640
FXUS64 KHUN 160351
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1051 PM CDT Tue Sep 15 2026

...New NEAR TERM, SHORT TERM, LONG TERM...

.KEY MESSAGES...
Updated at 1051 PM CDT Tue Sep 15 2026

 - A Heat Advisory is in effect through 8 PM Wednesday for much of
   the forecast area.

 - Moderate (Level 2/4) NWS HeatRisk values are expected for the
   majority of the forecast period. However, Major (Level 3/4)
   values are expected across parts of northwest and north-central
   AL (as well as southern Middle TN) through Friday.

&&

.NEAR TERM...
(This Evening through Wednesday)
Issued at 1051 PM CDT Tue Sep 15 2026

A strong mid-level high will remain centered across eastern TN
for much of the near term period, before beginning to retreat to
the west Wednesday afternoon. In the low-levels, our region will
remain under the influence of a surface high that will drift
slowly eastward from the New England coast into the northwestern
Atlantic and a ridge axis extending southwestward from the high
into the central Gulf Coast states. Although a few patches of
high-based cumulus have been spreading northwestward across parts
of the forecast area this evening, this has been largely related
to a modest SSE low-level jet of 10-20 knots (which is predicted
to progressively weaken throughout the night). Thus, we expect
skies to clear during the early morning hours, with overnight lows
ranging from the u60s in the east to the m70s in the west. Patchy
fog may briefly develop shortly before sunrise (primarily in the
wind-sheltered valleys of northeast AL).

Temperatures will begin to warm quickly after sunrise tomorrow,
and with with only a scattered cumulus field anticipated,
efficient solar insolation will force afternoon temperatures into
the u80s-l90s in elevated terrain and m-u 90s in the valley. In
this type of environment, gentle orographic ascent in the vicinity
of the Cumberland Plateau (as well as the ridges across northeast
AL) may be sufficient to initiate isolated weak convection
tomorrow afternoon, which would likely come in the form of showers
due to the presence of a strong subsidence inversion in the 8-10
kft layer. Although diurnal mixing may once again result in
dewpoints falling into the m60s during the afternoon (and
significantly reducing the coverage of heat indices around 105F),
a Heat Advisory will remain in effect for portions of the CWFA
through 8 PM.

&&

.SHORT TERM...
(Wednesday night through Friday night)
Issued at 1051 PM CDT Tue Sep 15 2026

Latest short range model consensus suggests that a mid-level
subtropical high will continue to retrograde slowly across the
Mid-South region and into AR on Wednesday night/Thursday, as a
developing trough (off the southeastern Atlantic Coast) begins to
shift southwestward. As this occurs, N-NE flow aloft will become
established across the TN Valley and dry advection in the
mid/upper-levels will contribute to PWAT values falling into the
1.1-1.3" range. In the low-levels, a weakening surface high
(centered well to our northeast) will drift further eastward into
the northwestern Atlantic, resulting in a weakening pressure
gradient and light/variable winds. Although the combination of
lower atmospheric moisture content and absence of low-level
convergence would normally support a dry forecast, subsidence
aloft will begin to weaken on Thursday, providing a more favorable
environment for terrain-induced showers and thunderstorms
(primarily to our north/east).

During the period from Thursday night-Friday night, a Canadian
surface high will migrate east-southeastward from eastern MB into
western QC in the wake of a northern stream shortwave trough. As
this occurs, a cold front will spread slowly southwestward across
the Lower Great Lakes and northern Mid-Atlantic states, with a
prefrontal surface trough/wind-shift axis likely to initiate a
greater coverage of afternoon convection on Friday from parts of
the Lower OH Valley into VA/NC. With less influence from the mid-
level subtropical high (as it weakens and retrogrades further
southwestward into the Arklatex/northeast TX), conditions will
become increasingly favorable for development of afternoon storms
across the Smoky Mountains as well, with prevailing N-NE flow
aloft likely to force some convection (from both regimes)
southwestward into our forecast area Friday afternoon. As PWAT
values increase back into the 1.6-1.8" range, higher CAPE coupled
with steep low-level lapse rates may support a risk for locally
damaging downburst winds with any convection during the afternoon.
However, storm coverage may be highest during the evening hours
(perhaps extending into early Saturday morning, and particularly
across the eastern part of the CWFA) contingent on the presence of
outflow boundaries.

Regarding temperatures, they should fluctuate very little over
the course of the period, with overnight lows in the u60s-m70s and
daytime highs ranging from the u80s-l90s in elevated terrain to
the m-u 90s in the valley. However, with diurnal mixing expected
to reduce afternoon dewpoints on a daily basis, we do not plan to
extend the Heat Advisory at this time.

&&

.LONG TERM...
(Saturday through Tuesday)
Issued at 1051 PM CDT Tue Sep 15 2026

By the weekend, the anchored ridge will be pushed to our west as
the wondering upper level low moves westward across FL and into
the northern Gulf. Models are even more split today on what the
strength and longevity of this low will be. It seems to stall for
a little bit over the NE Gulf on Saturday before either sliding
westward, or weakening and fading out completely. Regardless,
dangerous heat will persist into the weekend. Look for highs to be
in the lower 90s in NE AL/portions of Southern Middle TN, and the
mid to upper 90s elsewhere. Heat index values at this time look
to remain below heat advisory criteria sitting around 100 degrees,
however we will remain in a level 2-3 HeatRisk across the TN
Valley. So ensure to be heat safe/smart. Slow down, hydrate and
never leave people or pets in vehicles.

An upper level trough will move across the Rockies and Northern
Plains this weekend and into the Upper Midwest early next week,
but there is also uncertainty on this feature. A sfc low will move
into the OH Valley on Monday and try to pull a cold front towards
the TN Valley. Will see low to medium rain chances return
(20-45%) on Monday, but with the front most likely stalling on
Tuesday, we won`t see a frontal passage, but have rain chances
continue. This will at least help the temps lower a tad with some
seeing highs in the upper 80s Tuesday afternoon.

&&

.AVIATION...
(00Z TAFS)
Issued at 737 PM CDT Tue Sep 15 2026

Scattered patches of high-based Cu will continue to shift north-
northwestward across the forecast area early this evening, within
a southerly flow regime of 10-20 knots aloft. However, we expect
skies to clear later this evening, with development of patchy
BR/FG likely to occur btwn 10-13Z (mainly in wind-sheltered
valleys east of HSV). Strong heating of the boundary layer will
support redevelopment of few-sct high-based Cu by 15Z, with a few
aftn SHRA/TSRA expected to develop from the Cumberland Plateau of
Middle/East TN southward into northeast AL. Sfc winds will remain
from the S-SE thru the period, with prevailing speeds arnd 5 kts.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...

AL...Heat Advisory until 8 PM CDT Wednesday for ALZ001>009.

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

&&

$$

NEAR TERM...70/DD
SHORT TERM...70/DD
LONG TERM...JMS
AVIATION...70/DD