LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1120 AM CDT Fri Jul 28 2023
Valid 281630Z - 291200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATER THIS
AFTERNOON INTO EARLY TONIGHT FROM NORTHERN IA TO NORTHERN IN AND
VICINITY...
...SUMMARY...
Severe storms are most probable from Iowa and southern Minnesota
eastward to northern Illinois/southern Wisconsin late this
afternoon/evening, and continuing into southwest Lower Michigan and
northern Indiana tonight. Damaging winds and large hail are the
main threats.
...SD/NE to the Upper Midwest through tonight...
Within a largely zonal flow regime, embedded speed maxima will move
eastward over the central/northern Plains and the upper MS Valley -
the most pronounced of which is now over ND. Convection and an
outflow/frontal surge with this ND speed max will eventually
interact with the north edge of the more moist/unstable air mass
from southeast SD/southern MN into northern IA/southern WI later
this afternoon/evening. The timing of convective initiation and
details of subsequent storm evolution are both somewhat in question,
but effective bulk shear near 50 kt and MLCAPE of 2500-4000 J/kg
will conditionally favor splitting supercells initially with very
large hail. Convection could then grow upscale into an MCS this
evening into tonight, with an attendant threat for damaging winds.
...Upper OH Valley into the Mid-Atlantic this afternoon/evening...
A remnant MCV over northern IN will move eastward over OH today, and
additional convection expected today along the associated outflow
boundary/differential heating zone across central/eastern OH. The
stronger flow with the MCV will tend to trail the lead outflow, so
multicell storms with occasional downburst winds will be the primary
threat this afternoon. Farther east, vertical shear will be weak,
but surface heating over the higher terrain and weak convergence
along a diffuse baroclinic zone will support scattered thunderstorm
development this afternoon from the central Appalachians into parts
of the Mid-Atlantic. Isolated strong downburst winds for a few
hours this afternoon/evening will be the main concern this area.
...Northern ME this evening...
A northern stream shortwave trough and associated surface cold front
will cross Quebec and northern ME later this afternoon into this
evening. Midlevel lapse rates will not be steep, but MLCAPE near
1000 J/kg and relatively long hodographs will support the potential
for wind damage with a band of storms along and just ahead of the
cold front.
...Southern MT to northeast CO and vicinity through tonight...
Subtle speed maxima will move around the northern periphery of the
southern Rockies midlevel high, interacting with terrain
circulations and a deepening mixed layer later this afternoon.
High-based storm development is expected around mid afternoon from
southern MT to southeast WY/northeast CO, where storm clusters will
move off the high terrain in response to mid-upper westerlies, and
inverted-V profiles will favor isolated strong-severe outflow gusts
as the main concerns.
..Thompson/Weinman.. 07/28/2023
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