Area Forecast Discussion
Issued by NWS Jackson, KY
FXUS63 KJKL 210559
Area Forecast Discussion
National Weather Service Jackson KY
159 AM EDT SAT MAY 21 2016
Issued at 1054 PM EDT FRI MAY 20 2016
A few showers still lingered late this evening, mainly over the
northeast part of the area. However, they have been dissipating
more quickly than was forecast, and the pop for the remainder of
the night is lowered to 20-40%.
UPDATE Issued at 823 PM EDT FRI MAY 20 2016
After some thunder in our southwest counties late this afternoon,
lightning has dried up. Although models still show weak elevated
instability present this evening, they don`t show any meaningful
increase. That being the case, have removed thunder.
.SHORT TERM...(This evening through Saturday night)
Issued at 355 PM EDT FRI MAY 20 2016
19z SFC analysis shows an inverted trough developing and lifting
into the Tennessee Valley. This is spreading showers and a few
thunderstorms into East Kentucky from southwest to northeast. The
rain is also bringing a potential for heavy rains with PWATs
around 1.5 inches into the evening, but so far the worst of the
rain has stayed west of the CWA. Thin clouds in the east and
north allowed temperatures there to climb into the lower 70s while
readings are holding in the mid 60s to the southwest where the
steadier showers moved in a bit earlier in the afternoon.
Dewpoints rose into the low 60s in the southwest while they have
made it to the mid 50s north and east. Winds, meanwhile, have been
generally light and variable through the day.
The models are in good agreement aloft through the short term
portion of the forecast. They all depict a trough rolling into the
Ohio Valley tonight and spreading its core of energy through the
region. This low will deepen just to the northeast of Kentucky on
Saturday, but in a switch from 24 hours ago, is keeping this
fairly deep tough as just an open wave and moving it off to the
east of the area by Sunday morning. Have favored a general model
blend for forecast specifics with a strong lean toward the HRRR
and the NAM12, though did adjust the NAM`s heavy rain position
more easterly - closer to where the other models clustered for
Sensible weather will feature a wet evening of soaking rains for
the CWA as the southern SFC low lifts through western parts our
area with storms and heavy rain a potential. The highest QPF is
expected to be over our northwest counties in line with the
deformation zone of the low as it passes. Yet, the precipitation
should be progressive enough that any high water issues should be
in the urban and small stream advisory category, at worse. The
showers will eventually become more scattered later tonight from
southwest to northeast but low clouds and some fog is left behind
through the rest of the night and into Saturday morning. As the
low spins into eastern Ohio, low clouds and showers will remain
through much of the area starting in the north and spreading south
with the system`s cold front during the day. Some upslope flow in
the wake of the low and front will likely keep a few light showers
around into Saturday night.
Again used the ShortBlend as a starting point for most elements
of the forecast with only limited terrain adjustments for
temperatures through the period. During the latter part of the
forecast the SuperBlend was used to initialize the forecast with
adjustments made mainly to increase the PoPs later in the period
due to the models under doing the upslope potential.
.LONG TERM...(Sunday through Friday)
Issued at 400 PM EDT FRI MAY 20 2016
Model agreement is good through Wed. Thereafter differences crop up
as a result of models struggling with timing and strength of minor
impulses embedded in nearly zonal mid level flow. These features are
responsible for uncertainty through the latter half of the extended.
Felt best approach was to stay close to the blend of solutions and
guidance, especially through the latter portion of the period.
Shortwave dropping through the base of easter CONUS mid/upper level
trough will pass through the Ohio Valley-Tennessee Valley Region
Sunday. Mid and upper level ridging will build into the region by
Monday and then flatten out into a more zonal flow regime for the
remainder of the extended.
For sensible weather, Sunday`s shortwave appears strong enough to
generate some isold to sct shower activity with the help of diurnal
heating Sunday afternoon. NAM/GFS both have come more in line with
what has been a consistent ECMWF. Decent lift/cooling around 10 kft
associated with the aforementioned shortwave will combine with
diurnal sfc heating to create steep boundary layer lapse rates.
However, model guidance does not seem to be as impressed. For now
maintained inherited slight pops for Sunday but would not be
surprised if that has to be increased in the future, especially over
the higher terrain to our south and east. High pressure at the
sfc/ridging aloft will provide generally fair weather through the
start of the week. Thereafter tendency was to broad brush pops to
handle inconsistencies among the models in timing and strength of
impulses in zonal flow through the region. The end result was a
general chance pop, sct showers and thunderstorms through the entire
latter half of the extended window. Attm not seeing anything in the
fcst soundings that would indicate any type of widespread hydro or
severe weather issues.
Hard to tell how much convection, debris clouds, and rain cooled air
may have on temps through the period, but continue to see a slight
upward trend in highs, into the lower 80s each day. Not seeing as
much change in overnight lows, running near normal until mid week
when they also warm to above normal level, generally in the 60s.
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 158 AM EDT SAT MAY 21 2016
Very tough forecast tonight. Only a few light showers remain
across the region, mainly affecting KJKL and possibly KSJS.
Otherwise conditions varied greatly, with everything from lifr to
vfr cigs chaotically distributed across the region. Each TAF site
is also showing a great deal of variability as well. Tried to
forecast for the overnight based on the most likely longest lived
condition, which generally included lifr cigs at all TAF sites.
Other than some steam fog at KJKL, expect this to be more of a low
cig rather than a fog event overnight. Will continue to closely
monitor overnight and update as needed, as there will likely be
quite a bit of variability. Cigs will improve slightly during the
day tomorrow, generally to mvfr, as another round of isl to sct
showers move across the area in the afternoon. Uncertain at this
time how these will impact the TAF sites, so left at VCSH. The
system will begin moving east of the region tomorrow night.
However lingering moisture will likely lead to some fog at the TAF
sites and/or low cigs once more. Unfortunately confidence is low
in this set up as well.