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Area forecast discussion 
National Weather Service Jackson Kentucky
150 am EST sun Dec 28 2014

Update...
issued at 150 am EST sun Dec 28 2014

Made some minor tweaks to the grids for latest trends in radar and
observation. Overall no major changes to the forecast package. Light rain and
drizzle will continue to overspread the area as a cold frontal
boundary drops down into our forecast area over the next several
hours.

Update issued at 1030 PM EST Sat Dec 27 2014

Did an update to fine tune the probability of precipitation through the rest of the
night...more in line with the latest hrrr guidance. The hrrr showed
that the precipitation would push in most effectively from the northwest
during the early morning hours while the far east stays no worse than
scattered for much of the night. Also tweaked the T and dew point grids per
the latest observation and trends. These have been sent to the ndfd and web
servers along with a new set of zones.

Update issued at 750 PM EST Sat Dec 27 2014

23z surface analysis shows an area of low pressure pushing into eastern
Kentucky from the southwest. This has brought an early round of
showers to the Cumberland Valley. These have been battling the dry
air in place through the area...but have been able to reach the
ground with the heavier returns. These showers will continue to
moisten up the lower atmosphere this evening with the next surge
after midnight likely to bring widespread rain to the entire County Warning Area.
With dew points in the 40s...once the rain moves in properly...low
temperatures will be capped in the low to middle 40s. Have updated
the forecast to fine tune the pop chances and infuse some of the
latest near term guidance into the T and dew point grids. These updates have
been sent to ndfd and the web servers. A zone forecast product update will follow later
this evening once the widespread rains are on our doorstep.

&&

Short term...(this evening through Sunday night)
issued at 331 PM EST Sat Dec 27 2014

Current conditions across the region feature surface low pressure
strengthening as it moves northeast into the Great Lakes region.
Meanwhile...a surface cold front associated with this low as of 20z
is pushing into western Kentucky with a swath of rain moving up from
the middle MS River Valley into central Kentucky. Widespread cloud cover
and rain continues to push east but surface high pressure centered
just off the NC coast is retreating slightly slower than anticipated.
Hence some breaks in cloud cover still are present in eastern
Kentucky. This will keep precipitation out of the area a tad longer...but an
new developing surface low pressure along the western Gulf Coast and
strengthening low level jet will reinforce the moisture surge
northeastward into the Tennessee Valley and Ohio Valley by tonight and
especially Sunday. Models support this trend and as such...am quite
confident that measurable precipitation will materialize tonight and have
gone with categorical probability of precipitation.

The stubborn ridge over the Bahamas remains in place through the
rest of the weekend before weakening late Monday as the trough over
the eastern Continental U.S. Lifts into the New England states. Through this
period though...quite a strong moist low level southwest flow will
keep rain over eastern Kentucky through Monday morning before ending
from northwest to southeast on Monday night. Low level moisture may
be slow enough to exit behind the front that colder air moving in may
allow for some brief instances of snow mixing with the rain or
changing to all snow in the northwest Bluegrass counties and the
higher terrain in the counties bordering Virginia. Any instances that
do occur are expected to be brief and no accumulation is expected.
Overall...a wet and rainy end to the weekend and beginning to the new
week is on tap.

Long term...(monday through saturday)
issued at 358 PM EST Sat Dec 27 2014

A cold front...and weak waves of low pressure moving along it...will
be exiting the area to begin the extended period on Monday. Based on
the latest model time heights and soundings...weak upslope flow and
residual moisture behind the departing boundary may allow isolated to
scattered rain and snow showers to linger behind the front. Based on
moisture availability and the lack of ice Crystal growth
aloft...precipitation should initially be in the form of rain showers
through around 12z on Monday. After that...enough cold air should
spill into the region to allow some snow flurries to mix with
sprinkles or light rain showers Monday night through early Tuesday
morning. The nam12 soundings seemed to have the best handle on the
transition between precipitation types...so that model was used to create
the probability of precipitation and precipitation types through early Tuesday morning. Once the
precipitation exits the area Tuesday morning...a ridge of high pressure will
influence the regions weather through late Thursday morning. A fairly
potent area of low pressure is then forecast to form in the southern
jet stream over the southern Rocky Mountains. As this system advances
eastward...the models have it tapping into ample Gulf of Mexico
moisture Wednesday night and Thursday. Should the models pan out...the
first precipitation would enter eastern Kentucky around noon on Thursday and
gradually overspread the area from there. By 2 or 3z Friday...the
system will tap into some colder air...allowing for precipitation along the
northern fringe of the precipitation shield to mix with snow. The
precipitation should transition to all snow by around 6z Friday as more cold
air spills in from the north. Warmer air is then forecast to progress
northward into the area Friday morning...allowing precipitation to
transition back to a rain snow mix and then rain by early Friday
afternoon. At this time there is too much uncertainty as to the exact
track of the southern stream low and the amount of cold air that will
be available for the transition to snow. Therefore...have elected to
go with only minimal snow accumulations Thursday night into Friday
morning.

Temperatures throughout the extended period look to be well below
normal based on the current MOS guidance. Based on the latest model
soundings...decided to continue with this overall trend until the
data settles on a solution. The coldest days upcoming look to be
Tuesday through Thursday...as cold air invades behind the initial
frontal boundary. Daytime highs on those three days may not rise out
of the 30s across the area. Friday should be slightly warmer as winds
shift to the south...with high in the lower 40s on tap.

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 150 am EST sun Dec 28 2014

Flight conditions will deteriorate through the first few hours of the
forecast as drizzle and light rain overspread the area from the west.
Followed model guidance...bringing conditions down gradually. But
observations at least initially suggest a quicker transition. Light
rain and drizzle will linger through the day today with some
improvement possible at the end of the forecast window. Winds will
gradually veer out of the northwest at around 5 kts.

&&

Jkl watches/warnings/advisories...none.

&&

$$

Update...ray
short term...shallenberger
long term...Arkansas
aviation...ray

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