751
FXUS64 KBMX 172023
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
323 PM CDT Sat Aug 17 2024

...New MESOSCALE UPDATE...

.MESOSCALE UPDATE FOR SEVERE THUNDERSTORMS...
Issued at 304 PM CDT SAT AUG 17 2024

What appears to be a remnant MCV from previous days thunderstorms
was located near the Alabama Tennessee state line. This feature
has enhanced the Bulk Shear which the RAP analysis has at
30-40kts. The latest model guidance suggest that this effective
shear will increase across the northeastern counties this
afternoon. Therefore, there may be some storm organization and
possible elevated rotation with some storms. The north to south
boundary moving into central areas is a surface trough. This will
be a focusing mechanism for additional storms. The environment can
be characterized by MLCAPE values around 3500 and DCAPE values up
to 1200. This would provide conditions favorable for some microburst
or wind damage. It appears that the greatest threat area will be
east of a line from Demopolis to Tuscaloosa to Hayden. The
boundary south is a leftover outflow from yesterdays storms. The
environment is not quite as unstable, but a wet microburst is
certainly possible. This area will soon leave southern areas near
Troy and Eufaula. With all this said, increased rain chances this
afternoon and this evening for the eastern areas.

75

&&

.SHORT TERM...
(This afternoon through Sunday)
Issued at 1254 PM CDT SAT AUG 17 2024

Today`s forecast will be similar to yesterday with a combination of
heat and an isolated risk for a few strong to severe storms. The
strong ridge over the Desert Southwest and the upper-level trough
over the Great Lakes have both begun to drift eastward. The
interaction between the two opposing features is producing deep
northwesterly flow across Central Alabama with the base of the
trough extending south into the Tennessee Valley. There`s been
enough forcing to combine with the moist, unstable airmass across
the region to produce scattered thunderstorms, and the same is
expected this afternoon. Some adjustments were needed to the PoPs
due to a drier and warmer airmass advecting in across the
northwestern portions of the area which will limit both rain chances
and any severe potential for areas generally northwest of I-20. As
such, the highest rain chances will be focused generally along and
south of I-20. Downburst potential remains on the higher end of the
scale, so strong/severe wind gusts will be the primary concern. Some
mixing is occurring in the northwest due to the dry air advection,
but it`s still quite hot out there, and a Heat Advisory will remain
in effect for much of the area through the afternoon.

With the activity dissipating this evening, a surface low will move
across Ontario with an associated cold front drifting southward into
the Tennessee Valley. Much of the 12Z models are quicker with the
southward progression of the front, so it appears that drier air
will arrive across our north sooner than originally anticipated.
PoPs were adjusted to focus the highest rain chances across the
southern half of the area with scattered thunderstorms expected to
develop along the front by the afternoon, generally near and south
of I-20. With higher low-level moisture focused ahead of the front,
storms will develop within a supportive environment for some strong
to severe storms, especially for areas along and south of US HWY 80,
capable of producing strong wind gusts. Like the PoPs, the overall
severe risk shifted south. Temperatures will range from the lower
90s north to upper 90s south, and another Heat Advisory may be
needed for our far southern counties tomorrow. It`s likely dewpoints
will mix into the 60s across the north tomorrow as a dry airmass
arrives behind the front, so believe heat will be less of an impact
there.

86/Martin

&&

.LONG TERM...
(Sunday night through next Friday)
Issued at 143 PM CDT SAT AUG 17 2024

The latest guidance is trending toward a slightly faster movement
of the frontal system than previous runs. Thus, I have trended a
bit quicker shaving pops from NW-SE Sun evening with all pops gone
by 6z/Mon. After that, we get a strong surface ridge developing
over ERN Canada and ERN Conus for the first half of the week with
NRLY flow in the upper levels to help usher in some not as hot
and drier air into the area for the upcoming week. Mid week looks
almost pleasant compared to the temperatures and humidity of
recent. We could even see some mid/upper 50s for morning lows for
portions of the NE 1/3 of C AL for Wed morning, which is not bad
for Aug. The airmass slowly moderates back upward for the 2nd half
of the week, but should be generally rain free for most. We may
see enough moisture to squeeze a few showers out of the airmass in
the SE counties by next weekend.

08

Previous long-term discussion:
(Sunday night through next Friday)
Issued at 206 AM CDT SAT AUG 17 2024

A highly amplified pattern for late August will be in place for much
of the week as strong subtropical ridging remains centered over the
High Plains flanked by troughs along the West Coast and over the
eastern CONUS. A long fetch of deep layer northerly flow will allow
a modified Canadian air mass to reach the Deep South. The dry air
mass will still warm efficiently to allow for highs in the upper 80s
to lower 90s, but humidity will be low with cool overnight lows by
August standards. In fact, many of the typically cooler northern/
northeastern locations should reach the upper 50s by Wednesday
morning. The eastern CONUS trough will lift out by the end of the
week but will leave behind a weakness/possible weak upper low near
the northern Gulf Coast. As high pressure reaches the East Coast
and weak wedging develops, low level flow will become easterly
across Central Alabama, continuing to keep the heat at bay. Some
Atlantic moisture may move back into portions of the area, but the
better moisture looks to remain just south of the forecast area
at this time.

32/Davis

&&

.AVIATION...
(18Z TAFS)
Issued at 1254 PM CDT SAT AUG 17 2024

Scattered convection will develop again this afternoon. TEMPOs
were used at most TAF sites to handle the TSRA. Convection will
diminish from 00-03Z leaving behind some high-level clouds with
VFR returning at all sites. Winds remain from the west to
southwest at 5 to 8 kts.

86/Martin

&&

.FIRE WEATHER...

A few rounds of showers and thunderstorms will move across Central
Alabama through Sunday evening. Minimum relative humidity values
will remain above 40 percent through the weekend. A drier air
mass returns next week behind a surface front, with no rain
expected Monday through Friday and minimum relative humidity
values lower for Monday and from 30 to 40 percent Tuesday onward
through the rest of the week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     70  93  66  88 /  30  20   0   0
Anniston    72  93  67  88 /  50  30  10   0
Birmingham  74  95  69  88 /  30  30  10   0
Tuscaloosa  73  96  70  90 /  30  30  10   0
Calera      74  94  70  88 /  40  30  10   0
Auburn      73  95  70  90 /  40  40  20   0
Montgomery  75  98  71  93 /  30  40  30   0
Troy        73  97  70  91 /  30  40  40   0

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 9 PM CDT this evening for the following
counties: Autauga-Bibb-Blount-Chambers-Chilton-Coosa-Dallas-
Elmore-Fayette-Greene-Hale-Jefferson-Lamar-Lee-Lowndes-Macon-
Marengo-Marion-Montgomery-Perry-Pickens-Shelby-St. Clair-Sumter-
Talladega-Tallapoosa-Tuscaloosa-Walker-Winston.

&&

$$

SHORT TERM...75
LONG TERM....08
AVIATION...86/Martin