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074
FXUS64 KHUN 051521 CCA
AFDHUN

Area Forecast Discussion...CORRECTED
National Weather Service Huntsville AL
1021 AM CDT Sun May 5 2024

...New NEAR TERM...

.NEAR TERM...
-- Changed Discussion --
(Rest of Today)
Issued at 1019 AM CDT Sun May 5 2024

A cold front continues to very slowly move southeast today from
western Kentucky and extreme western Tennessee towards northern
Alabama and southern middle Tennessee. A surface low over
southeastern Oklahoma can be seen in CONUS observations. A pre-
frontal trough axis extends SSE from it ahead of this weak cold
front. These features have produced a cluster of heavy rainfall
and strong thunderstorms extending south along these features from
SE Oklahoma into southern Arkansas and Louisiana.

As an upper level disturbance moves NE along the front this
afternoon into tonight, this area of showers and thunderstorms
will move northeast into NW Alabama during the mid/late afternoon
hours. Not alot of surface based CAPE right now, but some is in
place (~500 J/KG) across the area. However, more instability is
in place aloft based on 12Z soundings anThen expect thicker and
lower cloud cover to build over northwestern Alabama and push east
tonight.d RAP13 forecasts (1000-2000 J/KG). Fog has lifted over
portions of northeastern Alabama. However, some mid/high clouds
remain over that area.

Elsewhere, very highs clouds or sunshine is in place primarily.
This insolation and warm air advection ahead of the front will
help to build additional elevated instability through the early
afternoon hours that could reach around 2500 J/KG.

Clouds west of the I-65 corridor will likely be fairly high
until around 3 PM. This should allow for locations near and west
of the I-65 corridor and south of the Tennessee River to
experience enough insolation to push temperatures into the 80 to
85 degree range in those locations. Upper 70s to lower 80s are
expected elsewhere. Then expect thicker and lower cloud cover to
build over northwestern Alabama and push east tonight.

There is a small window after 3 PM until around 6 PM, where just
enough instability and lower freezing levels could produce a
marginally severe hail threat. Lapse rates are better in the
afternoon as well. Downburst parameters though are not very
impressive, but some gusts to 45 or 55 mph look possible. CAPE
over 1000 J/KG will linger into the evening, lapse rates will not
be as steep. So, expecting this area of showers and thunderstorms
to weaken as it moves further east this evening. Heavy rainfall,
frequent lightning, and gusty winds still look possible, but a
severe threat is not expected during the evening hours.
-- End Changed Discussion --

&&

.SHORT TERM...
(Tonight through Tuesday night)
Issued at 451 AM CDT Sun May 5 2024

Guidance from the 00Z CAMs suggests that the risk for a few
strong-severe thunderstorms may continue for at least an hour or
so beyond sunset as the leading edge of the precipitation regime
(discussed above) spreads further northeastward across the local
area. However, nocturnal cooling of the boundary layer will
contribute to a gradual weakening trend with time over the course
of the evening, with a transition to widespread rain and embedded
thunderstorms anticipated by late this evening. It still appears
as if the warm front will make slow but steady northeastward
progress across the region and into southern KY during the early
morning hours, with widespread precipitation likely coming to an
end from SW-to-NE by 12Z Monday. An airmass of even greater
moisture content will be advected northeastward into the TN Valley
throughout the day as SSW low-level flow strengthens, with
dewpoints in the u60s-l70s supporting redevelopment of scattered
showers and storms in the vicinity of a subtle low-level
streamline confluence axis Monday afternoon even as abundant cloud
cover holds temps in the l-m 80s.

On Monday night, a mid-level ridge will translate eastward across
the forecast area downstream from a nearly stationary deep-layer
cyclone across the northern High Plains. Although this should
result in a lower coverage of nocturnal convection, we will
maintain a low-medium chance POP in the grids due to the
strengthening lower tropospheric warm/moist advection regime in
place across the region. Otherwise, it will be a warm, breezy and
humid night, with lows in the upper 60s for all but a small
portion of northeast AL.

The warm/moist advection regime discussed in the previous
paragraph should yield a gradual increase in the coverage of
mainly afternoon thunderstorms on Tuesday as temps warm into the
mid 80s. However, with little evidence of a well-defined source of
synoptic scale lift, we will keep POPs in the chance range at
this point. Regardless of storm coverage, conditions will become
increasingly favorable for strong-severe thunderstorms beginning
on Tuesday as WSW flow aloft will increase into the 30-40 knot
range in the wake of the departing mid-level ridge. Not only will
this improve vertical wind profiles, but it will also result in
steeper lapse rates aloft, which may yield CAPE in the 2500-3500
J/kg range given surface dewpoints in the lower 70s.

Although the details remain unclear at this point, a greater risk
for severe thunderstorms may materialize late Tuesday night/early
Wednesday morning, originating from convection that should
develop across a broad region from eastern OK/western AR into the
Lower OH Valley Tuesday evening as frontal wave begins to spread
eastward off the southern High Plains and into OK/KS. This
activity may grow into a broken MCS (or perhaps several smaller
but highly organized storm clusters) that would subsequently
propagate southeastward into our region early Wednesday morning.
Should this occur, the combination of shear and instability would
once again support damaging winds and large hail.

&&

.LONG TERM...
(Wednesday through Saturday)
Issued at 451 AM CDT Sun May 5 2024

Overall, there has been very little change in extended range
guidance from the global models this morning, with any nocturnal
storm clusters that survive as far southeastward as the TN Valley
early Wednesday morning expected to dissipate rather quickly by
mid-day. Attention will then refocus to the northwest of our
region, where explosive development of convection is expected to
occur on Wednesday afternoon as the frontal wave (discussed above)
shifts northeastward into MO. One region of potential convective
development will be downstream from the path of the surface low
(from eastern KS into central IL), with another region of
potential development along the trailing cold front extending
southwestward into northeastern TX. It still appears as if this
activity will grow upscale into a rather potent MCS that should
track southeastward into our CWFA early Thursday morning. With
mid-level WSW flow expected to easily be in the 45-50 knot range
at this point atop a southwesterly low-level jet of 30-40 knots,
all severe hazards (including tornadoes) will be possible with
this convective system.

Yet another round of rain and thunderstorms may occur with the
passage of a cold front Thursday night, but at least low-level
shear will be weaker with this final round, and airmass recovery
may not be sufficient to support a risk of strong-severe storms. A
refreshing surge of cooler/drier continental air will spread
southeastward in the wake of the cold front, bringing dewpoints
into the 40s for much of next weekend.

&&

.AVIATION...
(12Z TAFS)
Issued at 648 AM CDT Sun May 5 2024

Areas of BR/FG will continue across the region thru 13-14Z before
dissipating. Recent sfc observations indicate locally dense FG at
MSL, with lighter and more patchy FG invof HSV, and TEMPO groups
for vsby reductions have been included at both terminals early in
the period. VFR conds will return by 14Z, as sct Cu develops
beneath an expanding region of high-lvl clouds. A few SHRA/TSRA
may also develop around mid-day, but initial coverage is expected
to be too sparse for inclusion in the TAFs. A more widespread
coverage of SHRA/TSRA will occur this evening and overnight
(potentially beginning in northwest AL btwn 21-00Z), as a warm
front lifts northeastward across the TN Valley. MVFR cig/vsby
reductions in SHRA/TSRA can be expected thru the end of the TAF
period, as SSW winds increase to 5-10 knots.

&&

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

$$

NEAR TERM...KTW
SHORT TERM....70
LONG TERM....70
AVIATION...70