Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Jackson Kentucky
304 PM EDT sun Jul 13 2014

Short term...(this evening through Monday night)
issued at 305 PM EDT sun Jul 13 2014

Severe thunderstorm and heavy rain threat remain the concerns for the
short term portion of the forecast. Northern part of the forecast
area remains in the day 1 slight risk area with the remainder of the
forecast area in the day 2 slight risk. Also the excessive rainfall
outlook for day 1 highlights the northern forecast area and the day
2 outlook the southeast part of the forecast area. However the
evolution of the severe threat and the heavy rain threat remains
uncertain for eastern Kentucky.

Isolated to scattered convection that has developed over the
southeast part of the forecast area and over central Kentucky is expected
to die off this evening with loss of daytime heating. The more
organized broken line of convection that has developed across Ohio
and Indiana is expected to persist into the night. This area of
convection has developed ahead of the the initial rather nebulous
pseudo cold front or outflow boundary and in a corridor of better
instability and shear. There is a Severe Thunderstorm Watch just to
our north for this and there has been a severe report of 1 inch hail
over central Ohio. As this line drops south this evening into our area
there will be less support for severe storms...with less instability
and less shear. Thinking is that showers and thunderstorms will be
likely in the northern part of the forecast area tonight. While severe
threat is possible is looks unlikely.

The severe threat on Monday looks greater...but there is considerable
uncertainty due to the amount of ongoing shower and thunderstorm activity
and convective debris cloud that will be around at the start of the
period. The secondary...or primary cold front which will be the
leading edge of the much cooler and drier air will move into the
forecast area Monday night. The severe threat on Monday will likely
be tied to how much sunshine can be realized during the
afternoon...with the best chance for severe storms over the far south
part of the forecast area.

The other concern is the heavy rain threat through the entire short
term forecast period. With precipitable waters forecast to increase of 1.7 to
possibly over 2 inches from late tonight into Monday night heavy
rainers are a definite concern. Storm motion forecast to be 15 to 2o
knots will limit the time the heaviest rains with a given storm
remain over a local area...but there is a threat for multiple storms
to affect a given area. There is considerable uncertainty with
quantitative precipitation forecast. Given that part of the area is in d1 drought and flash flood
guidance is generally 2 to 2.3 inches per hour...it looks unlikely
that other than an isolated flash flood event would occur.

Long term...(tuesday through sunday)
issued at 305 PM EDT sun Jul 13 2014

The models begin the extended period in pretty good agreement. The
large scale weather pattern features a anomalously deep positively
tilted upper low centered over northern Michigan with a trough
extending across southern Illinois. This is a complex weather system
and it will involve multiple surface features moving across eastern
Kentucky. By Tuesday morning...the cold front is forecast to extend
from Rowan to Wayne County. The front will continue to move across
the area on Tuesday and will have moved into Tennessee and Virginia
by the late afternoon. The upper trough axis will hang in there and
not move out of the area until Thursday morning. Even though the
trough axis moves through the area...the eastern portion of the area
will continue to be under a weak trough. As a result...the
temperatures are going to stay below normal and will be quite a
please relief from the typical July heat and humidity. The low
temperatures on Wednesday and Thursday morning will be near or at
the records lows across eastern Kentucky. A short wave will generate
over the plains on Thursday night and will move across the area on
Friday. A front will be moving across the area and bring some
showers and thunderstorms. This front will lack deep moisture
because the Gulf air will not be able to move into the area before
the front arrives. By this point in time the models agree on the
general pattern...however the GFS is a little faster with the
trough. The front will be pushed to the south of the area on Friday
night...however should move back to the north on Saturday night.
Confidence is high through Friday...however really starts to plummet
on Saturday due to the model differences. By Sunday night there are
major phasing issues with the European model (ecmwf) and GFS.

&&

Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 112 PM EDT sun Jul 13 2014

VFR conditions will prevail into and through most of the upcoming
night...with MVFR expected late in the forecast period with showers
and thunderstorms. Convection this afternoon is not expected to
affect the taf sites. Isolated to scattered convection tied to a weak
area of instability over far southeast Kentucky should remain southeast of the taf sites.
Convection developing ahead of a cold front in Indiana and Ohio will
remain north of the taf sites today. The convection over southeast Kentucky will
die off after sunset while the showers and thunderstorms developing
over Ohio and Indiana should affect the taf sites late tonight and
early on Monday. More thunderstorms are expected Monday afternoon
beyond the current taf forecast period.



&&

Jkl watches/warnings/advisories...
none.
&&

$$

Short term...sbh
long term...jj
aviation...sbh

National Weather Service Glossary of Abbreviations