038
FXUS64 KHUN 130917
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
417 AM CDT Sat Jul 13 2024

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

.NEAR TERM...
(Today)
Issued at 417 AM CDT Sat Jul 13 2024

Light WSW flow aloft will continue across the region today, with
the TN Valley located between the southwestern edge of a
subtropical ridge centered over the North Atlantic and a longwave
trough that will progress slowly eastward from the Upper/Mid-MS
Valley into the Great Lakes. At the surface, light NE to calm flow
will persist as a surface ridge remains in place across the
central/southern Appalachians. This, along with narrow dewpoint
depressions, may support the development of light mist/fog in
outlying portions of the CWFA through sunrise, but with scattered
mid-level clouds spreading northeastward we expect coverage to
remain patchy. Abundant insolation later this morning will allow
for development of a deep/well-mixed boundary layer, with
dewpoints expected to mix down into the lower 60s as temps rise
into the m-u 90s (keeping heat indices in the 98-102F range).
Guidance from the 0Z CAMs suggests that intense heating of the
low-levels may result in the development of isolated/high-based
convection this afternoon, which may produce little measurable
rainfall but occasional strong wind gusts given steep lapse rates
between the cloud base and surface.

&&

.SHORT TERM...
(Tonight through Monday night)
Issued at 417 AM CDT Sat Jul 13 2024

Any showers/thunderstorms which manage to develop during peak
heating this afternoon should quickly dissipate around or shortly
after sunset this evening, with lows expected to fall into the
u60s-l70s Sunday morning and a similar coverage of patchy
mist/fog. Little change in the synoptic pattern is anticipated on
Sunday/Sunday night, and with this in mind, we have included a
very low (~15%) chance for development of high-based convection
during the afternoon hours, as temps warm into the m-u 90s once
again. On Monday/Monday night, the position of the low-level ridge
will shift southeastward, inducing a SSW flow across the region
as a deepening surface low tracks east-northeastward along the US-
Canadian border and into southern Ontario. A notable increase in
dewpoints (into the lower 70s) is anticipated as this occurs, and
this may allow afternoon heat index readings to reach the 100-105F
range for many locations. The resultant increase in CAPE may also
support a slightly greater coverage of afternoon showers and
storms, but in the absence of synoptic scale forcing for ascent we
will keep POPs in the 20-30% range. Locally heavy rainfall could
occur in a few locations, as steering currents will collapse due
to development of a broad weakness in the height field over the TN
Valley. Convection should dissipate shortly after sunset Monday
evening, with a warmer and more humid night in store, featuring
lows in the l-m 70s.

&&

.LONG TERM...
(Tuesday through Friday)
Issued at 417 AM CDT Sat Jul 13 2024

The most recent suite of global models suggests that conditions
on Tuesday will be very similar to Monday, with highs in the m-u
90s, heat indices in the 100-105F range and a 20-30% coverage of
afternoon showers and storms (which will likely be slow-moving and
capable of producing heavy rainfall in localized areas). By
Wednesday, however, our region will experience increasing
influence from an amplifying northern stream trough, which is
predicted to spread northeastward from Ontario into the Canadian
Maritime provinces by Thursday night/Friday morning. The cold
front related to this trough is expected to advance southeastward
during the middle portion of the week, with the prefrontal wind
shift axis expected to slowly cross the TN Valley at some point
Wednesday night or Thursday. A higher (60-80%) POP for showers
and thunderstorms is warranted as early as Wednesday afternoon
given the position of the front to our north and strengthening WNW
flow aloft. The greater coverage of convection will likely
continue on Wednesday night/early Thursday morning, before
becoming focused to the south/east of the wind shift (across our
southeastern zones) on Thursday afternoon. Due to some uncertainty
regarding the location of the front before it eventually stalls,
we will maintain a medium chance POP in the southeastern portion
of the CWFA on Thursday night and Friday. Fortunately, a modest
coverage of clouds and precipitation should keep highs in the
u80s-l90s from Wednesday-Friday, lowering the heat risk region-
wide.

&&

.AVIATION...
(06Z TAFS)
Issued at 1244 AM CDT Sat Jul 13 2024

VFR conditions will prevail at the HSV/MSL terminals throughout
the duration of the valid TAF period, with few high-based Cu
beneath a scattered coverage of Ci. Sustained winds will be AOB 5
kts, with a NE flow transitioning to lgt/vrbl later this morning.

&&

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

&&

$$

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