Valid 292000Z – 301200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM WESTERN SD TO
THE UPPER RED RIVER VALLEY…
…SUMMARY…
A few severe thunderstorms with large hail as the primary hazard are
most likely from western South Dakota into the Upper Red River
Valley, mainly this evening through tonight.
…20Z Update…
Primary change to the outlook was to remove severe probabilities
across the Mid MO River Valley where storms have moved north and no
additional activity is expected. Elsewhere, conditions described in
the previous outlook (appended below) still remain valid and no
changes are needed.
..Mosier.. 09/29/2019
.PREV DISCUSSION… /ISSUED 1129 AM CDT Sun Sep 29 2019/
…Dakotas…
Amplified upper-level trough will remain anchored across the West.
An embedded shortwave impulse will induce weak mid-level height
falls across the northern High Plains at peak heating and should aid
in storm development centered on northeast WY during the late
afternoon.
Outside of the Black Hills, the region is completely encompassed by
stratus as a plume of rich low-level moisture continues to advect
poleward beneath a slowly spatially expanding elevated mixed-layer.
This suggests the opportunity for surface-based storm development
should be rather short-lived and spatially confined to the western
SD area during early evening. Convection should be or will become
predominately elevated north of the surface warm front as it spreads
east-northeast across northern SD into southeast ND. The quality of
low-level moisture will favor an influx of moderate to large
buoyancy. In conjunction with strong speed shear through the
cloud-bearing layer, the setup could favor a long-track supercell or
two capable of producing a swath of large hail, some of which may be
significant.
…Eastern NE to IL and MN…
Clusters of warm-advection driven elevated, non-severe convection
are ongoing from the Mid-MO to the Mid-MS Valleys. This activity
should persist through this afternoon as it shifts east into IL.
Some guidance does suggest intensification may occur near the
surface warm front as destabilization is occurring across eastern MO
into central IL. However, based on the pervasiveness of
stratus/convection north of the front amid a weak mid-level lapse
rate environment, the scenario appears to favor maintenance of a
level 1-Marginal Risk.
A separate area of warm-advection elevated convection will develop
tonight in the central to northern MN vicinity. More muted effective
shear relative to areas farther west should yield a predominant
cluster mode. Marginally severe hail is possible as the periphery of
the High Plains elevated mixed-layer spreads toward the Upper
Midwest.
…Far West TX to eastern NM…
Latest guidance is fairly consistent in simulating isolated to
scattered storm development over the higher terrain of the
Trans-Pecos northward into eastern NM along/ahead of the dryline.
Effective shear will be weaker (20-30 kt) with southern extent where
convective coverage should be greater due to orographic ascent. Amid
moderate mid-level lapse rates, overall setup should tend to favor
isolated instances of severe wind and hail.
$$