Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 141608

Area Forecast Discussion
National Weather Service Louisville KY
1108 AM EST Sat Jan 14 2017

...Forecast Update...
Issued at 1108 AM EST Sat Jan 14 2017

Let the Dense Fog Advisory drop off at 11 AM EST as obs and webcams
have shown improvement. With widespread rain moving in, improvement
should continue through the afternoon. Will update products to
remove headline wording.

Issued at 835 AM EST Sat Jan 14 2017

Dense Fog Advisory still ongoing across our southern 2-3 tiers of
counties at this hour. Still noting visibilities 1/4 mile or less in
that area. Have noted that widespread visibilities at 1/2 mile are
now occurring south of I-64, pretty much where the SPS is ongoing.
Will keep the SPS as long as visibilities don`t drop down to a
quarter mile. Will continue to monitor obs/webcams for the next few
hours until relief comes with the rainfall.

Speaking of rainfall, have increased pops into the categorical range
for most spots as we head into the afternoon. A disturbance
currently over southern MO will push eastward across our region,
bringing a 1.2 PWAT bullseye and enough forcing to warrant pops
mostly around the 80-90% range. Still expecting a tenth to a quarter
inch of rainfall for most spots with today`s rain.

Issued at 605 AM EST Sat Jan 14 2017

Patchy light rain/drizzle now traversing the I-64 corridor, but that
is actually where the "best" conditions are being observed at this
time. Dense Fog Advisory still flying across south-central Kentucky
for fairly widespread visibilities of 1/4 mile or less. Have added a
Special Weather Statement for much of the rest of central Kentucky,
where vis currently runs 1 mile or less in quite a few spots.

Still expect the axis of precip to edge southward through the
morning, and as it does so the rain/drizzle will actually scour the
boundary layer, allowing vis to improve to 3-4 miles. Otherwise no
changes to what is shaping up to be a "pea soup" kind of day.

.Short Term (Now through Sunday)...
Issued at 255 AM EST Sat Jan 14 2017

Strong upper ridge is anchored over the Gulf of Mexico, while
confluence aloft over the northern Plains keeps a cold surface high
anchored over the Upper Midwest. Generally weak isentropic lift from
the Ozarks across the Ohio Valley will continue to support waves of
mainly light precipitation for most of the weekend.

Main near-term challenge will be the impact and extent of fog, which
has become fairly dense over parts of south-central Kentucky.
Advisory is in effect until 16Z, at which point we expect a band of
precip to shift back southward across Kentucky, and light rain or
drizzle will actually scour the boundary layer just enough that
visibility will actually improve.

Next challenge will be the timing of additional impulses moving
through, especially as it relates to temp fluctuations over southern
Indiana. There will be a few hrs late tonight into Sunday morning
that we could see light freezing drizzle in southern Indiana, mainly
along and north of a Paoli to Madison line. It`s a low-probability,
low-QPF situation, so the most we would do is issue a Special
Weather Statement, and may even delay that until this afternoon so
it is not lost in any fog-related messaging that may be needed this

Expect minimal diurnal temp ranges through tonight due to low clouds
and fog. Temp forecast is below guidance today, and above guidance
tonight. Actually should see a little better recovery on Sunday as a
weak warm front lifts through late in the day. This will shift the
axis of highest precip chances northward across the area Sunday into
Sunday night. Even weaker forcing will keep QPF quite low, and the
clouds/drizzle may be more extensive than suggested by the precip
chances which are largely capped at 50% tonight and Sunday.

.Long Term (Sunday night through Friday)...
Issued at 255 AM EST Sat Jan 14 2017

Rain chances will continue Sunday night through Tuesday, and be
accompanied by unseasonably warm temps as we break into the warm
sector. Low pressure lifting into the Great Lakes will phase with
the northern stream just enough to drive a cold front into the Ohio
Valley late on Tuesday. Precip chances will max out during the day
on Tuesday, with widespread showers and a few T-storms along the

Last few runs of the GFS and ECMWF ave been more aggressive in
pushing the front well to our south and east by Wednesday, but
without a strong high behind it, the post-frontal air mass is mild
enough that unseasonably mild temps will continue for the rest of
the week. Rain chances will ramp back up Thu night and Fri as the
pattern amplifies again and another low lifts from the southern
Plains into the Great Lakes.


.Aviation (12Z TAF Update)...
Updated at 605 AM EST Sat Jan 14 2017

Persistence is the best aviation forecast for this forecast period
at all three terminal sites.  For ceilings it`s pretty much a no-
brainer: LIFR, POSSIBLY rising to IFR heights for a few hours. For
visibility, though, persistence means anything from 1/2SM to 5SM in
BR and DZ, which is essentially what has been going on all night.
Regardless of the visibility fluctuations, however, ceilings will not
break out or rise to more than 007 at any of the sites, thanks to a
saturated sounding with a very strong temperature inversion from a
few hundred feet above the surface through 050.

The synoptic conditions responsible for the low stratus - a broad
high pressure area at the surface stretching from the upper
Mississippi valley to New England, with overrunning moisture and
warm air flowing above it - will persist through the weekend.  Flow
around the surface high will be mainly north to northeast at or
below 5kts, but will vary greatly in direction at times due to the
relatively weak pressure gradient.




Short Term.....RAS
Long Term......RAS
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