SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0800 AM CDT Sun Oct 11 2020

Valid 111300Z - 121200Z


Severe thunderstorms are possible late this afternoon and evening
across the Upper Midwest and Middle Missouri Valley. Some tornado
and/or damaging wind potential will also exist across parts of the

...Upper Midwest/Middle Missouri Valley...
Considerable upper-level trough amplification will occur over the
northern High Plains/Dakotas today, with height falls reaching the
Upper Mississippi River Valley and Middle Missouri Valley by late
tonight. As amplification occurs, a considerable strengthening and
backing of mid/high-level winds (50-80 kt at 500 mb; generally
south-southwesterly) are expected across the region by tonight. The
stronger winds aloft will be maximized just behind an
east/southeastward-moving cold front.

While moisture is quite limited early today, a steady moistening is
expected with a northward-transitioning warm front. By late
afternoon/early evening, a semi-narrow zone of upper 50s/lower 60s F
surface dewpoints are expected near/just ahead of the
east/southeast-advancing cold front. Mid-level capping will be
prevalent much of the afternoon, particularly given the modest
moisture scenario. Regardless, the increasingly pronounced forcing
for ascent will be instrumental in the development/maturation of
convection by late afternoon, and more so, into this evening. Such
initial development is likely to occur generally near the border of
the eastern Dakotas/western Minnesota into northwest Iowa, with
other storm development occurring a bit later southwestward into
eastern Nebraska/northeast Kansas.

Forecast soundings suggest ample deep-layer shear for potential
supercells capable of severe hail with initial development. However,
the strong degree of forcing and influence of the cold front should
result in relatively quick storm mergers, with the expected
evolution of a semi-continuous squall line by mid-evening across
southern Minnesota/western Iowa into southeast Nebraska/northeast
Kansas. Accordingly, damaging winds will likely be an increasing
concern this evening, while some line-embedded tornado risk cannot
be ruled out. Overall storm vigor will likely diminish overnight as
the storms encounter an increasingly stable boundary layer with
eastward extent.

The remnants of Delta will continue northeastward toward the
southern Appalachians today. Early morning water vapor imagery shows
substantial mid-level drying from Georgia into South
Carolina/western North Carolina. The overall system will tend to
weaken, as will low/mid-level winds preceding it. That said, some
severe risk in the form of a brief tornado or two and/or locally
damaging winds is still expected given sufficiently favorable
low-level/deep-layer shear and a moist environment. While a
particularly organized/sustained severe risk is not currently
expected, a corridor near the South Carolina/North Carolina border
in vicinity of the warm front would conditionally be the most
favorable area for a tornado risk.

..Guyer/Goss.. 10/11/2020

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