Scientific Forecaster Discussion
fxus64 kmrx 200701
Area forecast discussion
National Weather Service Morristown Tennessee
301 am EDT Fri Sep 20 2019
Short term...(today and tonight)...
Surface high pressure has built southwestward into the southern
Appalachians helping to push the old backdoor cold front farther
west into middle Tennessee. This has lead to rapidly clearing skies and
lower td's in a light easterly flow pattern of cool and dry
advection. Water vapor and infrared satellite indicate a weak perturbation
currently over southern PA and WV. This feature is moving
southwestward on the periphery of the mid level ridge over the
Mississippi Valley. With the surface high overhead, soundings are
dry, so only expect some mid and high cirrus clouds over southwest
Virginia and northeast Tennessee late tonight through mid morning. Current low
temps remain on track for the rest of the night. Temp and dew point
spreads have been rather larger in recent observations, so any fog
will be very isolated and will hold off until after 09z, mainly in
The above mentioned 500 mb ridging over the Mississippi and Ohio valleys
will start to build over our region during the day Friday. This will
lead to a slow increase in warm advection as the surface high is
forced a bit farther east. Due to the dry ground, nudged highs
slightly above guidance with most areas seeing mid 80's with a few
upper 80's in the southern valley. The NAM, GFS, as well as some of
the cams indicate another weak shortwave topping the building ridge
in the afternoon and are trying to develop a few showers in the east
Tennessee mountains. The surface high will still be in the vicinity, and
the soundings still show a dry profile, so have not included any
pops at this time. The relatively dry airmass continuing will bring
lows Friday night similar to past nights with upper 50's/low 60's
and only very spotty pockets of fog.
Long term...(saturday through thursday)...
Overall, persistent pattern of upper and surface ridging will remain
over the southern Appalachians except for Monday. For Sunday night
and Monday, a short-wave trough will move across the Great
Lakes/upper Ohio Valley pulling a frontal boundary through the area.
Dynamics with this trough stays well north and airmass remains
relatively dry. Due to the dry soil, will continue to go above
guidance highs and on the lower end of the MOS lows. Also, lowered
afternoon dewpoints a couple degrees in the afternoon. Now the
For Saturday and Sunday, upper ridging is evident with forecast
soundings showing a strong mid-level subsidence inversion
suppressing any convection.
For Monday, aforementioned trough moves well north of the area with
frontal boundary sweeping through. Given the persistent dry airmass
over the region, will only call for low pops (15-30 percent range)
with the highest over the northern/western areas which is closer to
the dynamics/slightly better moisture.
For Tuesday through Thursday, surface and upper ridge will build
back/remain across the southern Appalachians producing dry and
unseasonably very warm conditions.
Preliminary point temps/pops...
Chattanooga Airport, Tennessee 87 61 88 63 / 0 0 0 0
Knoxville McGhee Tyson Airport, Tennessee 86 62 87 62 / 0 0 0 0
Oak Ridge, Tennessee 86 61 87 62 / 0 0 0 0
Tri Cities Airport, Tennessee 83 58 85 58 / 0 0 0 0