824
FXUS64 KHUN 250511
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1211 AM CDT Wed Sep 25 2024

...New AVIATION...

.NEAR TERM...
(Tonight)
Issued at 800 PM CDT Tue Sep 24 2024

With the loss of daytime heating contributing to available
instability for storm potential, our severe threat has decreased
for the overnight hours. As the cold front continues to move
eastward through the Tennessee Valley, CAMs are continuing to hint
at additional development overnight into the early morning hours
along the frontal boundary in central northern AL and portions of
southern middle TN. Additional storm formation will bring low-
medium threats of heavy rainfall as well as lightning. As the cold
front moves into NE AL and southern middle TN, coverage of
showers/storms increases into the morning hours (particularly
along and east of the I-65 corridor).

&&

.SHORT TERM...
(Wednesday through Friday)
Issued at 233 PM CDT Tue Sep 24 2024

Rain is likely to start the day on Wednesday with continual
support from the frontal boundary. The front looks to stall over
our area as it begins to interact with Tropical Storm Helene.
A medium chance of showers and thunderstorms, scattered in
nature, are likely through most of the day tomorrow, however the
severe threat will be significantly less than today. Rain chances
will decrease through the evening however with Tropical Storm
Helene continuing to move NE, a brief period of low rain chances
will be our only relief between monitoring the cold front and the
transition to monitoring the tropics.

Tropical Storm Helene is forecast to make landfall as a major
hurricane on Thursday evening. While the center and worst of the
storm itself is forecast to move east of us, Helene is forecast to
be very large, thus its impacts will be felt well beyond the
center of the storm. For the TN Valley, we will begin to
transition into Helene`s influence Thursday during the day. Rain
chances and wind speeds will gradually pick up as Helene pushes
north. Current forecast has wind gusts 20-30 MPH from Thursday
during the day through Friday evening. NE AL overnight on Thursday
will see the highest gusts. While current forecast does not
warrant a Wind Advisory, it would still be a good idea to bring
in loose objects.

Rainfall will be our main concern as Helene moves through. Current
forecast supports widespread rain totals of 2-5 inches of rain
from Wednesday night through Saturday morning. While this amount
alone is likely manageable, we have two concerns regarding the
rainfall forecast. The first is that this rain is in addition to
the 2-4 inches of rain we are expecting with the cold front from
Tuesday (today) into Wednesday. It is very likely that soils will
be very saturated by the time tropical rain from Helene gets here
and make NE AL much more prone to flooding than it otherwise would
be. The second concern related to how Helene will interact with
the upper level low. As Helene pushes NE, the upper level low is
forecast to retrograde across our area. This will place us
squarely between the upper low and Helene, creating an enhanced
area of convergence as both will be contributing to SE flow. SE
flow will continue to pull in warm, moist tropical air and could
support an additional threat for very efficient rainfall
production. The impacts from this could lead to an increased flash
flooding threat Friday morning, yet this threat materializing
remains uncertain. We will be monitoring how both of these
concerns play out over the next several day yet the bottom line up
front front is concerns for flash flooding and river flooding
from Helene with our area of highest concern being NE AL. Make
sure to have multiple ways to receive warnings.

Rain will continue for most of the day on Friday yet chances will
quickly drop off Friday evening as Helene continues on her
northward journey. Lingering SE flow will support a low chance of
rain through the remainder of the short term but the flash
flooding threat will likely have ended.

&&

.LONG TERM...
(Friday through Monday)
Issued at 233 AM CDT Tue Sep 24 2024

The forecast going into the Long Term portion will of course be
dependent on the eventual track of the tropical system, but the
rainfall impacts to the area may transition more to the upper low
over the Mid South/lower MS Valley regions as opposed to the
remnant tropical system exiting to the ENE. Medium chances for
showers/tstms (30-50%) are expected on Fri, as the upper low
begins to drift eastward. However, given the slower movement of
this feature, rain chances look to taper off this weekend to
around 20-30%. In fact, any additional rainfall looks to remain as
showers, although an isolated storm cannot be ruled out Sun
afternoon. With less cloud cover/rainfall, highs this weekend look
to climb back into the lower 80s/near 80F. Those rain chances
increase slightly on Mon, as the upper low begins to lift into the
OH Valley area. Highs on Mon also look to trend more in the upper
70s/near 80F. Lows this weekend and into next week look to remain
in the lower/mid 60s.

&&

.AVIATION...
(06Z TAFS)
Issued at 1211 AM CDT Wed Sep 25 2024

A weak cold front continues to drift eastward into NW AL heading
into the overnight hrs. Some -shra may develop along/ahead of the
front into the early morning period, but this should have minimal
impact on any of the terminals. Sct shra/perhaps a few tsra are
expected to develop along/ahead of the front going into the
daytime hrs, especially near the KHSV airfield and a TEMPO group
has been included in the 14/18Z time frame to account for any
reduced cig/vis. Otherwise, MVFR cigs look to develop Wed morning
and persist into the early afternoon hrs before cigs perhaps lift
above 3K ft. A PROB30 group was maintained for both terminals
during the afternoon hrs for any additional -shra or -tsra. Precip
looks to taper off Wed evening, with cigs remaining above 3K ft.

&&

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

$$

NEAR TERM...HC
SHORT TERM....RAD
LONG TERM....09
AVIATION...09