Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 161355
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
955 AM EDT Mon Oct 16 2017

.UPDATE...
Issued at 955 AM EDT MON OCT 16 2017

Satellite shows the back edge of solid cloud deck continues to
move south. However, right behind the initial clearing line a
lower deck of cumulus and stratocumulus is quickly developing.
This developing cloud will bring mostly broken ceilings but should
eventually scatter out by early afternoon. Have updated NDFD for
latest observational trends.

UPDATE Issued at 707 AM EDT MON OCT 16 2017

Clearing of low clouds continues to work into the region from the
north as high pressure builds into the area. Sky cover has been
adjusted down in the north for the clearing trend. Also, some
adjustments have been made to hourly temperatures as temperatures
did not drop off as fast as earlier expected where clouds linger.
Overall, no substantial chances were needed at this time.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 410 AM EDT MON OCT 16 2017

The 500 mb trough axis will move east of the area this morning
with upper ridging building into the region this afternoon and
remaining in place through the period. Meanwhile corresponding
surface high pressure will build east into the OH Valley today and
remain in place through the short term period. Stratocu currently
lingers across parts of the OH Valley in the wake of the front
that moved across the region on Sunday. However, there is clearing
over OH and northern KY and these clouds are more patchy over IN.

Low clouds should gradually lift and mix out through the day
today. The main forecast concern through the entire short term
period is low temperatures and dewpoints tonight and how great
the threat for valley frost will be. MOS and blended guidance
generally points toward more in the way of fog development in the
valleys tonight with mainly upper 30s dewpoints. At this time, it
appears that locations that remained drier on Sunday north of the
Mountain Parkway should also experience a bit drier dewpoints
advect in first and would stand the greatest chance for patchy
frost in valleys tonight. Further south, where more rain fell on
Sunday, surface moisture should be greater and would favor more of
a fog threat. If dewpoints were to drop off more than expected
today, the threat for more valley frost would increase. Lows
should generally range from 35 to 40 tonight. Have highlighted the
potential for both dense fog and frost in valleys tonight and
opted to introduce patchy to areas of dense valley fog for valleys.

Temperatures today will be considerably lower than recent days
with highs reaching near the 60 degree mark. The airmass will
moderate a bit on Tuesday with highs in the mid 60s.

.LONG TERM...(Tuesday night through Sunday)
Issued at 300 AM EDT MON OCT 16 2017

Persistent and strong upper level ridging will remain in place
across the eastern US through the remainder of the upcoming week
and likely through next weekend. This will continue to support a
slow warming trend through the week as warm air builds under the
ridge. Tuesday night is still looking the coldest night of the
week for the valleys with coop guidance showing some potential for
readings as low as 34 degrees. The 12z guidance actually had a 32
degree reading. Thus, going to shoot for some low to mid 30s in
the eastern valleys. This should be good enough for at least some
patchy frost. The frost extent will be highly dependent on how low
dewpoints mix out on Tuesday. Based on the forecast, hard to go
with much more than patchy frost again, and mainly in the eastern
valleys once again. Hunch is guidance may still be a bit high on
those dewpoints and if we mix out better, than frost would be a
bigger concern. Either way, eastern valleys appear to see the
greatest threat of any frost. Still possible we see some mid 30
temperatures Wednesday night, but with dry air firmly entrenched
by then, not sure we will be able to squeeze out must frost and
aerial extent of valley fog will start to be more reduced. Will
continue to go with modest ridge/valley splits through Saturday
night. Also, plan to continue to go on the warm side of guidance
for highs given the 1000-500 mean level RH remains under 25% for
the entire week and next weekend. Dewpoints each afternoon, are
probably not low enough, but at least trended towards drier
afternoons as well. We will likely see RH`s under 25 percent from
Wednesday afternoon through at least Saturday. Fortunately, as
long as high pressure dominates, winds won`t be a concern and fire
weather concerns should remain low.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 728 AM EDT MON OCT 16 2017

Drier air continues to advect into the region on north to
northwest flow behind a cold front as high pressure continues to
build into the region. The far north has cleared, while low
clouds are leading to a VFR ceiling in the central part of the CWA
with some MVFR still lingering in the far southeast. Some additional
breif thin CU may develop today, but VFR should generally
prevail. The exception will generally be in the 6Z to 12Z period
when valley fog should develop and eventually lift onto nearby ridges.
This fog will likely become dense in some locations. SME may be
most affected of the TAF sites and vis below airport mins is
possible there as well as at other valley locations. North
northwest to north winds at 10KT or less should prevail through
the 22Z to 00Z window, before slackening with loss of daytime
heating and the center of the high nears.

&&

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

$$

UPDATE...SBH
SHORT TERM...JP
LONG TERM...KAS
AVIATION...JP



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