Area Forecast Discussion
Issued by NWS Birmingham, AL

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962
FXUS64 KBMX 250557
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1157 PM CST Sat Feb 24 2018

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...

Winds just above the surface will continue to increase through the
evening hours reaching 50-60kts at 850mb just ahead of the front
at 06z. Surface winds appear to remain south to south southwest,
but winds above the surface veer toward the west with time. 0-1
and 0-3 SRH values decrease with time with only areas near the
Mississippi state line appearing favorable by 05z. EHI values also
decrease with time and are limited due to the limited SBCAPE
values. Mid level lapse rates are poor in the 5.5-6 range. At the
same time, the upper level negative tilt trough starts pivoting
northward while the mid level winds also decrease a tad. With all
this said, the potential still exist that a few storms may become
severe, with wind gusts and a tornado possible. The area of
concern is rather limited and highest from Hamilton to Vernon to
Aliceville. Timing still looks good too with the threat lasting a
few hours around midnight northwest and progressing east northeast.
Will reduce the overall risk to Marginal in roughly the same location,
north of I-59.

75

Previous short-term discussion:Through Tonight.

A few clusters of showers have developed across Central Alabama
this afternoon in response to weak upper level energy and
increasing moisture. Cannot rule out isolated thunder with this
activity through the early evening. This is well ahead of the
expected strong to severe storms that will affect the area late
tonight/early Sunday morning. This activity will continue to
develop and push quickly to the north northeast. A few showers
will continue through the evening hours, mainly across the west,
but a general decrease in coverage is expected through midnight.

A cold front is currently approaching Little Rock, with a line of
strong to severe storms pushing eastward across Arkansas. This
activity will continue eastward tonight, and will likely see an
increase in strength this evening to our west as activity crosses
north Mississippi. Not much has changed with the forecast and
expected impacts across Central Alabama. The line of storms will
be weakening as it pushes into northwest portions of the area around
midnight, as upper level support pulls to the north. However, the
airmass will support a low end severe threat along and west of
the I20/59 corridor. Hi-res model guidance shows 0-3km SRH of
300-375 m2/s2 and 0-6km bulk shear of 55-60 kts just ahead of the
line. Damaging winds with any bowing line segments will be the
primary threat, but cannot rule out an isolated tornado.

The line will approach the I20/59 around 4-5AM, and be quickly
weakening, with the severe threat diminishing by 6AM. Moderate to
heavy rainfall will continue as the line continues to push
eastward. The system is looking more progressive, but high
rainfall rates could result in localized urban/nuisance flooding
problems.

14

.LONG TERM...
Sunday through Friday.

High rain chances will continue on Sunday as the front slowly
makes southeastward progress across the heart of the area. A brief
lull in the rain is expected Sunday afternoon, but an upstream
shortwave moving through the Southern Plains should induce a weak
wave of low pressure along the front Sunday night. This will cause
the front to stall, and another round of widespread rain should
occur Sunday night into Monday morning. The front and associated
rain should finally move out by Monday afternoon with a brief dry
period expected on Tuesday between weather systems.

Models are in worse agreement than they were 24 hours regarding
the evolution of the upper-air pattern for the middle and latter
part of the week. As a trough ejects eastward from the Southwest
CONUS, a surging warm front should cause increasing rain chances
Tuesday night into Wednesday. At some point between early Thursday
morning and late Thursday night, a frontal passage is expected
along with the potential for showers and storms. Models are not
showing much instability due to somewhat warm temperatures aloft,
but this seems somewhat unreasonable with dewpoints in the mid to
upper 60s underneath nearly westerly (typically cooler) 500mb
flow. The threat for severe storms will be watched closely since
models indicate very strong wind fields overspreading the region.

87/Grantham


&&

.AVIATION...
06Z TAF Discussion.

Slow moving front approaching Central Alabama. The trend from the
previous forecast was generally accepted. The front will move
slowly east and south and reach MGM/TOI near daybreak. Ahead of
the front, southerly winds remain breezy with some lower clouds
developing south and advecting northward. So northern terminals
will experience a pinch between the moisture advection and the
front for reduced ceilings. Thunder seems much less likely and
have removed its mention for the time being. Overall, a
predominant MVFR ceiling and light rain forecast.

Winds will be southerly 10-20kts ahead of the front. As the front
moves in, winds will swing initially west and then north
northwest around 10kts. The northern sites will experience the
veering winds behind the front that eventually make it back around
to the east southeast by periods end. A wave will move along the
front and pull the frontt back northward with more rain Sunday
night.

75

&&

.FIRE WEATHER...

High RH values persist through the beginning of the week. Isolated
showers with a slight chance of a thunderstorm will be possible
through this afternoon. A decrease in coverage is expected after
sunset, with isolated showers mainly across the west this evening.
Patchy fog is possible across the southern third of our forecast
area late tonight through early tomorrow morning. A line of
storms will move into the northwest around midnight tonight, and
move across the area through the day tomorrow. Although storms
will weaken, widespread rainfall can be expected tomorrow, with
increased rain chances continuing through much of Monday.

Drier conditions Monday night and Tuesday will be followed by
high rain chances Tuesday night through Thursday. There are no
fire weather concerns.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     60  63  53  67  40 /  90  90 100  20   0
Anniston    63  65  55  68  43 /  40  90 100  30   0
Birmingham  59  62  54  69  44 /  90  90 100  20   0
Tuscaloosa  60  63  54  71  45 / 100  80 100  10   0
Calera      61  62  55  69  45 /  70  90 100  20   0
Auburn      65  70  58  69  48 /  20  80  90  70   0
Montgomery  68  70  60  71  48 /  20  80  90  60   0
Troy        68  74  62  72  48 /  20  80  80  80   0

&&

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

&&

$$



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