Valid 201200Z – 211200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE MIDDLE MS VALLEY…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN
MN…
…SUMMARY…
An organized cluster of thunderstorms capable of severe wind gusts
and hail will overspread portions of the middle Mississippi and
lower Ohio Valleys today. Hail and isolated strong winds are also
possible across portions of Minnesota this morning.
…Mid MS Valley eastward across the OH Valley…
An organized MCS will likely be moving through
south-central/southeast IA early this morning. Expectation is for
this MCS to be near its mature phase at this point with a
well-developed rear-inflow jet and strong cold pool resulting in
strong wind gusts. A few of these gusts could be greater than 75
mph. As the MCS continues southeastward through northwest MO and
central IL later this morning and into the early afternoon, it is
expected to gradually lose intensity as its cold pool accelerates
and loses depth. By the time the MCS reaches IN and western KY, it
is expected to be characterized by weakly organized multicells along
the cold pool. Even with this anticipated weakening, strong wind
gusts are still possible.
…Central High Plains/Central Plains…
A cold front is expected to push into the Upper Midwest and central
Plains, likely extending from western WI southwestward into
northeastern CO during the late afternoon. Moist upslope flow is
anticipated into eastern WY/northeast CO behind this front, with the
resulting convergence along the lee trough expected to result in
thunderstorm initiation. Downstream environment characterized by
strong buoyancy and at least moderate vertical shear will support
supercell storm structures capable of very large hail and strong
wind gusts. These storms are expected to continue eastward into NE
during the evening. A strengthening low-level jet will lead to a
reinvigoration of any ongoing storms and/or development of new
storms, primarily across central and eastern NE. Given the presence
of ample low-level moisture and steep mid-level lapse rates, large
hail is probable with these storms. Isolated very large hail (i.e.
greater than 2″ in diameter) is possible. Dry mid-levels could also
contribute to strong wind gusts.
…Upper Midwest…
Ample low-level moisture and steep mid-level lapse rates will result
in strong buoyancy ahead of the approaching cold front this morning
across northern/central MN. Stable low-levels (below 850 mb) will
likely limit storm strength but large hail and occasional strong
gusts through the stable layer are possible.
…Northern Mid-Atlantic…
Showers and thunderstorms will likely develop during the afternoon
within the moist and diurnally destabilized air mass across the
region. Vertical shear will be weak, leading to predominately
disorganized, outflow-dominant multicells. Even so, the very moist
air mass and steep low-level lapse rates support water-loaded
downbursts capable of damaging wind gusts.
..Mosier/Nauslar.. 08/20/2019
$$