Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 171916 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
216 PM EST Sat Feb 17 2018

.UPDATE...
Issued at 208 PM EST SAT FEB 17 2018

Hourly grids have been updated based on KFGX observation and
social media reports to lower temperatures in mainly far northern
Fleming County to near or just above freezing. Some mixed
precipitation has been falling further south to locations north
of I 64. Generally a dusting to one half of an inch should fall in
most of this area. With a half of an inch to one inch possible in
northern Fleming County. The snow could come down hard enough,
mainly in northern Fleming County for a bit of slush on the
roadways at times. With accumulations expected to remain at no
more than an inch due to temperatures at or above freezing, and
locations nearing an inch expected to only be a fraction of far
northern Fleming County, an SPS was issued for the next couple of
hours for the far northwest counties.

The heavier rainfall closer to the TN border continues to remain
the main concern with rain rates having picked up over the past
couple of hours. Some locations are nearing an inch of rain if not
having exceeded an inch of rain already. Flooding of low lying
areas near the TN and VA borders is anticipated with rises on
area rivers.

UPDATE Issued at 1205 AM EST SAT FEB 17 2018

Rain continues to overspread the region late this morning with
KFGX observation pointing toward the possibility of mixed rain
and snow or even just plain snow and above freezing temperatures
in far northern Fleming County. Any snow or mixed rain and snow in
the far north should change to just plain rain in the next 1 to 2
hours. Rainfall rates so far have not been that intense, although
heavier rainfall rates recent in the 0.2 to 0.3 inch per hour
rain over parts of middle TN are upstream. Most of the guidance
points toward that activity to move into the Upper Cumberland
portions of the near the TN border and then spread northeast along
the VA border. The 6Z and 12Z model guidance, especially from the
NAM and GFS have higher qpf near the VA and TN borders,
especially in the Bell, Harlan, and Letcher county area. With this
in mind, QPF has been increased a third to a half of an inch
across the southernmost counties. The Flood Watch remains valid
with no changes at this time. Radar trends and rainfall rates will
continue to be monitored for any changes that might be needed.

Instances of rock and mudslides as well as ponding of water on
roadways are expected. Rises on creeks and streams may lead to low
lying area flooding with rises on several points on the rivers
expected. Confidence is greatest of downstream points reaching
flood stage on the Cumberland and Kentucky basins, but this is all
dependent on QPF.

UPDATE Issued at 640 AM EST SAT FEB 17 2018

Isolated rain showers will be moving into the southwestern
portion of the forecast area early this morning. The forecast is
still on track with this for the most part, so major update is
required at this time. The latest obs were ingested into the
forecast grids to establish new trends.

&&

.SHORT TERM...(Today through Sunday)
Issued at 300 AM EST SAT FEB 17 2018

An area of low pressure will bring precipitation to eastern
Kentucky today, as it makes it way across the Tennessee valley.
There may be a slushy mix of rain and snow along the leading edge
of the precipitation this morning, as it moves from south to
north across eastern Kentucky. There may be some light slushy
accumulations in isolated locations, but all in all the snow
should have very few if any impacts. The snow should be gone by
around noon today, as temperatures will have warmed well above
freezing by then. The rain should taper off quickly this
afternoon and evening, and should be gone by around dawn on
Sunday. Another weather system may bring a second round of rain to
the area by early Sunday evening.

Temperatures are expected to remain slightly below normal today,
with highs in the low to mid 40s on tap across the area. Tonight`s
lows will likely be above normal, due to the influence of cloud
cover and a brief period of southwest flow. A warm up is in store
for Sunday, as winds shift around to the southeast and south,
which could lead to some downslope warming during the day across
eastern Kentucky. We should see highs on Sunday rise into the mid
to upper 50s.

.LONG TERM...(Sunday night through Friday)
Issued at 410 AM EST SAT FEB 17 2018

The models are in good agreement with the broad scale pattern
aloft through the extended portion of the forecast. They all
depict a semi-static ridge through the southeast holding broad
and deep southwest flow in place over the Tennessee and Ohio
Valleys. This ridge will shift a bit through the seven day
forecast but its influence will be dominant for the weather
across Kentucky. Specifically, its burgeoning heights on Monday
off the coast of Florida will support higher heights for Kentucky
through Wednesday. The better energy lifts out of the area
initially Sunday night with the rising heights and as a result,
through Wednesday morning, the mid level energy stream remains
too far north to have a big influence on the convection chances
for our area. This changes later Wednesday with a better push of
energy into the state associated with a weakening trough sliding
through the Ohio Valley. After this point, the model variance
increases with the ECMWF holding the southeast ridge onshore
Florida compared to the weaker and more displaced to the southeast
GFS. While the model agreement suffers at the end of the period
it remains clear that eastern Kentucky will be in a wet and very
warm pattern through the entire latter parts of the forecast. A
general model blend looks reasonable for the extended.

Sensible weather will feature a drying trend for Sunday night as a
warm front lifts through and pulls away to the north. Mostly dry
weather should commence through early Wednesday under ridging
aloft and sfc high pressure off to the east. The pressure pattern
will continue to support ample southwest winds bringing in warm
and moist air from the south. This air mass will be activated on
Wednesday as a sfc cold front approaches from the northwest with a
potential for thunder. This boundary looks like it will stall out
over the area and we could see another surge of moisture and lift
develop for Kentucky into Thursday - prolonging the concerns for
excessive rainfall well into the upcoming week. Another wave will
then be possible for Friday extending this warm and wet period.

Did make some changes to the lows each night of the long term
portion of the forecast for terrain distinctions given a
prolonged environment favorable for ridge to valley temp splits.
As for PoPs, did beef them up for that latter wave from the ECMWF
on Thursday that may not be as well represented in the model
blend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 140 PM EST SAT FEB 17 2018

MVFR to IFR with rain showers are currently affecting the TAF
sites with this persisting in most areas through around 21Z to
01Z. Some locations may fall to near or below airport mins at
times. Although the rain will taper off by 3Z in all locations
MVFR and IFR should prevail in most locations through 9Z, with
improvements to VFR from northwest across the entire area
thereafter. Winds should be generally light and variable.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 10 PM EST this evening for KYZ080-084>088-110-
113-115>120.

&&

$$

UPDATE...JP
SHORT TERM...AR
LONG TERM...GREIF
AVIATION...JP



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