079
FXUS64 KHUN 151145
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
645 AM CDT Wed May 15 2024

...New AVIATION...

.NEAR TERM...
(Today)
Issued at 348 AM CDT Wed May 15 2024

Shower activity has ended or moved east of the area for the
moment with only few passing high clouds. Area temperatures were
in the lower 60s. A moist ground from the recent rainfall, mostly
clear skies, and light winds has resulted in the formation of low
clouds and patchy fog. Although we are in the warmer season with a
shorter night, there is still plenty of opportunity for more fog
to form before daybreak Wed. A weak frontal boundary was moving
across the Tennessee Valley as of this writing. Slightly drier air
moving in from the west may help temper development of widespread
fog - especially more to the west.

Fog otherwise should dissipate shortly after daybreak as the usual
diurnal warming begins. Although the front has moved to our east,
the parent low the front was trailing south of was still over OH
and KY. Moisture associated with this low extends southward to
this area. Daytime heating and resultant instability should
produce more instability, and the development of more showers and
thunderstorms from the late morning into the afternoon. This
convection should be more prevalent over our central and
especially eastern areas. Severe weather is not anticipated, but
the usual gusty winds and heavy downpours could accompany the
stronger storms should they occur. With more clouds, and a bit of
cold air advection, high temperatures today should be a tad
cooler than yesterday - in the mid/upper 70s.

&&

.SHORT TERM...
(Tonight through Friday night)
Issued at 348 AM CDT Wed May 15 2024

Under mostly clear to partly cloudy skies tonight, a break from
showers is expected. Lows should cool to around 60. W-NW winds of
5-10 mph should keep the lower atmosphere sufficiently mixed to
hamper fog formation. The "dry" spell continues Thu, with highs
rising into the mid 80s with light winds.

The dry period will come to an end Thu night, as yet another storm
system nears, and clouds increase from west to east. Shower and
thunderstorm chances also return mainly after midnight. This next
system will bring high chances of showers with isolated to
scattered thunderstorms on Fri. A bit cooler with highs in the
upper 70s. Of interest is a strong return of lower level moisture
to the region. The 00Z NAM in particular brings higher levels of
moisture and instability in a rather highly sheared environment.
Forecast soundings from this model look somewhat ominous far as
strong convection is concerned. The other models had decent winds
but lesser lower moisture return, with the ECMWF and Canadian
suggesting this moisture could be intercepted by convection to our
south (like with the system that just departed). This said, some
storms in this sheared environment could become strong to severe,
with damaging wind gusts the main threat. Storm relative helicity
values on Fri time range in the 200-300 m/sec, while CAPE values
were from the single digits to around 300 J/kg from the ECMWF and
Canadian. The NAM was showing CAPES over 2000 in comparison.
Shower and storm chances should continue Fri night with lows in
the mid 60s.

&&

.LONG TERM...
(Saturday through Tuesday)
Issued at 348 AM CDT Wed May 15 2024

To start the long term, an upper shortwave trough is expected to
traverse the Mississippi and Tennessee Valleys on Saturday. However,
there remains disagreement in the model guidance with regards to
timing and evolution of the trough. Once this feature moves east of
the area (Sunday morning), upper ridging looks to take hold and
persist through early next week. Although, a shortwave may sweep over
the Midwest and over the Ohio Valley on Monday. At the surface, a
low pressure system is shown to move over the lower Ohio Valley and
Tennessee Valley Saturday morning, with northern Alabama and southern
middle Tennessee in the warm sector. Anticipating this low to
continue eastward and move over Virginia and North Carolina by Sunday
morning, with high pressure building in behind it over our area for
Monday. This high pressure will then begin to shift east on Tuesday,
ushering moisture into the region with return flow.

Looking at thunderstorm potential, guidance varies a bit with bulk
shear and instability Saturday morning. But, values look to be at
least 40 knots with around 500-700 J/kg. 0-3 km SRH values also range
between 100-150 m2/s2 in the morning and into the afternoon. This,
the trajectory of the surface low, and potentially a LLJ around 40-50
knots moving over the Tennessee Valley Saturday morning increases
confidence in the potential for strong to possibly severe storms
Saturday morning and into Saturday afternoon. The main question is
with the timing of this system through the area. If it`s later
(afternoon hours), then there will be more time for warming which
would lead to more instability and high potential for severe. If it`s
earlier (morning hours), there may not be as much instability for
storms to tap into (especially with showers/storms possible Friday
night) and perhaps less of a severe threat. Although, that`s not to
say we can`t have strong to severe storms in the morning. Ultimately,
we`ll be monitoring this system and trends closely over the coming
days with subsequent model runs to better determine any severe
potential.

For sensible weather, expect medium to high chances (50-70%) of
showers and storms on Saturday. These could at least bring gusty
winds, frequent lightning, and heavy downpours. As was mentioned
previously, we`ll continue to analyze trends for the potential for
any severe weather. At this point, chances of showers and storms
dwindle from west to east in the evening, but timing could change a
bit in subsequent forecast updates. Sunday will then be mostly dry,
but some spots over the far northeastern portion of Alabama and
southern middle Tennessee could see a few showers/storms in the
afternoon. With an upper level shortwave moving over the Ohio Valley
on Monday (mentioned above), low chances (15-20%) of showers and
possibly a storm are forecast Monday evening and overnight. Low
chances (15-20%) of showers/storms are then possible on Tuesday.

Temperatures will be on the rise through Tuesday. Highs Saturday
afternoon are expected to top out in the upper 70s to lower 80s due
to the higher coverage of clouds and precipitation. Highs Tuesday are
then slated to reach the mid to upper 80s! As for low temperatures,
values will generally remain in the lower to mid 60s each night.

&&

.AVIATION...
(12Z TAFS)
Issued at 645 AM CDT Wed May 15 2024

Residual moisture from recent rainfall, plus daytime heating will
result in a more unstable environment, and help bring more chances
of showers and storms late this morning and afternoon. Shower
occurrence should be more over the east so kept KMSL dry, but have
a TEMPO in the afternoon for KHSV possibly being impacted. Showers
should end areawide this evening. Light winds this morning should
become westerly at 5-10kt, then veer to the NW in the late
afternoon and diminish to 5kt for Wed night.

&&

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

$$

NEAR TERM...RSB
SHORT TERM....RSB
LONG TERM....26
AVIATION...RSB