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

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FXUS64 KMRX 131114
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
714 AM EDT Wed Mar 13 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 301 AM EDT Wed Mar 13 2024

Key Messages:

1. Low afternoon relative humidity dropping into the 20s to
lower 30s.

2. Unseasonably warm today with highs 10 to 12 degrees above
normal.

Discussion:

A weak wave will try to move into the Ohio and Tennessee valley
today but persistent ridging and dry airmass will greatly limit
any effects. Main weather story will be dry airmass and
unseasonably warm temperatures producing low afternoon relative
humidity.

For tonight, upper and surface ridging and continued dry air will
allow temperatures to drop quickly. Only the Plateau and southeast
Tennessee will see a gradual increase on low-level moisture.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 301 AM EDT Wed Mar 13 2024

Key Messages:

1. Chances for showers and a few thunderstorms increase Friday.
Isolated flooding may become a concern if an area sees repeated
moderate to heavy convectively enhanced rainfall.

2. The weekend has generally been trending drier, especially for
Saturday. Following the passage of a reinforcing cold front Sunday,
much cooler conditions are expected early next week.

Discussion:

Upper-level ridging will influence the region Thursday as a surface
high pressure center slides off the southeast coast. Anomalous
heights and persistent warm-air advection will bring along well
above normal temperatures. High temperatures are expected to range
15-20 degrees above normal for mid-march. By Thursday night into
Friday a cutoff low will remain stagnant across the desert southwest
as surface low pressure shifts east across the Great Lakes region. A
trailing cold front will gradually sweep through the Ohio and
Tennessee valley, bringing widespread precipitation and some rumbles
of thunder throughout Friday.

Regarding impacts, the main concern we will be watching for is
flooding potential. As the parent low further extends away from the
area, the boundary progresses a bit slower. NAM model soundings
suggest Corfidi Upshear vectors approach WSW at 15 kts.
Additionally, a moderately sheared environment with tall and skinny
CAPE profiles of 200-600 J/kg of MUCAPE and PWAT values in the 90th
percentile and approaching climatological max suggest favorable warm
rain processes. Current forecast QPF is generally a 0.50 inches in
northern areas to 1.25 inches in the southern valley and higher
terrain. In the event of any training or repeated rounds of
convectively enhanced showers/storms, it is possible that 1 or 3hr
FFG could be met or exceeded. Less uncertainty exists on the
potential of a few stronger storms and that mainly falls on the
timing differences between ECMWF/GFS and the NAM as is it comes into
play these last few runs. The NAM has been a tad slower on arrival
time which would allow the morning inversion to break away and tap
into some surface instability. In this scenario, there would be
potential for a wind threat with the combination of precip loading
and momentum transfer. Given the higher uncertainty in potential for
some stronger storms will focus HWO wording only on isolated
flooding threat at this time.

For the weekend, guidance has trended with the front fully
progressing through the forecast area and leaving Saturday dry.
Shortwave energy translating through mean flow aloft sends a
secondary, more moisture starved front, towards the region Sunday.
Again, this front has been trending drier and PoPs has been limited
to slight chance for most of the area - the exception being the
higher terrain of the East TN mountains. This frontal passage will
bring much cooler conditions and a return of below freezing
overnight lows early next week.

&&

.AVIATION...
(12Z TAFS)
Issued at 712 AM EDT Wed Mar 13 2024

VFR conditions will prevail at all TAF sites through the forecast
period. Satellite and observations show areas of 4-6kft cloud
ceilings across east Tennessee so can not rule out an hour or two
of scattered to broken 4-6kft ceilings this morning at TRI, TYS,
and CHA.

Calm/light winds will increase out of the southwest up to 10kts
this afternoon due to daytime mixing. Calm winds will return
overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             74  49  79  59 /   0   0   0  30
Knoxville McGhee Tyson Airport, TN  71  46  79  58 /   0   0   0  20
Oak Ridge, TN                       71  46  78  57 /   0   0   0  30
Tri Cities Airport, TN              69  42  75  52 /   0   0   0  10

&&

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

$$

SHORT TERM...DH
LONG TERM....KRS
AVIATION...DH


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