ACUS01 KWNS 041218
SWODY1
SPC AC 041216

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0716 AM CDT Wed Sep 04 2024

Valid 041300Z - 051200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL ROCKIES INTO THE NORTHERN/CENTRAL PLAINS AND UPPER
MISSISSIPPI VALLEY...

...SUMMARY...
Isolated strong to severe thunderstorms capable of gusty winds and
hail may occur this afternoon and evening across parts of the
central Rockies into the northern/central Plains and upper
Mississippi Valley.

...Central Rockies into the Northern/Central Plains and Upper
Mississippi Valley...
A weak shortwave trough over the northern Rockies and adjacent Great
Basin this morning will become absorbed later today into an
amplifying upper trough over the Canadian Prairie provinces and
northern Plains. At the surface, a cold front related to the upper
trough will continue southward over the northern Plains, and
southeastward across the Upper MS Valley through the period. Modest
low-level moisture is forecast to be in place ahead of this boundary
across the northern Plains and upper MS Valley, with more limited
moisture expected farther west across the central Rockies and
adjacent High Plains. Relatively cool mid-level temperatures
associated with the weak shortwave trough and the presence of steep
mid-level lapse rates should aid in the development of weak
instability across parts of WY, northern CO, and vicinity this
afternoon. Sufficient deep-layer shear (generally 25-35 kt) should
support some updraft organization with convection that initially
forms over the higher terrain before subsequently spreading
eastward. Isolated instances of marginally severe hail and
strong/gusty winds may occur with the more cellular development.
But, some increase in strong to severe wind potential may be
realized as thunderstorms move into an area of steeper low-level
lapse rates across the central High Plains by late this afternoon
and early evening, especially if any small clusters can form.

The severe potential along much of the length of the front in the
northern Plains and upper MS Valley appears rather conditional.
While large-scale ascent associated with the approaching upper
trough should gradually overspread the warm sector by late
afternoon/early evening, most guidance continues to suggest that a
cap and substantial MLCIN will hinder robust convection from
developing through much of the day. Even so, sufficient instability
and shear should be in place along/ahead of the front to support an
isolated hail/wind threat if thunderstorms can form and be sustained
through the evening and early overnight period. The post-frontal
regime across much of MT into ND and western SD appears unlikely to
support severe convection. Accordingly, the Marginal Risk has been
trimmed southward to account for recent guidance and observational
trends.

..Gleason/Leitman.. 09/04/2024

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