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659
FXUS64 KMRX 111522
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1122 AM EDT Fri Jul 11 2025

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 1118 AM EDT Fri Jul 11 2025

Isolated showers have begun to pop up across the area. Previous
forecast had the morning and early afternoon hours mostly dry for
valley locations. Have now updated POPs to at least slight chance
for all areas. Isolated to scattered showers and storms expected
through the remainder of the day. No other forecast changes were
made. Heavy downpours and brief gusty winds still the main
concerns for today.
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&&

.SHORT TERM...
(Today and tonight)
Issued at 202 AM EDT Fri Jul 11 2025

Key Messages:

1. Patchy to areas of fog developing overnight into early Friday
morning. River Valleys will favor the most likely chances for
localized dense fog.

2. Mostly dry afternoon but some isolated afternoon shower and
storms will favor higher elevation locations.

Discussion:

Regional radar only shows a few isolated, small and shallow showers
in higher terrain as a mostly dry overnight is expected. Main focus
will be on the potential for some dense fog. Utilizing nighttime
microphysics and night fog GOES-16 products, some fog is
distinguishable within northern rivers valleys. Comparing low
ceiling and fog probabilities from the HREF ensemble, hi-resolution
models hint that localized dense fog will be more limited to river
valleys with more of a low ceiling developing throughout the morning
hours. Will monitor trends into the morning and issue any products
for fog as needed.

Upper ridge will replace a departing shortwave trough this
afternoon. Weak height rises of roughly 2dam will promote a slight
warming trend. The warm and humid summer airmass will allow for
additional diurnal convection. However, a notable subsidence
inversion around 650mb suggest the associated high pressure will
help limit afternoon storm coverage. Generally expect isolated to
weakly scattered showers and storms favoring higher terrain of the
Appalachian Mountains and Cumberland Plateau. Brief gusty winds and
heavy downpours are possible with the strongest storms. Mostly
dry for valley locations.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 202 AM EDT Fri Jul 11 2025

Key Messages:

1. Diurnal summertime convection continues through the forecast
period with some day-to-day variations in expected coverage. Troughs
passing to our north late weekend and again late next week are
expected to influence the most scattered convection.

2. Hot conditions return as an upper ridge builds back into the
region for the middle part of the work week, with heat indices in
the mid 90s to near 100F becoming more common across valley
locations.

Discussion:

As we head into the weekend the synoptic pattern in the upper levels
will consist of ridging across the western & eastern CONUS while a
shortwave trough sags through central Canada into the northern
Plains. Hot and humid conditions with heat indices in the 90s will
be widespread with additional diurnal convection Saturday. Though,
to varying extent, CAMs are depicting semi-organized tstorm clusters
with a weak southern stream impulse briefly enhancing effective bulk
shear near 15-20kts. MLCAPE will generally range from 1000-2000 J/kg
per 00Z HRRR soundings. A low-end strong to isolated severe threat
cannot be totally ruled out but timing of the potential impulse will
play a crucial role on whether or not that low-end threat plays out.

Sunday into Monday the aforementioned shortwave trough will swing
through the Great Lakes and Ohio Valley with an associated surface
boundary slowly advecting towards the region. Diurnal showers and
storms are generally expected each day but the exact coverage is
uncertain due to uncertainty in the timing and positioning of the
shortwave & boundary. Overall, any potential severe threat seems
rather low but we will continue to monitor hi-resolution models as
they come into temporal scale.

Upper ridging builds back into the region mid-week. Daily chances of
showers and storms continue but subsidence aloft should help inhibit
coverage. Main weather message will be to focus on the return of hot
conditions with heat indices potentially climbing back into the mid
90s to near 100F Tuesday and Wednesday. Long range guidance suggest
a deeper trough swings back through late week with increasing
coverage of showers and storms.

&&

.AVIATION...
(12Z TAFS)
Issued at 549 AM EDT Fri Jul 11 2025

After morning fog/low clouds dissipate, will see mainly VFR
conditions today outside of afternoon convection that has a chance
to impact the terminals (will include prob30 groups for thunder
all sites). Patchy fog/low cloud development late tonight can be
expected again, with the terminal(s) with the highest probability
to be impacted being TRI and/or any site that sees precipitation
this afternoon (although these are still unknown). For now will
include MVFR conditions at TRI, but lower conditions will be
possible there as will impactful fog/low cigs elsewhere.

&&

.PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN             91  71  92  73 /  40  10  40  10
Knoxville McGhee Tyson Airport, TN  91  71  91  72 /  30  10  30  20
Oak Ridge, TN                       90  70  91  71 /  30  10  40  20
Tri Cities Airport, TN              87  68  88  68 /  30  10  30  40
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&&

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

$$

SHORT TERM...
LONG TERM....KRS
AVIATION...