420
FXUS64 KMRX 071444 AAA
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1044 AM EDT Sat Jun 7 2025

...New UPDATE...

.UPDATE...
Issued at 1024 AM EDT Sat Jun 7 2025

...Enhanced Risk of severe thunderstorms with damaging winds this
afternoon and evening in southern sections...

This morning, showers are associated with a boundary that is
located across northern portions of the area, moving slowly
southeast ward. The boundary is becoming nearly parallel to the
low level flow, so it will likely stall out near the I-40 corridor
in the next few hours. In addition, we are seeing differential
heating with scattered to few clouds in the southern TN Valley,
and broken to overcast north and central. The upshot of these
features is that southern sections will have the best instability
and potential for severe thunderstorms later today. The CAMS are
now coming into better agreement in depicting the MCS in AR/West
TN reaching Marion County around 21Z, near the time of peak
instability. DCAPE values of 1000-1200 J/kg and a surface-to-
midlevel theta-E difference of 25C indicate a threat of damaging
straight-line winds. Hail will be possible as well with a WBZ
height around 10 kft at the expected time of arrival of the MCS.
The 06Z NAM really ramps up the low level shear/helicity around
00Z at CHA, suggesting a tornado threat, but this could be an
artifact of the post-convection environment. Flooding will be a
concern as well given yesterday`s high rainfall rates that could
be repeated today and the saturated ground. The question remains
how far north the severe threat will extend, but given the
aforementioned boundary setup, any locations near or south of I-40
are expected to have a threat of severe storm hazards.

A few changes will be made to the PoP/Wx grids based on the latest
timing, otherwise the forecast looks to be in good shape.


&&

.SHORT TERM...
(Today and tonight)
Issued at 340 AM EDT Sat Jun 7 2025

Key Messages:

1. A few lingering showers and storms this morning, primarily across
northern portions of East Tennessee.

2. Lower confidence than usual, but a line of strong to severe
thunderstorms is possible this afternoon into the evening. Wind
gusts up to 70 mph, lightning, and another round of torrential
rainfall are the expected hazards.

Discussion:

Yesterday morning I discussed the high resolution CAMs not really
showing the solutions I expected. 00z HRRR and 00z RRFS this morning
have delivered potential solutions more in line with my thinking.
Both feature a MCS type system with at least some bowing structure
racing across southern TN this afternoon into early evening. Having
said that, 18z runs of both models did not have these solutions, so
run-to-run consistency is poor and lower confidence exists for
today`s weather outcomes. As of this writing, the 06z HRRR splits
the difference between the two prior synoptic runs. Assuming we do
see thunderstorms later today though, we have a supportive
environment for severe storms and heavy rainfall. Effective shear is
40 knots, very moist atmospheric profiles in terms of PWATs, and
again high freezing heights. Yesterday some storms produced rain
rates of 2"/hr or greater while they progressed. With the atmosphere
once again moist, thunderstorms will have the capacity to produce
additional torrential rain today, and any location that experiences
round two, especially in the southern valley where the storms are
more likely, will be at a low risk for flash flooding.

There is a low tornado risk in the southern valley from the Storm
Prediction Center, this will be greatly dependent on the location
of the MCS - overall helicity is pretty low on model soundings so
a tornado isn`t something I`d necessarily expect today but weirder
things have happened. Straight line winds if we see a convective
complex will have more damage potential though.

Tonight rain chances will continue with potential redevelopment as
seen in the CAMs overnight. These later storms aren`t expected to be
severe, with a loss of potential energy by that point in the night.
Lighter rainfall amounts from those showers overnight into Sunday
morning.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 340 AM EDT Sat Jun 7 2025

Key Messages:

1. Unsettled pattern with daily chances of showers and storms
continues Sunday through Tuesday. Chances for severe weather are
marginal at this point, with isolated flooding possible due to the
repeated rounds of activity over multiple days.

2. Drier weather mid to late next week following a frontal passage
Tuesday evening.

Discussion:

The active pattern continues Sunday as a broad trough sits over the
Central and Eastern U.S. reaching all the way to the Gulf Coast. A
shortwave will slowly move through the Ohio and Tennessee Valleys
Sunday. At the surface, a low will be centered over the Ohio Valley
by Sunday morning. A weak cold front will move through the region
Sunday afternoon with a slight dew point drop noted after passage
and brief, slight wind shift. CAMs do not look impressive for Sunday
afternoon with isolated to scattered showers and storms mainly north
of I-40. However, forecast soundings look pretty impressive with
1500-2000 J/kg CAPE and 35 to 40 knots effective shear. So SPC`s
marginal risk looks appropriate for that timeframe.

Drier weather is expected Sunday night through Monday morning. Rain
chances return Monday afternoon as a cut-off low moving through
MN/WI strengthens the trough over the Midwest and Ohio Valley. This
round of wet weather will continue through Tuesday evening when the
trough passes as the low moves northeast into Canada. A cold front
will move through the region around Tuesday evening bringing drier
weather for the following couple of days. Severe potential looks low
Monday and Tuesday with CAPE below 500 J/kg and effective shear
around 20 knots.

Forecast rain totals are fairly low during this period, less than
one inch from Sunday through Tuesday. Spotty flooding issues will be
possible with either round of wet weather mainly in places that have
already received heavy rain. The biggest threat with any severe
storms that develop will be straight-line winds. Large hail will be
more difficult with freezing levels around 13k-14k feet.

&&

.AVIATION...
(12Z TAFS)
Issued at 739 AM EDT Sat Jun 7 2025

Messy next 24 hours. Scattered showers still linger this morning
over northeastern TN into VA, those should diminish as the morning
continues. A line of strong to severe thunderstorms is
increasingly likely this afternoon by CHA, with uncertain northern
extent. Strong gusty winds during storm passage are likely, along
with torrential rainfall lowering VIS. Tonight CIGs will
deteriorate, likely to MVFR. Light breeze overnight may prevent
fog formation.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             88  70  85  66 /  60  70  60  10
Knoxville McGhee Tyson Airport, TN  85  69  81  64 /  40  70  50  10
Oak Ridge, TN                       85  68  81  64 /  50  70  50  10
Tri Cities Airport, TN              81  65  78  62 /  70  70  60  20

&&

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

$$

UPDATE...DGS
LONG TERM....McD
SHORT TERM/AVIATION...Wellington