Johnson City, Tennessee 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

089
FXUS64 KMRX 152319
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
719 PM EDT Thu May 15 2025

...New AVIATION...

.SHORT TERM...
(This evening through Friday)
Issued at 251 PM EDT Thu May 15 2025

Key Messages:

1. Scattered showers and possibly a few thunderstorms are expected
mainly northern areas tonight into the first part of Friday, with
lower chances later Friday afternoon.

2. The convection is expected to be weakening as it comes in at
least initially, but a few strong to severe storms will be possible
mainly north and west portions later tonight into Friday.

Discussion:

We have an environment characterized by significant CAPE (HREF mean
MUCAPE values generally in the 1000 to 2000 J/kg overnight) with
increasing shear (EBWD climbing to 50+kts by the end of the night
especially north), but also with a significant cap in place. Models
have been doing a very poor job resolving any weak ripples in the
flow as the upper ridge over our area slowly shifts east, and the hi-
res CAMS have been undependable.  With no high confidence forcing
evident to latch onto, there is considerable uncertainty about how
any convection will evolve tonight and Friday.  Using an ensemble
approach, the best chances for showers and storms looks to be later
tonight into the first part of Friday especially north as a
weakening cluster of storms is likely to move through. In this
environment, the marginal risk of severe storms depicted by SPC
across the Plateau through SW VA looks reasonable for tonight,
but is dependent on how much the cap erodes and on the cluster of
storms actually materializing. Wind and hail will be the main
threats overnight.

Most of the models show a lull in the convection behind the expected
morning/midday convection as we await the main event expected Friday
night, although the environment will continue to be quite unstable
with plenty of shear, so again conditional on if any storms are able
to get going, there will continue to be a risk of them becoming
severe. Damaging winds and hail will be the primary threats, but
given that the shear will still be increasing during the day Friday
(including an increase in 0-1 shear), there will be a low threat of
a tornado. The threat of severe weather is highly conditional on
details that are still unclear for tonight through Friday, so stay
tuned as more information becomes available.

&&

.LONG TERM...
(Friday night through next Thursday)
Issued at 251 PM EDT Thu May 15 2025

Key Messages:

1. Strong to severe thunderstorms increasing likely Friday night
into Saturday morning. All hazards will be possible.

2. Another round of severe storms possible Tuesday night
into Wednesday, though details are uncertain.

Discussion:

A potent system will move across the region Friday night into
Saturday morning. Strong to severe thunderstorms look increasingly
likely during this time as thermodynamics and the upper dynamics
look supportive of all hazards. Higher confidence exists that the
mode will be linear. However, there is still the possibility that we
could see a few semi-discrete cells immediately ahead of the main
line of convection.

Timing:

For the early evening hours, there is some model uncertainty on
whether we see convection or not. HRRR runs show a line of showers
and storms moving into southwest VA around 00Z, other Hi-Res models
do not. Therefore, lower confidence exists that we see any impactful
weather early in the evening. Higher confidence exists that the main
threat window will occur between 03Z and 09Z Saturday. Again,
hazardous weather may occur outside of this window but this is the
best estimate for now.

Threats and Impacts:

All hazards will be possible. The main concern, due to higher
probability, will be straight line damaging winds with gust
potential up to 70 mph. Large hail up to 1.5" is possible. Areas
within the SPC Day 2 Enhanced risk have a 5% risk of a tornado within
25 miles of a point. As far as impacts, isolated to scattered tree
damage and power outages are probable. There may even be some
isolated areas that see scattered to widespread tree damage and
outages. Any storms that produce the larger 1.5" hail are
susceptible to siding and roof damage, as well as dents in vehicles.

Confidence:

High confidence in a line of showers and storms moving through
during the overnight hours. Moderate confidence on timing. Moderate
to high confidence the main threat will be damaging straight line
winds. Moderate confidence in large hail. Low to moderate confidence
for an isolated tornado.

Rest of the long term:

Showers and storms should weaken toward sunrise on Saturday morning,
but a strong and gusty winds still possible as this system exits by
mid to late morning. Saturday afternoon should be dry. POPs back in
the forecast on Sunday through Tuesday as we may see more impulses
move through the zonal flow. Another bout of strong to possibly
severe storms back in the forecast Tuesday night into Wednesday as a
more organized system moves through the area. The forecast after
Wednesday is low confidence as there are varying solutions on how
models handle the upper low across the forecast area. Because of the
uncertainty, will maintain POPs through the end of the period.

&&

.AVIATION...
(00Z TAFS)
Issued at 713 PM EDT Thu May 15 2025

VFR conditions will continue with mostly high clouds present.
There is a low chance for showers and storms throughout this
period but confidence is low on development and timing. The better
chance for activity is just beyond this time period. Southwesterly
winds will be gusty again tomorrow.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             70  87  68  87 /  10  10  80  30
Knoxville McGhee Tyson Airport, TN  70  86  67  84 /  20  40  90  30
Oak Ridge, TN                       69  86  66  85 /  20  30  90  20
Tri Cities Airport, TN              66  84  63  80 /  30  50  90  30

&&

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

$$

SHORT TERM...
AVIATION...McD