699
FXUS64 KHUN 300259
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
959 PM CDT Fri Aug 29 2025

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

.NEAR TERM...
(This Evening through Saturday)
Issued at 959 PM CDT Fri Aug 29 2025

Northwest flow of 15-25 knots will continue across the TN Valley
throughout the near term period, dictated by a mid/upper-level low
tracking slowly eastward across southern Quebec and trailing
trough extending southwestward into the north-central Gulf. At the
surface, a subtle area of low pressure will be maintained across
southern portions of MS/AL (within the base of the longwave trough
aloft), and light NE winds will persist across the TN Valley as a
surface high translates southeastward across the Great Lakes.
Although a subtle axis of low-level convergence may setup to the
southeast of our forecast area tomorrow in response to rising
surface pressures in the lee of the southern Appalachians, any
resulting light showers should remain confined to portions of
central AL/north GA, and we will maintain a dry forecast with
dewpoints in the 50s. Mid/high-level clouds related to a weak
disturbance tracking southeastward across the region will lead to
slightly warmer overnight lows in the u50s-l60s and may limit
development of fog to rivers/lakes and adjacent land areas. As
skies clear late tomorrow morning, temperatures will warm
efficiently, with highs reaching the lower 80s in elevated terrain
and 85-90F range in the valley.

&&

.SHORT TERM...
(Saturday night through Monday night)
Issued at 959 PM CDT Fri Aug 29 2025

During the period from Saturday night-Sunday night, a mid/upper-
level cyclone (initially across southern Quebec) will shear apart
as it ejects east-northeastward into the northwestern Atlantic.
However, a secondary/weaker closed low is predicted to evolve
across the northern Mid-Atlantic states in its wake and will
maintain NW flow aloft of 15-25 knots across the TN Valley as it
becomes blocked by a narrow mid-level ridge developing eastward
across southeastern Canada. At the surface, a high (initially
across the Great Lakes) will slowly strengthen as it shifts
eastward into the northeastern CONUS, reinforcing a cold air
damming regime from VA southwestward into northern GA. As this
occurs, winds across our region will gradually veer to SE
beginning Sunday afternoon, with naturally-induced convergence
perhaps initiating a few showers across the southeastern portion
of the CWFA. With the convergence axis predicted to lift slowly
northwestward through our region Sunday night, a few showers will
remain possible through early Monday morning. Highs and lows on
Sunday will be similar to Saturday, but lows on Monday morning
will rise into the mid 60s for much of the region as higher
dewpoints (l-m 60s) advect northwestward.

Latest model data suggests that the ill-defined convergence axis
will likely reside across the northwest portion of the forecast
area on Monday-Monday night, and should contribute to a greater
spatial coverage of showers and some thunderstorms, especially as
a mid-level shortwave trough drops southeastward from the northern
Plains into the Mid-MS Valley contributing to weak forcing for
ascent aloft. This activity will begin late Monday morning and
should continue for much of the night, and although mid-level
winds will remain in the 15-25 knot range and CAPE may only reach
1000-1250 J/kg, lightning will certainly be a concern along with
locally heavy rainfall (as PWAT values will return to the 1.3-1.5"
range by Sunday afternoon/evening). Highs will be a few degrees
lower on Monday due to the early onset of clouds and
precipitation, with lows Tuesday morning similar to Monday
morning.

&&

.LONG TERM...
(Tuesday through Friday)
Issued at 959 PM CDT Fri Aug 29 2025

During the fist half of the extended period, an amplifying
northern stream clipper system will dig southeastward from central
Canada into the northwestern Great Lakes, resulting in gradual
east-southeastward movement of a lower-latitude shortwave trough
across the Mid-MS Valley and into the TN Valley. Several embedded
disturbances will exist within the lower-latitude wave, and should
enhance the coverage of showers in the vicinity of a surface
convergence axis across our region at times on Tuesday/Tuesday
night. Due to widespread clouds, instability will be lower
compared to Monday and the risk for lightning/thunder is very
uncertain. However, sufficient CAPE will exist for convective
precipitation and with weak steering currents and fairly high PWAT
values, the risk for locally heavy rainfall remains apparent.
Rain should gradually end from W-to-E on Wednesday, as the
initiating shortwave trough begins to turn east-northeastward and
away from the region.

Present indications are that the northern stream clipper system
will intensify at a considerable rate on Wednesday night/Thursday,
resulting in deepening of a surface low as it tracks eastward
across the northern Great Lakes/southern Ontario. As the trailing
cold front spreads southeastward through the TN Valley on
Thursday, a second episode of showers and thunderstorms will be
possible, but the southern edge of the strongly forced convective
line may only reach as far south as northern Middle TN.
Regardless, this is something we will need to monitor over the
coming days, as mid-level westerlies increasing into the 35-45
knot range could support organized/severe thunderstorms in the
presence of sufficient moisture and lift. A cooler/drier
continental airmass will spread across the region in the wake of
the cold front, with dewpoints falling back into the u40s-l50s by
Friday.

&&

.AVIATION...
(00Z TAFS)
Issued at 700 PM CDT Fri Aug 29 2025

Multi-layer clouds (consisting of few high-based Cu and sct-bkn
As/Cs) will continue to spread southeastward across the TN Valley
this evening and overnight, as a weak upper-level disturbance
tracks across the region in NW flow aloft. However, conditions
will remain VFR at the HSV/MSL terminals, especially as the clouds
may confine development of BF/FG early Sat morning to valleys and
lakes. Mid/high-lvl clouds will clear the region btwn 12-18Z,
with a NE wind of 5-10 kts expected during the afternoon.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...None.
TN...None.

&&

$$

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