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482
FXUS64 KHUN 281902
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
202 PM CDT Fri Jun 28 2024

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

.NEAR TERM...
-- Changed Discussion --
(Remainder of today and tonight)
Issued at 202 PM CDT Fri Jun 28 2024

Light but moist SSE flow in the low-levels will continue across
the TN Valley for the remainder of the afternoon, with this regime
induced by a northern stream shortwave trough digging
southeastward across the northern High Plains and related surface
low that will shift from the eastern Dakotas into MN. Aloft, the
local area remains positioned beneath a narrow/flat subtropical
ridge extending from northern Mexico east-northeastward off the
Mid-Atlantic coast. Although deep-layer forcing for ascent will be
rather weak (especially given subtle height rises in the mid-
levels), moisture transport and weak lift in the lower troposphere
will support development of low-topped showers and perhaps a few
thunderstorms that should spread slowly northward with time in
conjunction with light southerly steering flow.

With this weak convection also forced in part by diurnal warming
of the boundary layer, we expect to see a sharp decrease in
coverage shortly after sunset. However, during the early morning
hours, low-level flow will begin to veer to SW ahead of a cold
front dropping southeastward into the Mid-MS Valley, and this may
provide sufficient convergence to initiate the development of
additional showers within the very moist airmass in place over our
region. Regardless of precipitation, low stratus clouds are
expected to develop across the local area, and will provide for a
warm/humid night, with lows in the l-m 70s.
-- End Changed Discussion --

&&

.SHORT TERM...
-- Changed Discussion --
(Saturday through Sunday night)
Issued at 202 PM CDT Fri Jun 28 2024

Latest model consensus suggests that a zone of subtle low-level
streamline confluence (likely related to the transition to
southwesterly flow ahead of an approaching cold front) will
continue to serve as a focusing mechanism for the development of
showers and thunderstorms through much of the day on Saturday.
Although there is uncertainty regarding the precise location of
this boundary, we have placed our highest POPs across the
southeastern portion of the CWFA given indications of
southwesterly steering flow in the lower/middle troposphere that
will support east- northeastward movement of showers and
thunderstorms with time. With indications of a typical early
summer shear and thermodynamic profile (featuring MLCAPE in the
1500-2500 J/kg range), strong outflow winds (perhaps up to 40-50
MPH) and frequent lightning will be concerns with the strongest
storms. Although morning low stratus clouds and afternoon
convective debris clouds will have an impact on high temps, heat
indices will still manage to reach 98-102F for most of the valley
(and perhaps close to 105F in larger urban locations).

Present indications are that afternoon convection will diminish
quickly once again around sunset, providing for a warm/humid
evening and perhaps early development of fog across portions of
northeast AL that experience wetting rains during the afternoon.
By early Sunday morning, we will be monitoring the progress of
thunderstorms to our northwest, which should initiate along a cold
front dropping into southeastern KS/southern MO late in the
afternoon. Most of the 12Z CAMs and global models indicate that
this convection may expand in coverage and spread southeastward
with time early Sunday morning, perhaps sending an outflow
boundary southeastward into the TN Valley after Midnight. Should
this occur, redevelopment of a few showers and thunderstorms may
occur during the early morning hours. However, the most likely
scenario is for redevelopment of convection to occur on Sunday
afternoon as the actual synoptic cold front shifts southward into
the local area. Although NW flow aloft will increase a bit by
Sunday as the subtropical ridge begins to amplify across the
southern Plains, shear will remain fairly weak but may be
sufficient for a few strong storms given comparable levels of
instability. Showers and thunderstorms should end from NW-to-SE
Sunday evening with frontal passage, and a drier airmass will
begin to spread into the region by Monday morning providing for
cooler lows in the m-u 60s.
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&&

.LONG TERM...
-- Changed Discussion --
(Monday through Thursday)
Issued at 1258 AM CDT Fri Jun 28 2024

Excessive heat will be the main story going into the latter half
of the forecast period. A large upper ridge axis over the Plains
states will begin to gradually move eastward heading into the new
work week. At the sfc, high pressure will build eastward across
the upper Midwest/Great Lakes regions in the wake of a departing
cold front to the south. Lingering showers/tstms will also taper
off to the south providing for a dry forecast at least thru Mon
night. The passing frontal boundary should also translate into
slightly cooler temps, with lows Sun night in the upper 60s/near
70F, before temps rebound into the upper 80s/near 90F later in the
day Mon.

The upper ridge pattern will then become entrenched across the
Gulf Coast region starting Tue, with afternoon temps climbing into
the mid/perhaps upper 90s. High pressure moving into the
northern/mid Atlantic Basin will also result in SFC flow veering
to the SE/S, thereby ushering moisture back into the central TN
Valley. Max heat indices likewise may climb near/above 105F,
especially on July 4th. Subsequently, Heat Advisories may be
needed Wed and Thu. In addition to the excessive heat, diurnally
driven showers/tstms (around a 20-40% chc) are possible starting
Tue. Any convective activity will likely be pulse driven given
ample buoyant energy, but little in the way of deep layer shear.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 1225 PM CDT Fri Jun 28 2024

VFR conditions are expected for the majority of the period at
KHSV and KMSL terminals over the next 24 hours, however there is a
slight chance (10-15%) of SHRA today, with SHRA chances
increasing after 12Z Saturday. A narrow belt of increasingly
agitated cu clouds can be observed in satellite imagery along
portions of W AL, with this line stretching towards the KMSL area.
Regional radars indicate lgt/mdt SHRA, but none near KMSL attm.
Confidence is too low to include in TAF, but warranted a mention
here. Otherwise, convection will be increasing tomorrow from the
SE, with better chances of SHRA/TSRA at KHSV, especially after
~14Z.
-- End Changed Discussion --

&&

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

&&

$$

NEAR TERM...70/DD
SHORT TERM...70/DD
LONG TERM...09
AVIATION...KDW