Day 1 Severe Weather Outlook

Valid 111300Z – 121200Z


Areas of strong to severe storms are expected over portions of the
northern through central High Plains this afternoon into tonight.
Large hail and severe gusts are the primary threats.

…Central High Plains to the middle MS Valley through tonight…
A belt of somewhat enhanced midlevel flow extends from the southern
Rockies to the central Plains, around the northwest periphery of the
midlevel ridge over the southern Plains. Within this belt, an MCS
and associated MCV are moving eastward over northeast KS. The
convection has been maintained overnight by warm advection on the
nose of a 30-40 kt low-level jet, within a corridor of PW near 2
inches and moderate buoyancy. The low-level jet will veer to more
westerly through late morning and weaken, and the MCS will likewise
weaken. Some additional storm development is expected during the
day along the leading edge of the residual cold pool and zone of
ascent preceding the MCV, but the storm environment will be less
favorable for organized severe storms with damaging winds/hail with
eastward extent across MO/IL.

In the wake of the morning convection, an upslope regime will
establish from northwest KS into northeast CO/southwest NE, north of
a lee cyclone in southeast CO. Recovery of low-level moisture and
surface heating will again boost MLCAPE to 2000-3000 J/kg by
mid-late afternoon. Thunderstorm development is expected first near
and immediately east of the Front Range in CO, while the boundary
layer should remain capped through much of the afternoon in far
northeast CO and vicinity. Buoyancy and deep-layer vertical shear
will be sufficient for both supercells and multicell clusters with
large hail/damaging winds with the initial deep convection east of
the Front Range. Wind profiles will be more favorable for
supercells farther east on the High Plains where low-level easterly
flow and hodograph curvature will be greater, though there will be a
tendency for cell interactions and upscale growth later into the
evening and farther east. Any semi-discrete supercells will pose a
threat for a couple of tornadoes and large hail, while the damaging
wind threat will increase with storm clustering into the evening.
Storms will likely evolve into an MCS tonight while spreading
eastward on the immediate cool/moist side of a quasi-stationary
front expected to reside a little south of I-70.

…MT/northern High Plains this afternoon/evening…
A midlevel trough near the OR/ID border will eject
east-northeastward over MT this afternoon and reach the northern
High Plains overnight. Easterly low-level flow will be maintained
through the day across southern MT, to the north of a surface
cyclone in central WY. This will help draw 58-62 F dewpoints
westward across southern MT, beneath steep midlevel lapse rates,
which will contribute to MLCAPE of 1500-2000 J/kg. Convective
initiation is expected by early afternoon over the high terrain of
southwest MT, with storms subsequently moving northeastward and
developing eastward across southern MT to northeast WY by mid-late
afternoon. Effective bulk shear of 35-50 kt will favor supercells
initially with large hail and possibly a couple of tornadoes, and
convection is expected to grow upscale into a couple of
clusters/line segments across MT/western SD by this evening, with an
accompanying threat for damaging winds.

..Thompson/Kerr.. 08/11/2019


Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.