SPC 0730Z Day 3 Outlook

Day 3 Outlook Image

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0222 AM CDT Tue Sep 14 2021

Valid 161200Z - 171200Z


Isolated severe storms may occur Thursday across parts of the
northern Plains and Upper Midwest.

...Northern Plains into the Upper Midwest...
A large-scale upper trough/low should move eastward across central
Canada on Thursday, with the southern portion of this trough grazing
the north-central CONUS through the period. A surface cold front is
forecast to advance east-southeastward across the northern Plains
and Upper Midwest through Thursday evening. Some low-level moisture
return is likely ahead of this front, and diurnal heating of this
airmass should foster weak to moderate instability across the warm
sector by Thursday afternoon. Rather strong low/mid-level flow and
related deep-layer shear associated with the upper trough is also
forecast to be in place across this region, which will likely
support storm organization. At least isolated storms should form
along/ahead of the front by Thursday afternoon, and subsequently
move eastward. Any storms that do form would pose a threat for all
severe hazards, as supercells appear possible. However, the main
uncertainty precluding higher severe probabilities for now is
concern about storm coverage. The best lift associated with the
upper trough will likely remain displaced to the north in Canada,
with either neutral or very modest 12 hour 500 mb height falls
forecast across the north-central states.

The remnant of tropical cyclone Nicholas should be located in the
vicinity of southern LA at the start of the period Thursday morning
per latest NHC advisory. The surface low is forecast by most
guidance to be quite weak by this time, with the low-level wind
field expected to further diminish through the day. At this point,
any severe potential associated with this system appears too low to
include severe probabilities on Thursday.

..Gleason.. 09/14/2021

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