421
FXUS64 KHUN 221147
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
647 AM CDT Sun Sep 22 2024

...New AVIATION...

.NEAR TERM...
(Today)
Issued at 438 AM CDT Sun Sep 22 2024

Regional weather conditions across the TN Valley this morning
continue to be dominated by a mid-level subtropical high
positioned across southeastern TX and a surface ridge that extends
southwestward into the northwest Gulf Coast from a parent
anticyclone across eastern Newfoundland. To the northwest of the
local area, a subtle frontal wave is likely to evolve across
southeastern MO and will focus early morning convection from the
Mid-MS Valley into the Lake Michigan vicinity. Thus, we will
maintain a dry forecast through sunrise, with patchy fog possible
in a few locations given calm winds and narrow dewpoint
depressions with temps in the m-u 60s.

Over the course of the day, the frontal wave is predicted to
develop northeastward into eastern IL/western IN, which will
induce a light SW return flow across the TN Valley. However, this
may impeded to some extent by the northeastward movement of an
upper low from the Four Corners region into western portions of
NE/KS and subsequent development of a secondary frontal wave that
will lift northeastward into the Red River Valley by late
afternoon. Strong diurnal warming of the moist boundary layer will
will result in CAPE in the 500-1000 J/kg range this afternoon as
temps warm into the l-m 90s, and thus we expect a few afternoon
showers and thunderstorms with highest POPs north of the TN River
(and especially in areas of enhanced orographic lift across
northeast AL/southern Middle TN). As the subtropical ridge to our
southwest begins to weaken today, mid-level winds will back from
NW to WNW but remain in the 15-25 knot range. Thus, we expect
convective cells to gradually spread east-southeastward with time.

&&

.SHORT TERM...
(Tonight through Tuesday night)
Issued at 438 AM CDT Sun Sep 22 2024

The subtropical ridge (discussed above) will shift eastward along
the central Gulf Coast from tonight-Monday as an upper low
(initially across the central High Plains) begins to open into a
trough and eject northeastward into the MO Valley. As this occurs,
winds aloft will back further to WSW and increase to 25-35 knots,
with a notable mid-level vort max predicted to bypass our region
to the north on Monday. At the surface, the secondary frontal wave
is predicted to develop northeastward into western AR tonight and
should reach northeastern AR by late Monday afternoon. Lingering
showers and thunderstorms from this afternoon should dissipate
across the northeast corner of the CWFA quickly after sunset, with
another warm night featuring lows in the m60s-l70s and a patchy
coverage of fog. Gradual moistening and destabilization of the
boundary layer will continue on Monday as temps warm into the l-m
90s, with redevelopment of showers and thunderstorms expected to
occur by late morning. However, this activity will once again
remain most concentrated across the northern half of the forecast
area, where mid-level WSW flow will be stronger and the influence
of the subtropical ridge will be weaker.

During the timeframe from Monday night-Tuesday night, the mid-
level trough (initially across the MO Valley) will acquire a sharp
negative tilt and accelerate northeastward ahead of another
developing cutoff upper low that will drop southward through the
central Plains during the mid-week period. A surface low across
northeastern AR will lift north-northeastward into southern IL
Monday night in response to this, with a narrow/broken line of
convection likely evolve along the cold front trailing south-
southwestward into eastern AR/western TN. Although a subtle
increase in the southwesterly low-level jet (to 15-25 knots) may
force the development of a few nocturnal showers and storms in our
region ahead of this feature early Tuesday morning, chances for
convection will not increase in our region until the frontal wind
shift axis enters Tuesday afternoon. With CAPE likely to reach the
1000-2000 J/kg range by mid-day as temps warm into the m-u 80s, a
few strong-severe storms will be possible given sufficient deep-
layer shear induced by mid-level southwesterly winds in the 35-45
knot range. The front will in all likelihood stall across our
region Tuesday night/Wednesday morning in response to the
developing cutoff low to our northwest, leading to a continuation
of medium chance POPs overnight.

&&

.LONG TERM...
(Wednesday through Saturday)
Issued at 438 AM CDT Sun Sep 22 2024

Latest extended range guidance from the global models indicates
that the remnant frontal boundary/low-level convergence axis will
remain positioned across our region on Wednesday/Wednesday night,
resulting in a continuation of medium chances for showers and
thunderstorms. Due primarily to clouds and precipitation, highs on
Wednesday should fall back into the u70s-l80s, with lows on
Thursday morning in the l-m 60s. Beyond this point in the
forecast, uncertainty increases considerably due to the potential
development of a tropical cyclone in the Gulf of Mexico. Aside
from the fact that the system has not even begun to develop, the
cyclone`s eventual path will likely be dictated by both the cutoff
low to our west and a subtropical high off the southeastern
Atlantic Coast, and the models currently offer a vast array of
solutions on where these features will be located and when. Thus,
we have deviated very little from blended guidance and indicated a
gradual decreasing trend in POPs through the end of the week,
with full acknowledgement that they could be increased
significantly or pulled out altogether in future forecast updates.
High temperatures will also be dependent on the amount of cloud
cover and precipitation in our region but should generally remain
in the u70s-l80s through Saturday.

&&

.AVIATION...
(12Z TAFS)
Issued at 647 AM CDT Sun Sep 22 2024

Current IR satellite data confirms the development of a sct-bkn
As layer across the region early this morning, which should
transition into a healthy Cu field (featuring VFR cigs btwn 5-10
kft) by 16Z. A few SHRA/TSRA will be possible this aftn, but this
activity appears as if it will be most concentrated across the
higher terrain to the N/E of HSV and we will not mention in the
TAFs attm. Few-sct mid-lvl clouds will persist overnight, with
another limited coverage of nocturnal BR/FG anticipated btwn 9-13Z
on Monday. Light SSE sfc winds will back to WSW and increase to
5-10 kts later this morning before subsiding once again this
evening.

&&

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

&&

$$

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