Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 021739

Area Forecast Discussion
National Weather Service Louisville KY
1239 PM EST Fri Dec 2 2016

...Updated Aviation Discussion...

.Forecast Update...
Issued at 955 AM EST Fri Dec 2 2016

The main forecast challenge for today is the low cloud deck over
southern IN/northern KY and how far south it will sink into our
region.  Regions that remain cloudy will be limited to highs in the
lower 40s today.  Locations that see mainly sunny skies will likely
reach the mid 40s to lower 50s.


.Short Term...(Today through Saturday)
Issued at 235 AM EST Fri Dec 2 2016

Upper troughs crossing New England and the Rockies will sandwich
weak ridging over the Plains and Mississippi Valley. Meanwhile,
surface high pressure will build from the Midwest into the Ohio
Valley. 925-850 RH profiles show moisture being pulled down from
central Canada on the back side of the northeastern upper trof. This
moisture has manifested itself as a large shield of clouds sweeping
from the upper Plains through the Great Lakes overnight last night.
Some clouds may form in this moisture along and north of I-64 today,
with more abundant sunshine to the south. As a result, we kept high
temperatures this afternoon in check across the north, in the middle
40s, while going warmer in southern Kentucky with lower to middle

After another quiet and cool night tonight with lows around the
freezing mark, high and mid clouds will begin to enter the region
Saturday from southwest to northeast ahead of an upper low digging
into northwest Mexico. These clouds will be harbingers of more
unsettled weather coming in the long term.


.Long Term...(Saturday Night through Thursday)
Issued at 308 AM EST Thu Dec 2 2016

The northwest Mexico upper low at the beginning of the period will
eject to central Texas by Monday morning, Kentucky Tuesday morning,
and off the New England coast Wednesday morning.

A weak wave ahead of the parent low will advance from the Ozarks to
the Ohio Valley Saturday night. Lowering and thickening clouds
during the day Saturday will begin to drop light precipitation
Saturday night, beginning in the Bowling Green region in the evening
and progressing to the Blue Grass by early Sunday morning. The
majority of the precipitation will be rain and will be quite light,
on the order of a tenth of an inch in southern Kentucky and even
less north of there. Some light snow still may mix in with the light
rain over southern Indiana and north central Kentucky, though, as
surface temperatures bottom out right around the freezing mark.

A weak northern stream upper trof will cross the Great Lakes and
Ohio Valley Sunday afternoon/evening with patchy light rain
continuing Sunday, then pulling off to the east Sunday evening.

Drier air will move in for Sunday night and Monday morning, but then
deep moisture will return by Monday afternoon and continue through
Monday night as the Desert Southwest upper low approaches. Also, a
surface low will spin up over the northwestern Gulf of Mexico and
accompany its 500hPa counterpart north northeastward, becoming
nearly stacked by the time the system reaches Kentucky.
Precipitation will return, this time from south to north and
entirely in the form of rain, Monday evening through the overnight.
The best chance for significant rains will be Monday night, with
precipitation becoming lighter and gradually ending Tuesday as the
system and its associated moisture pull away. Some weak elevated
instability shows up on sounding progs southeast of the surface low
over southern Kentucky Monday night and could spark a few rumbles of
thunder. Rainfall amounts should be in the one-half to one inch

By Tuesday night the next upper trof will be sinking into the
American Rockies, reaching the Ohio Valley Thursday. Though the
details at the surface are still uncertain, overall the pattern is
unsettled and suggests periodic chances of precipitation. Right now
the best chances appear to be Wednesday night into Thursday morning
with a possible cold frontal passage. Precipitation type will be
liquid through at least Wednesday evening. After that, it depends on
how quickly cold air can sweep in behind the departing front.

Looking ahead a bit, late this week and into next weekend (the 9th-
11th) looks chilly with morning lows Friday and Saturday 10 to 15
degrees colder than normal.


.Aviation...(18Z TAF Issuance)
Issued at 1230 PM EST Fri Dec 2 2016

Widespread low clouds exist at this time from central IL to southern
IN to northern KY on northward. SDF and LEX are on the southern end
of these clouds, with both sites reporting MVFR cigs (3 kft) at this
time. The clouds were making southward progress this morning but
this has slowed. Looks like cigs should hold in this afternoon at
SDF and LEX and probably for much of tonight at LEX. Have scattered
out clouds at SDF this evening, but cigs could hold as SDF should
remain on the edge of the cloud shield. Clouds will remain north and
east of BWG, with VFR conditions through the forecast period.

At least scattered low clouds should continue at SDF and LEX on
Saturday with cigs not out of the question at LEX. Otherwise, mid
and high-level clouds will begin streaming in from the southwest
ahead of the next weather system during the day.

Surface winds this afternoon will be from the W or WNW at 5-10 kts,
then light or calm tonight, then NW to N around 5 kts Saturday,
becoming NE at BWG.


.LMK Watches/Warnings/Advisories...


Short Term...13
Long Term...13
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