Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 261148
Area Forecast Discussion
National Weather Service Birmingham AL
648 AM CDT Wed Apr 26 2017
For 12Z Aviation.
A strong upper-level trough will take a swipe at the region late
tonight as the trough base swings from the Ark-La-Tex toward the
Ohio Valley. The latest model guidance suggests a sneaky severe
weather threat may be shaping up for tonight with most-unstable
CAPE of 1000-2000 J/kg expected to advect northward immediately
ahead of approaching QLCS. The 500mb trough axis is now expected
to flatten as the strongest forcing brushes by to our northwest.
This type of trough evolution along with 500mb winds becoming
more westerly, will be favorable for the QLCS to transition into a
broken line of bowing segments and supercells as it moves across
the CWA. Forecast soundings are rather concerning with 0-6km shear
of 50-65kt and clockwise-curved hodographs yielding 0-1km SRH in
excess of 300 m2/s2. This type of environment will certainly
support a damaging wind and large hail threat, but the tornado
threat will depend on how much of the aforementioned instability
becomes surface-based. Hi-res guidance indicates the potential for
at least a couple of robust surface-based supercells, and a
strong tornado cannot be ruled out if this occurs. The threat
should begin around midnight in the West and continue through 9 AM
Thursday in the East.
The next significant weather system will move into the region on
Sunday as a large trough takes shape across the Plains. Severe
weather appears possible Sunday afternoon and evening in
association with a QLCS. As a subtropical disturbance becomes
ingested into the larger 500mb trough, this should limit the
overall severe weather threat causing nearly southerly 500 mb flow
and poor directional shear. Damaging winds and brief tornadoes
embedded within the QLCS will be the main threats. Widespread
beneficial rainfall of 1-2 inches may also occur.
12Z TAF Discussion.
VFR conds will prevail thru 06z. South winds will increase after
17z, especially across the northern TAF sites. Winds could gusts
up to 20 knots at times. The air mass is very dry, so only mid to
high levels clouds expected thru 06z. A line of strong to severe
storms will move into west Alabama arnd 06z and could reach KTCL
arnd 08z, and KBHM and KEET before 12z. For now will handle with VCTS
until timing is more certain. Cigs 3-5 thousand feet agl will
likely develop after 06z as moisture advects in rapidly ahead of
the convective line.
High pressure will keep conditions dry through the afternoon. An
approaching cold front will bring a round of showers and
thunderstorms late tonight into Thursday morning. There are no
fire weather concerns.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 83 65 79 57 87 / 0 80 40 0 20
Anniston 83 66 79 60 86 / 0 70 50 0 20
Birmingham 84 65 80 63 88 / 0 80 20 0 20
Tuscaloosa 85 62 80 62 88 / 0 90 10 0 20
Calera 83 66 80 63 87 / 0 80 20 0 20
Auburn 81 64 80 66 85 / 0 60 60 10 20
Montgomery 85 68 84 67 89 / 0 60 50 10 20
Troy 82 69 84 69 88 / 0 60 60 10 10