SPC Jul 24, 2021 1730 UTC Day 2 Convective Outlook

Source: US National Oceanic and Atmospheric Administration

SPC AC 241728

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Sat Jul 24 2021

Valid 251200Z – 261200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
OHIO VALLEY INTO THE NORTHEAST…AND ALSO ACROSS PARTS OF SOUTH
DAKOTA…

…SUMMARY…
Thunderstorms with isolated wind-damage potential are possible
across parts of the Ohio valley and Northeast, and also across parts
of South Dakota, Sunday afternoon and evening.

…Ohio Valley into the Northeast…
A belt of 30-40 kt west-northwesterly midlevel flow will largely
remain in place from the northern Plains into the Northeast on
Sunday, along the southern periphery of a deep mid/upper-level
trough covering much of eastern Canada. An embedded midlevel
shortwave trough is forecast to move across New England during the
morning and early afternoon, with another shortwave trough glancing
northern New England Sunday night, but otherwise large-scale ascent
may remain weak from the OH Valley into the Northeast through much
of the period. As a result, coverage of robust afternoon
thunderstorm development remains uncertain. However, a few strong
storms will be possible along/ahead of a weak surface boundary
sagging into the region. Effective shear of 20-30 kt will support
the potential for weakly organized cells/clusters, with isolated
damaging wind possible where low-level lapse rates can steepen
during the afternoon.

…South Dakota…
Isolated thunderstorms may develop across portions of South Dakota
by late afternoon, as MLCINH is removed by strong surface
heating/mixing. Potential areas for initiation include a weak
surface trough across western SD, and a weak surface boundary near
the ND/SD border. Despite rather limited low-level moisture, MLCAPE
is expected to rise into the 500-1000 J/kg range as temperatures
increase to near or above 100F in some locations. Modest
west-northwesterly midlevel flow will support effective shear of
25-35 kt, sufficient for at least transient storm organization. A
very warm and deeply-mixed boundary layer will support an isolated
severe-wind risk with the strongest storms and outflows.

…Southwest…
As a midlevel trough continues to drift westward across Arizona,
moderate instability and modestly enhanced midlevel flow/deep-layer
shear may again support a few organized storms across portions of
the Southwest. The areal extent of the more favorable environment is
expected to be smaller than previous days, so no probabilities have
been included at this time. However, a few strong cells/clusters
cannot be ruled out, especially from northwest AZ/southwest UT into
southern NV and perhaps southeast CA.

..Dean.. 07/24/2021

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