SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Mon May 30 2022
Valid 301300Z - 311200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
EASTERN SOUTH DAKOTA...EXTREME SOUTHEASTERN NORTH DAKOTA AND WESTERN
TO NORTHERN MINNESOTA...
...SUMMARY...
Numerous severe thunderstorms are forecast across parts of the
Northern Plains and Upper Mississippi Valley, with more scattered to
isolated activity southward into the central Plains today into
tonight. Large to giant hail, 60-80 mph gusts, and tornadoes are
probable, including the possibility for a couple strong/long-tracked
tornadoes.
...Synopsis...
A large field of mid/upper-level cyclonic flow covers most of the
western/central CONUS, anchored by a broad, complex cyclone covering
much of the northern/central Rockies and Intermountain region.
Primary vorticity maxima are evident in moisture-channel imagery
over ID and central/eastern CO. The latter will eject northeastward
today, become a compact, closed cyclone in its own right, and deepen
considerably, with the 500-mb low reaching east-central SD by 00Z.
Meanwhile the western vorticity lobe will remain weaker and meander
around southern ID/northern NV through the period.
The 11Z surface analysis showed a low over extreme southeastern ND,
with cold front across eastern SD, south-central NE, northwestern
KS, and central CO. Another low was noted along the dryline between
GCK-HYS. The southern low will move northward, merge onto the
front, and intensify through the day as its mid/upper counterpart
approaches, until the lows become stacked over east-central SD
around 00Z. By then the surface low should be occluded, with a
triple point over southwestern MN and cold front arching across
western IA, southeastern NE and northern/western KS.
An outflow boundary from prior MCS activity was drawn across
southwestern MN, northwestern IA and northeastern NE. This boundary
may maintain its identity for a few more hours before retreating
northward and becoming more ill-defined amidst intense
surface-850-mb warm advection and moisture transport. Both ongoing
and future/intervening convective processes cast uncertainty over
specific timing/location of these features across the northern
Plains and Upper Midwest into the afternoon. A dryline -- drawn
initially across western KS, the TX Panhandle and southward into the
Big Bend region -- will shift eastward to central KS, western OK and
west-central TX this afternoon, before being overtaken from
north-south by the cold front over KS tonight.
...Northern Plains/Upper Midwest...
Scattered to numerous thunderstorms, offering tornadoes (some
potentially strong/EF2+), severe wind and occasional large/damaging
hail, will be possible into this evening. The greatest coverage
should be in and near the "moderate" and "enhanced" categorical
areas, where low-level convergence and convective coverage each
should be greatest. The main convective regime should develop as
early as midday near the retreating outflow boundary across northern
NE, southeastern SD and southwestern MN, growing upscale and
sweeping north-northeastward through the remainder of the outlook
area this afternoon and early evening.
With the passage of such an intense prior-overnight/morning MCS to
the south and east of the axis of the outlook area, and a
well-defined outflow boundary currently entirely displaced from the
greater severe probabilities, normally there would be great
concern/uncertainty about airmass recovery. To some extent there is
-- especially with northern extent across ND/MN. This is not a
"normal" scenario, however, with higher-end kinematic/mass response
to the approaching cyclone fostering very intense, deep-tropospheric
meridional flow (the direction needed for favorable thermodynamic
recovery) and related strong surface-850-mb warm advection. The
remains of the outflow boundary accordingly should disperse through
the day, and the stable air to its north will modify and advect
northward out of at least some, perhaps most, of the outlook area.
The probabilities supporting "enhanced" and "moderate" risks have
been adjusted slightly eastward and compacted on the west side, to
reflect the likely tight gradient between substantial and limited
severe potential. Still, the axis of greatest probabilities remains
somewhat uncertain and fluid, and may need further adjustment
through the day as mesoscale trends warrant.
Despite the component of mean-wind and deep-shear vectors off the
axis of strongest low-level forcing, the intense deep-layer lift may
compel a relatively quick transition from initial supercellular
characteristics to mixed modes, then quasi-linear with embedded
LEWPs/bows/mesocirculations. Forecast soundings suggest 2000-3000
J/kg MLCAPE can develop across the corridor from northeastern NE to
central MN before the main round of convection, along with 55-70-kt
effective-shear magnitudes, and effective SRH in the 150-300 J/kg
range, with long, somewhat curved hodographs.
...Western IA to eastern/southern KS...
Widely scattered to isolated thunderstorms may develop late this
afternoon into evening in a northeast/southwest corridor related to
the front and dryline. Though coverage may be limited by stronger
EML-related capping, and weaker deep-layer forcing that farther
north, the parameter space in the adjacent warm sector will be
favorable for supercells. The stronger MLCINH also may favor
longer-lasting, relatively discrete modes, further supporting the
somewhat conditional tornado and significant-hail threats. Enough
guidance indicates development of at least a few sustained cells in
this regime that unconditional probabilities have been increased.
This area will reside near the axis of the strongest 300-700-mb flow
this afternoon and evening, enabling 55-65-kt effective-shear
magnitudes, while low-level shear/hodographs enlarge with the LLJ
intensification in the 00-03Z time frame. Surface dew points
generally in the 60s F and steep low/middle-level lapse rates will
support a plume of 2000-3000 J/kg MLCAPE parallel to and ahead of
the front and dryline.
..Edwards/Mosier.. 05/30/2022
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