Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 121221
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
721 AM EST Fri Jan 12 2018

.UPDATE...
Issued at 721 AM EST FRI JAN 12 2018

Rain showers spreading back across eastern Kentucky out of the
southwest as the low churns up into the western Tennessee Valley.
Temperatures currently sit in the 40s/50s locally, with the cold
front bringing 30s and lower west of Frankfort to Bowling Green.
Northwest winds will filter in this cooler air across the
Bluegrass and Lake Cumberland regions later this morning.

&&

.SHORT TERM...(Today through Saturday)
Issued at 358 AM EST FRI JAN 12 2018

An upper level trough lifting out of the lower into the mid
Mississippi and Tennessee Valleys will bring a seasonably strong
mid-January cold front through eastern Kentucky this morning and
afternoon. While a current lull in rain remains in place, light to
moderate rain will fill back in across the Lake Cumberland and
Bluegrass regions near and after daybreak as the front makes
headway east. Regarding the ongoing Flood Watch, along and east of
a line from Sandy Hook to Jackson to Harlan, will in all
likelihood let this expire as planned at 10 am as additional
rainfall amounts should top out at 1 to 1.25 inches, following
widespread rainfall Thursday of generally less than one half of an
inch.

The bigger issue will be the impending rush of colder air blasting
in through the day, cooling temperatures into the 30s/40s by late
afternoon. As the base of the upper trough remains west of eastern
Kentucky, its attendant surface low will be pushing across the
Appalachians, positioned just east of the Commonwealth by this
evening. This will in turn place eastern Kentucky in the wrap-
around/deformation band conducive for additional upper lift. As
temperatures continue to cool, will see rain transition to a mix
of frozen precipitation by late afternoon to very early evening
across the Bluegrass and Lake Cumberland regions before quickly
transitioning to all snow. Far eastern Kentucky should see the mix
begin by about mid evening with all snow falling prior to
midnight. Regarding precipitation type, have kept the transition
period mainly confined to sleet as opposed to freezing rain given
the pattern. Rapid column cooling will very likely erode any
pronounced elevated warm nose much faster than the NAM suggests,
although this morning`s run does suggest the near-surface layer
cooling off more quickly compared to last night. While a few
elevated surfaces may see a quick/light glaze, the more likely
scenario points to graupel/ice pellets as rain/supercooled water
freezes above the surface prior to ice being introduced into the
-10 to -20C layer. Regardless, the changeover to snow should
happen fairly quickly this evening given the degree of the cold
air filtering in.

Snowfall amounts still look to generally range from 1-3 inches,
with portions of the Bluegrass region and areas north of
Interstate 64 seeing 3-4 inches. Therefore, have opted to keep the
Winter Weather Advisory in place across all of eastern Kentucky
for now as snow accumulations should be somewhat limited by
initial above-freezing ground temperatures, as well as drier air
filtering into the dendritic growth layer as higher snow ratios
develop tonight.

Light snow will taper off toward Saturday morning as the low
slides northeast, leaving scattered flurries in its wake with the
help of an upslope/cold air advection regime. A 1040+ mb surface
ridge building in from the northwest will keep a stout cold dome
in place, confining high temperatures to the upper teens to mid
20s.

.LONG TERM...(Saturday night through Thursday)
Issued at 358 AM EST FRI JAN 12 2018

A large trough over the CONUS will be the dominant pattern for
the long term at least until mid-week. This trough will have a few
shortwaves that progress through it, but not much moisture will
be associated with them to bring much precip into the CWA. Temps
on Monday will see a slight increase with the passage of a warm
front and with slight WAA from the south. However, as the trough
deepens, a cold front will pass through that will bring a round of
precip into the CWA Monday night and into Tuesday, increasing
chances of rain and snow showers. There is some uncertainty in the
models regarding the timing of this system and how much precip
will occur, but generally the models show low amounts at this
time. After the cold front passes, a clipper system will take hold
and much colder temperatures will be the main theme through mid
to late week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 721 AM EST FRI JAN 12 2018

MVFR conditions currently working back into the Lake Cumberland
and Bluegrass regions, with points east soon to follow this
morning as rain continues to work north/northeast. A cold front
will move into eastern Kentucky later this morning, veering
southerly winds quickly toward the northwest through the late
morning and afternoon. Ceilings will lower to IFR levels as rain
and reduced visibilities continue through the afternoon. Enough
cold air will filter into the eastern Kentucky airspace by late
afternoon/early evening to begin transitioning rain to a mix of
rain/sleet/snow, with all precipitation becoming snow Friday
evening as blustery northwest winds continue. Also expect at least
IFR ceilings and visibilities as all precipitation transitions to
snow, with conditions possibly improving toward MVFR levels later
tonight as snow tapers off toward the northeast.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 1 PM this afternoon to 7 AM EST
Saturday for KYZ044-050>052-058>060-068-069-079-080-083>087-104-
106-108-111-114-116.

Flood Watch until 10 AM EST this morning for KYZ088-104-106-107-
109-110-112-113-115-117>120.

Winter Weather Advisory from 4 PM this afternoon to 7 AM EST
Saturday for KYZ088-107-109-110-112-113-115-117>120.

&&

$$

UPDATE...GUSEMAN
SHORT TERM...GUSEMAN
LONG TERM...CGAL
AVIATION...GUSEMAN



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