Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 270019
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
719 PM CDT Mon Oct 26 2020

.UPDATE...
For 00Z Aviation.

&&

.SHORT TERM...
/Updated at 141 PM CDT Mon Oct 26 2020/
Through Tuesday.

A subtropical ridge is moving across the eastern Gulf of Mexico
into the western Atlantic and is producing dry, southwesterly mid-
level winds across the region. At the surface, high pressure is
expanding from the Midwest into the Ohio and Tennessee Valleys
producing a wedging effect along the Appalachians and light
northeasterly winds into Central AL. An associated wedge front is
situated from Central Tennessee into northwestern AL and will
linger in this area through tomorrow. There is a shallow layer of
moisture near 850mb which is producing a layer of low clouds over
much of the Deep South. There is a small chance for light drizzle
and areas of patchy fog, mainly across the east/northeast, early
tomorrow morning, but as we head into the afternoon, we really
begin to see deeper moisture and clouds surging northward ahead of
tropical system Zeta. Some scattered showers and a few
thunderstorms showers may reach our southern counties late
tomorrow afternoon with chances ramping up Tuesday night. Highs
will be in the mid/upper 70s today, but a few degrees warmer
tomorrow due to the reintroduction of southerly flow as the ridge
further establishes over the western Atlantic.

86

.LONG TERM...
/Updated at 141 PM CDT Mon Oct 26 2020/
Wednesday through Sunday.

Strong thermal advection along with a well defined band of low/mid
level UVM/ascent will set the stage for widespread showers and a few
embedded thunderstorms racing from south to north Tuesday night into
early Wednesday. With very high/tropical PWATS, these will be rather
efficient rainfall producers despite their rather fast movement.
We may see a lull in convection during at least a portion of the
day Wednesday as the modified warm sector overspreads central
Alabama. The combination of warm advection and likely approaching
bands from Zeta should lead to at least to scattered to perhaps
numerous showers after 21z.

Consensus of the guidance, along with the official NHC track, now
takes Zeta as a Category One Hurricane into Southeast Louisiana
Wednesday night and into central Alabama as perhaps a weak tropical
storm by late Wednesday night/early Thursday. Given the current
expected timing, the primary impacts likely would be heavy rainfall
and gusty to locally strong winds. If the current forecast track
were to verify the highest likelihood of winds 30 knots of higher
(and/or gusts exceeding 35 knots) would be along and south of the I-
59 corridor after midnight Wednesday night through midday Thursday.
Storm total precip amounts would also likely be maximized as well
between the I-59 and I-85 corridors 2-4 inch amounts (and perhaps
locally higher) would be possible.

Some question remain about severe weather/tornado potential for late
Wednesday night into early Thursday. Timing in not greatly
supportive given limited surface heating during diurnal minimal.
However, forecast proximity soundings from the NAM show a corridor
of low (but sufficient) CAPE on the order of 200-300 J/kg along with
strongly looped hodographs in the northeast/east quadrant of the
cyclone. In house experimental guidance produces a 30% probability
of tornadoes in our far southeast counties given the
current/expected parameter space.

Dry slot on the backside of the departing tropical system will push
through quickly by late Thursday into Thursday evening. However, the
region will remain under the influence of cyclonic flow due to an
approaching upper low across the Mid Mississippi Valley. Will trend
a bit more pessimistic with cloud cover, particulary north of I-20.
Otherwise, a dry and fairly cool but comfortable weekend will be in
store for the region as a broad ridge builds across the southeast
US/Deep South.

15/CBD

&&

.AVIATION...
00Z TAF Discussion.

All TAFs are currently VFR with SCT-BKN decks from 3500-6000ft.
Looking for another night of MVFR cigs with some IFR as well. The
exception should be TCL which looks to hold off until after
sunrise for some MVFR stratus with moving in/developing from GA
tonight into morning. Some drizzle is also possible in the NE
portions of C AL which may affect ASN/ANB in the late night/pre-
dawn hours. SHRA move in from the south in the afternoon on
Tuesday. TS chances are too low to mention in terminals at this
time.

08

&&

.FIRE WEATHER...

Mostly cloudy skies will persist through the remainder of the
afternoon and into the evening hours. Another round of low
clouds/fog/drizzle will likely develop overnight through Tuesday
morning, mainly across the east and northeast counties. More
substantial rainfall will begin to moves into southern Alabama late
Tuesday afternoon/Tuesday night in advance of the tropical system in
the Gulf of Mexico. Widespread rains will be possible Wednesday into
Wednesday night. Drier and cooler conditions will return to the area
Thursday night and remain through the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     62  79  65  75  67 /  20  20  60  70  90
Anniston    63  80  68  76  69 /  20  20  60  60  90
Birmingham  63  81  67  76  69 /  10  20  70  70  90
Tuscaloosa  61  82  69  78  69 /  10  30  70  80  80
Calera      63  81  69  76  70 /  10  20  60  70  80
Auburn      66  79  69  75  70 /  10  30  50  50  70
Montgomery  67  83  72  79  72 /  10  40  60  70  80
Troy        67  82  70  79  72 /  10  50  60  60  70

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

$$



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