Valid 070100Z – 071200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING INTO
THE OVERNIGHT HOURS ACROSS PARTS OF THE NORTHERN PLAINS…
…SUMMARY…
A few severe thunderstorms remain possible this evening into the
overnight hours across parts of the northern Plains, mainly across
parts of the central and eastern Dakotas into northern Nebraska.
…01Z Outlook Update…
…Dakotas/Nebraska…
Latest observational data and model output indicate that low-level
ridging remains a fairly prominent feature, centered across the mid
Missouri Valley, roughly between Pierre SD and Omaha NE. Some
erosion/weakening appears possible later this evening into the
overnight hours, as lower/mid tropospheric warm advection
strengthens across parts of south central South Dakota into northern
Nebraska, well ahead of a vigorous short wave trough and deepening
embedded mid-level low digging across Manitoba and northern Ontario.
Scattered thunderstorm development which initiated across
southwestern and central North Dakota, in response to a subtle
preceding perturbation migrating around the periphery of the western
U.S. mid/upper ridging, has shown recent signs of diminishing.
However, the environment across western and central Nebraska into
south central South Dakota, on the western periphery of the
low-level ridging into weak surface troughing, remains characterized
by moderate to strong potential instability (CAPE of 1500-3000
J/kg).
The latest Rapid Refresh continues to suggest that new vigorous
thunderstorm development is possible during the 03-06Z time frame in
response to forcing for ascent with the warm advection, perhaps
aided by a modest southwesterly low-level jet across the Nebraska
panhandle into the central South Dakota/Nebraska border area. In
the presence of strong shear beneath 30-40 kt northwesterly 500 mb
flow, some of this activity may become capable of producing severe
hail and strong wind gusts, with the evolution of an upscale growing
and organizing cluster of thunderstorms possible overnight.
…Parts of Tennessee Valley…
Instability ahead a conglomerate southward advancing, convectively
generated surface cold pool, modest deep-layer shear, and perhaps
forcing for ascent associated with a subtle perturbation within
broadly cyclonic mid-level flow, may maintain vigorous thunderstorm
activity south of the Kentucky/Tennessee border. This may be
accompanied by at least some continuing risk for wind gusts
approaching severe limits, across much of western and middle
Tennessee through 03-05Z, before activity begins to diminish in
weaker/waning instability.
..Kerr.. 08/07/2019
$$