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Area forecast discussion
National Weather Service Jackson Kentucky
1252 am EST Fri Feb 24 2017

Update...
issued at 1252 am EST Friday Feb 24 2017

The infrared Sat is showing a mix of high and low clouds moving across
the County Warning Area this hour. A band of low clouds at around 5 kft is moving
north across the central portions of the cwa, and actually played
a role in modifying some of the cooler Eastern Valley locales. One
example is quicksand modified a couple of degrees as cloud deck
moved across the site. This will make hourly temps difficult to
nail down perfectly and will require some updates to obs and
trends. Otherwise little needs to be updated at this time before
new forecast package is released.

Update issued at 1004 PM EST Thursday Feb 23 2017

Issued an update to the forecast to include the latest
observations in the grids. Some of the deeper valleys across
eastern Kentucky have begun to drop off this evening. The rest of
the forecast seems to be on track.

Update issued at 622 PM EST Thursday Feb 23 2017

Current conditions across the area continue to feature rather dry
conditions in place as some 10 to 15 degree dew point depression
are in place. As such with the best forcing to the north of the Ohio
River, have pulled the showers from the forecast this evening and
sent out a new zone forecast product along with freshened up grids with the latest
observations.

&&

Short term...(this evening through Friday night)
issued at 400 PM EST Thursday Feb 23 2017

South-southwest flow aloft will keep our weather warm through the
short term. Potent trough/low will plow into Great Lakes region
swinging a trough through the commonwealth by late in the period.
At the surface, high pressure is anchored over the Appalachians
with a nearly stationary frontal boundary draped from roughly dtw
southwest to stl. Low pressure currently taking shape over the
Central Plains will March east-northeast along the boundary and
into the Great Lakes by late Friday night. This feature will also
pull a cold front eastward through the region, and into eastern
Kentucky Friday night.

This dynamic storm system could bring a round of severe weather to
our forecast area Friday night. Main threat at this time appears
to be winds, with hail being a secondary threat. Shear is quite
strong with this system as well. Consequently could not rule out
an isolated tornado. Gradient winds will increase across the area
Friday ahead of the system, and from all appearances will become
gusty.

Main limiting factor to severe weather will be moisture
as dew points struggle to climb to near 60 Friday into Friday
night. Timing of the cold front is also not favorable for severe
weather as it will not enter into our area until sometime just
after midnight. Consequently any nocturnal inversion that develops
will have to be scoured out, though surface gradient winds appear
to be able to do just that, but generally only as the frontal
boundary is approaching. Bulk shear is quite strong with this
system as well, 40-60 kts, with the majority of the shear
realized in the lowest 3 km. Thus the potential for bowing cells
and line segments will be favored. Surface based instability to
support this storm Mode is not ideal but does appear to be
sufficient, again mainly just ahead and with the frontal boundary
itself. This has a distinctive qlcs flavor to it and considering
the environment as a whole feel an isolated tornado can not be
ruled out, though features of this type tend to be weaker than
most and short lived. Strong gradient winds mixing down may have
the potential for more damage should they occur. Low wet bulb
temperatures and freezing levels mean hail is a possibility as
well.

Long term...(saturday through thursday)
issued at 400 PM EST Thursday Feb 23 2017

The long term portion of the forecast will be active, with several
systems affecting the area. However there remains considerable
uncertainty on the timing, track and strength of a series of short
waves and associated surface lows and fronts that will affect the
area next week.

By 12z Saturday the cold front which brings our severe weather
threat Friday night will be east of the area, but some showers will
linger across the area mainly during the morning. Gusty west winds
will usher in cooler air on Saturday, with lows by Sunday morning
expected to dip down into the mid to upper 20s.

Surface high pressure will be over the area Sunday morning, but will
shift to the east during the day. This result in dry weather Sunday
with near normal afternoon temperatures in the upper 40s to lower
50s.

The mean flow for the first half of next week will be southwesterly
with a mean long wave trough axis centered over the western part of
the country. This will result in warming temperatures with highs
back in the 60s for Tuesday and Wednesday. The first in a series of
short waves looks to affect the area from Sunday night into Monday,
with rain shower chances increasing from Sunday night into Monday.
If precipitation moves in quick enough Sunday night a few flakes of
snow could mix with the rain before changing to all rain quickly by
Monday morning.

Tuesday still remains one of the least certain days of the forecast,
with the GFS quickly moving out monday's system, while the European model (ecmwf)
points to lingering rain chances for Tuesday. We will continue to
follow the blended forecast for Tuesday which maintains rain chances
but with probabilities generally lower than on Monday. There is
better agreement that a stronger short wave, surface low and
associated cold front will bring a better chance of showers and
thunderstorms on Wednesday. In fact we will be be going with likely
rain probabilities Wednesday. After the cold front passage cooler
air will spread into the area Wednesday night and Thursday.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1240 am EST Friday Feb 24 2017

A mix of high and even a narrow band of lower clouds are moving
across eastern Kentucky at this late night hour. The good news is we are
looking at VFR conditions for the taf sites, with lowest band of
clouds staying at or around to 5 kft level. Now some of the valley
locales have decoupled this evening and therefore some will see
patchy fog. The other concern is a increasing llj, as 850mb winds
increase ahead of strengthening surface and upper level system
progresses east. Therefore kept the low level wind shear in the forecast starting
around 08z to 12z timeframe. Places that will have to best chance
of seeing the stronger jet will be Lake Cumberland and Bluegrass
regions. This will mix out by around 14z and by tomorrow
afternoon we will see some of these stronger winds mix down
leading to gusty conditions. Think again the better mixing will
occur across the Lake Cumberland and Bluegrass regions where 25 to
30 mph gusts are possible. We are continuing to monitor the
potential for strong to severe thunderstorms to round out the taf
period. Right now a line of storms is expected to move into areas
west of a line from Sandy Hook, to Jackson, to Middlesboro at or
around 04z to 06z. The main threat with any stronger storms would
be for damaging wind gusts.

&&

Jkl watches/warnings/advisories...
none.
&&

$$

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