SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1227 PM CDT Sat Oct 10 2020

Valid 111200Z - 121200Z


Isolated strong to severe thunderstorms may occur Sunday across
parts of the northern/central Plains into the Upper Midwest, with
marginally severe thunderstorms also possible across parts of the
Southeast and Mid-Atlantic.


...Northern/Central Plains into the Upper Midwest...
A strong shortwave trough is expected to move into the Plains on
Sunday, contributing to the development of a mid-level cyclone
across Saskatchewan by Sunday afternoon. This shortwave trough will
also feature enhanced mid-level flow, which will spread across the
Plains early Sunday and into the Upper Midwest by Sunday evening. 

The deepening mid-level cyclone will be accompanied by an occluding
surface low and attendant cold front. Early Sunday, this cold front
will likely extend from central Saskatchewan south-southeastward to
another low in central ND and then southwestward back across central
WY. A surface trough/dryline will also extend south from the ND
surface low into the TX Panhandle. This surface features are
expected to push eastward throughout the day, with the faster motion
of the cold front allowing it to eventually overtake the dryline
Sunday evening. 

Low 60s dewpoints will likely be in place ahead of the front from
the central Plains into the Upper Midwest. A strong elevated mixed
layer will likely cap convection throughout much of the afternoon.
Even with this capping, ascent along the front, augmented by
increasing large-scale forcing, should be able to overcome the
convective inhibition as the front reaches far eastern
Dakotas/middle MO Valley. This scenario favors quick linear
development, with little opportunity ahead of the front for cellular
convection. Even so, the presence of steep mid-level lapse rates
suggest the possibility of severe hail in the strongest cores.
Strong low to mid-level flow will also contribute to a damaging wind
threat along the fast-moving cold front as it surges eastward.
Limited instability casts doubt on how much the squall line can
organize, with some undercutting of updrafts likely. However, this
limited instability may be countered by the strong flow, and the
general expectation is that strong, convectively augmented gusts are
probable along the front for at least a few hours during the late
afternoon and evening. Decreasing instability with eastern extent
adds to uncertainty on the eastern extent of the damaging wind
threat, but current thinking is that the line will outpace the
instability ahead of it as it reaches central IA/MN.

Current NHC forecast of Tropical Depression Delta places it over
central TN early Sunday morning, before the system then progresses
northeastward throughout the day. Mid-level flow will gradually
decrease as the overall system weakens. However, enough vertical
shear will remain present over the warm, moist, and modestly
unstable warm sector to support isolated strong to severe storms,
particularly in areas where even modest heating can occur. Primary
threat from any stronger storms is damaging wind gusts, but a
tornado or two is also possible, especially near the warm front.

..Mosier.. 10/10/2020

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