SPC AC 190502
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1202 AM CDT Sat Aug 19 2017
Valid 201200Z - 211200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SUNDAY INTO
SUNDAY NIGHT ACROSS MUCH OF THE MID MISSOURI RIVER VALLEY...
Strong thunderstorms may impact portions of the mid Missouri Valley
Sunday into Sunday night, accompanied by at least some risk for
Models suggest that the stronger mid-latitude westerlies will
retreat to the north of the Canadian/U.S. border during this period.
This regime is expected to become largely zonal, though ridging may
begin to build across the British Columbia coast and Canadian
Rockies, downstream of an upper trough and embedded closed low
digging to the southeast of the eastern Aleutians. It still appears
that one fairly significant short wave impulse will pivot northeast
of Manitoba, toward southern Hudson/James Bays, early in the period.
An associated cold front may advance as far south as the upper Great
Lakes and Upper Midwest, into the South Dakota/Nebraska border area,
In lower latitudes, western Atlantic subtropical ridging appears
likely to continue building westward across the Southeast, and
expanding westward/northward through the southern Plains, middle
Mississippi and Ohio Valleys. At the same time, broad troughing
with a number of embedded perturbations may continue to evolve, from
west of the California coast into the southern Great Basin and
...Much of the middle Missouri Valley...
Considerable spread has been evident among the various models
concerning the pertinent features that will impact convective
development during this period. This still includes the positioning
of the zone of potentially strong differential surface heating and
related plume of warm and potentially capping elevated mixed layer
air, on the southern fringe of the westerlies, and any possible
subtle mid/high-level perturbations traversing the region.
Additionally, portions of the pre-frontal environment across the mid
Missouri Valley region may be in the process of recovering from
impacts of convection developing late Saturday/Saturday night. And
the strength/position of the nocturnal low-level jet is becoming
Latest model output does continue to suggest the development of
moderate to large CAPE across at least portions of the region, with
continued low-level moistening beneath steep mid-level lapse rates.
In the presence of modest vertical shear, with a large contribution
from veering of winds with height, the environment may still become
conducive to severe storm potential Sunday/Sunday night. However,
this threat appears increasingly conditional, probably mostly on
where stronger lower/mid tropospheric warm advection provides a
focus for storm formation. Uncertainties appear too large for this
outlook to maintain earlier slight risk probabilities for this time
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