Scientific Forecaster Discussion
fxus64 kbmx 202100
Area forecast discussion
National Weather Service Birmingham Alabama
400 PM CDT Tue Aug 20 2019
/updated at 0359 PM CDT Tue Aug 20 2019/
Upper level ridge axis from the west and slightly warmer upper
level temperatures have kept showers and storms isolated or
confined to the far southeast so far today. Heat indices at a few
locations in the northwest have warmed above 100-103f. With an
hour or so of additional warming and lack of convection in that
area, will maintain the heat advisory.
A weak shortwave remains across southeast Alabama this afternoon,
aiding in thunderstorm coverage south of I-85. Expect most of the
activity to remain across the southeast through early evening, but
with colliding outflow boundaries, isolated to scattered coverage
is possible areawide. Rain chances diminish tonight. Another muggy
night expected with lows in the low to mid 70s.
/updated at 0359 PM CDT Tue Aug 20 2019/
Wednesday and Thursday.
By tomorrow, upper level ridging weakens slightly across the area
as does the weak shortwave. With similar upper level temps and no
real focus for convection, expect mainly scattered diurnal
activity and have lowered rain chances slightly. Although hot and
muggy, heat indices should remain below advisory criteria.
By Thursday, the upper level ridge strengthens across northeast
Florida, extending westward across the deep south. Low level winds
across the area become southerly, bringing additional Gulf
moisture northward. Precipitable water values reach 2 inches by Thursday
afternoon. Upper level winds do remain cyclonic around the ridge
axis with no significant focus in the low levels. Will lower rain
chances to 40-50%, keeping activity scattered and mainly
Friday through Monday.
/Updated at 0333 am CDT Tue Aug 20 2019/
At the same time Thursday, guidance is developing an upper low
pressure over the southwestern Gulf of Mexico and dragging it
northward toward the Texas/Louisiana coast by Friday. Thankfully,
at this time, there is no indication of any significant surface
feature to accompany it. That will be something that will bear
watching over the next couple of days.
By the weekend, guidance is in fair agreement bringing this upper
low around the ridge and onto the Louisiana/Mississippi/Alabama
coast. This low should eventually get absorbed into the mean flow
across most of conus during Sunday. At the same time over the
weekend a surface front will be attempting to make progress
southward. The question is how much influence will the upper low's
timing have on the mean flow thus affecting the southward
progression of the surface front. This front should stall
somewhere across Alabama Sunday into Monday. Regardless of where
the surface front stalls, we remain in an overall moist airmass
with rain chances continuing through the extended part of the
forecast thanks to the upper low then lingering trough across the
18z taf discussion.
Scattered showers and thunderstorms will continue to develop
across central Alabama through the late afternoon and evening.
Thunderstorms in the vicinity is included at each taf site for now due to uncertainty of
where convection will develop. Included a tempo for mgm and toi
for current shower location. Any activity that does move over a
taf site will cause gusty winds and MVFR visibilities...though the
possibility of IFR visibilities is possible due to weak mid and
upper level flow allowing for slow storm motion. There is a chance
for at least MVFR visibilities from fog development at each taf
site except bhm. Confidence is low on how much fog develops at
each site as its largely dependent on if a shower or thunderstorm
moves over any taf site and how long that storm lingers. Any
activity should weaken late tonight.
Increased rain chances continue each day this week, with scattered
to numerous mainly afternoon showers and thunderstorms. Friday is
the best chance for more widespread rainfall. Localized fog is
possible each morning, but locations will vary depending on the
previous day's rain coverage. Temperatures will gradually return
to normal levels by mid week as relative humidity values continue
Preliminary point temps/pops...
Gadsden 71 94 71 92 71 / 20 40 30 50 40
Anniston 72 93 71 91 72 / 20 30 30 50 30
Birmingham 73 95 74 93 74 / 20 30 20 50 30
Tuscaloosa 73 94 73 93 73 / 20 40 20 50 30
Calera 71 94 71 93 72 / 20 30 20 50 30
Auburn 71 91 72 91 72 / 30 30 20 40 20
Montgomery 72 94 73 93 73 / 30 40 20 40 20
Troy 70 91 71 91 71 / 30 40 20 40 20
heat advisory until 9 PM CDT this evening for the following