Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Jackson Kentucky
329 am EDT Thursday Jul 2 2015

Short term...(today through friday)
issued at 323 am EDT Thursday Jul 2 2015

As of 3 am...lingering evening convection over the County Warning Area is continuing
to dissipate as best energy turns its attention to the mesoscale convective system still
over Missouri...which is now generating scattered showers and
thunderstorms out ahead of it. These showers and thunderstorms are
currently making it into western and central Kentucky/Tennessee and will
likely make it into our southern County Warning Area over the next hour or so.
Given the high amount of rain this area of our County Warning Area has seen over
the last couple of days...and the very low ffg as of 0z
7/02...expect that flooding concerns will likely start arising in
this area just before dawn and continue through the morning...and
even through much of the day. An upper level shortwave will
continue to shift east-southeast today...pulling the mesoscale convective system with it. Expect The
Heart of the mesoscale convective system to be over western Kentucky and southern Illinois by 12z
today...with a cold pool driven outflow pulling heightened chances
for showers and thunderstorms into eastern Kentucky. The mesoscale convective system will
continue to shift across the state through the day following an
shortwave as it rounds an upper level longwave trough. As it
shifts eastward...it will become more cold pool driven once more
with multiple outflows likely creating their own means for
multiple areas of convection.

Despite widespread heavy rain through the day and into the
overnight hours...wpc and other models are still pegging the
southern half of the County Warning Area with the highest quantitative precipitation forecast amounts. As
mentioned above...this is the same area that has already been hard
hit...so expect an active day and overnight period as any rain
that occurs will likely result in runoff. Will keep with current
Flash Flood Watch...as this seems to line up well with latest guidance and
wpc quantitative precipitation forecast forecast.

There is some discrepancies in the European model (ecmwf) and the nam12 late tonight
as the mesoscale convective system reaches the far eastern extent of the County Warning Area. The NAM shows a
broader surface low pressure system forming and keeps multiple
heavier waves of precipitation over southern and eastern Kentucky through 12z
Friday. Meanwhile...the European model (ecmwf) has a slightly weaker but more
centralized low...and pulls most of the moisture out of the state
with the exception of far eastern Kentucky by this same time.
Regardless...expect there will be some degree of rain potential
centered over our County Warning Area...which warranted keeping likely and above
probability of precipitation across much of the County Warning Area through the night.

For Friday...any lingering moisture across the state will likely
result in a resparking of scattered to numerous showers and thunderstorms
during the daytime hours due to peak heating and interaction with a
stalled frontal boundary passing through the state /attached to
the departing low/. While convection will generally be in and
around the area of the boundary...expect coverage to include a
wide area across most of the state and areas southeast. One thing to
note...however...is that model soundings are showing a large
influx of dry air in the middle and upper levels after the
shortwave/MCS/and surface Low Pass through. This will keep most
moisture confined to a shallow low level layer. Latest nam12 forecast
soundings are also showing an inversion at all taf sites just
above this moist layer. With this in mind...expect strong to
severe storm potential to be very limited with this inversion in
place...and any showers to be much lighter in nature with lower
quantitative precipitation forecast values. This correlates well with the end of the watch period
as well.

Long term...(friday through wednesday)
issued at 354 PM EDT Wednesday Jul 1 2015

Period begins with decent agreement in the overall trough still
set up across the eastern Continental U.S. And strong ridge in the western
Continental U.S.. models are differing in the amplitude of the shortwave
energy dropping southeast into the region. This could have implications
on the overall surface features that develop during the first
portion of the long term. Then toward the end of the period the
pattern looks to shift from long wave trough to weaker troughing
across the east while ridging breaks down in the western US.
Models continue to very in this period...however agree with a
overall change in the pattern.

Surface boundary will continue to meander across the region
through the first part of the long term. There remains a fair
amount of variability in exact location of the boundary from model
to model. This will lead to continued unsettled conditions across
the region. Given this quasi-stationary boundary and multiple
upper level disturbances will lead to potential heavy rainfall
over some areas through the period...however a fair amount of
uncertainty still exists in exact location of heaviest quantitative precipitation forecast.
Another cold front approaches during the late portion of the
period that will increase probability of precipitation slightly late Tuesday into
Wednesday. Given variability in the front and overall pattern
change stuck close to model blends in the long term forecast.
Overall temperatures through the period will remain near to below
normal given the unsettled pattern and trough.

&&

Aviation...(for the 06z tafs through 06z Thursday night)
issued at 142 am EDT Thursday Jul 2 2015

While most showers and thunderstorms have dissipated across
eastern Kentucky...another area of heavy rain and thunderstorms
associated with a mesoscale convective system just moving into the Mississippi River
valley is making its way across central Kentucky and Tennessee...and should
begin impacting the eastern portion of the state over the next few
hours. Went ahead and kept mention of vcsh through the rest of the
night...though may need to update taf if any one location is
expected to see rain for a prolonged period of time. Despite low
cloud cover /generally IFR/...there is enough moisture that fog is
still popping up at taf sites as well. Unfortunately...the visible
will likely fluctuate throughout the night under a true patchy
dense fog environment...so tried to gear taf toward worst
conditions expected. As the mesoscale convective system continues to approach from the
west...expect numerous showers and thunderstorms by daybreak and
through the day tomorrow. Visible and ceilings will likely be dependent on
any passing storms...but general conditions should lie somewhere
between IFR and MVFR due to the low cloud deck expected to be in
place. By tomorrow night...any residual moisture will likely lead
to fog once more...despite lingering low ceilings and showers. Outside
of any storms...winds will be light through the period...at around
5 kts or less overnight and 10 knots or less during the day...and
generally from the southwest.



&&

Jkl watches/warnings/advisories...
Flash Flood Watch through Friday morning for kyz068-069-079-080-
083>088-114>118.

&&

$$

Short term...jmw
long term...dj
aviation...jmw

National Weather Service Glossary of Abbreviations