Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 311950
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
250 PM CDT Tue Mar 31 2020

.UPDATE...
Evening Update.

&&

.SHORT TERM...
/Updated at 0231 PM CDT Tue Mar 31 2020/

Through Tonight.

Surface low has exited Central Alabama and was into west central
Georgia. The associated cold front was near DHN. It appears that
mean relative humidity and lift are not high enough for any
showers south, but a rogue shower may be possible north. Will
leave a slight chance pops for the north the remainder of the
afternoon. Much cooler air was filtering into the region with 40s
north and still around 70 southeast.

Clouds will slowly erode/exit eastward this evening with a good
portion of the area partly cloudy by midnight. Cold air advection
combined with the decreasing clouds will allow temperatures drop
drop into the mid to upper 30s north and east central while most
others areas hit the low to mid 40s.

75

Previous short-term discussion:
/Updated at 1243 PM CDT Tue Mar 31 2020/

Surface low and associated instability has pushed into Georgia
early this afternoon. Therefore, no Central Alabama counties
remain in any watches or warnings. There may be up to 5 locations
where potential tornado damage occurred. Additionally, several
locations from Tuscaloosa due eastward received wind damage.

Drier air will continue filtering into Central Alabama behind the
exiting low. Temperatures will fall in the southeast but will
remain nearly stationary elsewhere. Rain chances will be 20-30 at
best as the overall column loses moisture.

75

Previous short-term discussion:
/Updated at 0923 AM CDT Tue Mar 31 2020/

QLCS currently extends from Randolph County southwestward to
Lowndes County to southeast Mississippi. This is associated with a
potent low-amplitude shortwave trough and associated speed max
moving through. A 1006mb surface low is centered northwest of
Montgomery with a warm front extending southeastward to near
Eufaula, and a cold front extending southwestward behind the QLCS.
A northern line segment moving through our east-central counties
is elevated but damaging wind gusts have still been able to reach
the surface. Note that there is no tornado threat that far north
as it is north of the front, but was included in a tornado watch
to avoid having two different watches out. Further south, activity
is weaker until you reach a bowing segment/commahead structure
approaching southern Lowndes County. This will be the main feature
of interest as it moves eastward across our southeast counties.
Instability is surging ahead of this feature as the warm front
lifts northward, with 6-7F dewpoint increases at Montgomery and
Troy in the past hour. This suggests that SBCAPE is likely higher
ahead of the line than indicated by SPC mesoanalysis. 45-50kts of
0-3km shear oriented perpendicular to the line and 0-1km SRH of
300-400 m2/s2 will support threats of both damaging winds and
embedded tornadoes as the QLCS moves eastward across our southeast
counties though midday. Also will need to watch the potential for
low confidence semi-discrete supercell ahead of the line as cells
are developing west of Dothan.

32/Davis

Previous short-term discussion:
/Updated at 0339 AM CDT Tue Mar 31 2020/

Through Wednesday night.

A strong short-wave trough will progress from the lower MS Valley
this morning through the Southeast and then slide off the Atlantic
Coast by late evening. Latest guidance suggest that severe weather
is still probable across the southern portions of the forecast area.
Looking at specific numbers, look for the system to be capable of
~500-1,200 J/kg MLCAPE and 50-60 kts eff. bulk shear. However, the
system still remains a touch separated with the best shear and best
instability. Through the morning hours, the wind shear near the
boundary lifts quickly eastward ahead of more favorable warm sector
instability. Despite this notion, many forecast soundings do suggest
enough (300 to 400 m2/s2) 0-1 km SRH to foster tornadoes in the
event a stronger updraft can establish in proximity to the shear
maxima near the front. All things considered, tornadoes, damaging
winds, and 1 inch hail all appear likely if ingredients come
together at the right time. Highest forecast confidence in severe
weather resides in the southeast portions of Central Alabama, this
morning into the early afternoon. Nonetheless, the severe forecast
remains on track and no major changes were made over previously
advertised.

Once the system moves out this afternoon, CAA will blast the region
and temperatures will fall into the 40s areawide with even a few
upper 30s in the far northern counties. Last time we were in the 40s
across the region was back on March 8th, so it will feel as quite
shock to the body if you get out and about early Wednesday morning.
Temperatures will warm up into the 60s pretty much area-wide with
a few near 70 degrees in the far south. With generally clear
skies, lows will drop into the 40s again Wednesday night into
Thursday morning.

16

.LONG TERM...
/Updated at 0231 PM CDT Tue Mar 31 2020/

The latest model guidance has general agreement with the ongoing
forecast, therefore, no significant changes were made through the
extended forecast. The main highlights remain a return to above
normal temperatures by the weekend along with relatively small
rain chances.

Thursday through Monday.

On Thursday, a combination of mid-level ridging across the Southeast
and mean 1000-500mb RH`s ~35 percent will continue to favor
stable conditions with afternoon highs in the 70s and periodic
sunshine. Upstream of the ridge, a weak 700mb shortwave will
propagate across the area on Friday. Negative omegas over Central
AL suggest there may be enough lift to produce a few light
showers, but a pocket of dry low-level air may prevent much of it
from reaching the ground, so I kept PoPs around 15 percent across
our west. Meanwhile, an upper-level jet will rotate through the
Northern Rockies and produce an elongated area of surface low
pressure across the Midwest with a weak trailing cold front
extending southward into eastern Texas. A widespread area of high
pressure will develop over the northern Plains and force the front
towards the Lower Mississippi Valley while the surface low
flattens across Ontario and Manitoba. The surface boundary will
provide weak support for isolated showers and partly cloudy skies
throughout the weekend. However, the overall coverage will be
limited by weak forcing due to a lack of upper-level support and a
building ridge across the Deep South. Guidance indicates the
aforementioned ridge will once again develop over the Gulf of
Mexico. Our temperatures will largely be influenced by the
aforementioned ridge and associated height rises. Expect to see
highs in the upper 70s to near 80F as we start the new week.
Towards the end of this period, a shortwave embedded in the ridge
will rotate across the area and may provide better chances for
additional rainfall given the return of moist southerly flow.
Trended PoPs upward, but kept chances around 50% since there are
still some timing difference between models.

86

&&

.AVIATION...
18Z TAF Discussion.

The terminals are all behind the front at this time. Mean moisture
will decrease and pops will be rather low. Most locations will
experience MVFR ceilings between 015-025. During the evening,
ceilings will improve to VFR. As the surface low exits eastward,
winds will pickup north to northwest around 12kts with gusts to
25kts or so. The gusts will diminish by 02-04z.

75


&&

.FIRE WEATHER...

By midweek, high pressure will produce cooler and drier
conditions across Central Alabama with afternoon RH`s ranging from
30 to 45 percent. Winds will be northerly around 5 to 10 mph on
Wednesday, then a slow shift to the south by Saturday. Relatively
low rain chances return to the forecast Friday and beyond.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     37  63  39  71  44 /   0   0   0   0   0
Anniston    40  64  40  72  46 /   0   0   0   0   0
Birmingham  41  66  43  73  49 /   0   0   0   0   0
Tuscaloosa  42  68  43  75  49 /   0   0   0   0   0
Calera      41  66  44  72  49 /   0   0   0   0   0
Auburn      42  66  42  72  48 /   0   0   0   0   0
Montgomery  44  70  44  75  50 /   0   0   0   0   0
Troy        45  70  42  75  50 /   0   0   0   0   0

&&

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

&&

$$


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