Scientific Forecaster Discussion
fxus64 kmrx 111949
Area forecast discussion
National Weather Service Morristown Tennessee
249 PM EST Wed Dec 11 2019
Short term (today through tomorrow)...
Quiet weather is expected for the rest of today and tomorrow as we
sit between weather systems. Generally zonal flow today will
transition to a slight ridging pattern as we head into the
overnight. Temperatures today are warming into the 40's across much
of the valley. Satellite imagery is showing that most of the snow in
the valley has already melted away early this afternoon, with snow
still lingering in the higher elevations of the Cumberland Plateau
and southwest Virginia/northeast Tennessee. So have gone slightly lower on
temperatures in snowpack areas compared to the drier parts of the
While the daytime highs are much warmer than yesterday afternoon, the
overnight lows will be similar to last night under the clear skies
with lows dropping below freezing. Any shaded areas that didn't have
wet roads completely dry out today could see refreezing overnight.
Expect pleasant weather again tomorrow with temperatures warming up
even more, and increasing clouds moving in from the west ahead of
our next system.
Long term (thursday night through wednesday)...
Surface high pressure will be located over the northeastern U.S.
Thursday night and Friday morning with a wedge of cold air on the
eastern side of the mountains. A stalled east-west boundary will be
present along the northern Gulf of Mexico as a shortwave trough
races into the Tennessee Valley. At 850 mb, the high will be well
out over the Atlantic with southerly flow established across the
region. Isentropic ascent will increase early Friday morning with
soundings showing saturation in the lowest 300 mb or so of the
atmosphere. Temperatures across portions of extreme northeast
Tennessee and southwest Virginia will dip below freezing Friday
morning. With 850 mb temperatures in the 4-6 degrees celsius range
the only two precipitation types possible will be rain or freezing
rain. The window looks to be rather small but expect freezing rain
early Friday morning with highest confidence in Johnson co TN,
Washington co VA, and Russell co Virginia. An advisory may become
necessary in later forecast issuances. For now, the limiting factor
is the time window appears to be around 3-6 hours at the most.
Temperatures will warm quickly on Friday ending the threat for any
additional ice accumulations as the surface high retreats to the
north and east.
An area of low pressure will ride along the surface boundary from
the northern Gulf late Friday into the Atlantic Seaboard later on
Saturday. A robust trough will move in during this timeframe. Precipitable water
values will climb into the 0.9-1.0 inch range around the 90th
percentile for mid-December. Model soundings support deeper
saturation later in the day on Friday. Rainfall will be widespread
across the forecast area through Saturday. Rainfall amounts will
range from around 0.75-1.00 inch on average. Precipitation will come
to an end Saturday night into Sunday morning. There could be enough
left over moisture for a few snow showers across the higher
elevations of east Tennessee and SW Virginia Saturday night/Sunday morning but no
impacts are expected at this time.
Sunday will be dry as high pressure quickly moves across the area as
the next system moves in on Monday. Cold air advection will feature
Saturday night into early Sunday but the low-level ridge axis will
shift to the east on Sunday afternoon with a return to southerly
Both the GFS and European model (ecmwf) are both in fairly good agreement about the
overall pattern going into the upcoming work-week. A deep surface
low will develop across the natural baroclinic zone along the
northern Gulf Coast and track to the northeast on Monday into
Tuesday. The path and strength of the surface low climatologically
supports a mountain wave event across the western foothills of the
Appalachians and will continue this mention in the severe weather potential statement. Models
indicate rather impressive rainfall amounts with this system with up
to 2 inches possible. Due to the heavy rainfall and antecedent
conditions, expect localized flooding will be possible and will
maintain this mention in the severe weather potential statement as well.
18z taf discussion.
Clear skies, light winds and quiet weather is in store for the
next 24 hours. Cloud coverage begins to increase starting tomorrow
Preliminary point temps/pops...
Chattanooga Airport, Tennessee 30 52 38 46 44 / 0 10 60 70 60
Knoxville McGhee Tyson Airport, Tennessee 28 50 35 46 43 / 0 10 60 70 70
Oak Ridge, Tennessee 29 50 35 45 42 / 0 0 50 70 70
Tri Cities Airport, Tennessee 23 49 32 49 41 / 0 0 50 80 80