Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 262022
Area Forecast Discussion
National Weather Service Birmingham AL
322 PM CDT Sun Mar 26 2017
Tonight and Monday.
Dry air aloft is capping convection across central Alabama this
afternoon and any showers that develop are dissipating quickly.
This pattern will continue during the overnight hours and removed
showers from the forecast. There is plenty of low level moisture,
so low clouds will likely develop after midnight. An upper level
shortwave trof and associated surface low will lift eastward out
of the southern Plains States tonight and likely produce severe
weather to areas west of the Mississippi River. This same system
will impact our area Monday afternoon and Monday night. A 500mb
cold pocket currently over Kansas will elongate southeast tonight
and Monday as the 500mb trof shifts eastward. 500mb temps around
negative 18 celsius will approach northwest Alabama by noon
Monday and quickly destabilize the air mass over north Alabama.
There will be a weak inversion just below 850mb during the day
Monday. However, with surface temperatures forecast to reach the
upper 70s to possibly lower 80s across west Alabama, the capping
inversion will be broken by early afternoon. The better forcing
does not arrive until later in the afternoon, but with CAPE values
forecast to be in the 1500-1700 j/kg range Monday afternoon,
isolated severe storms possible with large hail being the primary
threat, mainly west of I-65 in the afternoon. Rain chances will
likely increase Monday evening across north Alabama as the main
short wave trof passes through the area, but severe threat will
likely decrease as CAPE values and mid level lapse rates weaken.
Monday through Saturday.
A broad-based shortwave over the ArkLaTex at 12Z Monday is expected
to bring our next chance for severe storms Monday afternoon and
evening. It is a bit unusual to see the cold front lagging to the
west of the upper-level trough axis, but that appears to be the case
for this event. This will allow colder air aloft (-16C at 500 mb)to
overlap with a wide warm sector. SBCAPE up to 2000 J/kg with mid-
level lapse rates of 7-7.5 C/km, and 0-6 km shear of 40-50 kt should
spread eastward across MS into West AL through the afternoon. This
will support bowing segments and supercells. Although not explicitly
shown in the model QPF, convection seems likely to develop well
ahead of the surface cold front in association with the approach of a
500 mb vort max and nose of a 300 mb jet streak. The synoptic
signals are suggestive of an event that could exceed expectations.
Our forecast will reflect a threat east of that indicated by SPC,
for hail up to ping pong ball size and damaging winds particularly
near and west of I-59. There may also be a small threat for a brief
tornado or two depending on how mesoscale features play out. I would
not be shocked to see the threat area expanded eastward and/or
upgraded in subsequent forecasts. With the cold front still to our
west and a modest low-level jet in place, additional showers/storms
could continue Monday night into Tuesday. However, the severe threat
will decrease as the best shear moves east after 9 PM Monday.
Wednesday is looking warm and drier as a 500 mb ridge amplifies over
the region ahead of yet another upper trough which will affect our
area on Thursday into Thursday night. This system has trended toward
more of an open wave with a better chance for severe storms. SBCAPE
of 1500-2000 J/kg and relatively strong low-level and deep-layer
shear may support all modes of severe weather including tornadoes.
Drier weather should return for Friday afternoon into Saturday.
18Z TAF Discussion.
MVFR stratus is finally beginning to mix out early this
afternoon, and all sites should become VFR by 20z at the latest.
Surface winds will continue to prevail from the south to
southwest around 10 knots, with a few gusts possibly up to 15
knots. The planning period of the forecast continues to highlight
fog development and low clouds once again overnight tonight. IFR
conditions are expected once again for most terminals, with
highest confidence for the southern terminals of KMGM and KTOI.
Central Alabama will remain in a warm and moist pattern through
the middle of next week, with the highest rain chances on Monday
and Thursday. Critical fire weather conditions are not expected
through the next 7 days.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 58 77 60 77 54 / 10 40 60 30 10
Anniston 59 78 61 77 57 / 10 40 50 40 10
Birmingham 61 78 62 78 57 / 10 50 60 30 10
Tuscaloosa 61 80 63 80 60 / 10 50 60 30 10
Calera 61 77 63 78 59 / 10 40 50 30 10
Auburn 59 77 61 79 60 / 10 30 30 40 10
Montgomery 61 81 63 82 61 / 10 30 30 30 10
Troy 59 80 61 83 61 / 10 20 20 30 10