Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 222350

Area Forecast Discussion
National Weather Service Birmingham AL
550 PM CST Thu Feb 22 2018

For 00Z Aviation.


Through Tonight.

Slightly drier airmass and stronger upper level heights across the
area today. Clouds have been limited to low topped cu for much of
the area. Several bands of showers and storms developed along the
now stationary front in Mississippi, and pushed into northwest
Central Alabama. Activity quickly dissipated as it encountered the
more stable airmass.

For tonight, rain-free conditions expected as the front remains
to our west. Airmass will be similar to last night, with dewpoints
in the 60s and light boundary layer winds. Patchy fog can be
expected areawide. Lows will be in the low to mid 60s.


Friday through Wednesday.

Very warm conditions are set to continue on Friday and Saturday as
an upper-level ridge remains prominent from the Gulf of Mexico to
Bermuda. A shortwave trough swinging into the Four Corners region
will lead to a developing storm system to our west and an episode
of warm advection Friday night into Saturday morning. This may
kick off a batch of showers and possibly thunderstorms that could
affect areas mainly along and northwest of I-59. Moisture quality
will be highest across our western areas on Saturday and will
overlap with cooler temperatures aloft. This is where daytime
heating may cause spotty scattered showers to develop in the warm
sector of the approaching system on Saturday afternoon. Late
Saturday afternoon into Saturday night, a surface low is expected
to deepen as it moves from Arkansas toward the Great Lakes region.
As strong to severe storms approach from the west, they should
encounter an environment with weaker CAPE (800 J/kg or less), and
the departure of the best upper-level support also indicates
storms should pose less of a severe threat. However, temperatures
in the mid to upper level have trended cooler, leading to
somewhat more impressive lapse rates Saturday night into early
Sunday morning northwest of I-59. Falling 500mb heights also
suggest that the axis of convection could have enough forward
momentum for a low-end risk of damaging winds or brief tornadoes
along and northwest of I-59, where strong low-level shear is
expected. A low confidence risk for tornadoes and damaging winds
will be introduced into the HWO.

The front is expected to lose forward speed and become nearly
stationary on Sunday, with continued high rain chances. An
approaching shortwave could cause the front to move back northward
Sunday night, potentially leading to another round of strong to
severe storms. The GFS and ECMWF are not in good agreement, but
the ECMWF and EPS ensemble members strongly support a resurgence
of the warm sector south and east of I-59. A low-level jet of
40-45kt would support an isolated damaging wind or tornado threat,
but confidence is too low to introduce this potential into the
HWO for Sunday night.

The front and associated rain should finally move out by Monday
afternoon with a brief dry period expected on Tuesday between
weather systems. The next system may arrive on Wednesday as the
active and rainy weather pattern continues.



00Z TAF Discussion.

First off, no precipitation is expected at terminals tonight with
very low chances in the SW half of AL for Friday afternoon, so
will not mention anything in TAFs. While we did get some sun today
and mixing, we are still in a somewhat persistent overall moist
airmass albeit not as much as last night. Still have cigs
mentioned but for shorter time frames along with some patchy fog.
Flow stays generally south through the period but lighter winds
are expected for overnight tonight.




Unseasonably high RH values continue through at least the weekend,
with increasing rain chances Friday and Friday night. Widespread
rain and scattered thunderstorms are expected by Saturday night
through Sunday as a front slowly moves through the area. There
are no fire weather concerns.


Gadsden     63  79  60  78  61 /  10  10  30  40  70
Anniston    62  80  60  80  62 /  10  10  20  30  50
Birmingham  64  80  63  79  62 /  10  10  30  40  80
Tuscaloosa  64  80  65  80  61 /  10  20  40  40  80
Calera      63  80  62  80  63 /  10  10  30  30  60
Auburn      61  79  60  80  64 /  10  10  10  10  30
Montgomery  61  83  62  83  67 /  10  20  20  20  30
Troy        60  83  61  83  66 /  10  20  10  10  30





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