569
FXUS64 KHUN 260945
AFDHUN

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

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

.NEAR TERM...
(Today)
Issued at 445 AM CDT Thu Sep 26 2024

Surface observations in conjunction with satellite/radar data
suggest that the weak cold front (which drifted southeastward
through the region yesterday) now resides in northwest GA, with
only a very low probability for rainfall along the AL-GA border
for the next few hours. Patchy fog and low stratus clouds will
persist in the moist environment to the west of this boundary as
temperatures will remain steady in the l-m 60s, with significant
visibility reductions possible in the higher terrain of northeast
AL/southern TN through sunrise. The front is still expected to
begin shifting westward later this morning as it slowly becomes
absorbed in the broader circulation of Hurricane Helene (which
will begin lifting north-northeastward across the eastern Gulf of
Mexico). As this occurs, low clouds and light-moderate rain will
spread westward into region over the course of the afternoon, with
afternoon highs ranging from the mid 70s (E) to u70s-l80s (W).

&&

.SHORT TERM...
(Tonight through Saturday night)
Issued at 445 AM CDT Thu Sep 26 2024

Conditions across the TN Valley will continue to deteriorate
early this evening, as Hurricane Helene begins to interact with a
cutoff upper low over the Mid-South region and accelerates
northward across GA. Widespread moderate-locally heavy stratiform
rainfall on the northwestern periphery of the tropical cyclone
will encompass the entire forecast area by late this evening and
continue through the early morning hours on Friday, before
temporarily ending from S-to-N late Friday morning as the
weakening surface low begins to shift northwestward into the Lower
OH Valley. Storm total rainfall amounts will range from 2-4" (SW)
to 3-5" (NE), and with locally higher amounts possible in a few
locations, the risk for both areal and flash flooding will remain
high. Thus, the previously issued Flood Watch has been expanded to
include all counties in the WFO Huntsville CWFA through 18Z
Friday. There are indications that light-moderate rain may persist
across the northwestern half of the forecast area through the
afternoon hours Friday, and we will consider extending the Flood
Watch for this region in future forecast updates. Aside from rain,
the other pertinent hazard from this system will be gradient
winds, which should back to NW and strengthen considerably late
this evening, before backing to SW and increasing further late
Friday morning. Based on latest model projections, we have
modified the previously issued Wind Advisory a bit to include
Marshall County and constrain the timeframe for highest wind from
27/6Z-28/6Z. It is important to note that the highest sustained
wind speeds and gusts will likely occur in elevated terrain
locations.

During the period from Friday night-Saturday night, the weakening
remnants of Helene are predicted to make a slow cyclonic loop
across the Lower OH Valley and adjacent portions of western KY/TN.
Several bands of light-occasionally moderate showers will spread
northeastward across the region from Friday night through Saturday
afternoon, embedded within a strong southwesterly flow regime
around the deep-layer cyclone to our northwest. Although POPs will
remain in the high chance range during this period to account for
the fast motion of these bands, rainfall rates are not expected
to be high enough at this point to contribute to additional
flooding. Highs during this period will be in the l-m 70s, with
lows in the l-m 60s.

&&

.LONG TERM...
(Sunday through Wednesday)
Issued at 445 AM CDT Thu Sep 26 2024

Global models suggest that the deep-layer cyclone to our north
will continue to lift slowly northeastward on Sunday/Sunday night,
with SW flow to the east of a trailing trough axis maintaining a
moist airmass across the TN Valley. This will lead to cloudy skies
and some diurnally-driven shower activity on Sunday, but
precipitation coverage will be lower than previous days (25-35%).
Present indications are that the mid-level trough axis will
progress southeastward across the region at some point Monday,
with NW flow in the wake of the trough resulting in rapid drying
of profiles aloft and an even lower coverage of afternoon showers.
It appears as if the drying trend aloft will be complemented by a
drying trend in the low-levels by the middle of next week, as a
cold front tracks southeastward through the TN Valley. Although
the cold front may indeed advect a drier continental airmass into
the region, highs will warm back into the l-m 80s by
Tuesday/Wednesday due to abundant sunshine each afternoon.

&&

.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 ALZ001>010-016.

     Wind Advisory from 1 AM Friday to 1 AM CDT Saturday for
     ALZ008>010.

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

     Wind Advisory from 1 AM Friday to 1 AM CDT Saturday for TNZ097.

&&

$$

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