Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0804 PM CDT Sat Jun 21 2025
Valid 220100Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
NEW YORK AND NEW ENGLAND...
CORRECTED FOR FLIPPED THUNDER LINE IN SOUTHEAST
...SUMMARY...
Thunderstorms associated with severe wind gusts and hail will be
possible tonight across New York and New England. Isolated severe
storms will also be possible across parts of the Great Lakes and the
central to northern Plains.
...Northeast/New York/Great Lakes...
Latest water vapor imagery has a belt of strong anticyclonic flow
located from the upper Mississippi Valley into the Great Lakes and
Northeast. A ridge-riding mid-level shortwave trough is located over
Ontario. At the surface, a moist airmass is in place from New York
into western New England, where surface dewpoints are in the lower
to mid 60s F. The low-level moisture will contribute to continued
destabilization across the region, in the form of elevated
instability, this evening into tonight. As the shortwave trough
moves southeastward toward the Northeast, low-level flow will
markedly strengthen. In response, convective coverage is expected to
increase, and a line of thunderstorms appears likely to develop late
this evening. This line is forecast to move southeastward across New
York and western New England from late evening into the overnight
period.
Overnight, RAP forecast soundings ahead of the line in northern New
York have a low-level temperature inversion, with MUCAPE in the 1500
to 2000 J/kg range. Effective shear is forecast to be around 40
knots. This should be favorable for a severe threat. Although much
of the line could be elevated, isolated large hail and severe gusts
will still be possible, mainly with the more intense component of
the line. The line is expected to move through the western New
England and the Hudson River Valley late tonight, approaching
southern New England toward 12Z.
...Central Plains...
Southwest mid-level flow is in place across much of the central
Plains early this evening. At the surface, a moist airmass is
located over much of the High Plains, with surface dewpoints mostly
in the 60s F. In response to low-level warm advection, isolated to
scattered thunderstorms will likely develop along the western edge
of this moist airmass. This convection is expected to move
northeastward across Nebraska and southeastern South Dakota this
evening. In addition to moderate instability, mid-level lapse rates
are very steep. This, combined with moderate deep-layer shear, will
likely support a marginal severe threat. Hail and isolated severe
gusts will be possible.
...Northern High Plains...
A mid-level trough, evident on water vapor imagery, will move
northeastward into the northern High Plains tonight. Ahead of the
trough, a post-frontal airmass is in place with the western edge of
a moist airmass located over the western Dakotas. As large-scale
ascent increases across the northern High Plains later tonight,
scattered thunderstorm development is expected. These storms will
move northeastward across eastern Montana and western North Dakota,
mainly after midnight. Weak to moderate instability, combined with
steep lapse rates and moderate deep-layer shear should support a
marginal severe threat. Hail and a few severe gusts will be
possible.
..Broyles.. 06/22/2025
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