Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 161811
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
111 PM EST Tue Jan 16 2018

...Updated Aviation Discussion...

.Short Term...(Today through Wednesday)
Issued at 316 AM EST Tue Jan 16 2018

...Snow Accumulations Continue Mainly Across Central KY Today...

The main focus for frontogenetical forcing has now shifted solidly
to southern and eastern portions of the CWA as the right entrance
region of a 130 knot upper level jet churns over the area. The
associated SW to NE oriented moderate band of snowfall will very
slowly make eastward progress through the rest of the morning,
diminishing and pushing east of the area by mid to late afternoon.
At the surface, the Arctic boundary has undercut the upper level jet
dynamics, helping to crash temperatures, introduce dangerous wind
chills, and increase snow ratios. Will try to summarize each
geographic region below, but keep in mind the lack of reports this
time of night is making it a little difficult to determine how much
has already fallen in some spots. So, storm totals are a bit tough
to gauge.

...South and East of a Bowling Green to Lexington Line...

We had a 20:1 ratio here at the office, so another .1 to .15 of QPF
should yield an additional 2 to 3 inches roughly along and east of a
Bowling Green to Lexington, KY line. Can`t rule out isolated 4 inch
amounts somewhere just south of the line mentioned above. Overall,
this should yield storm totals of 2 to 4 inches in areas outside of
the current Winter Storm Warning so plan to keep the advisory for
now. If an area does see persistent snow this morning, we may still
have to upgrade. Still expecting another 1 to 2 inches in the
current Winter Storm Warning which should put totals well above
warning criteria, so need no changes there either.

...Southern Indiana...

Snow has either ended or is very light at this point, so expect
little to no additional accumulation. Will consider trimming a few
counties off of the current Winter Storm Warning and Winter Weather
Advisory in the near future.

...Advisory Counties in north central and the Kentucky Bluegrass...

Light snow will persist through daybreak before tapering around
midday. Additional amounts of 1 to 3 inches are possible which
should put most storm totals in the 2 to 4 inch range. No plans to
change the headlines at this time.

...Wind Chill Advisory...

The Wind Chill Advisory still looks good for much of southern
Indiana and far west central KY. Still coming up with values around
-10 C this morning as single digit temps combine with steady WNW
winds.

...The Rest of Today, Tonight, and Wednesday...

The low level NW flow behind the Arctic boundary will also help to
bring in another round of low level moisture from the NW later this
afternoon, tonight, and through part of Wednesday. Given that this
moisture will be associated with -12 to -20 C temps (the DGZ),
expect persistent flurries and/or light measurable snow showers
starting later this afternoon over our NW and spreading over the
area through the evening, finally tapering from W to E on Wednesday.
Given very high snow ratios, have a dusting to a half an inch of
additional snow accumulations associated with this low level
moisture. We`ve seen this a couple times already this winter, and
honestly that may be a bit conservative...We shall see. Not sure how
many additional road problems the snow will cause given it`s fluffy
nature.

Highs today only reach the low and mid teens. Low tonight will
mostly be in the 0 to 5 above range. Winds will only be around 5
mph, so not as concerned about a Wind Chill Advisory. Nevertheless,
values will still be dangerous in the -10 to 0 range in most spots.
Highs Wednesday should recover to around 20 degrees.

.Long Term...(Wednesday night through Monday)
Issued at 316 AM EST Tue Jan 16 2018

Wednesday Night - Sunday...

...Warming Trend On The Way...

We`ll go from well below normal to well above normal temps by the
weekend! Dry NW flow aloft and surface high pressure will control
the pattern through the end of the work week. Then, the upper
pattern shifts to a more zonal flow, with high pressure shifting off
to the east for the weekend. We`ll see dry conditions for much of
this time with moderating temperatures rising around 10 degrees from
each day`s previous high. So, highs on Thursday right around
freezing will jump to the low 40s Friday, the low 50s Saturday, and
to the mid and upper 50s by Sunday (possibly warmer). Lows will also
moderate during this time. Low temps on Thursday morning around 10
above will rise to around 20 on Thursday night, just above freezing
Friday night, and in the lower 40s by Saturday night.

By Saturday, lee cyclogenesis will occur over the central and
southern Plains, with a resulting tightening pressure gradient over
the Mississippi and Ohio Valleys. The associated warm/moist
advection will be responsible for our rapid warm up, but will also
be responsible for increasing rain chance by the end of the weekend.
In fact, a few thunderstorms may not be out of the question by
Sunday night or Monday morning. We could begin to see some small
chances for a rain shower associated with isentropic lift by
Saturday morning as the warm sector gets established over the area.
However, prefer a mostly dry forecast through Sunday afternoon,
before the real rain chances arrive ahead of a potent storm system.

&&

.Aviation...(18Z TAF Issuance)
Issued at 100 PM EST Tue Jan 16 2018

Currently, snow showers continue to move to the east out of central
Kentucky. BWG will clear and LEX will soon follow to join the
rest of southern Indiana and central Kentucky under clear skies.
Low level clouds are currently moving south from central Indiana
and will impact HNB first around 20z, then continue to move south.
TAF sites will likely fall to MVFR conditions as these clouds move
through the area. With the current low temperatures, light snow
is likely from any cloud cover today possibly dropping
visibilities.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...Winter Storm Warning until 4 PM EST /3 PM CST/ this afternoon
     for KYZ040-041-046>049-054>057-064>067-073>078-081-082.

     Winter Weather Advisory until 4 PM EST this afternoon for KYZ036-
     037-042-043.

&&

$$

Short Term...BJS
Long Term...BJS
Aviation...KDW



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