SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0754 AM CDT Wed Jun 29 2022
Valid 291300Z - 301200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
DAKOTAS INTO WESTERN MINNESOTA...
...SUMMARY...
Severe hail and thunderstorm gusts are most likely this afternoon
and tonight over parts of the Dakotas into western Minnesota.
...Synopsis...
In mid/upper levels, the northern-stream pattern will become more
zonal through the period, behind a shortwave trough now crossing the
upper Great Lakes region. The trough should cross the Lower Great
Lakes today, and most of New England (except for eastern ME) by 12Z
tomorrow. Upstream, a small cyclone over the Canadian Rockies will
devolve to a shrinking, open-wave trough, as it penetrates confluent
flow related to a stronger cyclone over Nunavut. The southern part
of this trough should reach ND by 12Z. In between, radar and
satellite imagery indicated a convectively induced vorticity lobe
and related shortwave trough over western ND, which should move
east-northeastward across northwestern MN to adjoining parts of ON
by 00Z.
Surface analysis at 11Z depicted a cold front from central/
southwestern QC to southern Lower MI, becoming a wavy warm front
over parts of southern WI, IA, and eastern/northern SD, to a low
over southeastern MT. An occluded front was drawn northwestward
from the low across southwestern SK. Another cold front extended
from the low southwestward over western WY. A dryline was drawn
from central SD across eastern CO and north-central/northwestern NM,
to northern AZ. The eastern cold front should move southeastward
across parts of northern/western NY and New England by 00Z, preceded
by a prefrontal trough. This front should move east of ME by 12Z.
Its western extension, as a warm front, should move northeastward
across the eastern Dakotas and MN, reaching near a FAR-MSP line by
00Z, then crossing most of Lake Superior and Upper MI, and parts of
Lower MI, overnight. The low should move eastward over
northwestern/north-central SD today, then weaken, with the western
cold front reaching northern MN, southern SD, western NE and
southern WY by 12Z.
...ND/SD/MN to central High Plains/Rockies...
Isolated to widely scattered thunderstorms are possible across parts
of northern, central and eastern ND this afternoon and evening, with
a substantial supercell or two potentially offering significant-
severe hail, damaging gusts, and marginal tornado threat.
Although the northern Plains area will be behind the leading/
convectively induced perturbation, any shortwave ridging or
large-scale subsidence that follows will be temporary, in the
broader presence of height falls and strengthening mid/upper winds
related to the upstream shortwave trough. Still, EML-related MLCINH
will limit convective coverage for much of the afternoon, with
strong heating supporting increasing buoyancy. So will increasing
boundary-layer moisture, with both moist advection and upstream
evapotranspiration supporting dewpoint increases into the 60s F
between dryline and warm front. A small corridor of MLCAPE in the
2000-3000 J/kg range will develop along and south of the warm front,
amidst steep midlevel lapse rates, and supercell-favorable deep
shear. Hodographs will be much larger along and north of the warm
front, but so will MLCINH, with considerable doubts that enough lift
will exist to overcome that. As such, the warm-frontal supercell
risk is too conditional and isolated to account for in an
unconditional probability set, but will need monitoring. However,
total forcing should be greater near the low and occluded front.
Farther south, greater convective coverage (widely scattered to
scattered) is possible this afternoon atop a hotter, drier boundary
layer from parts of SD into the central High Plains, becoming more
isolated again across the mountains to parts of central/northern UT.
Severe gusts (some potentially exceeding 65 kt over SD) will be the
main concern, especially as initially widely scattered convection
developing behind the dryline (but in sufficient residual moisture
and atop a very deep/well-mixed subcloud layer) coalesces and
potentially aggregates cold pools. The northeastern part of this
regime may merge with the southern part of the ND activity this
evening. Sporadic severe may be possible well into tonight across
parts of the eastern Dakotas and MN, though potential should
diminish after about 06Z with continued nocturnal stabilization of
the boundary layer.
...Northeast...
Scattered to widely scattered thunderstorms are expected to develop
this afternoon near the prefrontal trough, as already-weak MLCINH
becomes negligible through processes of sustained diurnal heating
(supported by broad clearing already evident in visible satellite
imagery) and moist advection. Scattered to numerous thunderstorms
also may develop along the front over QC where low-level and
mid/upper lift will be relatively maximized, but the coverage and
intensity of these is uncertain by the time the activity reaches
northern New England. In either event, isolated damaging gusts are
possible, and a 5% wind area has been introduced accordingly.
Cooling aloft, ahead of the shortwave trough, will steepen midlevel
lapse rates just enough to support deep buoyancy, with MLCAPE
generally reaching 300-800 J/kg atop 50s to near 60 F surface dew
points, and a well-mixed boundary layer. Low-level and effective
shear will be modest, limiting overall organization, and the
activity should weaken considerably after dark.
..Edwards/Goss.. 06/29/2022
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