Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
FXUS64 KMRX 280814
Area Forecast Discussion
National Weather Service Morristown TN
414 AM EDT THU JUL 28 2016
.SHORT TERM...(Today and Tonight)...Showers and thunderstorms over
the NE sections of the forecast area have moved northeast. However
a weak mid level low across western KY and TN is moving slowly east
with widespread showers and some storms across extreme northwest TN
and the western half of KY. This trough and associated surface low
will move across middle TN this morning and early afternoon and
then into eastern TN and western VA late this afternoon and
evening. Clouds over the NE area of the forecast area may delay
heating somewhat but a very moist environment across most of the
forecast area with dewpoints as high as the lower to mid 70s and
CAPE Values of 1000-2000 J per KG within moderately strong mid
level winds. A marginal risk for severe storms with damaging winds
the main threat in the afternoon and early evening will exist
across the eastern Tennessee Valley. Heavy rainfall will also be
possible with precipitable water values around 2 inches. High
temperatures will be affected by clouds northern half and should
only reach the mid to upper 80s lower elevations. Central and
southern Valley areas still may reach 90 or lower 90s if there is
enough morning sunshine. Tonight weak surface low moves up into the
central Appalachians with showers and storms persisting at least
through the evening...then likely decreasing after midnight as
atmosphere becomes more stable and shortwave energy shifts east
northeast tonight. Rainfall amounts expected to be about one inch
around Knoxville to 2 inches in the western part of southwest VA.
Most of this rain will fall between 18z and 06Z tonight. Localized
flooding will be possible mainly northern Plateau and northeast TN
and southwest VA. Because flash flood guidance is so high mainly
over 2 inches for one hour and 2.5 to 3 inches for 3 hours no Flash
Flood Watch will be issued.
.LONG TERM...(Friday through Wednesday)...
Middle level low that had ushered in deep layer moisture will
finally move NE of the area by Friday morning. With it, broad
middle level long wave trough axis extends southward across the
Great Lakes, Ohio Valley, and into Western TN. With predominate
westerly flow aloft, PW values return to more seasonal levels of
about 1.5- 1.75 inches by Friday afternoon across much of the area.
A series of weak impulses will move across this broad trough
through the weekend. This combined with a weak surface boundary
draped across KY and the Ohio Valley will keep chances for
afternoon/evening showers and thunderstorms with us through Sunday.
This is particularly true over northern half of CWA where influence
of these shortwaves will be most pronounced. With the area coming
under the influence of this broad trough, expect temperatures to
return to seasonal levels through the weekend.
Trailing edge of weak surface boundary expected to pass through the
area late Monday. With some instability and marginal shear fcst,
MLCAPE of near 1500 J/Kg and SFC-6KM shear of 10-15 kt, currently
cannot rule out isolated strong storms on Monday. Subtropical ridge
begins to build eastward from the Great Plains by Wednesday.
Temperatures will once again climb back into the lower 90`s across
much of the TN Valley Tuesday and Wednesday as POPs decrease through
the end of the forecast.
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 91 73 88 73 / 60 50 40 40
Knoxville McGhee Tyson Airport, TN 90 71 89 71 / 60 60 40 40
Oak Ridge, TN 88 71 87 71 / 70 60 50 40
Tri Cities Airport, TN 88 69 84 68 / 70 60 50 50