Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 240548
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1248 AM EST Fri Nov 24 2017

.UPDATE...
Issued at 1044 PM EST THU NOV 23 2017

Hourly temperature grids have been freshened up based on recent
observations. However, no additional changes were needed at this
time.

UPDATE Issued at 735 PM EST THU NOV 23 2017

High pressure remains in control across the region with mostly
clear skies. Upstream satellite imagery and model guidance
suggests this will continue. With the center of the high expected
to settle east of the Appalachians a steeper nocturnal inversion
is expected to develop across the far eastern and southeastern
counties with valleys several degrees colder than the ridges. The
previous Min T was overall in good shape. A couple of slight
adjustments were made based on recent trends. However, the main
changes so far this evening were to update hourly temperatures and
dewpoints based on recent observations and trends.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 259 PM EST THU NOV 23 2017

High pressure will dominate the weather through Friday. As the
airmass continues to moderate with time over the region, highs
here today reached the low 50s in some locations, and are expected
to be even warmer in the upper 50s by Friday. This will be aided
by southerly return flow as the area of high pressure starts to
shift east of the region. Overnight lows tonight will remain on
the cold side (below freezing) with light winds and clear skies
allowing for good radiational cooling. Kept a strong ridge-valley
split in the grids, with some of the sheltered valleys reading
some 10 degrees below the neighboring ridges.

An approaching cold front will lead to an increase in clouds
Friday night into Saturday morning. Expect the night to start off
clear with clouds moving in generally after 6Z, which should keep
temps from dropping as low. Low 40s are forecast for most
locations. There is some concern with mid/upper level moisture
making it through the surface dry layer and producing some
sprinkles as the front nears, though no other moisture is expected
in connection with this system. Used 75 percent sky cover as a
threshold for mentioning isolated sprinkles.

.LONG TERM...(Saturday through Thursday)
Issued at 305 PM EST THU NOV 23 2017

Extended begins with models in good agreement but continue to
diverge by early next week, lowering confidence in the forecast.
Overall the pattern aloft is amplified and progressive. Main feature
of interest will be a center of low pressure, or trough that will
move into the lower 48 by early next week. This system then splits
into northern and southern stream components. Models are having a
considerable time with the timing and strength of energy as it
crosses the CONUS, particularly with the southern stream. The GFS
has been typically too fast, opposite of much slower ECMWF
solutions. The Canadian has turned out to be a fairly reasonable
compromise. Unfortunately there has been no tangible or consistent
trend to pick up on as solutions have been all over the place.
Consequently the blended solution is the best option at this time,
though PoPs were reduced just a bit for overall uncertainties,
resulting in a more consistent forecast with neighboring offices.

Sensible weather features a roller coaster of sorts with respect to
temperatures, fluctuating between brief periods of cooler and warmer
weather. Overall temperatures will likely average out to near
normal, possibly a little above. After an extended period of dry
weather we will see the threat of rain increasing at the very end of
the period. However, would not be surprised if future cycles see
that threat trend a little slower with time, in line with more of a
compromise of the ECMWF and GFS solutions. Made minor adjustments to
the temperature grids each night anticipating a small to moderate
ridge to valley split during those times when high pressure is
centered more directly over our forecast area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 1248 AM EST FRI NOV 24 2017

VFR conditions to prevail as near calm winds this morning become
south/southwesterly at 5-10 knots later Friday morning through the
afternoon. Mid-high clouds will increase tonight with any
ceilings likely remaining above FL100 through 12Z Saturday.

&&

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

$$

UPDATE...JP
SHORT TERM...JMW
LONG TERM...RAY
AVIATION...GUSEMAN



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