FXUS63 KLMK 161718

Area Forecast Discussion
National Weather Service Louisville KY
118 PM EDT Thu Aug 16 2018

.Forecast Update...
Issued at 950 AM EDT Thu Aug 16 2018

Widespread showers and storms continue this morning in a NE to SW
axis across central KY and parts of southern IN. The rain is being
forced by isentropic and mesoscale upglide and significant moisture
transport within a low-level axis of 30-40 kt SW flow (as shown by
the latest KLVX vertical wind profile). Here are a few rain totals
we have seen so far:

KY Mesonet sites (24 hr amounts from 8 am yesterday to 8 am this
morning): Meade County 3.9; Breckinridge 2.84. Also 3.49 24-hr total
ending 8 am this morning at our NWS office, with additional rain
since then.

Latest short term models suggest low-level jet will continue from
the SW for much of today but tend to weaken a bit (as is normal) and
veer slightly. This means that the ongoing rain should continue to
work its way slowly east as a whole (away from the areas hit
hardest so far) with a tendency for some weakening this afternoon.

The question then becomes whether additional cells will develop
farther to the west this afternoon over southern IL and IN and
western KY and even western parts of our forecast area before moving
east into our area. Current GOES-16 visible data shows some agitated
cumulus in southern IL where mesoanalysis data shows marginal
instability. Forcing, however, should be weaker. Therefore,
additional development "may" remain scattered, but with a moisture-
rich atmosphere, additional heavy rain is likely from these cells.
The current Flash Flood Watch remains in effect til 20 UTC. Will
evaluate the need for a timing and/or areal extension later today.
No changes to tonight's forecast at this time.

High temps this afternoon are tricky given all the clouds and rain.
Have lowered temps some but air mass should have some time to
recover this afternoon in the wake of the current rain as it moves


.Short Term...(Today and tonight)
Issued at 245 AM EDT Thu Aug 16 2018

Today - Expect multiple rounds of rain and storms flowing up the
Ohio River Valley.

Models haven't had the best handle on timing, but they agree for the
most part on location. Moisture continues to be carried up the
Mississippi and Ohio River Valleys by the low level jet. Southern
Indiana has moisture pooling overhead with precipitable water values
over 2". This low level flow sits between a surface high sitting
over western North Carolina and a surface low over northern
Missouri. This pattern won't change much today.

This afternoon, precipitable water values in central Kentucky begin
to go over 2". With the added moisture and warm temperatures pushing
temperatures to the the convective temperature, more showers and
thunderstorms will form and cause heavy rain and gusty winds. Heavy
rainfall is expected and could cause some isolated problems with
localized flooding and ponding on surfaces with poor drainage.

Temperatures today are expected to be in the mid 80s for most with
upper 80s in south-central Kentucky.

Tonight - Expect more rain with areas further south and east getting
in on the action.

In the mid-levels, a closed low over South Dakota will dive
southeast towards northern Indiana tonight. This will bring a
shortwave on a shallow mid-level trough. This shortwave will help to
initiated move rain during the overnight hours. It will likely
expand rain showers further south and east in central and eastern

Temperatures will stay mild with mid 70s in south-central Kentucky
and in the low 70s everywhere else.

.Long Term...(Friday through Wednesday)
Issued at 330 AM EDT Thu Aug 16 2018

...Multiple episodes of showers and storms to continue through the
extended period, with a possible break on Sunday...

Upper low along the northern IL/IN border Friday morning will push
to Lake Erie later in the day. Underneath it though, a weaker
shortwave should get to the Wabash at the same time. These two
features and the moist airmass in place will mean continued
excellent rain chances along with some flood potential. Forcing
aloft later in the day could be in the right rear quad of a jet
associated with the first upper low.

The second upper feature takes its time exiting the area and it
leaves in its wake a quasi-zonal flow that keeps enough moisture in
the area for rain chances through Saturday. The CMC/Euro both argue
for a drying out period Sunday, whereas the GFS continues its
bullish precip ways in the extended. Will be optimistic here and
lean toward the former consensus.

Monday and Tuesday still look like the days for the next front to
try and cross the region slowly. Timing varies between models, but
consensus shows us drying out. The usually drier Euro actually
brings one more wave of precip through here Wednesday, behind the
cold front...as another wave crosses the region. Blended model
guidance argues for a dry period here, so have gone that way.


.Aviation...(18Z TAF Issuance)
Issued at 1250 PM EDT Thu Aug 16 2018

Well...the main convection is over the ern CWA affecting LEX for
next several hours and is over for HNB and SDF. The very tale end
of the precipitation is just moving thru BWG. The mesoscale models
generally only have isolated convection...albeit the NAM has more
substantial development later today.

Next upper air sharp vort max sliding down from IA/MO and will pivot
sharply over MO/IL bringing PVA and more convection after 06z. Most
pronounced will be 09z-15 along and west of I 65 and will put VCSH
late for HNB and SDF towards 12z.

Meanwhile...main issue may be low clouds and stratus tonight. I
plan to drop CIGS down to high end IFR/low MVFR at HNB and BWG.


IN...Flash Flood Watch until 4 PM EDT /3 PM CDT/ this afternoon for

KY...Flash Flood Watch until 4 PM EDT /3 PM CDT/ this afternoon for



Short Term...KDW
Long Term....RJS
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