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Area forecast discussion 
National Weather Service Jackson Kentucky
414 PM EST Friday Jan 30 2015

Short term...(this evening through Saturday night)
issued at 308 PM EST Friday Jan 30 2015

Surface high pressure passing over the region tonight into Saturday
will provide mostly clear skies and lighter winds.

The elements for a late weekend weather system will be coming
together over the western Continental U.S. On Saturday...with warm/moist air
spreading northward on isentropic lift over the Great Plains during
the day. High clouds from this will be carried eastward and ride over
an upper level ridge to bring US increasing clouds in the afternoon.
The surface low will begin to take shape on Saturday night and should
be over Missouri by 12z Sunday. Models have come into better
agreement concerning this system...and now point to a more northerly
track than what looked probable in earlier model runs. This will be
dealt with in more detail in the long term discussion. This trend in
the models results in warm air advection setting in on Saturday
night...and most of the precipitation on Saturday night being to our north and
northwest. Will only carry 20-40 percent probability of precipitation in the jkl forecast area. Have
used precipitation type of snow for most of the area...with rain/snow mix
in our SW. Temperatures in soundings may support more in the way of rain.
However... the low levels are not saturated in the soundings. If
precipitation makes it to the ground...would expect some evaporational
cooling to allow snow.

Long term...(sunday through friday)
issued at 412 PM EST Friday Jan 30 2015

As we head into the extended period...an upper low displaced in the
southwestern Continental U.S. Ejects a shortwave into the southern plans while
another wave over the northern stream of the polar front jet moves
southeast across the upper plains. By Sunday these two features
merge over the Midwest and move east through the Ohio Valley. At the
surface...a strong low develops and tracks right along/just north of
the Ohio River. Models are finally starting to show continuity in
their runs...which is giving more confidence to the forecast. If the
GFS holds true based on the last 4 model runs...the center of the
low will track along and just south of the Ohio River. One thing to
note however is that the last 2 model runs...12z and 6z today...show
an increase in the intensity of the low to from 1012mb to 1006mb.
Even the latest 0z and 12z European model (ecmwf) is in strong agreement with the
GFS. And though it is towards the end of its run...the nam80 is
finally starting to show agreement with both the GFS and European model (ecmwf) as
well...showing 1005mb low tracking along the Ohio River during the
same time period. The 12z Gem still seems to be too far south with
the system...so did not use this model in the forecast for this
event.

All things considered...if the GFS/ECMWF/NAM tracks do pan out...by
12z Sunday the precipitation will likely be spreading across the County Warning Area from
the northwest...quickly encompassing much of the County Warning Area within a few hours.
While the moist layer will be well below freezing...and surface
temperatures will be very near the freezing mark...a warm/dry nose just
above the surface will keep temperatures in the low levels just above the
surface well above freezing. The shallowness of this dry layer will
likely result in a quick wetbulbing down to the surface...with
moisture overcoming and hitting the surface from north to south.
Given the cold moist layer...despite the warming near the
surface...expect most of the precipitation to still fall as snow...possibly
mixing with rain in the far south where the warmest low temperatures will
occur. Southerly winds at the surface will then allow temperatures to rise
throughout the day to above freezing in the first 6-7kt feet. This
should allow enough time for ice crystals to melt as they fall and
precipitation to change to rain. Temperatures will increase into the
low to middle 40s across the County Warning Area by the afternoon...with warmest temperatures
expected in the southern County Warning Area. The cold front itself should pass
through the region sometime after 6z Monday. At this point...dry air
will begin working in the upper levels...and much colder air will
begin filtering in as winds shift to a more nwrly direction in the
low levels. During this transition...while quantitative precipitation forecast is expected to
lesson...precipitation will likely quickly transition back from rain to
frozen precipitation late in the night...near 12z Monday. Note...this is a
much later transition time than what was previously forecast with a
slightly more northward track.

Shallow moisture and light snow is expected to persist throughout
the day Monday under strong northwest flow. This will lead to upslope flow
and better chances for accumulating snow amounts across the higher
terrain. The 6z Tuesday sounding looks to finally pull in enough low
level dry air to cut off any linger precipitation...though some low clouds
may continue to linger through the night. Highest quantitative precipitation forecast amounts will
be across the northern County Warning Area and points just to our
north...corresponding with the low track as well as the center of
best qvector convergence. However...upslope flow could lead to
higher amounts in the higher terrain in the far southeast counties as well.
All together...generally a half inch or less of snowfall is expected
Sunday morning and Sunday night into Monday. However...the highest
terrain above 2500 feet could see between 1 and 2 inches due to the
upslope flow and temperatures falling more quickly at these higher
elevations Sunday night.

By Monday night...the shortwave will have finally transitioned east
of the region...putting much of the Ohio River valley area in a more
zonal flow pattern through middle week. Colder air will continue to
filter into the region...with overnight temperatures Monday night/Tuesday
morning models sinking down into the low teens in the north...and
into the upper teens to around 20 in the south. Models lose
significant agreement by this point...so will have to rely on the
model blend to come up with a forecast solution. The GFS shows a
disturbance clipping our far northern counties Wednesday...while the
other models keep this system well to our north. This is a downgrade
from previous model runs...and as a result...probability of precipitation have lowered
compared to the previous forecast. Another system could sweep from
the northwest to the southeast sometime late Wednesday night and into the day
Thursday. This will result in precipitation...as well as another burst of
colder air filtering into the region behind the system. After
collaborating with the surrounding offices...lowered temperatures
considerably from what the model blend gave on Thursday based on the
amount of cold air filtering into the region. Went ahead and
included some light snowfall amounts Wednesday night and
Thursday...but this is subject to change to higher or lesser amounts
as models continue to come into better agreement.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 101 PM EST Friday Jan 30 2015

MVFR ceilings may linger early in the period near the Virginia border.
Otherwise...VFR is expected through the period. Northwest winds gusting
between 15 and 20 kts will die down by evening...with light winds
expected for the remainder of the period.



&&

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

$$

Short term...hal
long term...jmw
aviation...hal

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