SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Mon Aug 26 2024
Valid 262000Z - 271200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTH-CENTRAL PLAINS AND UPPER MIDWEST...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTHERN NEW
ENGLAND...
...SUMMARY...
Severe thunderstorm wind gusts, large to very large hail and a
couple of tornadoes are possible this afternoon through tonight
especially across parts of South Dakota, northern Nebraska,
central/southern Minnesota, and into Wisconsin.
...20z Update...
The primary change with this outlook update was to expand the
Marginal Risk southward across Virginia to account for ongoing
convection that will track southward with potential risk for
damaging wind. Instability will gradually weaken, however modest
shear for organization may sustain this threat further south than
previously forecast.
The previous forecast remains on track with no changes needed based
on recent observations and trends in guidance for the Enhanced Risk
across the north-central Plains to Upper Midwest. A few initial
supercells have developed across Minnesota. See MCD#2000 for more
information. Further west across WY/SD, severe threat along the
primary cold front continues with potential for enhancement of the
earlier MCS moving eastward out of Wyoming. See MCD#1999 for more
details on evolution of this severe threat.
..Thornton/Guyer.. 08/26/2024
.PREV DISCUSSION... /ISSUED 1141 AM CDT Mon Aug 26 2024/
...North-central Plains to Upper Midwest...
A relatively active severe-weather day is expected regionally,
especially late this afternoon through tonight, with multiple rounds
of severe storms possible potentially including eastern South Dakota
and parts of central/southern Minnesota into far western Wisconsin.
Strong to locally severe storms have already occurred this morning
across interior Wyoming, in relatively close proximity to the
northeastward-ejecting shortwave trough that will cross the northern
High Plains toward the Dakotas through tonight. This convection is
thought to be harbinger of a broader/increasing severe risk that
should develop this afternoon from far northeast/east-central
Wyoming into southwest South Dakota including the Black Hills/Pine
Ridge vicinities. Some initial supercells capable of large hail will
be possible, but these storms should organize into an MCS and
expand/intensify as activity proceeds into greater moisture,
instability and post-frontal low-level flow to the east. These
storms could persist eastward this evening across southern South
Dakota/far northern Nebraska, and all the way into southern
Minnesota/far northern Iowa overnight through the predawn hours.
Another area of potential severe thunderstorm development including
supercells will be across eastern South Dakota east-northeastward
into central Minnesota early as mid/late afternoon near the front,
where a very moist (middle to upper 70s F surface dewpoints) and
very unstable (4000+ J/kg MLCAPE) air mass will reside. This could
somewhat relate to ongoing thunderstorms across central South Dakota
at late morning, or perhaps more likely, ahead of it into central
Minnesota. While potentially intense severe storms/supercells are
plausible, some uncertainty exists regarding the diurnal extent of
deep convective development given the likelihood of residual
mid-level capping. Even if diurnally related development through
peak heating is more limited, severe-weather potential should
steadily increase from west-to-east across east/southeast South
Dakota, southern Minnesota/northern Iowa into western Wisconsin
tonight via likely upstream MCS development.
...Northeast States/Mid-Atlantic...
A belt of generally strengthening northerly flow aloft, along with
modestly cool mid-level temperatures, will reside across the region
on the western periphery on offshore-shifting upper-level trough.
Coincident with low/some middle 60s F surface dewpoints, moderate
destabilization (1000-1500 J/kg MLCAPE) is expected this afternoon
across southern New England/eastern New York southwestward toward
the Delmarva/coastal Mid-Atlantic. Multiple corridors of at least
widely scattered south/southeastward-moving storms should evolve
this afternoon, including southern New England/southeast New York as
well as the Pennsylvania/Maryland/Virginia border vicinity. Isolated
severe wind and hail will be possible this afternoon through
early/mid-evening. For additional short-term information, see
Mesoscale Discussion 1995.
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