Valid 102000Z – 111200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
NORTHERN NE AND SOUTHERN SD…
…SUMMARY…
An enhanced threat for severe hail and damaging winds will likely
develop this afternoon and evening across parts of the north-central
Plains, focused near the Nebraska/South Dakota line. A tornado
threat exists in this area as well.
…20Z Update…
The Enhanced Risk for damaging winds has been expanded eastward to
include more of southeastern SD and northeastern NE. Storms are
still expected to form and quickly strengthen across the northern
and central High Plains through the remainder of this afternoon and
into the evening. All severe hazards may occur with this activity as
it moves eastward, as both strong shear and instability are present
along/south of a front located near the NE/SD border. Damaging
winds, some potentially significant, will likely become the primary
threat this evening as convection grows upscale into a bowing
complex in tandem with a 40-50 kt southerly low-level jet centered
over KS/NE. The Slight and Marginal Risk areas have also been
expanded eastward to include more of the Upper Midwest, as isolated
strong to severe wind gusts may persist with the MCS through much of
the overnight.
For more information on the near-term severe threat across the
northern/central High Plains, see Mesoscale Discussions 1947/1948,
and recently issued Tornado Watch 640.
..Gleason.. 09/10/2019
.PREV DISCUSSION… /ISSUED 1124 AM CDT Tue Sep 10 2019/
…Central/Northern High Plains…
A shortwave trough currently moving across UT will track into the
central and northern High Plains this evening. Model guidance
suggests that midlevel height falls and lift will overspread parts
of western WY and the NE Panhandle after 18z, with convective
initiation occurring a few hours afterward. Storms will be focused
along a surface baroclinic zone that extends from northeast WY
southeastward into the NE Panhandle – then eastward across NE.
Forecast soundings in vicinity of the boundary show MLCAPE values
around 3000 J/kg and a weak cap. Initial storm structures will
likely be supercellular, with a risk of very large hail and isolated
tornadoes. A consensus of CAM solutions agree that storms will
congeal and grow upscale through the evening as they track eastward
along the boundary across NE, with a focused area of enhanced
damaging wind threat.
…ID/UT/WY/MT…
Scattered thunderstorms are expected to intensify early this
afternoon beneath the core of the midlevel shortwave trough over
northern UT and southeast ID. These storms will be relatively
fast-moving and in a steep lapse rate environment. The strongest
cells in this region will pose a risk of hail and damaging wind
gusts. Some activity may remain strong as it moves across
northern/western WY into southern MT this evening.
…Western KS into northeast NM…
Full sunshine will lead to an axis of moderate CAPE values this
afternoon along the dryline from western KS into northeast NM. All
model guidance shows the development of isolated thunderstorms in a
deeply mixed but weakly sheared environment. A few of the storms
will be capable of strong downburst winds for a few hours this
afternoon and evening.
…Lower MI…
A weak convectively-enhanced upper trough is moving across WI. This
feature will move eastward into Lower MI this afternoon, with
scattered thunderstorms likely to form. Rather strong winds aloft
and sufficient CAPE suggest a risk of gusty/damaging winds in the
strongest cells.
$$