Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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FXUS64 KMRX 081855

National Weather Service Morristown TN
255 PM EDT Sat Aug 8 2020

.SHORT TERM...(This Afternoon through Sunday)...
Latest Near Storm Environment Awareness application shows the
airmass is quite stable across the region except for far southeast
Tennessee and southwest North Carolina (MLCAPEs of 400-800 J/Kg).
Forecast sounding show an inversion inhibiting convection over most
of the area except for the southern areas. Will keep a slight PoP of
mainly showers for southeast Tennessee and southwest North Carolina
into early evening.

For tonight, another pleasant night expected with ridging over the
region. Plenty of radiational cooling to allow some patchy fog
development for mainly southwest Virginia/northeast Tennessee and
along the area streams/lakes. Some locally dense possible.

For Sunday, ridging will begin to weaken with a weakening short-wave
moving toward the area. Enough instability for 20-30 PoPs for mainly
southeast Tennessee and southwest North Carolina. Otherwise, dry and
very warm.

.LONG TERM...(Sunday night through Saturday)...
Quasi-zonal flow will be in place to end the weekend and begin the
work week leading to a relatively persistent weather pattern through
Tuesday. Surface high pressure and weak ridging in the mid-levels
means we`ll see plenty of sunshine and temperatures will respond by
rising a few degrees above normal through the middle of the week.
Forecast models are still showing that higher dewpoints and moisture
in the atmosphere should remain just outside of the eastern
Tennessee Valley meaning PWAT values in our area will remain
limited. With the warm temperatures still expect diurnally driven
showers and thunderstorms (mainly confined to the higher elevations)
Sunday through Tuesday, but coverage of these storms will be
inhibited by the lack of moisture.

Pattern becomes more active on Tuesday and beyond as systems tries
to develop over the central plains and move through the eastern half
of the US. It will struggle under the mid level ridging, but this
system could act as a focus for increased shower and thunderstorm
activity during the middle of the week into the weekend as it stalls
out across the Ohio Valley area. Forecast models indicate that there
may be some strong instability with this system as it first tries to
move through on Tuesday/Wednesday. At this same time the PWAT values
will begin to increase again, so the coverage storms is expected to
increase as well.

Diurnally driven shower and thunderstorm chances are expected to
continue through the rest of the week and into the weekend. Will
continue with moderate to low end chances for precipitation each day
for the end of the forecast, as models typically take several days
to come into agreement with summer thunderstorm chances.
Temperatures are expected to remain several degrees above normal for
the middle of the work week through the weekend.



Main concern during the TAF period is potential redeveloping of
LIFR Fog and low-clouds especially at TRI early Sunday morning.

Otherwise, VFR conditions anticipated. There is a very low chance
of a shower at CHA late this afternoon and again afternoon 16-17Z
Sunday. Too low to mention in the TAF.

Surface ridging will keep winds light, less than 10kts.


/ISSUED 119 PM EDT Sat Aug 8 2020/

Satellite and area observations show fog is dissipating across the
area. A good deal of sunshine is expected. Forecast soundings show
an inversion around 775mb. This inversion will help limit any
convection development. The weakest cap is across southwest North
Carolina/southeast Tennessee.

Can not rule out an isolated shower/storm over the far east
Tennessee Mountains, southwest North Carolina, and southeast
Tennessee but not confidence enough to include.

Overall, current forecast looks good.


Chattanooga Airport, TN             70  94  71  94  72 /  10  20  20  40  20
Knoxville McGhee Tyson Airport, TN  66  92  69  92  70 /   0  10  10  30  20
Oak Ridge, TN                       65  92  68  93  69 /   0  10  10  30  20
Tri Cities Airport, TN              61  89  64  89  65 /   0  10  10  20  30



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