- Day Three
acus02 kwns 210532
Storm Prediction Center ac 210531
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1231 am CDT Sat Apr 21 2018
Valid 221200z - 231200z
..there is a marginal risk of severe thunderstorms across southeast
la...much of MS...southwest/southern Alabama...and Florida Panhandle...
Isolated severe thunderstorms are possible across portions of the
southeast states and Florida Panhandle.
Upper low, centered over eastern OK at the beginning of the period,
is expected to move gradually southeastward, reaching northern Alabama by
the end of the period. Associated surface low will take a similar
track with the overall system becoming increasingly vertically
stacked throughout the day. Widespread showers and thunderstorms are
anticipated across the Tennessee Valley, southeast states, and Florida as the
system moves eastward.
..eastern la into Florida Panhandle/Big Bend...
Widespread showers and thunderstorms will likely be ongoing at the
beginning of the period across portions of the lower MS valley and
mid-south. This activity may impede the moisture return across the
southeast states. Current expectation is for modest moisture
advection (i.E. Dewpoints in the low 60s) to occur ahead of the
surface low (and attendant surface trough) across much of MS and Alabama
but the better moisture (i.E. Dewpoints in the upper 60s) will
remain confined to the coastal areas. Strong low-level jet
accompanying the cyclone will support widespread elevated
thunderstorms north of the warm front and ahead of the surface low.
Greater likelihood for surface-based convection is expected along
the surface trough as it moves across southern MS/Alabama and Florida
Panhandle. Instability will be limited but strong wind field may
support occasional updrafts organized enough to produce isolated
damaging wind gusts and perhaps a tornado or two. Farther northwest
(in central ms), clearing between the surface trough and cold front
may result in enough insolation for destabilization and another
round of thunderstorms. Limited low-level moisture is anticipated
across the region but cold temperatures aloft (associated with the
approaching upper low) will still support modest instability.
Additionally, generally weak low-level wind fields are expected but
mid-level flow will still be strong enough to support enough bulk
shear for transient storm organization. Marginal severe
probabilities were extended back northwestward to account for this
scenario. Overall severe potential remains too low for anything but
marginal severe probabilities.