Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 231721
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1221 PM EST Wed Jan 23 2019

...Updated Aviation Discussion...

.Forecast Update...
Issued at 855 AM EST Wed Jan 23 2019

Precip shield is slowing its progression into central Kentucky,
allowing for just enough diurnal warming to mix down some 40+ mph
gusts in the Bluegrass region. This combination will require an
extension of the Wind Advisory in both time and area. Rest of the
forecast remains on track.

&&

.Short Term...(Today and tonight)
Issued at 320 AM EST Wed Jan 23 2019

Early morning surface analysis revealed an area of surface low
pressure near St. Louis with a cold front extending back to the
southwest.  Across southern Indiana and central Kentucky, skies were
cloudy with temperatures in the the upper 40s.  Some scattered rain
showers were working their way across the region.  In the near term,
not expecting much change in the weather.  Temperatures will remain
in the upper 40s with a rise into the 50s after sunrise.  Wind gusts
have been generally in the 25-30 MPH range.  Strong inversion aloft
is likely keeping the higher momentum air just off the deck. Rain
showers will continue to move eastward across the region, but the
intensity looks to remain generally light.

For Today, area of surface low pressure is forecast to move
northeastward into the Great Lakes states.  As this occurs, surface
cold front out over Missouri will slice eastward and pass through
the region during the early afternoon hours.  Ahead of the cold
front, widespread rain showers are expected.  We could have low-
topped line of heaver showers near the surface frontal interface as
it passes through.  Winds out ahead of the front will remain gusty.
The area at most risk for 40 MPH gusts still looks to be SW of a
line from Jasper to Elizabethtown.  Further east, not confident that
temperature inversion aloft will break enough to allow the higher
momentum air to come down to the surface.  So for now, will continue
the Wind Advisory as is.  Highs will surge into the 50s this morning
and then we`ll see falling temperatures through the afternoon from
west to east.  QPF amounts look to average between 0.75 to 1 inch.
Quite a bit of the snowpack has melted due to the warm temperatures
of yesterday and this morning.  So our current thinking is that
flooding threats continue to look minimal.

For tonight, temperature crash still looks on target with
temperatures falling sharply this evening.  The freezing line will
likely remain west of I-65 early this evening, but will advance
eastward during the evening and should be east of the I-75 corridor
by midnight.  As the colder air arrives, it may catch up to the back
side of the departing precipitation shield.  This would result in
rain changing to a period of snow before ending.

In terms of accumulations, there are a couple of negative aspects
here.  First the residence time of snowfall over any one area looks
to remain rather limited (just an hour or two).  Secondly, surface
temperatures and wet ground will limit initial accumulations,
especially of precipitation is light.  Right now, there is a risk of
some minor accumulations mainly east of the I-65 corridor.  A
slushy quarter to three quarters of an inch is possible this
evening.  The more likely issue will be the cold temps allowing
residual water to freeze on roadways leading to hazardous road
conditions late tonight.  For now, will be covering these impacts
with a Special Weather Statement.  Lows by tomorrow morning will
likely be in the lower to mid 20s.

.Long Term...(Thursday through Tuesday)
Issued at 315 AM EST Wed Jan 23 2019

Thursday...

A few light snow showers could linger in our far east Thursday
morning, otherwise expect a cool and dry day. Despite some peeks at
the sun, highs are only expected to top out in the mid to upper 30s
under steady cold advection.

Thursday Night...

Deep troughing will encompass most of the CONUS to end the work
week. Within the parent trough, a clipper will move through the
Great Lakes region. This feature will drag a cold front through the
region, but we will also have a shot at some flurries or light snow
ahead of the front in the warm advection/isentropic lift regime
Thursday evening. Moisture isn`t very deep (1000-850 mb), but there
should be deep enough saturation for available ice crystals for
snow. Perhaps a dusting would be possible across our NE CWA, with
mainly just an increase in clouds or some flurries for other parts
of the CWA. The strong cold front passes Thursday night with lows
dropping down into the low to mid teens. Some upper single digits
would be possible across southern IN. Given the decent surface winds
combined with the cold temps, wind chills could bottom out in the -5
to 5 above range Friday morning.

Friday...

Expect another cold and dry to end the work week as strong Canadian
high pressure controls at the surface. Temps only struggle to the
low and mid 20s for highs, despite expected mostly sunny skies. One
thing you can say about these arctic airmasses is that at least you
can get rid of the stratus decks that seemed to plague us the entire
first part of winter.

Friday Night - Tuesday...

Deep upper troughing will continue over the eastern two thirds of
the CONUS through the weekend into the early part of next week.
Within the parent trough, several disturbances will move through the
Great Lakes and Ohio Valley region. It appears most of the
associated surface low tracks move at or just north of our latitude
which will lead to warm advection ahead of, and cold advection
behind each system. This would ultimately result in systems starting
as rain and transitioning to snow or a rain/snow mix. At this time,
the Saturday and Sunday disturbances look fairly weak and starved of
moisture, however the early next week system looks stronger and will
have to be monitored over the coming days.

After lows in the upper teens Friday night, highs will still be
below normal on Saturday despite some warm advection. Look for low
30s north to near 40 south. Highs gradually warm into Sunday (upper
30s north to mid 40s south), and especially Monday (mid to upper
40s). Temps crash behind the aforementioned Monday/Monday night
system with highs only expected to be in the mid to upper 20s in
most spots by Tuesday.

&&

.Aviation...(18Z TAF Issuance)
Updated at 1210 PM EST Wed Jan 23 2019

Cold front has crossed the Wabash, pushing the main rain band into
SDF and momentarily BWG. HNB is also still under this band, but not
for much longer. Until fropa later this afternoon, expect wind gusts
near 25 kt with fuel-alternate cigs and IFR vis in rain. Precip
remains intermittent and winds remain frisky at LEX, with 30-35 kt
gusts still in play.

Front will move slowly east this afternoon, reaching HNB shortly
after valid time of the TAF, then into SDF and BWG late afternoon
and LEX early this evening. Low cig/vis will persist with mainly IFR
conditions, and wind gusts will ease with the shift to westerly.

Cold air just barely catches up with the departing precip late this
evening and overnight, and we are carrying a window for rain/snow
mix that is on the generous side for the sake of simplicity, with
maybe 2 hrs of opportunity for light snow before precip ends.

Should be free of any precip by daybreak, but MVFR ceilings will
linger well into Thursday.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...Wind Advisory until 1 PM EST /noon CST/ this afternoon for
     KYZ026>028-036-037-039>043-045>049-053>057-061>067-070>078-
     081-082.

&&

$$

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


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