Calhoun, Tennessee Weather Forecast Discussion

811
FXUS64 KMRX 201127
AFDMRX
Area Forecast Discussion
National Weather Service Morristown TN
727 AM EDT Sat Sep 20 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 719 AM EDT Sat Sep 20 2025
-  Above normal temperatures will persist through early next
    week.
-  A few afternoon showers and storms will be around today
    through Tuesday. Coverage will be more isolated in valley
    locations but could become more scattered across higher
    terrain.
-  Chances for showers and storms will trend upward by the
    middle and latter portions of the work week.
&&
.DISCUSSION...
Issued at 129 AM EDT Sat Sep 20 2025
A ridge over the forecast area will be pushed northeast by a
shortwave trough today, leading to the potential of a few PM showers
and storms. Greatest coverage is expected in the higher terrain, but
some isolated convection cannot be ruled out in valley locations as
well. MLCAPE near 1500J/kg and DCAPE near 1000J/kg suggest the
strongest updrafts could lead to localized gusty winds up to 40mph.
Will continue to keep low probability wording in the HWO.
The most notable change in the forecast from previous night comes
with increased PoPs for Sunday and Monday. Models now show some
additional impulses that may traverse mean flow aloft over the next
few days, and some of the CAMs such as the HRRR and ARW have
responded with an upward trend in convective coverage as a result.
20-40% PoPs are generally in place Sunday through Tuesday, though
coverage will be some what reliant on how well any impulses and
associated vort lobes align with diurnal heating. It can also be
noted that temperatures will remain above normal through this time
frame. Southwesterly surface flow will bring increasing dewpoints
and it will be a tad more muggy feeling relative to the lower
humidity afternoons we have seen the past few days.
Regarding the mid to late week system, models are showing signs of
increasing agreement as the GFS has trended more towards Euro with a
developing cutoff low. Still some discrepancies associated with the
amplitude and exact position of the system, but Wednesday through
Saturday PoPs have increased to around the 50-70% range per latest
NBM. Mean ensemble suites from the GFS and Euro begin to paint
probabilities of total rainfall 1" or greater around the 50-60%
range by the end of the week. While details are still coarse it is
worth mentioning that latest WPC days 3-7 hazards highlight portions
of the southern Appalachians for heavy rain by Thursday.
&&
.AVIATION...
(12Z TAFS)
Issued at 719 AM EDT Sat Sep 20 2025
VFR and mostly dry conditions expected today, though introduced a
PROB30 at KTRI for potential scattered convection in the early
evening. Winds will remain light today outside of any thunderstorm
winds. Tonight light winds with potentially patchy fog, fog
slightly more likely for any areas that receive rainfall today.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             91  67  89  68 /  10  10  20  20
Knoxville McGhee Tyson Airport, TN  88  64  87  65 /  20  10  20  20
Oak Ridge, TN                       87  63  86  64 /  20  10  30  20
Tri Cities Airport, TN              84  59  83  61 /  30  10  20  10
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
DISCUSSION...KRS
AVIATION...Wellington

NWS MRX Office Area Forecast Discussion