Area Forecast Discussion
Issued by NWS Birmingham, AL

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369
FXUS64 KBMX 251729
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1229 PM CDT Sat Mar 25 2017

.UPDATE...
For 18Z Aviation.

&&

.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 of 347 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...
18Z TAF Discussion.

Line of TSRA with occasional TSRA continues moving east and is
presently located near TCL. Expect RA at all terminals with TSRA
most likely across our southern terminals. Winds will remain gusty
out of the south through this evening and CIG`s will fall into
MVFR category once the storms arrive. CIG`s may locally improve
behind the line, however, the surface cold front remains further
west and additional RA with some TSRA is currently ongoing across
central MS. SHRA will remain possible at all sites tonight through
Sunday morning as the cold front moves east across the area.

05

&&

.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     59  75  58  77  58 /  80  60  20  60  60
Anniston    59  76  59  78  59 /  80  50  20  60  50
Birmingham  60  78  60  79  61 /  80  50  20  60  50
Tuscaloosa  60  81  60  79  62 /  70  40  10  60  40
Calera      59  78  61  78  61 /  80  50  10  60  40
Auburn      58  77  59  78  59 /  70  40  10  40  30
Montgomery  60  83  61  81  61 /  80  40  10  40  30
Troy        60  81  61  82  60 /  70  40  10  30  30

&&

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

&&

$$



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