Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 222111
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
411 PM EST Thu Feb 22 2018

.Short Term...(This evening through Friday night)
Issued at 400 PM EST Thu Feb 22 2018

...MULTIPLE ROUNDS OF RAINFALL CONTINUING INTO THE WEEKEND...

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

(Tonight - Friday Night) - Rain continues and intensifies at night.
Expect river flooding.

Currently, light rain continues across southeastern Kentucky with
the northern edge of this rain stretched across a line from Logan
County through the Bluegrass. This rain is expected to continue for
the rest of the day as the low level jet continues to overrun the
stationary front. The rest of southern Indiana and central Kentucky
will continue to sit under cloudy skies. With the front running
horizontally through Kentucky, southeastern Indiana is seeing mid 40s
as southeastern Kentucky sees mid 60s.

(Tonight - Friday Night) - Rain chances increase bringing heavier
rain to southern Indiana with a gradient dropping through Kentucky.

Near 0z the stationary front in northern Tennessee will begin to
push north with a 50 knot lower level jet with precipitable water
around 1.5". During this general time the CWA will remain in the
right entrance of the upper level jet. Several global models have
the axis of heaviest rain setting up through south central Indiana.
The HRRR is showing precipitation further south. Based on recent
rainfall trends, it is believed the axis of highest rain will fall
in northwestern Kentucky near Henderson and Daviess Counties through
southern Indiana near Crawford and Perry Counties. Around an inch is
possible between 6-12z along this axis. Rain amounts will fall off
further north, south, or east. The rain is expected to move into the
area shortly after 6z from the southwest.

As the warm front continues north, the heavier rain is expect to run
into Saturday afternoon. Along that axis of heaviest rainfall
another 0.5 - 1" is expected. Winds from the south are expected to
be 10-15 mph with gusts near 25 mph in central Kentucky. The warm
front will occlude and settle across central Kentucky.

Friday night, the upper level trough axis along with a cold front
begins to move east from Utah. This will be the force that pushes
the rain chances out of the area.

Confidence is high that the area will see 1-2" near and north of the
Ohio River tonight and tomorrow. Expect local rivers to react the
this additional rainfall.

&&

.Long Term...(Saturday through Thursday)
Issued at 330 PM EST Thu Feb 22 2018

...SIGNIFICANT FLASH FLOODING POSSIBLE SATURDAY NIGHT AND SUNDAY...

...STRONG TO SEVERE THUNDERSTORMS POSSIBLE SATURDAY EVENING THROUGH
SATURDAY NIGHT...

A warm frontal boundary is likely to be draped somewhere over the
area Saturday morning. The upper pattern will continue to be
dominated by western troughing and strong ridging over the Gulf and
southwestern Atlantic. The highly anomalous and persistent stream of
Gulf moisture will continue over the Ohio Valley. The latest 12z GFS
guidance features PWATs of 1.4-1.5 during the day. Widespread
showers are likely in addition to scattered thunderstorms. Areal
flooding is certainly a possibility on Saturday, especially after
whatever rain falls Friday and Friday night. River flooding will
only continue to worsen over the weekend. 12-hour QPF looks to range
between 0.25-0.75 through 00z Sunday, with the highest totals along
the Ohio River and in southern Indiana.

Saturday night, the upper level trough slides east a bit with a
modest boost in the upper level jet. A strong 500 mb wave ejects
northeast into the Upper Midwest, taking on an increasingly negative
tilt. This will allow a surface cyclone to strengthen and track from
near Missouri/Iowa to northern Wisconsin Saturday night, shoving a
potent cold front through central Kentucky and southern Indiana.
This is a very potent system, with the latest models hinting at a 70
kt LLJ.

This LLJ may be able to push surface dewpoints into the 60s along
and just ahead of the front, with PWATs up to around 1.6. Strong
deep layer shear and marginal (but sufficient?) CAPE may result in a
squall line with a damaging wind threat. At this time, MLCAPE could
even reach 200-300 J/kg, but confidence in the details is low at
this point. However, given flooded soils, trees will be quick to
topple in the face of relatively less wind. So we could see quite a
few trees come down Saturday night.

Given our ongoing, significant prolonged rainfall/river flooding
event, flash flooding is the other primary threat Saturday night and
Sunday. Significant flash flooding is possible. Given a strong
convective environment, excessive rain rates are likely. Additional
rapid rises on small creeks and streams are also likely.

Dry weather looks to finally return Sunday and early next week.
However, the Ohio River and other rivers will continue to rise.
Additional rainfall will be possible on Wednesday and Thursday, but
details and amounts are uncertain.

&&

.Aviation...(18Z TAF Issuance)
Issued at 100 PM EST Thu Feb 22 2018

Moderate showers will spread northeast into portions of south-
central KY this afternoon, mainly south and east of BWG. However,
some light rain is certainly possible in the vicinity. Fog/mist
are also more prevalent near BWG due to light winds and a surface
boundary draped nearby. Lower ceilings will continue through much
of the TAF period given plenty of low-level moisture and rounds of
moderate to heavy rainfall. The next chance for heavier rainfall
will be overnight, particularly at HNB and SDF. Expect lower
ceilings and visibilities at those sites. Some light to moderate
showers can be expected at LEX as well Friday morning. Winds will
be variable tonight with a surface boundary overhead, becoming
more southerly across the area on Friday. Low-level wind shear is
likely again during the early to mid morning hours on Friday, with
40-45 kts at 2-3 kft.


&&

.Hydrology...
Updated at 335 PM EST Thu Feb 22 2018

Minor flooding continues along the Ohio River at Louisville and
Cannelton, with moderate flooding expected. Tell City is in moderate
flood.

Synoptic models continue to advertise an additional 2 to 4 inches of
rainfall through Saturday night across much of the region. This
range has been very consistent over the past few days. As with any
convective, long term event, some locally higher amounts will be
possible depending on where multiple axes of heavier precipitation
develop. The most likely geographical area to get the most rain will
be those locations along and either side of the Ohio River.

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 and potentially
some flash flooding. In addition, ongoing river flooding will become
worse with time as the runoff makes its way into the rivers.

Current river forecasts are based on forecasts that contain 72 hours
of future rainfall. Thus, the current forecasts capture rainfall
through Sunday morning. The forecasts that are being issued now are
able to incorporate all of the expected rainfall for this prolonged
event.

Some of the following stage information comes from various ensemble
model packages, and is likely to change as new data are ingested by
those models. Other data is based on current official forecasts.
**Also remember that some of the rain that will be responsible for
the rises on the rivers hasn`t even fallen yet, so significant river
stage forecast changes should be expected over the coming days.**

...Ohio River...

The river from Louisville to Tell City is forecast to reach moderate
flood levels. Tell City has just reached moderate flood, and
Cannelton is expected to do so later this evening. McAlpine Upper is
expected to go into moderate flood by early Saturday morning, with
McAlpine lower going into moderate flood by Sunday afternoon. Clifty
Creek will likely enter minor flood later this evening and is
expected to get into moderate flood by Monday morning.

...Green River and Rough River...

At Dundee, minor flooding is occurring, with moderate flooding
possible.

Minor flooding is occurring at Woodbury today and expected at
Rochester by midday Friday. Munfordville and Alvaton will approach
flood stage, but are not forecast to hit flood stage at this time.

...Rolling Fork River...

Boston is forecast to rise to minor flood stage by early this
evening and has a chance to rise to moderate.

...Kentucky River...

Minor flooding may be possible at Lockport this evening and again
late this weekend. Peaks Mill on Elkhorn Creek is a smaller,
flashier stream and is more difficult to predict very far in advance
but it is in minor flood now and may go into minor flood again
late this weekend as well.

Given the consistent and consecutive heavy rainfall forecasts from
the guidance, a Flood Watch is in effect for the northwestern 2/3rds
of KY and all of southern Indiana for the duration of the overall
event, through Saturday night.

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 through Sunday morning for INZ076>079-083-084-
     089>092.

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

&&

$$

Short Term...KDW
Long Term...EBW
Aviation...EBW
Hydrology...EER/BJS



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