Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 211726

National Weather Service Jackson KY
126 PM EDT Sat Apr 21 2018

Issued at 126 PM EDT SAT APR 21 2018

A nearby surface high across the Great Lakes, and a upper level
ridge axis extending from the Gulf Coast into the Upper Midwest
will lead to tranquil and dry conditions across eastern Kentucky.
This leads to little if any changes needed for this update cycle.

UPDATE Issued at 709 AM EDT SAT APR 21 2018

Areas of valley frost will continue early this morning with
temperatures having dropped into the upper 20s to near 30.
Temperatures will warm above freezing by mid morning and continue
quickly warming through this morning into this afternoon.


.SHORT TERM...(Today through Sunday)
Issued at 400 AM EDT SAT APR 21 2018

High pressure continues to assert itself across eastern Kentucky
with only a few strands of cirrus streaming in.  These will increase
through the day downstream of an upper level low pressure system
currently churning overtop Denver. Shortwave ridging will nudge
eastward across the Commonwealth as it flattens, but
heights/thicknesses will nonetheless increase as subsidence keeps
dry conditions in place and leads to further warming this afternoon
with highs topping out in the mid-upper 60s north of Mountain
Parkway and low-mid 70s south.

Light north/northeast winds will veer a bit more easterly tonight in
response to surface ridging across the Great Lakes to mid-Atlantic
coast crawling eastward. While cloud cover will gradually
thicken/lower tonight, valleys in the Big Sandy region should still
see a sizable dropoff in temperatures, cooling to the mid 30s. A
few areas of frost will thus be possible once again along with some
patchy valley fog.

The previously mentioned upper low will dig south across the
southern Plains and into the lower Mississippi Valley Sunday with an
attendant surface low immediately downwind. Increasing precipitable
water values and at least mid clouds will stream northeast into the
Lake Cumberland region. Still some uncertainty as to how much the
upper low will dig and subsequently how fast it will shift east,
keeping the best rain chances southwest of Kentucky through the day.
Downslope winds will aid in maintaining a dry near-surface layer,
but will still keep low-end PoPs in for the Lake Cumberland region
and far southeast Kentucky. Any rain that does occur through the
afternoon will be light at less than one tenth of an inch, prior to
better chances taking shape into early week.

.LONG TERM...(Sunday night through Friday)
Issued at 445 AM EDT SAT APR 21 2018

The period is expected to begin with an upper level ridge axis
extending from SC and VA northwest toward Lake Michigan and mid
and upper level low centered over eastern Arkansas. At the surface
high pressure is expected to be centered to the northeast of the
area. Moisture is expected to gradually increasing from the south
with PW expected to be near 0.50 inches in the north at the start
of the period and nearing an inch in the southwest.

Moisture will continue to increase Sunday night and into Monday
as the center of the mid and upper level low meander toward
southern Middle TN. This closed mid and upper level system should
move north into the central portion of the Commonwealth Monday
night and into Tuesday. At the same time a northern stream trough
should pass by to the north and many not merge with this system.
Meanwhile the southern end of the northern stream system is
progged to get left behind as the northern stream shears to the
north and east. The first mid and upper level low should open up
and move least of the area at midweek with the next closed
low/shortwave at mid levels approaching the Lower OH Valley on
Wednesday. A more potent northern stream trough should then dig
into the Great Lakes and MS Valley near the end of the period.
This progression of system should lead to several days of
unsettled weather with rounds of showers or even more of a
stratiform rain from time to time. There should be some breaks in
the precipitation at times through the Sunday nigh through Monday
period from time to time. Cloud cover should be persistent with
limited diurnal ranges and below normal high temperatures on
average. The highest chances for measurable rainfall across the
entire area appear to be from Monday into Tuesday and then late in
the period depending on timing.

With models generally good agreement through Tuesday and decent
agreement from Tuesday night through the end of the period, did
not stray far from the model blends. Some minor upward adjustments
into the likely range were made across western and southwestern
sections for Monday and Tuesday. Despite the prolonged rainfall
chances, qpf is not expected to be particularly heavy especially
given the meager instability and anticipated absence of thunder.
Five day rainfall totals from Sunday night through Friday evening
are only expected to average from around an inch in portions of
the Big Sandy region to an inch and a half to an inch and three
quarters near Lake Cumberland.


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

A nearby surface high across the Great Lakes, and a upper level
ridge axis extending from the Gulf Coast into the Upper Midwest
will lead VFR condition for this TAF period. Winds will remain
light and variable through the period.




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