Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 272007
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
407 PM EDT Tue Sep 27 2016

.SHORT TERM...(This evening through Wednesday night)
Issued at 405 PM EDT TUE SEP 27 2016

After the passage of a cold front yesterday, surface high pressure
has set in across Kentucky. Meanwhile a strong upper level low
remains in tact across the UP of Michigan, with a troughing in place
across much of the eastern half of the conus. This is resulting in a
strong pull of colder and drier Canadian air from Canada, southeast
and into the Ohio River Valley. This combination of colder and drier
air has resulted in clear conditions across the region through
today, with afternoon temperatures cooling down to more seasonable
normals.

As we head into the overnight this high pressure should continue,
with strong subsidence in place helping temperatures to drop off
into the 40s once again by early morning. While dry air advection
has been in play through the day, still expecting some of the deeper
valleys to see some fog development overnight, especially near
bodies of water. Also throughout the overnight, the upper level low
will begin to make a southward push, reaching the southern extent of
Lake Michigan by 12Z Wednesday.

Heights will continue to lower aloft through the day Wednesday as
the upper level low bowling balls itself southward, reaching central
Indiana by 0Z Thursday. At the surface, a closed surface low will
follow along the same southward path, moving into Kentucky during
the afternoon hours Wednesday. From this low will sprout a secondary
cold front, which is expected to traverse eastern KY tomorrow
afternoon. Winds will become more southerly ahead of the frontal
passage, which will pull some moisture into the region in the form
of clouds ahead of the frontal system. Precipitation will accompany
the frontal passage as well, with best chances moving across eastern
KY late afternoon and into the first part of the overnight. A bit
concerned about the coverage with this system. Overall I think the
models are overdone with the moisture considering the overall upper
flow is still pulling in an abundant amount of dry air aloft.
Superblend gave likely pops, while many of the hi-res CAMs are
showing a more scattered line of convection moving through the
region. Ultimately decided to cap pops at high end chances given
uncertainty, though further updates may deem increasing pops to be
necessary.

There is actually a small bit of instability with this frontal
passage. While not much, it was enough concern to introduce some
isolated thunder into the forecast for Wednesday afternoon/early
evening. This instability should cease during the late evening after
the frontal passage, cutting off any further thunder potential.

Forecast soundings are showing llvl moisture sticking around through
the end of the short term forecast period (the remainder of
Wednesday night). There is enough moisture that light rainfall could
continue through much of the night, so kept isolated to scattered
pops in play. Wouldn`t rule out some drizzle in a few locations as
well. Generally cloudy skies and ongoing precip will keep conditions
insulated a bit more compared to tonight, despite the northerly wind
shift after the cold frontal passage. Lows tomorrow night should
bottom out in the upper 40s and low 50s.

.LONG TERM...(Wednesday night through Monday)
Issued at 310 AM EDT TUE SEP 27 2016

The models remain in decent agreement with the amplified and
blocky long wave pattern to dominate across the CONUS through the
majority of the period. An upper level low will drop south out of
the Great Lakes/Ohio Valley regions through Friday, before
gradually shifting back to the north and diminishing through early
next week.

This will result in below normal temperatures and periods of
unsettled weather across eastern Kentucky through the first part
of the weekend. Dry weather and a gradual warm up will then ensue
as the low pulls away, and 500 mb heights recover.

The blended guidance came in very reasonable with the rain
chances through the period, so stuck close to the given values.
Sky cover did look on the high side, so dialed this back
somewhat. Also allowed for slightly warmer lows at night,
particularly when the system is closest to our area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 149 PM EDT TUE SEP 27 2016

Surface high pressure has taken temporary control of the region
after the passage of a cold front yesterday. Deep dry air flowing
into the region from the west and northwest have allowed skies to
remain clear across the region, while winds at the surface remain
light and variable. This regime will last into the overnight, with
some of the deeper valley locations expected to see fog
development under the stable airmass. Not expecting the TAF sites
to be affected for the most part, so continued to leave out of all
but SME at this time. Tomorrow, a strong low pressure system to
our north will begin to sink southward. This will push another
weak cold front through Kentucky during the day. Winds will
become more southerly throughout the day, promoting increasing
cloud cover. However, clouds should remain well above VFR through
the forecast period, and any precipitation associated with the
front should hold off until after the forecast period as well.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...JMW
LONG TERM...GEOGERIAN
AVIATION...JMW



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