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Area forecast discussion 
National Weather Service Jackson Kentucky
1102 am EST Tuesday Jan 27 2015

issued at 1101 am EST Tuesday Jan 27 2015

Current observations are showing low level cloud cover and a few
flurries moving through eastern Kentucky but mainly over the southern
portion. Much of the heavier returns on radar have dissipated and the
snow shower activity has dwindled significantly. Still can rule out a
slight visibility reduction into this afternoon with some flurry
activity. Have updated the grids and removed snow shower wording but
will continue to include some isolated to scattered flurries
through the afternoon. Have issued a new zone forecast product for these changes but
overall the forecast is on track.

Update issued at 725 am EST Tuesday Jan 27 2015

A new snow band developed over the Bluegrass area and has now slipped
southeast into our County Warning Area riding just a tad northeast of the previous
one. Only belatedly did the hrrr catch on to this latest band...
though. Accordingly...have updated the grids to reflect the snow
movement and adjusted the light snow amounts. Also fine tuned
temperatures and dewpoints per the latest observation and trends. These have
been sent to the ndfd and web servers.


Short term...(today through wednesday)
issued at 335 am EST Tuesday Jan 27 2015

07z surface analysis shows a deep area of low pressure off to the
northeast while locally the pressure gradient is rather relaxed and
this is limiting the upslope component of this night/S snow threat.
The main bands of snow are being primarily driven by a surface trough
axis splitting the state and a stream of middle level energy running
north northwest to the south southeast over parts of central and
eastern Kentucky. On radar...this band lines up well with this
energy stream and is also able to tap into extra moisture from Lake
Michigan. The snow associated with this has been relatively light
with most sites reporting snow seeing 4sm or better visible...though it
is likely that under the highest radar returns visible is less than 2
miles. For these locations...a couple of tenths of an inch or so of
accumulation will be possible while most other places will see just a
thick dusting or less. An Special Weather Statement is in effect for this and it will be
continued through dawn and the morning rush hour for good measure.
Temperatures...meanwhile are in the middle to upper 20s across the area
with dewpoints a degree or so lower and winds light to calm.

The models are in good agreement aloft through the short term portion
of the forecast as a closed low deepens off the New England coast and
a stream of energy flows north-northwest to south-southeast over Kentucky and into the
broader East Coast trough today. This flow will be nudged east by a
moderately strong ridge in the southern stream crossing the Southern
Plains later tonight. This ridge will be pushed south by a developing
trough coming out of the central rockies and moving into the Central
Plains later Wednesday. Given the good model agreement have favored
the higher resolution hrrr and nam12 through the first part of the
forecast and a blend thereafter.

Sensible weather will feature a batch of early morning snow showers
targeting mainly the Cumberland Valley of eastern Kentucky. A few
flurries will then linger into early afternoon for far southeast
parts of the County Warning Area before also coming to an end by early evening as the
clouds attempt to clear. This...along with some continued cold air advection from
the East Coast storm...will make for a chilly night with lows in the
teens for Wednesday morning. Despite high pressure passing through...
a batch of low clouds could develop overnight and hug our eastern
zones into dawn Wednesday...which may spare these areas the coldest
temperatures. This low level moisture will also need to be watched for a
potential of spotty freezing drizzle if the stratus gets thick
enough. For looks like this will not be the
case...but the potential is there. Otherwise...the approach of
another northern passing surface low will help to warm the area up on
Wednesday with temperatures rebounding into the middle 30s northeast to the
lower 40s southwest. However...high clouds will start to move in by
afternoon from the northwest limiting sunshine once any low clouds
break up.

Used the bcconsshort as a starting point for temperatures...
dewpoints...and winds through this afternoon before plugging in the
superblend thereafter. Did make some minor...terrain based...
adjustments to hourly and minimum temperatures tonight. As for
probability of precipitation...ended up close to a combination of the wetter mav and drier
met today while agreed with the low probability of precipitation from all guidance tonight
and Wednesday across east Kentucky.

Long term...(wednesday night through monday)
issued at 419 am EST Tuesday Jan 27 2015

The period begins with high pressure centered to the north and east
with some weak upper level ridging across the region. Eyes turn
quickly to approaching surface low across the Midwest that is
forecast to progress east into the Great Lakes. A cold front
extending south from the low will be the driver for chances of precipitation
as we move into Thursday morning into Thursday night. Therefore
Wednesday night will be met with increasing clouds and chances of
precipitation increasing as we move toward daylight on Thursday. The precipitation
will bring a chances of snow or rain/snow mix Thursday morning before
changing to all rain late morning into Thursday as warmer air makes
its way into the region. This is also evident in the sounds as dryer
air is seen in the upper level leading to less ice by Thursday
afternoon. Otherwise this low pressure system and associated
shortwave will move east Thursday night with low deepening across the
northeast US. Here we switch to west to northwest flow and therefore
have kept some probability of precipitation across east and southeast Thursday night into
early Friday. This will likely mix with or change to snow as we move
through the night. Given limited moisture at this point would think
little to any accumulations would be expected with best chances
across the higher terrain.

Moving into Friday expect decreasing clouds and high pressure to drop
south out of the upper plains. This will usher in generally below
normal temperatures for Friday. The question remains Friday night as to how
much the temperatures bottom out. Right now would seem like best chances for
decoupling would be across the north and far eastern portions of the
County Warning Area. Did introduce some teens to better match neighboring offices.
After this the high pressure moves east with return flow Saturday
with temperatures generally able to rebound into the upper 30s to
lower 40s.

Then focus shifts to next system developing across the southwest US
and plains states. This low pressure will eventually get pick up by
northern stream shortwave and progress east into the Mississippi
River valley late Saturday night. We do introduce slight to chance
probability of precipitation Saturday night with some of this mixing with snow and rain
before changing to all rain Sunday as low pressure deepens along and
near the Ohio River valley through the day Sunday. This rain will
once again transition to mix and snow Sunday evening and Sunday
night from north to south as colder air filters into the region
behind this low. Given the more northern track of this surface low
and best quantitative precipitation forecast ahead of colder air would think that accumulations would
be light in terms of any snow we are able to get. Keep in mind this
is still in the farther reaches of the long term forecast and will
have to be fine tuned as we get closer to the event. After this
system moves east with some northwest flow snow showers continuing across
the east and southeast. Otherwise colder air continues to filter into
the region with temperatures struggling to make it above freezing


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 705 am EST Tuesday Jan 27 2015

A stream of shortwave energy aloft will keep the chances of snow in
the forecast through middle morning for much of eastern Kentucky. The
earlier bands of light snow set up mainly over the southwest portion
of the forecast area...but the next batch...and likely last one...
looks to pass through the area more to the northeast of the earlier
ones with a better chance of affecting the jkl/sym/sjs taf sites.
Have updated these with a tempo for some MVFR and IFR ceilings and MVFR
visible with any snow showers through middle morning. The rest of the area
will see their current IFR ceilings improve to MVFR shortly and then VFR
likely by 17z. Looking at the time height series for tonight decided
to add some IFR stratus in the eastern taf sites in the predawn
hours. Winds will generally be light and variable through the period.


Jkl watches/warnings/advisories...


short term...greif

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