Valid 121200Z – 131200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
IA TO CENTRAL IL…
Severe thunderstorms are likely today over the middle Mississippi
Valley to the Ohio Valley. Damaging gusts are the primary risk but
a few tornadoes are possible.
…Mid MS/OH Valley Region…
An impressive amount of deep convection has developed over the
central Plains early this morning ahead of a disturbance that should
approach western IA by sunrise. A reservoir of untapped buoyancy
currently extends ahead of the MCS over eastern KS which should aid
eastward progression of organized convection into the beginning of
the upcoming day1 period. Latest NAM model guidance suggests leading
edge of this activity will be near the MO River at sunrise; however,
current speed/movement of the convection is considerably faster and
storms could advance into western IA by 09z. It’s not entirely clear
whether the MCS will slow its forward propagation so confidence in
timing/placement of this complex of storms is somewhat in doubt.
Current outlook is predicated on MCS slowing a bit toward sunrise.
For these reasons have adjusted severe probs west across IA/northern
MO to account for possible severe at the beginning of the period. If
boundary layer is able to warm/destabilize ahead of this activity,
as NAM currently depicts, environmental parameters would seem
supportive of organized convection continuing downstream, with some
upward evolution expected by late morning. If convection maintains
MCS structure then damaging winds will be the primary threat.
However, forecast soundings across southeast IA into west-central IL
exhibit favorable CAPE/shear for supercells and possible tornadoes.
Will introduce low tornado probs to account for possible discrete
updrafts by early afternoon.
Early-morning water-vapor imagery depicts a well-defined short-wave
trough over MT/WY shifting east toward the northern Plains. This
feature is forecast to advance into the western Dakotas by 13/00z
where it should aid scattered convection along/ahead of progressive
wind shift. Hail/wind are the primary risks with scattered storms
Weak mid-level height falls are forecast to spread south across ME
later Monday. Deep westerly flow should allow boundary layer to warm
such that inhibition is removed by 17z ahead of a zone of weak
low-level confluence. Isolated thunderstorms are expected to develop
across northern New England within a flow regime that could support
storm organization capable of producing isolated damaging wind