-- Discussion containing changed information from previous version are highlighted. --
636
FXUS64 KHUN 200929
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
429 AM CDT Fri Sep 20 2024

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

.NEAR TERM...
-- Changed Discussion --
(Today)
Issued at 429 AM CDT Fri Sep 20 2024

North-northwest flow aloft of 15-20 knots continues across the TN
Valley this morning, to the north/east of a 500-mb subtropical
high centered across northern Mexico and adjacent portions of
south TX. In the low-levels, light/variable-calm flow exists
withing a broad region of high pressure extending from New England
southwestward into the northwestern Gulf Coast. Conditions will
remain favorable for radiational cooling until sunrise, with
development of patchy fog expected across much of the forecast
area as temps fall into the l-m 60s.

Over the course of the day, there will be essentially no change
in the synoptic pattern across our forecast area, with mostly
sunny skies this afternoon contributing to a hot afternoon
featuring highs in the l-m 90s. Although a brief shower may occur
across the higher terrain of northeast AL, POPs in this region
remain very low (10% or less).
-- End Changed Discussion --

&&

.SHORT TERM...
-- Changed Discussion --
(Tonight through Sunday night)
Issued at 429 AM CDT Fri Sep 20 2024

Short term model consensus suggests very little (if any) change
in the general weather regime across the TN Valley through the
upcoming weekend, as the subtropical ridge (noted above) will
remain the dominant weather feature for our region. A gradual
increase in high-level cloudiness within NW flow aloft will begin
tonight, which will result in warmer overnight lows (m-u 60s) but
should also reduce the overall coverage of fog on Saturday
morning. During the day on Saturday, a weakening cold front will
shift southeastward across Middle TN as the parent mid-level wave
digs southeastward over the eastern Great Lakes. Although a few
showers and thunderstorms may occur as the wind shift axis enters
the northern portion of the forecast area on Saturday
afternoon/evening, POPs at this point remain in the 5-10% range.
With abundant sunshine during the afternoon hours, highs will once
again reach the l-m 90s on Saturday.

Light SW return flow in the low-levels is predicted to begin on
Saturday night and will persist through Sunday night as as upper
low lifting northeastward from the Four Corners region into the MO
Valley induces development of a frontal wave that will shift
northeastward from the southern High Plains into southeastern MO
by Monday morning. Boundary layer moisture advection will
strengthen in this regime, and (combined with a decent coverage of
high clouds) will result in lows in the u60s-l70s for many
locations on Sunday/Monday mornings, further reducing the risk for
fog. Highs will once again reach the l-m 90s on Sunday, with a
few showers and storms possible north of the TN River as the
initial front begins to return northward, but POPs remain 10-15%.
-- End Changed Discussion --

&&

.LONG TERM...
-- Changed Discussion --
(Monday through Thursday)
Issued at 429 AM CDT Fri Sep 20 2024

Extended range guidance from the most recent suite of global
models suggests that an upper low (initially across the MO Valley)
will open into a trough as it shifts northeastward into the Lower
Great Lakes by Tuesday. The surface frontal wave will move in
conjunction with the trough, with a trailing cold front predicted
to enter the region at some point Tuesday afternoon. Thus,
although POPs will remain fairly low across the area on Monday, we
do anticipate a general increase in the spatial coverage of
showers and thunderstorms beginning in the northwest early Tuesday
morning and continuing for the entire region during the day.
Although forecast soundings depict a general increase in
instability during this timeframe (due to higher surface
dewpoints), profiles will remain dry aloft, and for this reason we
will keep rain chances in the low-medium (20-30%) chance range.

Forecast uncertainty increases considerably by Wednesday and
Thursday, as the global models offer vastly differing solutions
regarding how far south/east the cold front will track before
stalling in response to the development of a cutoff upper low over
the Mid-MS Valley. If a deeper cool/dry airmass manages to
penetrate through the entire CWFA, then we will remain in a dry
weather pattern during the mid-week period. However, current
thinking is that the front will stall in our region (or perhaps to
our immediate south/east), which could support the development of
widespread anafrontal precipitation across our region. We have
indicated a low POP to account for this level of uncertainty, but
these values will likely be adjusted over the coming days. Temps
will also be impacted by the ultimate outcome of the forecast, but
at this point we have indicated highs falling back into the l-m
80s.
-- End Changed Discussion --

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 1202 AM CDT Fri Sep 20 2024

Light fog may develop early this morning, promoting a brief
period of MVFR to localized IFR conditions around daybreak.
Thereafter, VFR conditions will return through the remainder of
the period.
-- End Changed Discussion --

&&

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

&&

$$

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