Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 280008
Area Forecast Discussion
National Weather Service Birmingham AL
608 PM CST Mon Feb 27 2017
For 00Z Aviation.
Tonight and Tuesday.
A complicated pattern through the evening hours with one area of
showers exiting southeast Alabama and another area of convection
tracking eastward across northern Mississippi and western Alabama.
The outflow boundary from today`s activity has pushed southward to
Dothan, while the northern edge of rain shield was near the I-85
corridor. With a west to southwest flow above 850mb, the push of
the rain has slowed down. Will continue with high pops through the
afternoon and may need to raise rain chances for the early
evening hours across the southeast counties if activity stalls
out. The short term models are not really handling the activity
over Mississippi very well. This activity has some lightning and
will need to update forecast to include thunderstorms for the
I-20 corridor. A short wave trof will pass to the north of Alabama
later tonight. The models are fairly good agreement in developing
showers and a few thunderstorms across the northern counties of
central Alabama after midnight. This activity will continue into
the morning hours on Tuesday. The rain will lift northward by
early afternoon Tuesday as a warm front lifts into the Tennessee
Valley region of north Alabama, so minimal activity expected in
the afternoon. There may not be a lot of sunshine on Tuesday, but
strong low level warm air advection will push afternoon
temperatures into the 70s, possibly some low 80s across the far
Wednesday through Sunday.
Looking at Wednesday`s severe weather threat, models have trended
faster and further north with the track of the surface low moving
from Michigan quickly northeastward into Canada. Sfc-850 mb flow
is looking more veered especially as the afternoon progresses and
also weakens with time, with hodograph curvature decreasing. Will
continue to mention a threat of an isolated tornado or two across
the north, with helicity around 200 m2/s2 and good low-level and
deep- layer shear, but any tornadoes would likely be weak/short-
lived with the better threat remaining north of the forecast area.
Relatively best tornado chances may be with any storm that gets
going earlier, around mid-day. The main threat with this system
instead will be damaging winds with a large squall line near the
front moving into an air mass with 60-65 dew points, CAPE around
1000 J/kg, steep mid-level lapse rates, and strong wind fields
aloft. Hail will also be possible with WBZ heights around 10k ft
and steep mid-level lapse rates. The GFS remains a bit too fast
with the timing of the front with the ECMWF and NAM looking more
reasonable with the front moving through during the afternoon and
evening. There is no change to the threat areas with the highest
threat being in the northern and western counties.
Thursday through Saturday the forecast area will be under a dry
west to west-northwest flow pattern with more seasonable
temperatures. Moisture may begin to return as early as Sunday with
better rain chances ahead of a cold front just beyond the extended
00Z TAF Discussion.
Terminal forecast this period will generally be restricted with
MVFR/IFR ceilings and some vis reductions. Showers and isolated
thunderstorms over Central Alabama will be most numerous the next
few hours far south, mainly affecting TOI. Then expect a break in
the rain activity. Plenty of low level moisture from recent
rainfall and southerly flow will allow the restrictive ceilings to
develop or redevelop overnight. Timing will be an issue as the
rain activity stirs the environment. Rain chances redevelop by
13-15z for the northern sites with the approach of another upper
level wave. Ceilings will rise just enough to get into MVFR
mainly 18z and beyond. At this time, did not drop vis to minimums
with little change in the overall environment overnight. Will
monitor this prospect through the evening. Expect some changes to
the timing of the specific categories as we keep this chaotic
environment going the next few days.
A wet pattern will continue through Wednesday with several rounds
of showers and thunderstorms. A cold front will bring an end to
the rain Wednesday night. No fire weather concerns.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 52 72 64 73 42 / 50 50 30 90 50
Anniston 52 75 63 76 42 / 40 40 20 80 60
Birmingham 57 76 65 75 42 / 40 40 30 90 50
Tuscaloosa 60 79 66 78 45 / 30 30 20 80 40
Calera 57 76 65 77 43 / 40 30 20 70 60
Auburn 52 76 63 75 46 / 50 20 10 30 70
Montgomery 57 81 65 81 48 / 50 20 10 40 70
Troy 56 79 65 80 49 / 80 20 10 30 70