Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 300840

Area Forecast Discussion
National Weather Service Birmingham AL
340 AM CDT Thu Mar 30 2017

Today and Tonight.

A broad zone of upper level ascent was producing showers and
embedded thunderstorms across large portion of Mississippi.  Model
consensus is for the eastern edge of the activity to dissipate as it
nears or crosses over into west Alabama early this morning. Radar
imagery has shown an increase in convection across the northern
Mississippi since midnight, and there could be more rain across west
Alabama this morning than suggested by models. Raised rain chances
slightly before 9 am. A downward trend in convection still expected
during the morning hours, with the rain mostly dissipated across
west Alabama by 9 am.

There will likely be a break in the action today across central
Alabama from the morning activity until the next round of storms
this afternoon, roughly from 9 am until 3 pm. Pre-frontal storms
will likely develop across Mississippi by mid afternoon and track
into west Alabama by late afternoon.  Discrete supercells appear
more favorable across northern Mississippi and northwest Alabama
during the mid to late afternoon, with the activity becoming more
linear as it shifts into west Alabama.  SRH values and hodographs
certainly suggest a tornado threat, but shear in the 0-1km layer is
mostly speed shear with the boundary layer winds veering after
sunset. Even with loss of daytime heating, severe threat will be
maintained during the overnight hours due to decent influx of low
level moisture and strong forcing aloft as jet max sweeps across the
area. Mid level lapse rates also stay near 7 degrees Celsius into
the evening hours, mainly west of I-65, so large hail also a threat.
The models are showing the convective activity ending sooner tonight
with the back edge of the activity near I-65 by midnight tonight,
and out of east Alabama by 6 am Friday.


Friday through Wednesday.

Consensus of model guidance, with the exception of a spurious
feature in the NAM, indicates that precipitation will be out of
the area by 12Z, and rain chances have been removed from the
forecast for Friday morning. 500 mb heights will be rising as
ridging builds in behind the negatively tilted trough lifting into
the Mid-Atlantic. West-northwesterly flow will bring drier air
into the region. Cold air advection will be weak and with westerly
winds expect highs to easily reach the 70s. Cooler air will filter
in by Friday night as a surface high noses in from the Midwest
allowing lows to fall into the upper 40s to low 50s. A split flow
pattern will remain in place on Saturday with upper-level ridging
over the area between the subtropical jet over the Gulf and the
northern stream jet over the Great Lakes. Temperatures will climb
back into the 80s Saturday for most with plenty of sunshine.

The next upper-level system will be moving into Texas by Sunday.
There are some timing differences with this system with the GFS
being quicker and keeping it as an open wave while the ECMWF is
slower with a closed low. This also results in differences in
surface low tracks with the ECMWF continuing to track a sub-1000
mb low from Arkansas to Tennesse while the GFS tracks a sub-1000
mb low through Alabama. The ECMWF has been more consistent and
also agrees well with the European ensemble mean, so its timing
is preferred. Included some small rain chances as early as Sunday
afternoon in the far west to account for any weak waves/possible
MCS remnants ahead of the system. Widespread precipitation is
expected Sunday night and Monday with strong lift and plenty of
moisture being brought in by a LLJ. There is the potential for
beneficial to locally heavy rainfall amounts given the high PWATs,
but that will be dependent on whether convection near the Gulf
Coast cuts off the deeper moisture. Despite the strong dynamics,
widespread precipitation will likely limit instability and
potentially keep the effective warm front from lifting northward.
Therefore, will keep the severe threat in the HWO as low
confidence/low end for Monday. The relatively best chance of
destabilization may end up being in the far southeast counties in
association with a LLJ surge Monday morning. Rain chances will
linger into Monday night and possibly Tuesday due to wraparound
moisture/deformation zone precipitation around the back side of
the system.

A high-amplitude trough will move across the central US Wednesday
and Wednesday night, sending a cold front towards Central Alabama.
Strong to severe storms may be possible with this front, but it`s
too early for any details.



06Z TAF Discussion.
Intently watching ongoing (as of 05z) convection to the west of
central Alabama. Looks like two areas of convection may survive
the night, but those two areas may very well split our area to the
north and south. Will continue to watch it, and will make updates
as needed. Otherwise, 06z TAFs will continue the trend
established with the previous forecasts with lower ceilings
developing in most areas around sunrise. Still some lower
confidence on the exact timing, but feeling better about the
general idea of MVFR category ceilings developing at some point in
the next 6 to 9 hours.




Central Alabama will remain in a warm and moist pattern through the
week, with the highest rain chances today and then again on
Monday. Critical fire weather conditions are not expected through
the next 7 days.


Gadsden     77  55  71  49  76 /  30  90   0   0   0
Anniston    79  56  73  51  78 /  30  80   0   0   0
Birmingham  78  54  74  52  80 /  30  90   0   0   0
Tuscaloosa  78  54  76  52  81 /  40  90   0   0   0
Calera      78  55  75  53  80 /  30  90   0   0   0
Auburn      80  59  74  53  80 /  30  80  10   0   0
Montgomery  82  58  78  54  83 /  30  70   0   0   0
Troy        82  58  78  52  83 /  30  80  10   0   0




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