979
ACUS48 KWNS 170903
SWOD48
SPC AC 170901

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0401 AM CDT Tue Jun 17 2025

Valid 201200Z - 251200Z

...DISCUSSION...
...D4/Friday...
A surface cyclone is forecast to deepen over the northern/central
High Plains on Friday, as a mid/upper-level trough shifts gradually
eastward across the western CONUS. Strong to extreme buoyancy will
develop by afternoon across parts of the central/northern Plains,
along/south of an effective warm front that will extend east of the
surface low. Much of the warm sector will likely remain capped, but
isolated storm development will be possible by late afternoon
near/north of the warm front, with increasing storm coverage during
the evening in response to a strengthening low-level jet. Supercells
will be possible initially, though the pattern suggests potential
for an MCS to develop and move eastward Friday night across the
upper Great Lakes vicinity.

Guidance continues to vary substantially regarding the most favored
corridor for an organized severe threat. For example, the GFS/GEFS
is farther north across ND/northern MN, while the ECMWF/ECENS is
farther south across central MN/northern WI. Severe probabilities
will eventually be needed for this scenario, but confidence is the
favored corridor is too low for a 15% area.

Strong to severe storms may also develop across the northern Rockies
and spread eastward across MT, in association with the approaching
mid/upper-level trough. Probabilities will likely be needed for this
scenario in future outlooks, though confidence is too low for a 15%
area at this time.

...D5/Saturday...
A similar surface pattern is expected over the Great Plains and
upper Midwest on Saturday compared to D4/Friday. However, an
amplifying upper ridge may tend to suppress storm development
through much of the period. Some severe potential may again evolve
across MT along the northwest periphery of the ridge. There may also
be some potential for strong to severe storms along the northeast
periphery of the ridge into parts of the lower Great Lakes and New
England.

...D6/Sunday - D8/Tuesday...
An upper-level ridge will remain prominent through the weekend into
early next week across parts of the central/eastern CONUS. Strong to
severe storms and possible MCS development could continue to occur
along the periphery of the ridge, but predictability becomes quite
low at this range regarding the details of any organized threat.

..Dean.. 06/17/2025