FROM NWS BMX
.SHORT TERM...
(Today through Saturday)
Issued at 338 AM CST FRI MAR 8 2024
/Concern for
flash flooding continues to increase tonight through
Saturday, along with a chance for severe storms across the southern
half of Central Alabama./
Radar is already starting to light up to our west early this
morning, as the potent longwave upper
trough axis continues to dig
southward into the southwestern US.
Upstream, southwesterly
flow of
130+ knots at 300mb and 60-80 knots at 500mb will push into the mid
south region this afternoon. Ample
divergence will be present aloft
as as result, and we currently have
cyclogenesis occurring as we
speak in eastern Texas and northern Louisiana. As the surface low
continues moving eastward, we`ll see a warm
front stretch from west
to east across southern Mississippi and southern Alabama. This
front
will be a focusing mechanism for
parcel lift, combined with
southerly 850mb
moisture transport of 40 to 50 knots. Latest 00z
CAMs this morning are actually in decent agreement with an
MCS
developing over Central Mississippi, moving rapidly eastward into
Central Alabama between noon and 3pm. The
MCS and the evolution and
development of
convection will strongly dictate the locations where
we may see
flash flooding and will influence the amount of low-level
instability available.
According to multiple CAM solutions, the
MCS would produce a cold
pool outflow boundary that will drift slowly southward through the
afternoon and evening hours near the U.S. 80/I-85 corridor. If that
solution verifies, we could see almost continuous shower and storm
development due to the
cold pool boundary and stationary
front
draped over the area. Rains will be very efficient due to deep low-
level
moisture and PWATs increasing almost to 2 inches this
afternoon through this evening.
Confidence continues to increase of
an axis of heavy rainfall of 2 to 5 inches with locally higher
amounts along and south of the I-20 corridor. WPC this morning
mentioned a potential of up to 8 inches of storm total rainfall
somewhere within this heavier axis, which is certainly not out of
the question. All locations along and south of I-20 will need to be
on alert through this event, as soils remain wet and will rapidly
respond to rainfall rates of 2-3 inches per hour. A Moderate Risk of
Excessive Rainfall is currently in place over this region, along
with a Flash Flood Watch. Heaviest
rainfall is expected to finally
push eastward by Saturday morning as a trailing cold
front moves
from northwest to southeast across the area.
Severe storms will also be possible with this event, but the threat
is currently very conditional. As mentioned earlier, low-level
instability is expected to be confined to our far southern counties
through the afternoon and potentially the evening hours due to the
presence of the
MCS and ongoing
convection/
cold pool boundary. What
isn`t as clear at this point is where the surface low to our west
will move and develop through the overnight hours into Saturday
morning. If the surface low moves off to our north and west, we
could see a potential overnight for the
warm sector/warm
front to
lift northward with a better severe potential across our eastern and
southeastern counties tonight through Saturday morning. The HREF
ensemble mean is presenting a possibility of at least 1000-1500
J/kg
of
SBCAPE available and 0-1km
SRH of 150-300 between midnight and
6am Saturday. As such, the
Slight Risk (2 of 5) of severe storms
remains in the forecast for roughly the southern half of Central
Alabama through 9am Saturday. Damaging winds up to 60mph and
tornadoes are the main hazards.
Mesoscale conditions will be need to
be monitored throughout the event.
The cold
front will move across the area during the day on Saturday,
with cooler and drier air filtering into the deep south. Behind the
front, temperatures will cool into the upper 50s to lower 60s, while
far southeast counties will warm into the low to mid 70s before the
frontal passage.