Valid 041630Z – 051200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS EARLY TONIGHT
ACROSS NORTHWEST NE AND SOUTHERN SD…
…SUMMARY…
Isolated thunderstorms could produce marginally severe hail from
northwest Nebraska into southern South Dakota early tonight.
…WY/NE/SD through tonight…
A midlevel trough over the northern Rockies/northern Great Basin
will progress eastward to the High Plains, with associated lee
cyclogenesis expected from eastern WY into SD tonight. Low-level
moisture will remain somewhat limited as a result of a prior frontal
intrusion into the southern Plains, and clouds will limit surface
heating from extreme northeast CO to southwestern SD. There will be
a low chance for surface-based convection late this afternoon near
the eastern WY border and vicinity along the lee trough, though it
is not clear that either low-level moisture or the depth of vertical
mixing will be sufficient for storm initiation. The more probable
scenario is for elevated storms to form tonight farther to the east
across western NE/SD, as moisture increases above the surface in the
zone of ascent preceding the midlevel trough. Midlevel lapse rates
will be steep, and buoyancy could become sufficient for isolated,
marginally severe hail with the strongest storms tonight.
Otherwise, a few high-based storms will be possible along the cold
front crossing western/northern WY this afternoon. Inverted-v
profiles and increasing flow aloft will support a threat for gusty
outflow winds, though storm coverage/intensity should be relatively
limited, and the potential for severe winds appears to be too low to
warrant an outlook area.
..Thompson/Kerr.. 10/04/2019
$$