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fxus63 kjkl 162101 
afdjkl

Area forecast discussion
National Weather Service Jackson Kentucky
501 PM EDT Wed Oct 16 2019

Short term...(this evening through Thursday night)
issued at 429 PM EDT Wednesday Oct 16 2019

An upper level low is moving across the Great Lakes region as of
late afternoon with an initial shortwave east of the area, but
another rotating south of the Great Lakes with a third further
upstream. A parent sfc low was also over the Great Lakes region
in the Lake Huron vicinity with the cold front that crossed the
area late last night and early this morning having moved east of
the Appalachians. A triple point low is starting to deepen over
the mid Atlantic states. Surface high pressure centered in the
arklatex region is building east into the Ohio and Tennessee Valley. Low
level moisture lingers across the area and in advance of the
secondary shortwave with low clouds more broken to overcast in
northern locations.

The upper level low will move east across Ontario and into the
northeastern conus tonight and reach the Canadian Maritimes to end
the period. The low along the coast should deepen quite rapidly
tonight as it moves into New England before reaching the Maritimes
to end the period. At the same time, the surface ridge of high
pressure will build east of the MS river and be centered over the
Ohio Valley to end the period. The second shortwave is expected to
move across the area this evening and move east overnight. The
third shortwave should pass north of the area Thursday afternoon
and evening with height rises as an upper level ridge builds into
the Ohio toward the end of the period.

The pressure gradient and mixing behind the front will keep winds
on the gusty side early in the evening, but the pressure gradient
will decrease overnight. Low clouds lingering around especially
over the north and east will also keep temperatures from bottoming
out initially. In addition, drier air will arrive first in the
more western and southwest locations. These areas will have the
best chance for experiencing some patchy frost late along with
some deeper valley fog. Meanwhile, the recent rainfall has led to
increase sfc moisture and soil moisture and once skies begin to
clear and then as winds slacken valleys over the central and
eastern locations may experience some valley fog as well.

Fog and any patchy frost will dissipate an hour or two past
sunrise and with high pressure and the coldest airmass so far this
fall in place, give way to below normal high temperatures. With
high pressure building across the area along with height rises on
Thu night the potential for frost will be more widespread than
tonight. A couple of normally colder locations may reach or
briefly fall below the freezing mark. Deeper valley locations
along rivers will probably experience some fog as well.

Long term...(friday through wednesday)
issued at 501 PM EDT Wednesday Oct 16 2019

Quite of bit of disagreement in the extended forecast, especially
concerning timing of systems moving through the region. This
resulted in quite a bit of tweaking of the nbm, which seemed over-
zealous on continuous precip chances throughout the forecast.

We will start off during the day Friday with a strong upper level
ridge moving across the Ohio Valley, coinciding with a broad area of
high pressure at the surface. This will boost temperatures back into
the 60s for Friday afternoon. As the surface high begins to shift
east of the state Friday night, winds will become more serly,
keeping temps a bit warmer compared to the night before. Still,
deeper valleys could see temps as low as the mid 30s, which could
lead to some frost potential.

More active weather is then expected for the remainder of the
extended forecast. However, as mentioned above, the problem with
this forecast is agreement. Both the 12z GFS and European model (ecmwf) have a deep
longwave trough pushing into the Ohio vally following the exit of
the upper level ridge during the day Saturday. At the surface, a
center of low pressure will be moving into northern Quebec during
the afternoon, dragging a cold front eastward through the mid-
Mississippi Valley and towards the commonwealth. However, the GFS
has almost no quantitative precipitation forecast along this front, and what little there is will
dissipate before making it into the state. Meanwhile, the European model (ecmwf)
exhibits much more quantitative precipitation forecast along the frontal boundary, encompassing much
of the state with rain by Saturday night. Furthermore, a tropical
system will be moving northward through the deep south during the
same time frame. The GFS has the precip shield barely skirting the
far southeast County Warning Area Saturday afternoon/evening, while the European model (ecmwf) has it
bringing substantial quantitative precipitation forecast and merging with the incoming frontal
passage Saturday night. The European model (ecmwf) then continues the pops and quantitative precipitation forecast
across the southeast portion of the County Warning Area through the day Sunday, while all
the while the GFS keeps US dry and clear.

Clearing will then follow the European model (ecmwf) by Sunday night as well.
However, another strong upper level low and longwave trough will be
in place across the northern plains during this time. A strong
surface low pressure system will also be in place just east of the
upper level system, moving northeastward and becoming more wrapped
up and occluded. A cold front will extend southward from the
occluded surface system, and should sweep eastward towards Kentucky.
The GFS quickly moves the front and associated precip through the
County Warning Area Monday night. However, the European model (ecmwf) has the system becoming more
occluded with slower forward motion, which will result in the front
and associated precip moving across the state some 6 to 12 hours
slower compared to the GFS. As noted above, the nbm is trying to
blend the 2 systems together, which is likely resulted a much longer
duration of pops than what is actually warranted for such a system.
A general favor towards the European model (ecmwf) is noted, with the highest
forecasted pops lining up better with the timing of this model. But
given the uncertainties, do not have any pops higher than the chance
category. Hopefully models will start coming into better agreement
over the next 24 hours. Regardless of which solution is correct, the
impact will be the same...as both models have fairly high quantitative precipitation forecast
impacting the entirety of the cwa, bringing much needed rain to the
region. Also noted that there is almost no instability in the
models, so did not have enough confidence to include thunder at this
time.

When the front finally does exit the state, whether it be Monday
night or Tuesday afternoon/evening, the axis of the deep longwave
trough will begin making its way across the Ohio Valley. Meanwhile,
high pressure will take hold at the surface, and allow for clearing
conditions through the end of the forecast period.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 230 PM EDT Wednesday Oct 16 2019

Cold air advection behind a cold front and lingering low level
moisture in the 925 to 850 mb layer, is leading to some stratocu
and cumulus either side of the MVFR and VFR category break.
Locations generally north of sjs and jkl should initially be MVFR
ceilings. Improvement to all VFR in these locations should occur
between 0z and 6z with some MVFR possibly lingering near the Virginia
border as late 12z. Winds initially will be on the gusty side
with gusts up to 20kt. The pressure gradient will slacken after 0z
with winds becoming less than 10kt for most locations out of the
northwest to west.

&&

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

$$

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