425
FXUS64 KHUN 260544
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1244 AM CDT Thu Sep 26 2024

...New AVIATION...

.NEAR TERM...
(Tonight)
Issued at 838 PM CDT Wed Sep 25 2024

The frontal boundary that brought showers and a few thunderstorms
earlier in the day has shifted just south and east of the area.
As a result, the TN Valley will be treated to a brief period of
benign weather tonight prior to the arrival of impacts from
Hurricane Helene (more on this in the section below). In wake of
the frontal boundary, drier air has temporarily worked its way
into the region as seen by dewpoints falling into the lower 60s.
Cloud cover is also diminishing as mostly clear conditions have
developed along and west of I-65. Still think clouds will hang on
in our far eastern zones for most of the night, and have also kept
a low chance of showers and an isolated storm there after
Midnight. In general though dry conditions will prevail and lows
in the low to mid 60s will be common in an otherwise fairly
pleasant night. Only minor tweaks made to the forecast as
everything remains on track.

&&

.SHORT TERM...
(Thursday through Saturday)
Issued at 212 PM CDT Wed Sep 25 2024

The broad overview for the short term forecast is as follows.
Helene is forecast to make landfall in the Florida Big Bend
Thursday evening. From there, Helene will initially push NE and
move through most of Georgia. Helene pushing NE will cause the
low pressure as associated cold front to retrograde back to the
NW. As Helene pushes north and begins to dissipate, it is forecast
to get wrapped into the upper low that passed in the near term
and bring continued impacts into NW AL through the short term.

Now, what does all of this mean for us locally? Rain is forecast
to move into NE AL tomorrow mid morning yet impactful weather is
not forecast until Thursday evening. Our main threat will be heavy
rainfall. As Helene moves NE overnight on Thursday, tropical
moisture will quickly move into the area creating a very favorable
environment for efficient rainfall production. PWATS are likely
to increase above 2" for most of NE AL. With an incredibly
saturated profile, heavy, continual rainfall is forecast creating
a significant risk for flash flooding. Around 3-4" are forecast
area wide with locally higher amounts of 5-7" possible. WPC has
placed NE AL in a Moderate Risk (3/4) of excessive rainfall
highlighting at least a 40% risk of rainfall exceeding flash flood
guidance within 25 miles of any given point in the Moderate Risk.
The remainder of the CWA remains in a Slight Risk for excessive
rainfall. Thus, a Flood Watch has been issued for NE AL and
portions of southern middle TN from now through 1 PM Friday. We
will continue to assess the flooding potential for the remainder
of the CWA to see if the Flood Watch needs to be expanded to the
west.

Winds will be our secondary concern. NE AL will see the highest
wind gusts near 35 MPH. A Wind Advisory is in effect from 7 PM
Thursday through 7 PM Friday for NE AL and portions of southern
middle TN. Highest winds speeds will be seen in NE AL in terrain
areas with gusts near 35 MPH. Elsewhere, gusts are forecast to
remain closer to 20-25 MPH. Again we will continue to monitor
this to see if the Wind Advisory needs to be expanded. One concern
we wanted to highlight is an elevated risk for downed trees due
to saturated soils. Locations that see significant rainfall will
be more susceptible to down trees as wet, saturated soils will
make it easier for trees to be blown over. The biggest threat for
this will be in NE AL where the heavy rainfall threat and higher
wind threat will overlap, however this threat could materialize
anywhere heavy rainfall and strong winds coincide. Winds should
pretty quickly drop below Wind Advisory criteria by Friday
evening. That about covers the threats in the current forecast.
What we will be closely watching is for any changes in Helene`s
track which would significantly impact our current forecast.
Should Helene trend any further east, both wind speeds and
rainfall amounts will likely significantly increase. The westward
potential of Helene is uncertain at this time.

The heavy rain and wind threat looks to end Friday afternoon with
more stratiform rain lingering through the Saturday morning as
what remains of the upper-level low and Helene move into the Ohio
Valley. Widespread rain will likely come to an end mid morning on
Saturday with medium rain chances (30-60%) remaining through the
remainder of the day due to lingering bands of light showers.
These showers will be more scattered in nature. Rain chances will
greatly decrease by Saturday night and remain below 30% for the
remainder of the weekend.

&&

.LONG TERM...
(Saturday trough Tuesday)
Issued at 233 AM CDT Wed Sep 25 2024

The upper low will then begin to lift N/E of the central TN Valley
this weekend, providing for a low chance of showers (20-30%) both
Sat/Sun with some decreasing cloud cover. Minimal rain chances are
expected into the first half of the work week as well, as a
reinforcing cold front out of the NW sweeps thru the region. With
the decrease in cloud cover/rainfall, highs this weekend will be
more in the mid/upper 70s, before climbing into the upper 70s/near
80F Mon/Tue. Overnight lows thru the latter half of the forecast
period also look to remain in the mid 60s/near 60F.

&&

.AVIATION...
(06Z TAFS)
Issued at 1244 AM CDT Thu Sep 26 2024

Conditions have temporarily improved at the HSV/MSL terminals,
and we expect this trend to persist thru the early morning hours
as a weak cold front will continue to drift southeastward into NW
GA. However, rain and low stratus clouds will quickly overspread
the region from E-to-W later this aftn as Hurricane Helene lifts
north-northeastward through the eastern Gulf of Mexico, with an
extended period of moderate rain and MVFR-IFR cigs/vsby beginning
arnd 27/0Z. Sfc winds will remain from NE at 5-10 kts today, but
will back to N or perhaps NNW and strengthen overnight, with gusts
up to 25 kts possible at times.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...

AL...Flood Watch through Friday afternoon for ALZ005>010-016.

     Wind Advisory from 7 PM this evening to 7 PM CDT Friday for
     ALZ009-010.

TN...Flood Watch through Friday afternoon for TNZ076-096-097.

     Wind Advisory from 7 PM this evening to 7 PM CDT Friday for
     TNZ097.

&&

$$

NEAR TERM...AMP
SHORT TERM...RAD
LONG TERM...09
AVIATION...70/DD