Powells Crossroads, Tennessee Weather Forecast Discussion

508
FXUS64 KMRX 221133
AFDMRX
Area Forecast Discussion
National Weather Service Morristown TN
733 AM EDT Mon Sep 22 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 728 AM EDT Mon Sep 22 2025
-  Patchy to areas of fog are expected this morning. Some fog may
    become locally dense, especially for locations that observed
    rainfall this past afternoon and evening.
-  Above normal temperatures will persist through early portions
    of the week.
-  Scattered showers and storms will be possible especially in
    the afternoon and evening hours today and Tuesday. A few
    storms may produce strong gusty winds.
-  Cooler temperatures and increasing chances of showers and
    storms are expected Wednesday into late week. There is potential
    of isolated severe storms and flooding concerns but
    confidence is low at this time.
-  Next weekend will likely see decreasing chances for showers
    and storms, with temperatures a bit below normal.
&&
.DISCUSSION...
Issued at 138 AM EDT Mon Sep 22 2025
Bulk of the rain has cleared out and minimal chances of
precipitation(15%) exist through the overnight. Main focus over the
next ~6 hours will be on fog potential. A handful of ob sites
have already fallen into the 3-8mi visibility range with dewpoint
depressions ranging from 0-3 F. A few sites are hovering around
1mi vis. Feel confident saying that we will continue to see some
patchy to areas of fog throughout the night, but less confident in
how widespread any dense fog may become as there will be some
degree of convective debris cloud lingering aloft. Believe the
most likely location to see potential dense fog will be along and
on the northern side of the I40/I81 corridor where a swath of
0.5-1.5" radar estimated rainfall occurred this past afternoon and
evening. Will continue to monitor and issue any products as
necessary.
For today, we will see a somewhat persistent forecast in the fact
that temperatures will continue to be a few degrees warmer than late
September normals and additional scattered showers and storms are
expected primarily in the afternoon and evening. Pretty decent
agreement between CAMs that convective initiation will begin in and
be confined to the mountains around mid-day to early afternoon. By
mid afternoon and evening a broken line of showers and storms will
approach from the west as vort lobes swing through the southern
Appalachians. The main discrepancy among the CAMs is how far south
activity will span. Some HREF members limit the bulk of convection
along and north of I-40 while a few maintain some isolated precip
into the southern valley. NAMBufr soundings depict MLCAPE between
1000-1500 J/kg, modest DCAPE of 500-800 J/kg, and poor lapse rates
around 5.8C/km. Thus, in either case it seems concerns for strong to
severe storms is limited with maybe a few stronger storms
promoting wind gusts upwards of 40 mph and lower chances of
isolated severe criteria. The best chance for strong/severe will
likely be along the northern Plateau and near the TN/KY/VA borders
in closer proximity to the shortwave impulses and slightly
enhanced effective shear of 15kts.
The pattern of scattered afternoon/evening showers & storms and
above normal temperatures will carry over into Tuesday as well,
though, a few showers and storms may linger during Monday
night/early Tuesday morning. Precipitation chances will become more
widespread as an upper low enters the Mississippi River Valley by
Wednesday and gradually progresses eastwards towards the Tennessee
Valley by Friday. Wednesday into Thursday PWAT values will be
nearing or even exceeding 90th percentile values, with an
approaching surface front expected Thursday. With repeated days of
rainfall and anomalous moisture it is possible some flooding
concerns may develop across the southern Apps. Enhanced synoptic
forcing and improved effective shear could also lead to a few strong
to severe storms given enough CAPE Thursday.
Wrap around moisture with northerly flow behind the front will
linger precipitation chances Friday. By the weekend model agreement
is lacking but there are signs that perhaps a drying trend will
accompany cooler than normal temperatures. NBM currently advertises
slight chance PoPs into the weekend, bridging the gap between the
dry Euro model runs and the GFS that maintains some rain chances.
&&
.AVIATION...
(12Z TAFS)
Issued at 728 AM EDT Mon Sep 22 2025
Fog is beginning to show signs of lifting and will continue to
lift and scatter out over the next 1-2 hours, returning all sites
to VFR thereafter. Another day of showers and a few TS, but not
clear on extent of coverage again. Bulk of the storms should be
located north of Interstate 40 through the period. A low chance
for additional rainfall tonight, but not certain enough to include
in the TAFs. Winds are light, outside of any strong downburst
winds in TS.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             87  67  88  69 /  20  20  30  20
Knoxville McGhee Tyson Airport, TN  85  66  85  67 /  40  30  40  30
Oak Ridge, TN                       84  66  84  66 /  40  40  50  40
Tri Cities Airport, TN              82  62  81  63 /  20  30  40  30
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
DISCUSSION...KRS
AVIATION...Wellington

NWS MRX Office Area Forecast Discussion