Cosby, Tennessee Weather Forecast Discussion

045
FXUS64 KMRX 191135
AFDMRX
Area Forecast Discussion
National Weather Service Morristown TN
735 AM EDT Fri Sep 19 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 710 AM EDT Fri Sep 19 2025
- Unseasonably warm temperatures will persist into early next week.
   However, no threat of any daily max T records being broken.
- Mostly dry valley conditions expected today through the
   weekend, though a few isolated showers and storms cannot be
   ruled out Saturday afternoon and evening.
- More widespread chances for rain and storms in place by early to
   mid next week. The severe weather threat is uncertain at this
   time.
&&
.DISCUSSION...
Issued at 146 AM EDT Fri Sep 19 2025
Light winds and clear skies will promote favorable radiational
cooling conditions as we head throughout the early AM hours. Blended
NBM10th percentile into the hourly temperature forecast to account
for this, resulting in morning lows in the upper 50s to low 60s
areawide. Patchy fog will be focused around area waterways but HREF
prob of visibility less than 1mi is no greater than 20% in very
limited, sheltered valley locations.
A shortwave ridge holds influence over the region this afternoon and
evening. Isolated diurnal convection possible across the E TN
mountains into southwest NC, with valley locations dry. Main focus
will be continued above normal temperatures, though no daily records
are threatened.
A shortwave trough will kick ridging north and east on Saturday,
with bouts of vort lobes swinging through the southern Appalachians.
Hi-res guidance continues to suggest the greatest coverage of
afternoon convection will be across higher terrain, however, slight
chance PoPs have been introduced across the whole forecast area with
this package. Nonetheless, both the NAMBufr and RAP soundings depict
MLCAPE between 1500-2000J/kg, DCAPE hovering near 1000J/kg, and
effective bulk shear around 15kts - suggesting the possibility to
have a stronger storm or two with gusty winds up to 40mph due to
evaporational cooling. Will shift to low probability wording in the
HWO for that reasoning, but not confident enough to add anything
more than that. Upper flow becomes more quasi-zonal with a return of
drier conditions but continued above normal temperatures to round
out the weekend.
We begin to see a pattern shift by early to mid next week as a deep
upper low approaches our region. This system will increase rain and
storm chances areawide, with the greatest chances generally expected
Wednesday through Friday. That being said, model discrepancies are
commonplace and uncertainty to how the system evolves leaves us with
not much detail to confidently speak on this far out. We will
continue to monitor this system closely for potential impacts or
hazards.
&&
.AVIATION...
(12Z TAFS)
Issued at 710 AM EDT Fri Sep 19 2025
Fog development late tonight is possible but looks unlikely, so
will have a VFR forecast all sites for the period along with light
winds.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             90  65  91  65 /  10  10  20   0
Knoxville McGhee Tyson Airport, TN  87  65  86  62 /  10  10  20   0
Oak Ridge, TN                       87  63  87  61 /  10  10  20   0
Tri Cities Airport, TN              85  59  84  58 /  10  10  20   0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
DISCUSSION...KRS
AVIATION...99

NWS MRX Office Area Forecast Discussion