Day 1 Severe Weather Outlook

Valid 041300Z – 051200Z


Isolated thunderstorms could produce marginally severe hail from
northwest Nebraska into southern South Dakota this evening.

…North-central Plains…
A shortwave trough over the northern intermountain region/Great
Basin early this morning will continue steadily eastward and reach
the northern High Plains tonight. In response, a lee cyclone will
deepen over the central/northern High Plains through the afternoon
and evening. A plume of very steep (8-8.5 C/km) mid-level lapse
rates will overspread a corridor of limited moisture return, with
surface dewpoints generally only in the upper 40s to low 50s F near
the lee trough and ahead of the cold front.

While a cold front will accompany the shortwave trough into the High
Plains by late afternoon with increasing forcing for ascent,
surface-based initiation appears uncertain/limited given the
likelihood of a residual capping inversion. However, isolated to
widely scattered thunderstorms are expected to develop during the
evening from northwest Nebraska into southwestern South Dakota along
and ahead of the front within a zone of strengthening low-level warm
advection and deeper forcing for ascent. These storms will likely be
elevated above the stable surface layer, but steep mid-level lapse
rates, 1000 J/kg MUCAPE and 40-45 kt effective bulk shear will
support the potential for mid-level updraft rotation and severe hail
with some of these storms.

..Guyer/Broyles.. 10/04/2019


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