Valid 021630Z – 031200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF KANSAS/OKLAHOMA…AND PARTS OF IDAHO INTO WESTERN MONTANA…
…SUMMARY…
Isolated severe thunderstorms are possible over parts of central
Kansas to central Oklahoma, and over parts of eastern Idaho to
western Montana.
…Synopsis…
With the main belt of westerlies confined to far northern portions
of the U.S. and Canada, generally weak flow aloft will reside over
most of the CONUS. In the East, weak troughing will persist, while
in the West, ridging — centered over the Four Corners states —
will prevail. However, several small-scale disturbances will rotate
anticyclonically around the ridge — across the northern
Intermountain Region and Plains states, accompanied by areas of
active convection/thunderstorms.
At the surface, a weak/largely nondescript pattern will prevail,
though a cool front will advance across southwestern Canada and
adjacent portions of the northwestern U.S. as an associated upper
short-wave trough crosses this region.
…Kansas/Oklahoma vicinity…
Widespread cloud cover persists across much of Kansas and into the
eastern half of Oklahoma — remnants of an earlier MCS across this
region. With breaks in the cloud cover now occurring over parts
central and western Kansas and especially into the western half of
Oklahoma, diurnal heating/destabilization is expected. This —
combined with small-scale disturbances aloft shifting
south-southeastward across the Plains on the fringes of the upper
ridge — should result in widely scattered convective redevelopment
this afternoon, which may then grow upscale this evening into one or
two small MCSs.
Though deep-layer flow — veering from southerly to northwesterly
with height — is sufficient to support organized/rotating updrafts,
cellular storm mode will likely be temporary/transient. An isolated
tornado cannot be ruled out this afternoon/evening, along with some
potential for hail with a stronger storm or two. However, locally
strong/damaging gusts with stronger convective elements will be the
more likely severe risk, particularly where a band of
southeastward-moving convection can evolve.
Overall, it appears that the severe risk should remain isolated,
with any zone of potentially greater coverage difficult to
anticipate at this time. A possible upgrade to a small slight risk,
within the broader MRGL risk area, could be added in later outlooks,
if confidence increases that such a corridor can be highlighted.
…Parts of eastern Idaho into western Montana…
Latest water vapor imagery shows a small disturbance crossing the
Idaho/Montana border area at this time, with another cyclonic
circulation center over the Oregon/California border moving
northeastward. With daytime heating of the steep-lapse-rate
environment across the region yielding weak/high-based CAPE, expect
isolated to scattered afternoon storm development across the
Idaho/western Montana area as the aforementioned disturbance
approaches from the southwest.
With flow veering/increasing with height sufficient to support
organized updrafts, and given the deep, well-mixed boundary layer
expected, potential for locally damaging winds remains evident, with
a couple of the stronger/relatively fast-moving storms which are
expected. Thus, will maintain 5% wind/MRGL risk across this area,
from afternoon through mid-evening.
..Goss/Jirak.. 08/02/2019
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