543
FXUS64 KHUN 212254
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
554 PM CDT Tue Jul 21 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 932 AM CDT Tue Jul 21 2026

 - A Heat Advisory is in effect for most of the Tennessee Valley
   through 8 PM.

 - Major (Level 3/4) Heat Risk will develop across the Tennessee
   Valley today, with peak heat index values between 105 to 110
   degrees likely in many locations.

 - Low chance for a few strong to severe storms tonight into early
   Wednesday morning along and ahead of a cold front. Gusty to
   damaging winds, frequent lightning, and locally heavy rainfall
   will be the main threats.

&&

.NEAR TERM...
(Tonight)
Issued at 147 PM CDT Tue Jul 21 2026

Major Heat impacts continue this afternoon as temperatures in the
low to perhaps mid 90s combine with dewpoints in the mid to upper
70s to create heat index values as high as 105-110 degrees. A Heat
Advisory remains in effect through 8 PM. Current satellite shows a
very flat scattered Cu field in place, with subsidence from the
ridge building in from the west evident on model soundings.
Despite this, we do have a low to medium chance of showers and
storms late this evening and overnight (with a conditional risk
that a few could be strong or marginally severe).

A cold front along the Ohio River will serve as a focus for
thunderstorms late this afternoon into the evening hours. Upstream
from us the environment remains very favorable for severe
thunderstorms, but as they push further to the south during the
evening hours, the environment becomes less favorable across
middle Tennessee and especially into northern Alabama. The latest
hi-res guidance continues to maintain a late arrival of this
activity into the Tennessee 10 PM to 5 AM (with many solutions
favoring after Midnight. Should the storms arrive a little
earlier there may be just enough instability to support a low
threat for a few strong to severe outflow driven storms. Should
this activity move in after 06z, we may struggle to realize
thunderstorms, let alone severe weather as any surface-based
instability will be very limited as will low/mid-level lapse
rates. We`ll have to watch trends closely over the next 12-18
hours and adjust PoPs/timing accordingly.

&&

.SHORT TERM...
(Wednesday through Thursday)
Issued at 932 AM CDT Tue Jul 21 2026

On Wednesday, the aforementioned cold front will be pushing
through the region during the morning into the early afternoon
hours. The storm environment should be fairly worked over thanks
the activity overnight into the early morning hours as surface-
based instability will be far more limited. However, a low-
medium (30-60%) chance for showers and a few storms will exist
through the afternoon (especially for locations south of the
Tennessee Valley where instability will be slightly higher). The
aforementioned rain chances and denser cloud cover will lower
temperatures and subsequently heat index values slightly. Still,
highs in the upper 80s to lower 90s, and heat index values around
the 100 degree mark could create some Moderate (Level 2/4) heat
risk concerns.

A slightly cooler and drier air mass will filter into the area in
wake of the front on Thursday, with high temperatures dropping
into the mid to upper 80s and any appreciable precipitation
chances remaining just to the south of the area along the front.
As a result, most of the region will be devoid of any diurnally
driven convection, save for a low chance (20-30%) clipping our far
southeastern zones.

&&

.LONG TERM...
(Thursday night through Monday)
Issued at 905 PM CDT Mon Jul 20 2026

The general upper level setup will consist of a ridging west and
troughing east pattern over the greater North American domain. This
pattern was being kept in place by Omega-style upper blocking over
the northern Pacific basin. At the beginning of the extended, upper
troughing will be in place off of the west coast (the eastern anchor
of the upper block), with strong upper level ridging situated over
the southern Great Plains. A passing upper low over the central
Ontario and Quebec region will deepen, and help amplify upper
troughing from the eastern Great Lakes to northern Florida. This will
place the Tennessee Valley in a WNW-ESE flow from the late week into
early next week.

A northwesterly upper level flow across this area, especially if it
is disturbance laden, is known for bringing showers and thunderstorms
to the Valley. Convection in these regimes can be accompanied by
strong winds. For this area, a few complications to that simplistic
view. First, a cold front should be south of the area by late Thu.
Moisture from Tropical Storm Bertha should be streaming back to the
NE, with some of it impacting the area Fri into Sat. Along with lower
level tropical moisture, some of the extended guidance was suggesting
that upper level support moving across the area from late Fri into
Sun could bring more thunderstorms to the area. It is way too early
to discern if this convection could become more significant, given
much model uncertainty this far out. With a main synoptic front to
our south and with some shower/storm chances, daily high/low
temperatures should trend a bit milder, with highs Fri/Sat in the mid
80s to around 90. Warmer conditions look return for the start of the
new week, with highs from the upper 80s to lower 90s Sun, and low/mid
90s next Mon. Lows Thu night should range in the mid/upper 60s, with
mainly lower 70s for the Fri - Sun night period.

&&

.AVIATION...
(00Z TAFS)
Issued at 554 PM CDT Tue Jul 21 2026

VFR conditions are forecast to continue through the evening and
overnight. A PROB30 group was added at KMSL for a low chance of
MVFR conditions due to showers reaching the area from the north
between 08-10Z Wednesday. Additionally, a PROB30 group is in
place at KHSV late Wednesday afternoon into the evening for a low
chance of thunderstorms causing MVFR conditions.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Heat Advisory until 8 PM CDT this evening for ALZ001>009-016.

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

&&

$$

NEAR TERM...AMP
SHORT TERM....AMP
LONG TERM....RSB
AVIATION...HC