Scientific Forecaster Discussion
fxus64 kmrx 102012
Area forecast discussion
National Weather Service Morristown Tennessee
312 PM EST Tue Dec 10 2019
Short term...(tonight through wednesday)...
the primary headline of the short term period continues to be
strong cold advection behind a departing cold front amidst deep
longwave troughing aloft. Temperatures across the region continue
to fall this afternoon on a non-diurnal trend with freezing
temperatures observed across portions of the Cumberland Plateau at
this time with snow showers reported as well. Likewise, valley
locations have fallen off nicely as well with cha currently seeing
rain at 41 degrees, rain and 42 at tys, and rain at 45 for tri. Further
cooling will favor a phase change from rain to snow (with sleet
mixed in initially) across the Tennessee Valley and into the southern
Appalachians through the remainder of the evening. Deep moisture
does look somewhat limited further west, thus still thinking sub
advisory level snowfall accumulations across the vast majority of
the region. However, prolonged precipitation and lowered snow
levels across the high terrain of the east Tennessee mountains will favor
accumulations in the 1-3 inch range, therefore an advisory was
issued for these areas. Otherwise, generally a half inch or less
is expected in the valley, closer to an inch over the plateau and
portions of SW Virginia. Precipitation will move out of the area
overnight into Wednesday morning yielding clearing skies amidst
light nly winds. Lows tonight will fall into the 20s areawide,
with highs struggling to top the mid 40s in the valley on
Wednesday, and low/mid 30s over the mountains.
Long term...(wednesday night through monday)...
we will be transitioning between systems on Wednesday night into
Thursday as weak mid level ridging attempts to build in. Models
are finally coming into better agreement that on Friday a
shortwave should zip through the area bringing the next chance of
precipitation. With the system expected to move very near the
forecast area it means we could see a brief round of wintry
weather Thursday night into Friday morning in far northeast
Tennessee and southwest Virginia. Forecast soundings indicate that
there may be a warm nose around the 850mb layer with colder air
at the surface. This means we could see a wintry mix of
precipitation types in northeast Tennessee and southwest Virginia.
We will get a much better handle on how this system should evolve
once the currently ongoing precipitation moves east of the area
and the atmosphere has a chance to settle. For the rest of the
eastern Tennessee Valley temperatures near the surface look to
remain warm enough that precipitation that falls on Thursday night
into Friday should remain as cold rain. Precipitation will linger
into Friday evening/night but should be all liquid by this point
as temperatures warm up during the day on Friday.
A drying out period behind this system will occur through most of
the weekend with only a few spotty showers, and temperatures near
normal on Saturday and Sunday.
A low pressure system with leading warm front will then move out of
the plains states early next week. As this system moves through
models are indicating that we should in general see all rain in most
of the valley locations. Higher elevations of the Cumberland Plateau
into southwest Virginia and northeast Tennessee may see a wintry mix
on Sunday night into Monday morning. Moderate rain chances will
continue through the end of the 7-day forecast. Looking just beyond,
current models are indicating that rain chances should begin to
taper off by Wednesday morning.
18z taf discussion.
A fairly restrictive taf cycle ahead for all sites as a cold front
moves through the region. With that, am expecting periods of
MVFR/IFR at times with rain this afternoon, with snra moving into
the region this evening. Moisture will move out of the region into
Wednesday morning allowing all restrictions to recover favoring
solid VFR to round of the taf cycle. Winds through the period will
initialize in the 8-12kts range nwly, slowly weakening overnight
and veering nly.
Preliminary point temps/pops...
Chattanooga Airport, Tennessee 29 47 29 54 39 / 80 10 0 10 60
Knoxville McGhee Tyson Airport, Tennessee 27 44 28 51 34 / 90 10 0 10 50
Oak Ridge, Tennessee 26 44 27 51 34 / 80 10 0 10 50
Tri Cities Airport, Tennessee 26 40 25 48 30 / 90 10 0 10 50
Tennessee...Winter Weather Advisory from 7 PM this evening to 7 am EST
Wednesday for Blount Smoky Mountains-Cocke Smoky Mountains-
Johnson-Sevier Smoky Mountains-southeast Carter-southeast