Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Jackson Kentucky
1020 PM EDT sun Aug 30 2015
issued at 1020 PM EDT sun Aug 30 2015
Some changes were made to the forecast for the rest of tonight.
Based on the lack of convective activity occurring in eastern
Kentucky...and considering the extremely slow northward movement
of rain showers that are ongoing across eastern Tennessee...and
with very little precipitation showing up in the latest short term
model data...decided to decrease rain chances for the rest of the
night across the entire to only slight chance. It does appear that
the current conditions will support isolated rain shower activityovernight...but
little more than that. The quantitative precipitation forecast forecast for the rest of tonight
was also changed to match up with the new pop forecast. The
hazardous weather outlook was also updated to remove mention of
thunder for the remainder of the overnight period.
Update issued at 752 PM EDT sun Aug 30 2015
The primary issue with the forecast this evening will be the
coverage of shower and thunderstorm activity across the area. As
of now...only a few meager showers are ongoing in some of our far
southern counties...and it is questionable whether or not any
precipitation from those is reaching the ground. Will continue to
monitor radar imagery and the latest model data over the next few
hours to determine whether or not the forecast needs to be
updated. For now have only ingested the latest observation into the hourly
grids to freshen things up a bit.
Short term...(this evening through Monday night)
issued at 322 PM EDT sun Aug 30 2015
An upper level low continues to circulate northward through the
State of Georgia and towards the Appalachians this afternoon.
Meanwhile...the remnants of Erika are being pulled north-northeast with this
upper level low movement...pulling moisture across eastern Tennessee and
eastern Kentucky under SW flow. This has resulted in some elevated returns
across the region...though some of these returns are finally
starting to make it to the ground. Given diurnal heating and a
stalled frontal boundary to our west as well...can/T rule out some
other isolated showers and maybe even a rumble of thunder as we
continue throughout the afternoon...though it appears as the best of
this activity will remain to our west over central and western Kentucky.
Overall...the pattern looks a bit benign...with very little impacts
expected for the rest of the afternoon.
Loss of daytime heating overnight will cut down on most of the
shower and thunderstorm activity across the region...especially west
of our County Warning Area. Some isolated to scattered showers across the eastern
portion of the state can/T be ruled out as the upper level low and
the remnants of Erika continue to track NE across the Appalachians.
Regardless of if it rains or not...expect high clouds /and maybe
even some low to middle clouds/ to linger around throughout the night.
All models are still pointing at enough of a surface inversion
forming that fog will be possible between 9 and 13z despite the
presence of these clouds. As such...will include mention of valley
fog in forecast...but not confident enough to go above patchy at
this time. If a location does receive a decent amount of rain this
afternoon...that could lead to some better fog development.
Otherwise...expect fog to remain generally in the deeper valleys and
near bodies of water.
For Monday...the upper level low will finally fizzle out just NE of
the region. However...another upper level wave will shift northeast
and stretch from the Gulf Coast...up the lower Mississippi...and
eastward across the Ohio River valley by Monday morning. While high
pressure will remain in general control at the surface...this
feature will work with daytime heating to create enough
instability/lift that some diurnally driven isolated showers and
thunderstorms cannot be ruled out. However...as mentioned in
previous forecast discussion...there is no good temperature gradients or
frontogenesis in the region...and there is a good cap in the
middle/upper levels according to the forecast soundings. As such...not
expecting many impacts from these showers or thunderstorms outside
of some brief light rains. And once again...as we lose daytime
heating Monday night...expect any diurnally driven convection to
come to an end as high pressure subsidence regains control.
Long term...(tuesday through sunday)
issued at 239 PM EDT sun Aug 30 2015
While some differences exist in the modeling...an upper level
ridge appears poised to dominate our weather through the long term
period. A few weaknesses in the ridge combined with modest low
level moisture in place may allow for the development of an
isolated afternoon shower or storm at times...but most locations
will likely remain dry. Baring any widespread rain in the short
term...which appears unlikely...we will likely complete a two week
stretch without any appreciable precipitation by the weekend. Due
to this dry spell...forecast highs were nudged up a bit above the
blended guidance late in the week into the Labor Day weekend with
the Mercury likely reaching around 90 each day. On the
flipside...the dry conditions should allow for a decent diurnal
range with overnight lows falling into the 60s each night.
Aviation...(for the 00z tafs through 00z Monday evening)
issued at 752 PM EDT sun Aug 30 2015
The taf period begins with a few low cumulus clouds moving across
portions of the forecast area...with an extensive deck of high
clouds in place above. Little if any precipitation is occurring in
the forecast area at this time...but this will need to be
monitored to see if weak lift and moisture flux from the remnants
of Erika is able to spark further convective activity this evening
and overnight. For now will go with VFR conditions at the taf
sites...with the potential for some fog at the airports from 8 to
12z Monday. The fog should only lead to MVFR visibilities at the taf
sites where it occurs. The latest model soundings continue to
indicate the loz may see a low deck of stratus clouds later
tonight that could lead to IFR or LIFR ceilings.