Valid 242000Z – 251200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM WESTERN
AND CENTRAL KANSAS INTO FAR NORTHERN OKLAHOMA…
…SUMMARY…
The greatest severe-storm threat this evening into tonight is from
central and western Kansas into northern Oklahoma, with severe wind,
damaging hail and a few tornadoes possible.
…20Z Outlook Update…
Expected evolution of convection remains in line with the ongoing
convective outlook. Initiation of storms is expected to occur
across far northern Kansas this afternoon/early evening although
specific timing remains uncertain. A few of these storms may
already be underway across western and southwestern Nebraska. The
expectation is that convection will congeal into a
southeastward-moving complex that will migrate through the Enhanced
area and reach northern Oklahoma late tonight, with additional
storms expected in west-central and southwestern Kansas during the
afternoon. A more isolated threat for severe storms will exist
across central/western North Dakota and also central Montana.
..Cook.. 08/24/2019
.PREV DISCUSSION… /ISSUED 1130 AM CDT Sat Aug 24 2019/
…KS/northern OK through tonight…
An initial convectively enhanced midlevel trough is pivoting
northeastward over northern KS/southern NE, as an upstream trough
over southeastern WY/northern CO moves toward western KS by this
evening. In the wake of widespread overnight convection, steeper
midlevel lapse rates will spread east-southeastward from CO toward
western KS, above low-level moisture advecting northwestward from
central KS and OK. Clouds will linger today across most of KS aside
from the southwest, but the combination of increasing midlevel lapse
rates/low-level moisture and surface heating in cloud breaks will
boost MLCAPE into the 2000-3000 J/kg range by mid-late afternoon
across western KS.
Substantial uncertainty exists regarding the location(s) and timing
of convective initiation this afternoon into early tonight. One
scenario appears to be for convection to start late this
afternoon/evening near the KS/NE border, in a zone of low-level warm
advection along the southern flank of the MCV. This area will be
just north of the stronger deep-layer vertical shear, so there would
be a tendency for storms to cluster/merge and begin to grow upscale
and move southeastward on congealing outflow into early tonight.
The environment farther south into the western half of KS will be
conditionally favorable for supercells with large hodograph
curvature/SRH in the low levels, and effective bulk shear near or
greater than 40 kt. However, the focus for storm initiation south
of the MCV/warm advection is a bit more nebulous across western KS
this afternoon, other than weak ascent preceding the midlevel trough
moving southeastward from CO. If surface-based storms can form
across western KS, all severe hazards will be possible. Will
largely maintain the previous outlook to cover the possibility for
an MCS central KS overnight, and for evening supercells in western
KS that could move toward northwest OK.
…Western ND this afternoon/evening…
A surface trough could provide a focus for thunderstorm development
this afternoon/evening across western ND. Forcing for ascent will
be weak, along with vertical shear, which suggest that marginally
severe hail and gusty outflow winds will be the main concerns.
…Central/eastern MT this evening…
Some high based convection should form later this afternoon/evening
across central MT, in advance of an embedded speed max moving
eastward from northern ID. Though low-level moisture will be
limited, inverted-v profiles and an increase in midlevel flow prior
to stabilization of the boundary layer could support isolated storms
with strong outflow gusts.
$$