648
FXUS64 KHUN 052257
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
557 PM CDT Sat Sep 5 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1018 AM CDT Sat Sep 5 2026

 - A Heat Advisory remains in effect through 8 PM Sunday due to
   Major to Extreme HeatRisk, along with afternoon heat indices
   rising up to 105-109 degrees in portions of the forecast area.

 - A low chance (30% or less) of thunderstorms are forecast this
   afternoon into the late evening, with a low chance of some
   becoming strong to severe. Damaging winds are the primary
   threat.

&&

.NEAR TERM...
(Tonight)
Issued at 312 PM CDT Sat Sep 5 2026

No changes were needed to the forecast at this time. We are
monitoring a large outflow boundary (and subsequent outflows from
storms that have developed from it) to our northeast. This
activity has a history of producing strong to severe storms near
Knoxville. We have also seen small showers develop a couple
counties to our NW as well as to our south. Development over NE
AL, southern middle TN, and into north-central AL is expected
within an hour or so. Damaging downburst winds, frequent
lightning, and heavy downpours remain the main threats. Stay
weather aware and have multiple ways of receiving warnings should
one be issued for your area!

Additionally, temperatures have risen into the mid 90s for most
locations with dew points in the lower to mid 70s. This has
resulted in heat indices in the 103-108 range so far this
afternoon. Make sure to drink plenty of water and take frequent
breaks in the shade!

Previous Discussion:

The upper ridge will be pushed back west today as an upper trough
digs over the eastern seaboard into the Southeast. In addition,
surface high pressure over the Appalachians will shift south as a
backdoor cold front sweeps into and over the Ohio and Tennessee
valleys. Even so, for any storms today, the main lifting mechanism
will be remnant outflows over the region helping create a domino
effect of convective initiation. Instability will be abundant,
with minimal bulk shear. Looking at parameters conducive for
downbursts such as WINDEX, DCAPE, theta-e difference, and lapse
rates, all thresholds are met by various guidance for strong to
severe downbursts.

With DCAPE exceeding 1000 J/kg, damaging winds will be the main
threat, along with frequent lightning and brief, heavy downpours
(due to 1.7-2.0 inch PWATs). Observed soundings show a freezing
level around 15.5 kft at BMX and around 14 kft at BNA. Model
soundings for the afternoon show freezing levels around 15.5 kft
as well; therefore, not anticipating much in the way of hail with
the storm activity today. With LCL heights above 1000 m, not
expecting a tornado threat either. This concurs with SPC`s
Marginal Risk of severe weather over a portion of the local area
(generally east of I-65) along with only damaging winds being
outlooked (versus any hail or tornado threat). Overall, expect a
low chance (20-30%) of "pop up" thunderstorms to occur generally
between 3-10 PM this afternoon/evening, especially over portions
of north-central AL, NE AL, and into southern middle TN. Stay
weather aware in case any warnings are issued for your area! When
thunder roars, go indoors! See a flash, dash inside!

Even with thunderstorm activity, it will still be very hot.
Temperatures are forecast to reach the mid to upper 90s before
storms really begin to form. This, in addition to dew points in
the lower to mid 70s will result in expected heat index values
between 105-109 degrees. Furthermore, WBGTs this afternoon rise
into the upper 80s to around 90 degrees and NWS HeatRisk is slated
to be in the Major to Extreme categories (levels 3 and 4 of 4).
The Heat Advisory therefore remains in effect for all of north
Alabama and southern middle Tennessee through 8 PM Sunday evening.
Please exercise heat safety, especially if working outside or if
you have outdoor activities! Stay hydrated, wear loose-fitting and
light colored clothing, take frequent breaks in the shade and/or
AC, and never leave people or pets in vehicles!

Not much relief will be felt tonight as lows merely dip into the
lower to mid 70s. While a low chance of some patchy fog exists
(especially in river valleys, near bodies of water, and where rain
falls today), not expecting this to be widespread at this time.

&&

.SHORT TERM...
(Sunday through Monday)
Issued at 1018 AM CDT Sat Sep 5 2026

Northwest flow then sets up aloft on Sunday as the upper ridge
begins to slowly push eastward once again. The aforementioned
backdoor cold front is slated to traverse the Tennessee Valley
during the afternoon. However, there is some uncertainty in the
timing of this front through the region. A quicker passage would
result in slightly cooler temperatures, but more importantly lower
dew points as drier air is ushered into the region. Most guidance
that agrees with this scenario suggest dew points falling into
the 60s, with others hinting at upper 50s for some areas. However,
if this front is slower to move through the area (which has
seemed to be the trend the past couple of days), dew points will
continue to be higher (in the lower to mid 70s) with highs in the
mid to upper 90s once again. This would result in heat indices
reaching between 102-109 degrees, NWS HeatRisk mostly in the Major
category (level 3 of 4), and WBGTs in the upper 80s to around 90
degrees.

Current thinking is that the front is likely to be slower, so the
Heat Advisory was extended in a previous update through 8 PM
Sunday evening. This will be monitored through the weekend; but,
please remain weather aware. Drink plenty of water and take
frequent breaks in the shade! As for any thunderstorm activity,
chances are very low (less than 10%) and would be most likely
caused by orographic mechanisms in the higher terrain of NE AL and
into southern middle TN Sunday afternoon. Any activity will
quickly taper out in the early evening, with lows in the upper 60s
to lower 70s.

For Monday, the slightly drier and cooler air filtered into the
region will result in forecast highs in the upper 80s to lower 90s
east of I-65 and in the lower to mid 90s west of I-65. There is a
low chance (15-30%) of pop up showers/storms again Monday
afternoon, but this will likely be concentrated over NE AL and
portions of southern middle TN due to terrain influences.

&&

.LONG TERM...
(Monday night through Friday)
Issued at 937 PM CDT Fri Sep 4 2026

Heat will persist through the long term as well. The vast ridge of
high pressure that is centered over the Southern Plains and Mid MS
Valley will expand eastward to encompass the rest of the Southeast
early this week. Mid week, a trough will swing through the southern
Canadian prairie provinces dampening the ridge, and sfc high
pressure will set up along the Appalachians. This set up could create
a CAD expanding into NE AL and portions of Southern Middle TN. If
this comes to fruition, adjustments to POPs (slight increase) and
temps (slight decrease) would be needed. Regardless, it looks like
temps will remain in the 90s throughout the week, which is par for
the course this month, but running a tad higher than seasonal norms
which is 87-88 degrees. Heat index values will hover around 100
degrees and the NWS Heat Risk will be a level 2 (Moderate Level) for
the large majority of us. Remain heat smart:
slow down, cool down, stay hydrated and NEVER leave people or pets
in vehicles.

&&

.AVIATION...
(00Z TAFS)
Issued at 557 PM CDT Sat Sep 5 2026

VFR conditions are forecast to persist through the TAF period. A
low chance of thunderstorms making it into the vicinity exists
this evening, but confidence is extremely low so this was kept out
of the TAF. Additionally, a low chance of patchy fog exists
tonight, but confidence remains low in this impacting either site
so this was also kept out of the official TAF package.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Heat Advisory until 8 PM CDT Sunday for ALZ001>010-016.

TN...Heat Advisory until 8 PM CDT Sunday for TNZ076-096-097.

&&

$$

NEAR TERM...26
SHORT TERM....26
LONG TERM....JMS
AVIATION...HC