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

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FXUS64 KMRX 101149 AAA
AFDMRX

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
749 AM EDT Mon Aug 10 2020

.SHORT TERM...(Today and Tonight)...

Regional radar imagery shows an area of showers moving southeast
from Kentucky into the TN valley early this morning, likely a weak
MCV from convection Sunday afternoon well to our west. Despite
a rather poor appearance overnight, an uptick in convective
activity in the vicinity of this disturbance has been noted over
the last hour or so. Guidance shows this expanding across the
northern plateau, and central TN valley through daybreak and
shortly thereafter. PoPs reflect this accordingly. Later today,
diurnal trends should take over, with scattered convection
developing during the afternoon hours. Forecast soundings,
especially the NAM BUFR points, show fairly substantial
instability this afternoon with CAPE values nearing 3,000 J/kg in
the far southern valley and near 2,000 J/kg as far north as the
Knoxville metro area. This may be slightly too high though as the
NAM keeps surface dewpoints well north of 70 degrees into the
afternoon hours, whereas the GFS shows dewpoints mixing out
into the mid 60s. There is a moisture gradient in place across
the region, with higher dewpoints noted in the southern valley.
Given dewpoints mixed out into the upper 60s in the south
yesterday afternoon, am inclined to believe instability will
likely be somewhere in the middle of the NAM and GFS values.
Still, there`s a chance a few storms could be strong to severe,
with precip loaded updrafts yielding a slight chance for some
damaging winds.

For tonight, expect convection will die off mostly but guidance is
indicating a chance for another nocturnal MCS moving into the
region from the northwest. As such, will continue with some slight
chance PoPs during the overnight hours.

Otherwise, not much to talk about. Temperatures will be around or
slightly above normal again, with low to mid 90s possible in the
south and upper 80s to around 90 expected for central and northern
areas.

CD

.LONG TERM...(Tuesday through Sunday Night)...

Numerous chances of rain are in the forecast for the extended
period as the area remains underneath lowered heights. The
synoptic pattern will feature two area of high pressure aloft
located across the southwest and western Atlantic. The tennessee
valley will be under the influence of broad troughing through the
extended which supports increasing coverage of showers and
thunderstorms. An H50 cold pocket will increase low-mid level
lapse rates on Tuesday which should provide increasing
instability. Overall dynamics remain weak, with model soundings
showing a very weak wind profile. DCAPE values greater than
500j/kg suggests the potential for an isolated strong to possibly
severe storm with the main hazard of damaging winds. A secondary
hazard of heavy rainfall and isolated flash flooding also may
exist given high PW and weak steering flow.

Guidance suggests the upper level wave moving across the
Mississippi river valley will begin to amplify and strengthening
the shortwave ridge downstream across the region. This should lead
to lowered PoPs Tuesday night and into early Wednesday. This dry
period will be short lived as the wave moves closer to the local
area. Scatted to numerous showers and embedded thunderstorms
increase Wednesday through Thursday with localized heavy rainfall
possible given continued high PW values and moist adiabatic
profiles. Temperatures will hover near to slightly above
climatology.

By the end of the week, a more significant trough moves out of
the Pacific northwest and across the northern Rockies. Lowered
heights continue to dominate the region with chances of showers
and thunderstorms continuing with greatest coverage in the
afternoon and early evening. Temperatures may begin to cool with
more seasonable temperatures Friday and into the weekend. Upper
wave and low level front moves through the area late Saturday and
into Sunday with better synoptic scale forcing for ascent with the
region in the right rear quadrant of a 60 knot upper level jet.
This should support higher end chances of rain but for now will
keep PoPs capped at likely.

Diegan


&&

.AVIATION...
12Z TAF DISCUSSION.

Morning convection streaming southeast across the central TN
valley is accounted for at KTYS through the next few hours, but
what happens later today is uncertain. It seems the most likely
outcome is this morning convection will set out some outflow
boundaries, on which more storms will form later this morning and
into the afternoon hours. Have some VCSH and TEMPO TSRA at KCHA to
account for this. Left out any mention of showers at KTRI as it
should remain south of that terminal. For tonight, some fog seems
likely but whether it affects any terminals is uknown so left that
out of the forecast for now.

CD

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             92  73  94  73  94 /  60  30  60  30  60
Knoxville McGhee Tyson Airport, TN  88  71  91  71  93 /  50  30  60  30  60
Oak Ridge, TN                       88  70  92  71  93 /  50  30  60  30  60
Tri Cities Airport, TN              83  66  88  67  90 /  30  30  60  40  60

&&

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

$$


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