421
FXUS63 KJKL 170721
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
321 AM EDT Fri May 17 2024

.KEY MESSAGES...

- After a lull in shower and thunderstorm chances for most places
  tonight, higher chances return to close out the week and carry
  over into Saturday and Saturday evening, before tapering off
  Saturday night into Sunday.

- High pressure brings dry weather back to the area Sunday night
  through Tuesday. A couple areas of low pressure will bring rain
  back to the area Tuesday night through Thursday.

- Near normal to slightly above normal temperatures are expected
  to continue into the weekend. A further warm up is then
  expected into the first part of next week.

&&

.SHORT TERM...(Today through Saturday)
Issued at 320 AM EDT FRI MAY 17 2024

A large-scale positively-tilted pair of northern stream and southern
stream upper troughs will bring unsettled weather to the region for
the short-term (through early Saturday evening), with much of the
jet energy ahead of the southern stream system moving across the
Gulf Coast states and Tennessee Valley. With the region on the cold
side of the jet stream, instability will be modest by mid-May
standards. Nevertheless, showers and a few thunderstorms will move
into the region by early Friday afternoon and persist into Friday
overnight and early Saturday morning, before high pressure ridging
aloft builds over the Midwest Saturday, causing the upper trough to
pinch off over the Southeast US. Thus, another round of showers and
thunderstorms is expected to develop Saturday afternoon within a
weakly unstable and modestly moist environment.

With modest shear and instability, no severe weather is expected,
with showers more likely to be the prevailing precipitation rather
than thunderstorms today and tonight. Instability increases a bit
Saturday but within an environment with practically no wind shear.
The main concern especially today and tonight is the potential
for locally heavy rain causing minor flooding concerns, but even
this concern is very low.

With thickening cloud cover and precipitation concerns, temperatures
will be limited to near normal with 70s for highs, cooler in the
west where precipitation will arrive earlier in the day and a bit
warmer in the east where precipitation may not arrive in some
locations until late afternoon or early evening. Lows tonight will
return to the upper 50s and lower 60s with precipitation chances
continuing, with mid-50s in the deeper sheltered valleys, especially
where any partial clearing can occur. A more uniform distribution of
mid-70s can be expected Saturday given expected redevelopment of
showers and thunderstorms by early afternoon and continuing into the
evening.


.LONG TERM...(Saturday through Thursday)
Issued at 415 PM EDT THU MAY 16 2024

Models are indicating an upper level split flow expected across the
CONUS at the start of the period, with the southern portion of the
flow having troughiness from the ArkLaTex region northeastward over
the Ohio Valley. A weak upper low is expected to be embedded in this
trough, but there is poor model agreement on its position. Ample
moisture should be present beneath and ahead of the upper trough,
allowing for precip. The regime will shift east with time, but the
aforementioned model discrepancies result in uncertainty down the
line as to how quickly it departs. A model blend being used for the
forecast continues to lack details, but has an overall decreasing
POP trend during the weekend, overlaid with diurnal tendencies. Dry
weather is forecast by late Sunday evening. Ridging at all levels
approaching and passing over from late Sunday night through Tuesday
will result in dry weather persisting during that time. Slightly
drier low level air should also arrive.

Beyond this, a shortwave trough aloft originating in the northern
part of the flow is expected to approach and pass over Tuesday night
and Wednesday, with the bulk of the wave to our north. This supports
a surface cold front which both the GFS and ECMWF pass through our
area on Wednesday afternoon or evening. The best upper level support
is weakening and shifting to our north as the system goes by. It
would also appear that the best moisture return ahead of the front
will be to our west and probably not make it here before cold fropa.
These considerations as well as models only generating light precip
here, will limit the POP to chance category.

By Thursday, the deterministic/operational ECMWF has deepened an
upper level trough over Ontario and the eastern CONUS much more so
than the deterministic/operational GFS. In terms of surface features,
this allows the ECMWF to take the cold front further south than the
GFS. The GFS`s stalling of the front further north results in
additional precip in our area on Thursday, compared to a dry ECMWF.
The GFS ensemble mean points toward more eastern CONUS troughing
than in the operational/deterministic run, lending some support
toward the ECMWF idea. That being the case, will go with POPs a
little below the values in the model blend on Thursday, with nothing
higher than slight chance.&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 142 PM EDT THU MAY 16 2024

Based on current trends, the TAF sites will continue to experience
BKN low level cover through around 0Z this evening, before the
clouds begin to scatter out a bit. VFR should be the rule at JKL,
LOZ, and SME, but SJS and SYM will continue to see MVFR CIGs of
around 2K this afternoon, before the clouds scatter and lift a bit
this evening. Winds should be generally light and variable through
out the period, but especially tonight. Clouds will be on the
increase late tonight, as an area of low pressure moves in from
the west, leading to periods of BKN clouds. A few showers and
storms could begin moving into the I-64 corridor in our
northwestern counties late this evening. The rain will continue to
advance slowly eastward overnight into early Friday, and could
begin to affect JKL, LOZ ,SME, and SYM toward the end of the
forecast period. MVFR fog will be possible again tonight as
moisture advects in ahead of the incoming storm system. LOZ and
SME might even see brief periods of IFR fog between 10 and 12Z on
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 142 PM EDT THU MAY 16 2024

Based on current trends, the TAF sites will continue to experience
BKN low level cover through around 0Z this evening, before the
clouds begin to scatter out a bit. VFR should be the rule at JKL,
LOZ, and SME, but SJS and SYM will continue to see MVFR CIGs of
around 2K this afternoon, before the clouds scatter and lift a bit
this evening. Winds should be generally light and variable through
out the period, but especially tonight. Clouds will be on the
increase late tonight, as an area of low pressure moves in from
the west, leading to periods of BKN clouds. A few showers and
storms could begin moving into the I-64 corridor in our
northwestern counties late this evening. The rain will continue to
advance slowly eastward overnight into early Friday, and could
begin to affect JKL, LOZ ,SME, and SYM toward the end of the
forecast period. MVFR fog will be possible again tonight as
moisture advects in ahead of the incoming storm system. LOZ and
SME might even see brief periods of IFR fog between 10 and 12Z on
Friday.

&&

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

$$

SHORT TERM...CMC
LONG TERM...AR
AVIATION...JP