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000
FXUS64 KMRX 190708
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
308 AM EDT Sat Aug 19 2017

.SHORT TERM...(Today and Tonight)...
Surface high pressure and a drying upper level northwest flow
will result in calm, pleasant conditions today. Some patchy fog is
possible around sunrise this morning, but it is not expected to
become widespread. Otherwise, skies will be mostly sunny with
light winds and highs generally in the 80s.

.LONG TERM...(Sunday through Friday)...
For the second half of the weekend, an upper-level ridge begins
to build on Sunday increasing max temperatures by 1-3 degrees
compared to Saturday. With the drier low-level airmass and a
building ridge, anticipate dry and pleasant conditions with highs
in the mid 80s to low 90s and lower humidity.

Taking a look at Monday (Eclipse Day) the 500mb ridge will continue
to expand with heights expected to be around 594-596 dm which is
near the 95th-98th percentile compared to climatology for this time
of year. Subsidence aloft will act to dry the air column and limit
clouds and convection. Cannot rule out about 10-20 percent PoPs
around the higher terrain where differential heating could act as a
forcing mechanism for convection. Models are showing the potential
for convection along the mountains, and to a lesser extent, the
plateau with the NAM being most vigorous with convective
development. Taking a closer look at soundings, the 0z NAM sounding
shows cooler mid-levels as opposed to the 0Z GFS which has a more
typical sounding for a strong summer ridge with subsidence and
associated warmer mid-levels. Based on the very strong ridge for
Monday, believe that the NAM is over-doing convection and trended
toward the drier GFS and ECMWF solutions. Further, effective deep
layer shear is very low around 5 kts which means any ordinary
convective development would not be able to be maintained for very
long. As has been mentioned previously, it will be interesting to
see the effects of decreasing incoming solar radiation during the
mid-afternoon on Monday as the eclipse reaches its max for our
area between 17z-20z. Hourly temperatures are expected to drop 2-8
degrees during maximum eclipse with the greatest drop in
temperatures occurring within the path of totality. High
temperatures may even be slightly cooler by a degree or two than
on a similar day without a total solar eclipse. With near surface
temperature reductions, may actually start to see a boundary layer
profile similar to evenings near the path of totality where a
stable or neutral thermal layer forms near the surface. This would
likely further limit convection and cumulus development during
the hours around the eclipse and this was reflected in the
forecast. Overall, it is still looking like good viewing
conditions for the area. After the eclipse has ended on Monday
afternoon, temperatures will quickly rebound with highs in the
upper 80s to lower 90s. Heat index values will be in the 90-95
degree range on Monday afternoon. It will be a very hot and mostly
sunny day, so anyone spending a lot of time outdoors on Monday
needs to stay hydrated, find shade, and use sunscreen with very
high UV index values of 8-10 around midday before the solar
eclipse even begins.

The ridge will break down and rain chances will increase through
midweek. PoPs increase late Tuesday and Tuesday night with likely
PoPs on Wednesday as a cold front moves through the area and
troughing deepens across the region. Long term models are actually
in good agreement with this system. Drier air is expected to move
in behind the front, but we may continue to see some additional
clouds and rain showers on Thursday primarily across the
mountains. Temperatures late next week expected to be cooler than
average with troughing across the Eastern U.S.


&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             91  72  93  72 /   0   0  10  10
Knoxville McGhee Tyson Airport, TN  88  69  91  70 /   0   0  10  10
Oak Ridge, TN                       89  69  91  70 /   0   0   0  10
Tri Cities Airport, TN              86  64  89  65 /   0   0  10  10

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...None.
TN...None.
VA...None.
&&

$$

EMH/JB