROUGH SUNDAY...

The highly amplified upper level pattern is expected to remain in
place throughout the remainder of the week and into the weekend
before flattening out early next week.  The pattern will feature a
trough in the western US and a ridge in the eastern US.  The Ohio
Valley will remain in between with a deep southwest flow of moisture
and in the main storm track.  Multiple perturbations will move
through within the mean flow brining multiple rounds of moderate to
occasionally heavy rainfall to the Ohio Valley.

The aforementioned front from the short term period is forecast to
stall out to our southeast by early Thursday. Much of the rainfall
will shift from our western areas to our southeast areas for
Thursday.  In fact, we could see a decent break in the precipitation
during the day on Thursday as we await for the next weather system
to arrive from upstream.  By Thursday night, the next wave will
approach from the southwest.  The frontal boundary to the south will
zip back to the north as a warm front and we`ll be on the warm side
again.  Multiple rounds of showers and a possibly a few
thunderstorms will be possible from Thursday night into the day on
Friday.  Heavier rainfall may refocus a bit more to our west Friday
night as the warm front surges back to the northwest.

By Saturday, a stronger perturbation aloft will move into the Plains
which will induce surface cyclogenesis in the Plains.  This feature
will move northeast Saturday afternoon and evening bringing a cold
front through the region.  The GFS is particularly aggressive with
its instability.  CIPS Analog guidance suggests the potential for
severe weather Saturday afternoon and Saturday night across the TN
Valley and into the Ohio Valley.  The details remain a bit unclear,
but there is a clear signal for a low-topped convective event with
wind damage being the primary severe weather threat.  So this will
bear watching over the next few days.   The cold front should push
through and end the long term heavy rain threat by Sunday afternoon
with drier conditions anticipated for Monday and into Tuesday.

As for QPF, as mentioned below in the hydro section, the
deterministic and ensemble runs are suggesting 3-6 inches of
rainfall through Sunday.  If this QPF is indeed correct, moderate
flooding will be likely on many of our river basins.  If the QPF
ends up being more widespread on the higher end of the guidance, say
5-6 inches, moderate to potentially major flooding could occur at
some sites.  In addition to the river flooding, low-land, flood
prone, and poor drainage areas could see hydro issues later this
week.  For this reason, we have hoisted a Flood Watch for the
northwest 2/3rds of KY through Sunday morning.  At this time, we
have opted to keep our southeast areas (Lake Cumberland Region) out
of the watch as the heaviest rainfall looks to remain northwest of
that area.  It is likely that this flood watch will be expanded
eastward in subsequent forecasts.  However, the current watch is in
good agreement with the WPC Excessive rainfall forecasts that go out
through three days.

People with interests along rivers need to keep an eye on the
forecast for the next few days. remember that river forecasts are
available via the "Rivers and Lakes" link on our webpage at
weather.gov/lmk.

&&

.Aviation...(00Z TAF Issuance)
Issued at 614 PM EST Tue Feb 20 2018

LLJ will ramp up again tonight, and it appears the latest suite of
model guidance develops a weak nocturnal inversion, so have
introduced LLWS into TAFs. If the lower boundary layer does not
stabilize tonight, there could be some +25mph gusts reaching the
surface and LLWS will not be as big of a factor.

A line of showers and isolated thunderstorms will approach from the
west after midnight, first impacting KHNB and then reaching KLEX
after sunrise. Gusty and variable winds will be possible in any
thunderstorm, but given the isolated coverage, do not have them in
TAFs at this time. IFR/MVFR cigs/vis will accompany the
precipitation overnight, and expect those conditions to persist
through the end of the TAF period.

&&

.Hydrology...
Issued at 300 PM EST Tue Feb 20 2018

Minor flooding continues along the Ohio River at Tell City,
Cannelton, and Louisville.  Along the Green River, all the sites
have dropped below flood stage, though this is just temporary.

Thankfully, we have had a dry today to help dry out things. However,
the latest forecasts continue to look ominous with a long duration
heavy rainfall event on tap.  Synoptic models continue to advertise
3 to 6 inches of rainfall through Sunday afternoon across much of
the region.  Some locally higher amounts will be possible depending
on where multiple axes of heavier precipitation develop. The Euro and
Canadian GEM generally agree with their heaviest rainfall from NE TX
through western TN.  The OP GFS and its ensembles continues to be
further north with its axis across southern MO into southern IL and
southern IN.

We`ve gone closer to the Euro runs here which matches well with our
previous forecast.  In general, we currently have around 3-3.5
inches across the Lake Cumberland region with generally 5-6 inches
in areas west of I-65.  This rainfall combined with already
saturated soils will lead to excessive runoff through the period.
This will result in flooding issues in the typical low-land and
flood prone areas.  In addition, ongoing river flooding will become
worse with time as the runoff makes its way into the rivers.  Quick
rises are expected later this week.

Current river forecasts that are out are based on forecasts that
contain only 48 hours of rainfall.  Therefore, with the additional
rainfall coming later this week, these river forecasts will likely
trend upward over the next few days.  Ensemble river forecasts
suggest that some of our points will rise into the moderate flood
range.  It is important to note that there are some QPF forecasts
that could push some of our points into major flood status.  Again,
these forecasts are *highly dependent* on where the heavy rainfall
actually develops.

Given the consistent and consecutive heavy rainfall forecasts from
the guidance, a Flood Watch will be posted with this forecast update
for the northwestern 2/3rds of KY and all of southern Indiana.  This
will be a long term flood watch that runs through Sunday morning.

Residents of southern Indiana and central Kentucky should remain
alert this week for flooding.  Stay tuned for the latest forecasts
and updates through the week.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Flood Watch from Wednesday morning through Sunday morning for
     INZ076>079-083-084-089>092.

KY...Flood Watch from Wednesday morning through Sunday morning for
     KYZ023>043-045>049-053>055-061>065-070>074.

&&

$$

Short Term...MJ
Long Term....MJ
Aviation...DM
Hydrology...MJ



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