Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kmrx 182305 aaa 

Area forecast discussion...updated
National Weather Service Morristown Tennessee
605 PM EST Mon Nov 18 2019

for 00z aviation.


Short term...(tonight and tuesday)

Much of the cloud deck has exited to the east as the weak shortwave
continues to move away from the region. This has allowed temps to
pleasantly warm into the middle 50's in many areas. Clouds will
begin to filter back into the area after about 23z as the next
shortwave begins to approach from the northwest.

Deep, negatively tilted longwave troughing will continue tonight and
Tuesday across the eastern Continental U.S. Downstream of western Continental U.S.
Mid/upper ridging. As the aforementioned mid level shortwave drops
into Kentucky in the northwest flow pattern tonight, increasing mid level
moisture will lead to mostly cloudy skies. Despite weak and variable
surface flow, the insulation from the clouds will prevent temps from
bottoming out tonight. Nbm lows look reasonable, so expect mid/upper
30's across the valley with low/mid 30's across the plateau, eastern
mountains, southwest VA, and southwest NC. That shortwave and
associated weak surface trough will cross our region from mid
morning through the afternoon Tuesday. Soundings show moisture
remaining confined to above the 850-700 mb layer most of the day
until late afternoon, when deeper moisture finally shows up around
tys and tri. However, the upper support and surface trough will be
quickly moving east by that time, so think that Tuesday will be
similar to today with just isolated light showers and drizzle in far
northern and northeast Tennessee and southwest VA, as well as the east Tennessee
mountains. Brought in slight chance pops for light showers and
drizzle to the northern plateau around 13z expanding to northeast Tennessee
and southwest Virginia after 16z, then confined to these northeastern
areas after 21z. Much of it will again fall as virga due to the lag
time of better low-level moisture. 850 mb temps cooling to -0.3 to 4
c behind this wave, mostly cloudy skies, and low sun angle will hold
highs below average at upper 40's/low 50's in northern areas and
low/mid 50's in southern areas. Westerly 850 mb winds of 30+ kts in
the cold air advection behind this shortwave will lead to 15-20 knot gusts across
the region in the afternoon, with some slightly higher gusts on the
plateau and across the mountains.


Long term...(tuesday night through monday)

Models continue to struggle a bit with the late week system, so
forecast confidence still not high for the details of
Friday/Saturday time frame. Before then, we will see somewhat
colder air pushing in on northwest winds Tuesday night. There may
be a few showers/snow showers over the north and the Smoky
Mountains, but will keep pops in the slight chance to low chance
range. Wednesday will be dry with surface high pressure drifting
east across the region and a mid/upper level ridge building in.

The next chance for precipitation will occur mainly in the Thursday
night through Saturday time frame. As mentioned above, models
continue to struggle with details of this system, but are coming
into better agreement that the northern and southern stream waves
will phase, sweeping a cold front into our area Friday. They do
disagree on the surface wave that forms on the front, with the GFS
showing a weaker wave and more southerly track than the European model (ecmwf).
However, both show a fairly wet period with rain at times starting
as early as late Thursday near the plateau and continuing through
Saturday into Saturday night, despite the uncertainties of the
details. By Sunday and Monday this system should be out of the area,
allowing for a couple of dry days with temperatures not far from
seasonal normals.



00z taf discussion.

Clouds will gradually be increasing across the area over the next
few hours. Much of this will be at VFR levels and remain so
through the night, with the possible exception of tri where cigs
may drop to MVFR late tonight and through tomorrow morning. Some
light sprinkles are possible at tri but not enough to lower vis
and thus not Worth mentioning in the taf. Winds will be light from
the west-SW through the period.



Mrx watches/warnings/advisories...

National Weather Service Glossary of Abbreviations