SPC AC 201615
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1115 AM CDT Fri Sep 20 2019
Valid 201630Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING OVER PORTIONS OF THE NORTHERN PLAINS...
Scattered severe storms capable of producing wind damage, isolated
large hail and a couple tornadoes are possible today across the
northern Plains, with more isolated severe storms possible in parts
of the southern High Plains.
...Northern and Central Plains...
Morning water vapor loop shows a large upper trough over the western
US, with southwesterly midlevel flow strengthening across the
Rockies and High Plains. Several weak impulses are noted from CO
northeastward into the Dakotas, with clusters of showers and
thunderstorms occurring at this time. The timing and effects of
this ongoing convection will result in a rather complex forecast for
this afternoon and evening.
Activity currently over the western Dakotas is expected to intensify
later today as air mass destabilizes and winds aloft strengthen.
Occasionally severe storms are expected to affect parts of central
and northeast ND into central SD through the mid-late afternoon,
with damaging winds, hail, and a couple of tornadoes possible.
Later this afternoon, forcing associated with the a stronger
shortwave trough will help to initiate thunderstorms from southern
MT into eastern WY. These storms will be in a favorable environment
for supercells early in the convective life cycle, capable of large
hail and a couple of tornadoes. These storms will likely congeal
and grow upscale during the evening as they track across parts of
NE/SD with a continued threat of damaging winds and hail.
A weak remnant outflow boundary extends from near LBB into southern
OK. Thunderstorms are expected to develop in vicinity of this
boundary this afternoon in a moist and very unstable air mass.
Deep-layer shear will be marginal for convective organization.
However, convergence along the boundary coupled with slightly
enhanced low-level shear may be sufficient for a few supercell
storms capable of hail, damaging winds, and perhaps a tornado.
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