Day 1 Severe Weather Outlook

Valid 181300Z – 191200Z


Weakly rotating storms may occur near the southeast Texas/southwest
Louisiana border today, and a few strong storms are possible this
morning and again tonight from western Wisconsin to Iowa and eastern
Nebraska. However, the threat for severe storms appears too low for
any outlook areas.

…WI/MN to eastern NE through tonight…
A compact shortwave trough over ND will eject east-northeastward
across northwest MN to ON by this evening, as an associated surface
cold front moves eastward across MN, but stalls across eastern NE.
A broad zone of mainly elevated convection is ongoing this morning
from northern IA into eastern MN in conjunction with low-level warm
advection. The low-level jet will develop northeastward toward ON
by this afternoon, with weakening flow and forcing for ascent
farther south contributing to weakening of the convection through
the day. Additional thunderstorms may form along the stalling front
this evening into tonight from northwest WI across IA to eastern NE,
though relatively weak deep-layer vertical shear suggests that
organized severe storms are unlikely.

…Extreme upper TX/southwest LA coasts today…
The remnant center of tropical depression Imelda continues to drift
generally northward to the northwest of Houston. The primary
confluence band has established near the coast to the south of the
cyclone center. Earlier this morning, some mass response was
apparent due to latent heat release with 30 kt low-level southerly
flow just offshore, and a few rotating storms were noted just off
the upper TX coast. However, the convection has developed a bit of
a cold pool and more linear structure, and the 12z sounding from LCH
immediately east of the main band shows limited potential for
rotating storms, at best. While a brief/weak tornado cannot be
completely ruled out, the overall threat appears too marginal to
warrant the addition of an outlook area.

A few low-topped thunderstorms can be expected near the Pacific
Northwest coast this morning, and spread inland during the day with
the midlevel trough and steeper lapse rates. A few thunderstorms
are also expected with a backdoor cold front that will move
southwestward across GA/FL.

..Thompson/Kerr.. 09/18/2019


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