Area Forecast Discussion
Issued by NWS Birmingham, AL

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319
FXUS64 KBMX 251257
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
757 AM CDT Sat Mar 25 2017

.UPDATE...
MESOSCALE UPDATE.

&&

.DISCUSSION...

Upper level low pressure was analyzed across southeast Kansas with a
surface low analyzed across southeast Missouri. Two pre-frontal
disturbances are inferred from regional NEXRAD mosaics with the
first moving across our western and into our central counties,
resulting in light shower activity with the second and more robust
line of showers and storms extending from southwest Tennessee
through north-central Mississippi and into west-central Louisiana.

A review of global model output indicates most models position the
upper level low across eastern Oklahoma compared to the current
position based upon satellite. Models take the upper level low into
central Missouri toward 00z tonight, however, attempting to correct
the misplacement of the current position, the upper low may be even
further north into northeast Missouri by 00z tonight. Good news
is with the upper level support and dynamics pulling northeast
tonight will result in decreasing severe potential this evening
and overnight.

Surface observations indicate temperatures range from the mid
to upper 50`s southeast to the low 60`s west-central with highest
temperatures across our northwest counties. The surface dew point
field shows more of a spread across the CWA this morning with
readings in the low 50`s east to the mid to upper 50`s west with
highest values southwest. Surface wind fields remain out of the
southeast throughout the CWA this morning with speeds ranging from 3-
8 knots east to a range of 2-10 knots west. Winds remain breezy at
times with gusts generally from 3-5 knots east to the range of 9-
14 knots west. The low level advection pattern will support
continued increases in temperature and dew point values through
early afternoon.

The KBMX 12Z sounding indicates a reduced layer of dry air compared
to last evening`s 00Z sounding roughly between 450mb and 850mb. The
light showers moving east across the CWA are encountering this drier
layer and this is keeping rainfall amounts on the light side. Expect
this layer to continue to moisten over the next few hours as the
line of storms approach from the west. Weak subsidence inversions in
the lower levels are limiting instability, higher temperatures and
dew points will be required along with steepening lapse rates aloft
to realize additional instability. Low level shear is impressive
with 0-1 km SRH values of 314 m2/s2 and 0-3 km SRH of347 m2/s2  but
bulk shear values are generally less than 40 knots and the absence
of a low level jet along with marginal upper jet winds (not much
more than 50 kts) are providing more marginal dynamical support.

The main concern will be with the line of showers and thunderstorms
presently pushing through west-central Mississippi. While some
airmass recovery is expected after this line moves east across our
area, the level of instability obtained does not appear to be
sufficient to support an organized severe weather threat. With that
said, upper level forcing will still remain sufficient to encourage
the development of shower and thunderstorm activity as the surface
front nears from the west this afternoon and evening.

05

&&

.AVIATION...
12Z TAF Discussion.

Shifting all eyes to the west as we watch a storm system slide
toward the area. This system will affect all terminals today, tracking
west to east across the state. We should begin with spotty/VCSH
showers before a line of thunderstorms moves through. Sub-VFR
conditions are expected with the convection (visibility and/or
ceilings). Given the surface front hanging upstream, areas of
lingering showers/storms are possible through 06Z. There could be
some redevelopment along the front overnight and will need to
monitor that to see if any inclusion of showers and storms will
need to be added then.

16

&&

.FIRE WEATHER...

Low level moisture will gradually increases today from west to east
as a line of strong to possibly severe storms moves across central
Alabama during the day. Rain chances will continue tonight and into
Sunday due to a moist southwest flow holding over the area. An
active weather pattern will continue into next week. Critical fire
weather conditions are not expected through the next 7 days.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     78  59  75  58  77 /  90  90  60  20  60
Anniston    77  59  76  59  78 /  80  90  50  20  60
Birmingham  78  60  78  60  79 /  90  80  50  20  60
Tuscaloosa  74  60  81  60  79 /  90  70  40  10  60
Calera      77  59  78  61  78 /  90  80  50  10  60
Auburn      79  58  77  59  78 /  60  70  40  10  40
Montgomery  79  60  83  61  81 /  90  90  40  10  40
Troy        79  60  81  61  82 /  60  80  40  10  30

&&

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

&&

$$



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