Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 230805
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
405 AM EDT Mon Apr 23 2018

.UPDATE...
Issued at 240 AM EDT MON APR 23 2018

Despite east to southeast flow with a downslope component a band
of showers continues to progress north across the area. Dewpoints
across southern sections of the area have climbed into the 40s
with light measurable rain having fallen in many locations out of
a mid level deck from around SME to Bell and Knox counties per KY
Mesonet observations and regional RAWS, HADS, and IFLOWS. This
band will continue to move to the northeast with additional
showers upstream. Pops will be updated to account for timing of
this with hourly temperatures and dewpoints also freshened up
based on recent observations.

UPDATE Issued at 1120 PM EDT SUN APR 22 2018

Updated the forecast to remove outdated wording from the text
forecast product and to speed up precipitation onset in our
southwest and southern counties by a couple of hours per current
trends in model data and obs.

UPDATE Issued at 740 PM EDT SUN APR 22 2018

The forecast remains on track so far this evening. Mostly to
cloudy skies will persist overnight, with rain showers expected to
move into the area from the southwest late tonight into early
tomorrow morning. Will leave the forecast as is for now, but will
need to update later in the shift to make other small adjustments
and to remove outdated wording form the zone forecast text
product. Ingested the latest obs into the hourly forecast to
establish new trends.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 351 PM EDT SUN APR 22 2018

The latest surface analysis shows an area of surface high pressure
continue to retreat northward. The east to southeast winds
continue to lead to downslope flow and drier conditions across the
region this afternoon. The latest scans of the regional WSR-88D
radars suggest some of the rain shower activity is just now
creeping into Wayne County. Given the continued slower trend, did
opt to lower POPs for the afternoon. This upper level low to our
south will continue to rotate east and eventually divergence aloft
will lead to best chances of rain showers early Monday. Then a
lull in activity is expected later in the day mainly in the far
east, as 1000 to 850 mb winds increase leading to increased
downsloping. The 00Z NAEFS standard anomaly tables show the 850mb
winds are going to be oriented southeast and running greater than
3 standard deviations above normal. There is some weak
instability in the Lake Cumberland region Monday afternoon and did
lean toward slight chance thunder. The upper level divergence
becomes broad Monday night, but the surface low and trough will
come east. This will lead to increasing chances of POPs once again
Monday night.

.LONG TERM...(Tuesday night through Sunday)
Issued at 405 AM EDT MON APR 23 2018

A 500mb low will be collocated with a surface low pressure system
across Kentucky starting out at 0Z Wednesday. This will continue to
shift eastward out of the state throughout Tuesday night and into
the day Wednesday, with pops/rain chances expected to be on a
decreasing trend during this time. Upslope flow will keep some
chance pops in place through the day Wednesday, especially across
the SE, but additional QPF will be under a tenth of an inch through
0Z Thursday.

Models then lose considerable agreement by 0Z Thursday, with the NAM
and GFS planting a developing closed low over the south/central
Plains, and the ECMWF showing a strong closed low over the northern
Ohio Valley and southern Great Lakes region with a shortwave trough
over the central/southern Plains instead. The ECMWF shows this
closed low shifting SE across Ohio Wednesday night and into the day
Thursday, while both the GFS and ECMWF show the other shortwave/low
system tracking just south of Kentucky into the deep south during
this time. Surprisingly, which ever model pans out, neither actually
pulls precip from either system into the state, so will keep
Thursday dry in the forecast. Models then come into much better
agreement for another system which will affect the region to end out
the workweek.

A 500mb shortwave will follow deep troughing across the region,
deepening the trough as the axis moves through Kentucky Friday night
into Saturday morning. At the surface a cold front is expected to
shift from west to east across the state during the day Friday and
into Friday night, bringing with it a swath of chance pops.
Instability is still lacking, so will not include any mention of
thunder at this time. In fact soundings are actually quite dry, so
not expecting much QPF from this either. Even after tweaking QPF up
slightly from the Superblend, still only have well under a tenth of
an inch for the duration of the system.

During much of the extended period, temperatures will actually
remain relatively uniform, with highs in the low to mid 60s and lows
in the 40s. However, if clearing occurs overnight Friday night and
Saturday night (coupled with light winds), some sheltered valleys
may fall into the upper 30s. Ridging will slowly take hold
throughout the day Sunday and continue into Monday. This will allow
temperatures to climb into the low 70s both days.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 235 AM EDT MON APR 23 2018

An upper level low will meander into western TN through the
period. For much of the period the region will maintain a
downslope component of the flow with lower levels slow to
saturate. Thus mainly mid level clouds are expected through about
12Z with some low clouds thereafter but still in the VFR range.
Some brief MVFR is possible in showers or any thunderstorms across
western and northwestern sections of the area after 12Z, but vis
should remain 6SM or higher through the period. Winds should
increase to near or in excess of 10KT at the TAF sites during the
first 6 hours of the period out of the east southeast to
southeast.

&&

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

$$

UPDATE...JP
SHORT TERM...DJ
LONG TERM...JMW
AVIATION...JP



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