SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1138 PM CST Mon Nov 09 2020

Valid 101200Z - 111200Z


Thunderstorms capable of producing isolated strong to locally
damaging winds and perhaps a few tornadoes are possible this
afternoon and evening across portions of the Middle Mississippi
Valley vicinity.

...Mid-Mississippi Valley Vicinity...

A potent midlevel shortwave trough will become negatively tilted
today as it ejects east/northeast from northern/central Plains to
the upper Great Lakes. At the surface, low pressure will deepen at
it track northeast from MO into eastern IA by midday. Strong
southerly flow ahead of the surface low and eastward-advancing cold
front will transport low 60s dewpoints as far north as southern WI
and southern lower MI. While heating will be limited by cloudy
skies, cooling aloft will result in steepening midlevel lapse rates
and modest instability (generally less than 750 J/kg MLCAPE) is
expected during the afternoon and early evening. Thunderstorms are
first expected to develop and intensify during the afternoon across
northern MO into eastern IA. Deep layer flow will generally be
parallel to the cold front, supporting a more linear storm-mode with
line segments/QLCS development expected. 

Given the deepening surface low, some backing of near-surface winds
is expected closer to the low from eastern IA into northern IL and
southern WI. This could increase the potential for mesovortex
formation within the broader QLCS/bowing segments. Forecast
soundings indeed show enlarged, curved hodographs with both
increasing directional and speed shear leading to 0-1 km SRH values
greater than 250 m2/s2. As a result, a few tornadoes are possible,
in addition to isolated strong/locally damaging wind gusts. The
severe threat should decrease with time and eastward extent as the
boundary layer stabilizes with the loss of daytime heating and
strong forcing ejects northeast over the upper Great Lakes and


Strong deep layer easterly flow on the eastern periphery of Tropical
Storm Eta will maintain a moist airmass over the region. Heating
through cloud breaks will allow for some destabilization of the
airmass over the Peninsula, but poor lapse rates and weak effective
shear will limit storm organization. While a couple of storms could
produce gusty winds, convection is expected to remain sub-severe.

..Leitman.. 11/10/2020

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