- Day Three
acus03 kwns 040648
Storm Prediction Center ac 040647
Day 3 convective outlook
National Weather Service Storm Prediction Center Norman OK
0147 am CDT Tuesday Aug 04 2015
Valid 061200z - 071200z
..there is a marginal risk of severe thunderstorms over portions of the middle south
from eastern Arkansas to northern Alabama...
..there is a marginal risk of severe thunderstorms over portions of the northern plains
from eastern South Dakota into MN/IA...
Isolated strong thunderstorms will be most likely from portions of
Lower-Middle Mississippi River valley east to the central
Appalachians and middle-Atlantic on Thursday. Another area with the
likelihood for isolated strong storms will be across the northern
plains and upper Mississippi Valley.
Westerly/northwesterly midlevel flow at or below 40kt will exist from the northern High Plains
east-southeastward across the middle MS valley and east to middle-Atlantic coast. A
few disturbances are forecast to be embedded within this belt of
weak to modest flow. The strongest of these will be a shortwave
trough ejecting east across Montana during the day. Downstream from this
stronger impulse...an elongated shortwave trough...partly resulting
from a number of mesoscale convective vortex mergers...will move east across the central to
northern plains from Thursday afternoon through Friday morning. Another
mesoscale convective vortex/shortwave impulse over the middle/lower MS valley will spread east
to the Tennessee Valley during the day. Generally weak forcing for ascent
with these disturbances will combine with diurnal destabilization to
promote strong to isolated severe weather during Thursday afternoon
Expect strong destabilization to occur along the southwestern flank of
decaying mesoscale convective system from eastern Arkansas to adjacent areas of northern MS during the
morning/early afternoon. Strong capping persisting across these
areas may prohibit more widespread storm development. However...
degree of instability in the presence of persistent and focused low
level convergence...in combination with modest to locally strong
speed/directional shear...suggest at least a marginal and
conditional risk of severe storms.
Warm advection and increasing deep-layer forcing for ascent will
develop across these areas through the period as a leading/weak
shortwave trough moves east and is quickly followed by a stronger
impulse spreading east from Montana through Thursday night. Strong
destabilization should occur on the flank of residual mesoscale convective system
outflow/developing warm front from eastern South Dakota into Minnesota during the day.
Lift across the region will then increase into the evening as the
next system moves east and height falls induce surface wave
development on the front across eastern South Dakota. Severe weather risk should
evolve and persist into the evening given the developing surface low
and strengthening flow/shear across the region.