883
FXUS64 KMRX 111115
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
715 AM EDT Tue Mar 11 2025

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 306 AM EDT Tue Mar 11 2025

1. Sunny and warm today then clear tonight.

2. Low relative humidity values this afternoon/evening.

Discussion:

We will have quasi-zonal flow aloft for the short term period with a
large area of surface high pressure extending into our area from the
south. The atmosphere will be quite dry, and we will see a sunny and
warm day today with highs in the low to mid 70s in most valley
locations. Good mixing this afternoon will lead to relative humidity
values dropping into the 15 to 25 percent range which will increase
the fire risk across the area. Winds are expected to be light
overall with afternoon winds generally from the southwest around 5
to 10 mph. Will highlight the low afternoon RH in the FWF for now.

Tonight will be clear, with temperatures slightly above seasonal
normals.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 306 AM EDT Tue Mar 11 2025

Key Messages:

1. On Wednesday, there are elevated fire weather concerns due to dry
and breezy conditions.

2. A weak system will move through Thursday night into Friday
morning, bringing limited rainfall to the southern half of the area.

3. A dynamic system will impact the region Friday through Sunday,
initially bringing mountain wave winds Friday night into Saturday.

4. A chance for severe storms remains Saturday afternoon through
Saturday evening, along with increasing flash flooding concerns.

Discussion:

At the start of the period, quasi-zonal flow will be in place with
high pressure centered to our south. A system will be ejecting out
of the Rockies. Locally, recent WAA and continued subsidence will
allow for deep mixing. Most sources predict RH values to drop below
30 percent across much of the region. Also, 850mb flow of 20 to 25
kts and the MSLP gradient will produce breezy southwesterly winds
and gusts in excess of 20 mph. A Fire Danger Statement/SPS may be
considered in future updates. Wednesday night, this system will
progress towards the area with the latest model data continuing to
show a weakening trend as it arrives by Thursday. This is also in
addition to the better moisture remaining to our south. Northeastern
portions of our area are likely to stay dry because of this lack of
moisture and weakening trend. Places in the south will maintain high
PoPs but very limited QPF totals of less than a tenth of an inch.

On Friday, focus will turn towards the development of the weekend
system. Its development begins as a deep, negatively tilted trough
ejects out of the Rockies with the rapidly deepening surface low
progressing over Nebraska/Kansas and then up towards Minnesota. The
central pressure will likely be below 980mb, values that are
record- breaking for portions of this region. Locally, this system
and subsequent developments may produce multiple days of
impactful weather, listed in order of occurrence:

1. Mountain Waves/Fire Weather

Ahead of this system, height rises and a broad southerly 850mb jet
will make for unseasonably warm temperatures. Additionally, a very
strong MSLP gradient will be in place across the mountains and
really much of the central and eastern U.S. During the day on
Friday, values of 40 to 50 kts are indicated to our west, which
become 60 to 65 kts by Friday night into early Saturday morning.
While RH`s are may not be too low, this will make for breezy
conditions and a high likelihood of mountain wave winds, all before
any substantial precipitation reaches the area.

2. Severe Weather

As the system tracks very far north, a very broad warm sector is
expected to develop across much of the region. However, with how far
north the surface low is, there still remains uncertainty as to how
everything will evolve. Friday night into Saturday, convection is
expected to be ongoing to our west with some remnants moving into
the area. With how far north the system tracks, the focus for our
area will be on the development of a secondary surface low Saturday
into Saturday evening. Based on the 00Z GEFS, this could be anywhere
from central Alabama up to northwestern Kentucky. The location of
this surface low will certainly have implications as to the severe
weather type and extent of impact in our area. A further north
and/or west location (shown in the GDPS), would present an all-
hazards type of outcome. Regardless, very strong 850mb flow of over
50 kts (enhanced by divergence to our north) will highlight the
threat of damaging winds at a minimum. There are also questions
about how much instability will be present, mainly due to the timing
and evolution of everything. Most sources suggest instability of 500
to 1000 J/kg at some point during the day on Saturday, which will be
coupled with impressive deep-layer and low-level shear. The earlier
timing in the western half of the area could be more favorable for
better instability. Overall, a lot of model spread understandably
still exists, but the severe weather threat will continue to be
monitored as we approach the weekend. In any case, additional
periods of high winds in the mountains are likely, with mountain
wave winds possibly exceeding 24 hours in duration.

3. Flooding

Ahead of the approaching cold front, models show strong 850mb
moisture transport from the south with PWATs reaching near 1.5
inches along the Cumberland Plateau and in southeast Tennessee. It
should also be noted that the mean flow will be nearly parallel with
the cold front, supportive of training. There will also likely be a
slower progression of the frontal boundary. Exact rainfall amounts
and the location of the heaviest rainfall are uncertain at this
time, but most ensemble and deterministic data show a pretty strong
signal for over 2 inches in many places.

Sunday and Monday

It is unclear when the cold front will be past our area as it could
be anywhere from Sunday morning to Sunday afternoon. In any case,
rain chances will be diminishing west to east on Sunday with high
pressure building in from the southwest. This will promote a
return of cooler and drier conditions Sunday night into Monday.

&&

.AVIATION...
(12Z TAFS)
Issued at 513 AM EDT Tue Mar 11 2025

VFR conditions expected for the period all sites. Light/calm winds
will become southwest less than 10kts this afternoon, then back to
light/calm overnight.


&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             75  44  77  52 /   0   0   0   0
Knoxville McGhee Tyson Airport, TN  72  44  75  48 /   0   0   0   0
Oak Ridge, TN                       73  42  75  48 /   0   0   0   0
Tri Cities Airport, TN              70  39  72  43 /   0   0   0   0

&&

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

$$

SHORT TERM...
LONG TERM....BW
AVIATION...