Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 242036

National Weather Service Jackson KY
436 PM EDT Sat Sep 24 2016

.SHORT TERM...(This evening through Sunday night)
Issued at 309 PM EDT SAT SEP 24 2016

A strong upper level ridge is in place across across much of the
lower Mississippi and Ohio River valleys early this afternoon,
caught between two upper level closed lows... one off the eastern
Canadian coast, and another more progressive low moving northward
across the Dakotas. Meanwhile another disturbance remains positioned
across much of Florida and the southern extent of the SE gulf
states. This will show little progression through the remainder of
the weekend, staying well to our south and with little impact on the
region`s weather. However, the closed low over the Dakotas will
continue to track northeast today, pushing the associated troughing
pattern eastward toward the Upper Great Lakes by Sunday evening.
This will work to break down the high pressure ridging over time,
though is should still have general control of the Ohio River Valley
during this time.

At the surface, a very weak boundary is pushing southward across the
state this afternoon. This is connected to a surface low pressure
center currently in the Dakotas, being driven by the upper level
low. However with such strong upper level ridging in place, this
frontal passage is dry and overall benign. The only change will be a
deeper northerly post frontal wind component and some continued
diurnal CU through this evening. Strong surface high pressure to our
NE will push into the state behind this frontal passage overnight,
with light winds and strong subsidence expected once more. This
pattern will lead to temperature differences between the ridges the
valleys overnight. Also, any lingering moisture, especially in the
deeper valleys and near bodies of water, will likely lead to more
fog development overnight, with some locally dense spots possible.

High pressure will be in control once again during the day tomorrow
(Sunday). Temperatures will only be a degree or two lower than today
at best, despite the weak cold frontal passage, with such strong
ridging and dry air in place. Meanwhile, the strong surface low will
push into south-central Canada Sunday morning, and continue an
eastward track throughout the day. This will pull with it a stronger
cold front, moving eastward and into the Mississippi River Valley by
Sunday evening, then eventually into central KY to end out the
forecast period Sunday night. Weak southerly flow just ahead of this
line will do little to increase moisture across the region, keeping
best POPs and QPF at bay, especially for eastern KY, through the end
of the forecast period. However, can`t rule out some low end pops
making it into portions of the CWA late in the night. Clouds will be
slow to develop as well, allowing temperatures to be very similar to
that of tonight, with a ridge valley split likely to occur as well.

.LONG TERM...(Monday through Saturday)
Issued at 436 PM EDT SAT SEP 24 2016

The period starts out with models in fairly good agreement, but
ends much differently. A cold front will move through from NW to
SE on Monday and Monday evening. There are differences between
models regarding the QPF and POP, but there is a general
agreement that the greater precip and highest POP will be
southeast of the JKL forecast area. Have used just a chance pop
area wide for our forecast area at this point. With the high
temperatures expected, there should also be instability to fuel
some thunder ahead of the front. High pressure builds in from the
west with fair and cooler weather behind the front for Tuesday
into at least early Wednesday.

For the later part of the week, the ECMWF and GFS part ways
regarding the evolution of the upper trough which initially
supports the cold fropa. In the GFS, the trough axis passes on
Wednesday and it remains progressive, lifting NE off the New
England coast by Friday, with upper level ridging again building
into our area from the SW. This would mean mainly fair weather and
moderating temperatures. Meanwhile, the ECMWF closes off an upper
low (nearly cutting it off for a time) over our area, with the
system lingering into the weekend. There are some members of the
GFS ensemble which lend support to this, but the spread of
solutions takes in a wide range regarding the upper trough/low.
An GFS ensemble mean solution is preferred, which does not linger
an upper low for a long period, but does hold onto troughiness
longer than the operational GFS. This would mean a few showers
possible (mainly east) on Wednesday as the upper trough passes,
and dry weather with a subdued warm-up late the week. However,
considering the range of possibilities, confidence is not high.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)

High pressure will remain in control of our weather through the
weekend resulting in VFR conditions for most areas with light and
variable winds. Some diurnal CU has developed across the CWA,
mainly between 4.5 and 5k ft. These clouds should dissipate with
loss of daytime heating this evening. Patchy valley fog will form again
overnight, possibly affecting SME with some MVFR BR for a couple
of hours late in the night into early Sunday morning. Otherwise
have continued to keep the TAFs to one line.




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