SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0220 AM CDT Wed Jun 29 2022
Valid 011200Z - 021200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
The risk for severe thunderstorms currently appears negligible
across the U.S. Friday through Friday night.
...Synopsis...
A prominent blocking regime with amplified split flow will persist
across the eastern Pacific into western North America through this
period and beyond. Downstream, broad mid-level troughing will be
maintained across much of Canada and the northern tier of the U.S.,
to the east of the Rockies, with a deep embedded low of Arctic
origins forecast to slowly turn eastward across the southern
Hudson/James Bay vicinity. Lower/mid-tropospheric ridging extending
from the southwestern Atlantic through the southern Rockies likely
will also be maintained, while mid-level ridging builds further
across the northern Rockies, downstream of the deepening troughing
offshore through inland of the U.S. Pacific coast.
An occluding surface cyclone initially forecast over southern Hudson
Bay by early Friday may tend to develop to a position closer to the
mid-level low, while a secondary frontal wave forms across northern
Quebec into the Newfoundland and Labrador vicinity by late Friday
night. While gradually stalling and weakening across parts of the
Ohio Valley into middle Mississippi Valley and central Great Plains,
the trailing cold front may not advance southeast of the lower Great
Lakes and St. Lawrence Valley until Friday night.
...Central Great Plains into the Northeast...
Destabilization near and south of the surface front will provide one
possible focus for scattered thunderstorm development Friday through
Friday night. However, due to a lack of both steeper mid-level
lapse rates and more substantive low-level moistening, most of the
various model ensemble output suggest that mixed-layer CAPE may only
become seasonably modest, with the larger CAPE mostly focused to the
south of the stronger westerlies. Furthermore, it appears that the
pre-frontal southwesterly low-level flow will weaken Thursday into
Friday, with stronger deep-layer mean wind fields on Friday
generally confined to areas north of the international border.
There remains a signal within the various model output that the
environment may become marginally conducive to organized convection,
including supercells, in a narrow corridor north of the
international border (across parts of southeastern Ontario into the
St. Lawrence Valley) by late Friday afternoon. However, given the
rather weak forecast boundary-layer instability across this region,
it seems probable that this activity will tend to weak as it spreads
into a less unstable air mass near and southeast of the
international border Friday evening.
It might not be out of the question that at least low severe weather
probabilities may eventually be needed across parts of New York and
New England, near the international border, as well as perhaps areas
west-southwestward ahead of the front into the Great Plains, as
model spread begins to decrease. At this time, though, it appears
that any severe weather will be rather isolated/sparse in coverage
Friday through Friday night.
..Kerr.. 06/29/2022
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