971
FXUS64 KHUN 150953
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
453 AM CDT Mon Jul 15 2024

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

.NEAR TERM...
(Today)
Issued at 453 AM CDT Mon Jul 15 2024

Light southwesterly return flow in the low-levels has begun to
develop across the TN Valley early this morning, and will
strengthen over the course of the day as the region will remain to
the north of an elongated Bermuda ridge extending through the
Gulf of Mexico and to the south of a cold front attached to a
deepening area of low pressure over northern Quebec. Aloft, a
light WSW flow regime will persist along the northwestern rim of a
subtropical high cell centered off the Atlantic Coast of FL. The
combination of deep-layer warm/moist advection in this regime,
coupled with weak lift downstream from a shortwave trough
(currently across the Mid-South region) has resulted in broken-
overcast altostratus clouds across most of the CWFA, as well as a
few light showers. We have included a low (~15%) POP in the grids
through sunrise to account for returns noted in radar data at the
present time, and also indicated patchy fog in a few of our
northeastern AL valleys.

A consensus of near term model data suggests that the mid-level
cloud deck will gradually dissipate over the course of the
morning, allowing the boundary layer to rapidly destabilize as
dewpoints should remain in the u60s-l70s with impacts from mixing
offset by SW flow and moisture advection in the low-levels. With
this in mind, the approach of the shortwave disturbance to our
west will likely contribute to a greater spatial coverage of both
showers and thunderstorms this afternoon compared to previous days
and POPs range from ~20% (NW) to ~50% (SE). HREF guidance
suggests that MLCAPE will reach 1500-2000 J/kg (perhaps a bit
higher in some locations), with gusty outflow winds (up to 40-50
MPH) and frequent lightning possible in the strongest activity.
Otherwise, weak steering currents will yield slow storm motions,
creating a risk for locally heavy rainfall given PWAT values in
the 1.8-2" range. Highs should be able to briefly reach the m-u
90s in valley locations prior to the development of convection,
with heat index readings of 100-105F (highest in large urban
areas).

&&

.SHORT TERM...
(Tonight through Wednesday night)
Issued at 453 AM CDT Mon Jul 15 2024

Afternoon shower and thunderstorm activity will begin to diminish
in both coverage and intensity around sunset this evening, but
with some large scale ascent still being provided by the shortwave
disturbance (noted above), convection may not dissipate as
quickly as in previous nights. Thus, we will leave a low- medium
POP in the grids this evening, ranging from 20% (NW) to 40% (SE).
Patchy fog may develop in a few areas late this evening
(especially those locations that experience rainfall), with a
warm/muggy night in store featuring lows in the l-m 70s. Little
change in the weather pattern is anticipated on Tuesday, although
the departure of the shortwave trough to the east may result in
weak subsidence and drying aloft, which could limit the coverage
of afternoon showers/storms and result in temps a degree or two
higher than Monday. If this trend continues, then a Heat Advisory
may be warranted for portions of the local CWFA.

It still appears as if the synoptic pattern across our region
will begin to change on Tuesday night, as a northern stream
shortwave trough digging into the Upper MS Valley will induce an
increase in SW flow aloft. Although the slow-moving cold front
related to this trough will remain well to the north of the region
(in the OH Valley), strengthening deep-layer southwesterly flow
may foster the development of nocturnal thunderstorms over
portions of the TN Valley (especially during the early morning
hours on Wednesday). Latest model solutions indicate that the
slow-moving cold front will drift southward into the I-40 corridor
of TN by Wednesday afternoon, with the greatest concentration of
convection throughout the day likely to remain to our north.
However, there is some concern that a prefrontal trough may
initiate showers and storms in our region by late Wednesday
morning, and we have maintained suggested POPs of 55-65% during
the afternoon hours. Due to the potential for morning clouds and
early development of convection, highs should only reach the
u80s-l90s, reducing the overall Heat Risk. A fairly widespread
coverage of showers and thunderstorms will continue on Wednesday
evening as the cold front makes its way southward into our region.

&&

.LONG TERM...
(Thursday through Sunday)
Issued at 453 AM CDT Mon Jul 15 2024

Extended range guidance from the global models still suggests
that a slightly cooler and wetter weather pattern is in store for
the local area beginning later this week and extending into the
weekend. This will take shape as a mid/upper-level longwave trough
axis becomes established to the west of the local area, inducing
modest (20-30 knot) SW flow atop a stalled frontal boundary that
may reside across the CWFA for much of the period. With the
potential for several smaller scale disturbances to track across
the region in the SW flow aloft and PWAT values predicted to be
near or slightly in excess of 2", several rounds of showers and
storms will occur both during the day and at night. Locally heavy
rainfall may eventually become a concern (especially across the
southeastern portion of the forecast area, where the impacts of
drier continental air will not be felt). Fortunately, the
combination of clouds and precipitation will yield cooler
temperatures in the m-u 80s (afternoon) and u60s-l70s (overnight).

&&

.AVIATION...
(06Z TAFS)
Issued at 1258 AM CDT Mon Jul 15 2024

Recent trends in IR satellite data suggest that a broken mid-
level As layer will persist across the region for much of the
early morning period, providing VFR cigs arnd 15 kft atop few-sct
Cu. Although a few light SHRA will be possible to the east of a
slow-moving disturbance across the Mid-South region, we have not
included VCSH due to limited coverage of this activity. Patchy
BR/FG may also develop btwn 8-13Z in valleys and near large bodies
of water, but we have also elected to not include this in the
official TAFs. There are indications that the As layer will begin
to erode later this morning, permitting rapid destabilization of
the boundary layer and development of sct aftn SHRA/TSRA that
should dissipate within a few hours of sunset this evening. This
activity could impact the terminals btwn 20-02Z, when PROB30
groups for vsby reductions have been included. Prevailing sfc
winds will remain from the SW at speeds of 5-10 kts.

&&

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

&&

$$

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