Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 281907

Area Forecast Discussion
National Weather Service Birmingham AL
207 PM CDT Wed Oct 28 2020

Midday Update and 18Z Aviation.


/Updated at 0153 PM CDT Wed Oct 28 2020/

Today through Tomorrow.

An impactful weather event is likely to unfold across Central
Alabama over the next 24 hours as tropical system Zeta quickly moves
across during the overnight hours and into early Thursday morning.
We continue to highlight gusty and damaging winds capable of downing
numerous trees and power lines as the primary threat. Additionally,
there will be a threat for heavy tropical downpours in a short
period of time capable of producing flash flooding, and conditions
may become favorable for a few brief tornadoes in the
east/southeastern portions of Central Alabama.


Zeta is rapidly moving north-northeastward around 20
mph with conditions deteoriorating along the Louisiana coast. The
system will begin to accelerate northeastward in the following
hours as it comes under heavy influence of a strong upper low
moving eastward over the southern Plains. Current intensity
projections, place the system as an low end Category 2 hurricane
at landfall which will occur in the coming hours. Thus far, we
have seen a lull in rainfall east of I-65 with showers ongoing
west of I65 & along the AL/MS state line for much of the day as
moisture continues to surge inland within strong, deep southerly
flow. This evening, rain will become widespread over the area as
the center of Zeta moves into southern Mississippi with just
enough instability for a few rumbles of thunder, but not seeing
enough indications for strong storms this afternoon. The center of
the system will reach our southwestern counties by midnight,
rapidly track towards the Carolinas, and exit around sunrise with
a few light showers lingering on the back end of the low for much
of the morning. Once Zeta and the upper low move away from the
area, dry and cooler air will begin entering from the west by
Thursday night.



The fast motion of Zeta will produce a different scenario
than what we dealt with the previous tropical systems this year.
This system will be able to maintain more of its intensity as it
tracks inland due to the lower residence time over land. From a
messaging stand point, we want to continue emphasizing wind impacts
as the primary threat with most modeling indicating the potential
for tropical storm force winds over much of Central AL with gusts
up to 60 mph (potentially higher in isolated cases). 925mb winds
will be roaring aloft ~80-90kts due to enhancement from the strong
upper low, so a concern is for some of those winds to mix down
(although with a reduction in speed), especially on higher
elevations and ridge tops. Due to this, we have issued a Tropical
Storm Warning for the counties previously highlighted in the Watch
and added Russell & Bullock counties to the Warning due to being
on the southeastern extent of the strong wind field. Most of the
higher winds will be found on the eastern side of circulation.
Based on the current track which takes the center just south of
I-20, we have issued a Wind Advisory for Fayette, Walker, Blount,
and Pickens where winds are not expected to reach Tropical Storm
force, but may increase to 15 to 25 mph with gusts up to 35 mph
for a few hours as the center passes near. Expect numerous trees
to go down across Central AL overnight producing power outages and
obstructions to roadways. The period of highest, damaging winds
will only last around 4 to 5 hours at each location.


The thought process remains the same regarding potential for heavy
tropical downpours, although limited in time due to the fast motion,
an additional 1 to 3 inches will fall in a relatively short period
within the Flash Flood Watch area. Some areas have already been
saturated by preceding rainfall with isolated reports of nuisance
flooding that occurred with rain earlier this morning. Therefore, we
will continue with the Flash Flood Watch until 10 AM tomorrow


Current guidance indicates around 1500-2000 J/kg of SBCAPE spreading
over the area now that dewpoints are in the lower to mid 70s with
surface temps in the lower 80s in our south. As we lose daytime
heating tonight, those values will diminish ahead of the strong
shear zone associated with Zeta. Some instability will linger due to
the strong southerly Gulf inflow, but the availability of enough
unstable air to support sustained updrafts remains in question as
with most tropical situations. A plume of SBCAPE ~500-700 J/kg is
progged to move across our southeastern tier of counties mainly east
of I-65 but south of I-20. Activity in this area may become more
cellular, while values will be lower within the primary rain shield
just east of the circulation. This provides enough concern to expand
the Marginal Risk area a touch more to the north, but will continue
to watch short term trends to see if a risk upgrade will be needed
in the south, mainly near I-85. We continue emphasizing the
potential for a few brief tornadoes if a sustained updraft is able
to develop.


/Updated at 0153 PM CDT Wed Oct 28 2020/

Friday through Wednesday

Friday will be a day of transition across Central Alabama with the
departing upper trough exiting the northeast US and a broad longwave
ridge building across the northwest Gulf of Mexico. Close to home,
we may see some lingering wraparound clouds early in the day but
increasing anticyclonic flow and subsidence should lead to a mostly
clear and relatively cool day across the region.

Upper flow quickly becomes zonal for the weekend as the next system
begins to take shape across the intermountain region and high
plains. Expect a sunny and somewhat cool day on Saturday with
morning lows well down into the 40s (perhaps upper 30s far north)
and highs rebounding nicely to near 70. We may see a few more
mid/high clouds Sunday (particularly by afternoon) ahead of the
aforementioned plains system. Some differences in the timing with
this front (which looks to be on the dry side), so will likely trend
with the blends and lower temps a touch for Sunday.

The coolest morning will be Monday with areas north of I-20 likely
been in the middle to upper 30s. An isolated freezing temperature
not out of the question. A dry and cool pattern to start the
upcoming work week behind the departing dry front with some
moderation by late Tuesday into Wednesday. All in all, other than
some minor temp adjustments for Sunday the current forecast looks in
fine shape.



18Z TAF Discussion.

The latest guidance from the National Hurricane Center continues
advertising Tropical Cyclone Zeta running across the middle of
Central Alabama. Therefore, increased winds and wind gusts can be
expected overnight with some wind shear too.

A combination of conditions over Central Alabama to start off.
MVFR/IFR floating around in the north while some improvement noted
south on latest satellite imagery. Forecast will start of MVFR
ceilings most terminals with some VFR improvements by late
afternoon. The surface high east and Zeta south will keep east to
southeast winds mainly 5-10kts this afternoon. Just after sunset,
winds increase 10 near 15kts with gusts near 30kts starting from the
south and southwest and migrating northeastward this evening. Rain
will be increasing to sustained 20-35kt with some gusts near 50kts
possible. The directions will be solely dependent on the position of
the low and expect chance the the low transits the region. Ceilings
dive back to MVFR during this period. Spotty IFR is also possible.
Thunder does not look to be widespread with this tropical system so
let out any mention at this time.

The storms exits northeast rapidly by 12z as winds become southwest
and lower to 10-20kts. Rain chances also lower as the storm exits
but a few showers may be around the area.




Showers and isolated thunderstorms will begin to move in from the
south, becoming more numerous through this afternoon. Widespread
rain, heavy at times, will move through tonight into early
Thursday morning as tropical system Zeta moves through along with
strong winds. Wind gust up to 60 mph will be possible with the
band of rain as the system moves through. Drier and cooler
conditions will return to the area Thursday night and remain
through the weekend.


Gadsden     69  76  47  60  42 / 100  60  10   0   0
Anniston    69  77  50  62  45 / 100  60  10   0   0
Birmingham  69  75  48  60  44 / 100  50  10   0   0
Tuscaloosa  69  72  48  63  43 / 100  30  10   0   0
Calera      69  74  49  62  44 / 100  50  10   0   0
Auburn      71  78  50  64  48 / 100  50  10   0   0
Montgomery  72  79  50  67  47 /  90  30  10   0   0
Troy        72  81  48  66  47 /  80  20   0   0   0


Tropical Storm Warning for the following counties: Autauga...

Flash Flood Watch through Thursday morning for the following
counties: Autauga...Bibb...Blount...Calhoun...Cherokee...
Shelby...St. Clair...Sumter...Talladega...Tallapoosa...

Wind Advisory from 7 PM this evening to 7 AM CDT Thursday for
the following counties: Blount...Fayette...Pickens...Walker.


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