Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 161506
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1006 AM EST Thu Nov 16 2017

.Forecast Update...
Issued at 1000 AM EST Thu Nov 16 2017

Forecast cloud cover has been increased this afternoon based on
latest model and satellite trends. GOES-16 visible satellite shows a
broad area of stratus with some clearing in central IN/IL, but this
area of clearing is beginning to fill in with strato-cu.
Additionally, low level RAP moisture profiles keep boundary layer
moisture content high through the morning and afternoon under a
strong inversion. While we should see some breaks in the clouds this
afternoon, it doesn`t look like we`ll get enough dry air in the low
levels to scour out the clouds. Otherwise, rest of forecast is on
track.

&&

.Short Term...(This afternoon through Friday evening)
Issued at 242 AM EST Thu Nov 16 2017

Surface analysis early this morning shows initial cold from
yesterday now across eastern Kentucky and eastern Tennessee while a
secondary cold front with a more notable wind shift across central
Illinois and Indiana. Satellite imagery has a variety of features
with stratus remaining generally east of I-65 while patches of
locally dense fog have formed in the clearing skies and lighter
winds in its wake. Finally, another area of stratus lies across
central IL and central IN, steadily moving southeast. Readings are
generally in the 40s.

Through this morning, there will continue to be patches of fog
across southern Indiana and central Kentucky, especially in lower
lying areas, that could reduce visibility down to less than 1/2
mile at times into the morning commute. As winds pick up and begin
to mix the boundary layer, this should erode in a few hours. The
other stratus deck across central IL/IN will likely brush parts of
southern Indiana and north central KY later this morning. This too
should mix out by mid-morning. Overall, more sun is expected later
this afternoon for all areas as high pressure drifts into the area.
Plan on temperatures to be seasonably cool with readings topping out
in the 40s to around 50.

A mostly clear and cool night is in store for the area. Plan on lows
to fall into the upper 20s to lower 30s. On Friday, winds will
become southerly ahead of the next weather system with afternoon
breezes 10 to 15 mph. Look for highs to reach the 50s with some
across south central Kentucky approaching 60.

.Long Term...(After midnight Friday night through Wednesday)
Issued at 245 AM EST Thu Nov 16 2017

...Strong Winds Friday Night through Saturday Night...
...Strong Thunderstorms Possible Saturday...

The main weather concern in the long term is the strong system to
impact the area late Friday night through Saturday night. Wind and
the potential for strong thunderstorms are the main potential
hazards.

As low pressure deepens Friday night across the central Plains, a
warm front will set up just north of the area. A strong low-level
jet will keep winds sustained 10 to 15 mph at night and we should
see a non-diurnal temperature trend as readings bottom out in the
low 50s early Friday evening then rise into the upper 50s to near 60
by Saturday morning.

As the surface low deepens and races from Kansas City to Chicago to
Detroit Saturday, scattered showers may develop ahead of the cold
front. It will be very windy ahead of the front as well, with
south/southwest winds sustained 15 to 20 with gusts 30 to 35 mph
possible.

The frontal passage looks to be in the afternoon hours across
southern Indiana and central Kentucky. Looking at the latest
instability forecast, between 100-500 J/kg of most-unstable CAPE is
forecast right along and ahead of the front Saturday afternoon. This
combined with the very strong environmental wind fields could yield
a line of low-topped strong showers/thunderstorms. If some of these
strong winds aloft mix down to the surface, damaging wind gusts
could occur.

Behind the front, west to northwest winds will remain strong with
the potential for 35 to 45 mph gusts. Outside of the thunderstorm
wind gusts, the gradient winds alone could produce damage as well.
Will continue to highlight this in the hazardous weather outlook,
and raise the possibility of a wind advisory being needed for
Saturday that later shifts can analyze further.

Crashing temperatures and cold advection kicks in quickly Saturday
evening behind the front. The latest runs of the NAM indicate wrap
around moisture swinging across the northern half of the forecast
area late Saturday night. Soundings show there could be enough
saturation in the -7 to 10C range to squeeze out flurries or wet
snowflakes on the backside. After topping out in the 60s Saturday,
temperatures Saturday night will fall into the lower 30s.

Seasonably cool weather will finish out the weekend with highs on
Sunday staying in the upper 30s to lower 40s. As the upper level
pattern transitions to more zonal early next week, temperatures will
moderate back to near normal. Looking ahead to the Thanksgiving
holiday period, another weather system could impact the area but
forecast confidence isn`t too high. For now, will advertise 20
percent rain chances.

&&

.Aviation...(12Z TAF Issuance)
Issued at 640 AM EST Thu Nov 16 2017

Clouds will be the main challenge today. Satellite and observations
show a corridor of 015-020 ceilings dropping southward from Illinois
and Indiana into Kentucky. These clouds will provide MVFR ceilings
to HNB/SDF/LEX for much of the morning.

There is also a large cloud field, with similar base heights, spread
across the upper Mississippi Valley and Great Lakes. The thought
right now is that most of these clouds will stay to our north, plus
some erosion of the clouds should take place by the time they would
get this far south this afternoon. Still, something to keep an eye
on.

High pressure crossing the region will provide us with mostly clear
skies tonight. Winds, generally below 10 knots, will shift from
northwest today to east tonight to southeast on Friday as the high
moves by.


&&

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

$$

Update...DM
Short Term...ZT
Long Term...ZT
Aviation...13



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