Scientific Forecaster Discussion
fxus64 kbmx 231141
Area forecast discussion
National Weather Service Birmingham Alabama
641 am CDT Sat Jun 23 2018
for 12z aviation.
today and tonight.
A stalled frontal boundary is stretched through central Alabama this
morning. A few scattered showers have lingered along this boundary
for most of the night, and should continue through the morning
hours. The main story for today is the mesoscale convective system currently moving
through eastern Oklahoma and into western Arkansas. This mesoscale convective system will
continue to propagate eastward along the frontal boundary through
today. By the afternoon, the boundary will lift slightly northward
as an effective warm front and be stretched through northern Alabama
by mid- afternoon. Models are in pretty good agreement with the
mesoscale convective system redeveloping across portions of north-central Alabama this
afternoon and evening with surface cape exceeding 3000 j/kg. The
NAM has been painting the area with 4500+ cape, but I believe this
is overdone and isn't supported by the higher resolution cams.
0-6km bulk shear is in that 20-30kt range, so while it's not
overly impressive,it is sufficient to support strong to severe
storms, especially when considering the 3000+ cape. I have added
mention for severe storms in the severe weather potential statement for this afternoon, and will
highlight a slight risk area similar to the Storm Prediction Center outlook - mainly
for the northern portions of central Alabama. The main threat will be
damaging winds as vertical shear profiles really don't support a
significant tornado threat. The big uncertainty in the risk area
comes down to timing and where that frontal boundary is located.
If the mesoscale convective system pushes through in the early to mid-afternoon, the
boundary is likely over our area, but if the mesoscale convective system slows and doesn't
come in until the evening, that boundary may have already pushed
north of our area (limiting our severe risk). Models have been
going back and forth on the timing and coverage of storms with
each New Run, so it's hard to get a handle on what exactly will
take place, which isn't unusual with these mesoscale convective system patterns as it
highly depends on strength of outflows and the propagation speed.
Essentially, this will be a day where the exact risk and risk
areas will need to be re-evaluated frequently.
The mesoscale convective system pushes out of central Alabama by this evening/tonight, clearing
out the rain chances for the area.
Sunday through Friday.
Height rises on Sunday should lead to hotter conditions and very
minimal prospects for rainfall. The upper-level ridge should
continue to limit rain chances on Monday and Tuesday, but isolated
convection cannot be ruled out. The ridge may weaken on Wednesday
as a trough moves through the Great Lakes and Ohio Valley. There
is good model support for a weak shortwave near the base of the
trough over the Tennessee Valley which would lead to enhanced
rain chances. This features may end up getting pulled south and
west across the forecast area on Thursday and Friday as ridge
develops to our north. This scenario would lead to a continuation
of somewhat enhanced rain chances.
12z taf discussion.
MVFR conditions for most sites this morning with toi experiencing
IFR cigs. Ceilings and should improve to VFR area-wide by 14-16z. Line
of storms is moving west to east across northern portions of
central Alabama. Kbhm, kanb, and kasn may be impacted by thunderstorms in the vicinity and thunderstorms and rain
through much of the day today and periods of visible reducing rain.
This should all move out of the area by 23-00z, leading to VFR
conditions through the evening hours.
High rain chances will continue for today especially across the
northern third of the area. Patchy fog may develop in the
overnight and early morning hours where rainfall occurs. Rainfall
is not expected on Sunday as a suppressive ridge develops. There
are no fire weather concerns at this time.
Preliminary point temps/pops...
Gadsden 87 68 91 71 92 / 70 20 10 10 30
Anniston 87 69 91 72 93 / 60 10 10 10 30
Birmingham 89 73 93 74 94 / 60 10 10 10 30
Tuscaloosa 92 74 95 74 95 / 40 10 10 10 30
Calera 90 73 92 73 93 / 50 10 10 10 30
Auburn 90 72 91 73 92 / 50 10 10 10 30
Montgomery 94 73 93 75 94 / 30 10 10 10 30
Troy 94 74 92 73 93 / 30 10 10 10 30