RSS Mesoscale Discussions from Storm Prediction Center
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1051 AM CDT Tue Apr 21 2026
Valid 211630Z - 221200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
OVER THE CA CENTRAL VALLEY...AND OVER PORTIONS OF NORTHERN IL/IN...
...SUMMARY...
Isolated strong thunderstorms are possible in the California Central
Valley, capable of gusty winds and perhaps a tornado or two. Other
strong storms are possible in parts of northern IN/IL where gusty
winds may occur.
...Central CA...
Morning water vapor loop shows a well-defined shortwave trough
approaching the coast of central CA. An associated mid/upper level
jet will nose into CA, with forcing for ascent in the left-front
quadrant of the jet aiding in the development of afternoon/evening
thunderstorms over parts of the Central Valley. Forecast soundings
show steep low and mid level lapse rates and sufficient CAPE for a
few robust updrafts. Vertical shear will be strong enough for
supercell structures, including a risk of a tornado or two, small
hail, and gusty winds.
...Northern IN/IL...
A fast-moving shortwave trough currently over IA/MN will track
quickly southeastward into WI/IL/IN this afternoon. Visible
satellite and radar imagery show a line of high-based thunderstorms
developing ahead of the trough over southern WI. As these storms
track into northern IL/IN, continued heating/weak destabilization
will increase the risk of gusty/locally damaging wind gusts and
small hail in the strongest cores this afternoon.
..Hart/Flournoy.. 04/21/2026
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1224 PM CDT Tue Apr 21 2026
Valid 221200Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
HIGH PLAINS...
...SUMMARY...
Severe thunderstorms capable of hail and gusty winds may develop
during the late afternoon and evening on Wednesday across portions
of the High Plains.
...Synopsis...
A broad trough within parts of the Northwest and Great Basin will
progress eastward through the day Wednesday. The mid-level jet will
round the base of this trough and impact the northern High Plains
during the evening overnight. A secondary mid-level jet will dig
into the Southwest by early Thursday morning. The upper-level ridge
across the Plains will begin to break down and shift eastward. At
the surface, a deep surface low will track along the Montana/Canada
border. Strengthening flow across the Rockies will promote a
moderately strong lee trough. Surface moisture will continue to
advect north and west during the period. Richer moisture will
generally remain within the southern Plains and adjacent High Plains
with less certain moisture quality farther north.
...Western Nebraska...western South Dakota...
With greater large-scale ascent and closer proximity to the surface
low, confidence in storm development is higher in these areas. The
main question will be the degree of moisture return that can occur
through the day. Model guidance still varies widely in this regard.
Dewpoints near 50 F are possible into southwest Nebraska, but this
may occur towards 00Z or later. Farther north, dewpoints in the 40s
F may be the ceiling for late afternoon/early evening. A probable
scenario is that high-based convection develops within the terrain
of eastern Wyoming/western South Dakota and within the surface
trough. Some intensification is possible as this activity encounters
greater surface moisture to the east. Severe wind gusts will be the
main hazard given the steep low-level lapse rates and inverted-v
thermodynamic profiles. Linear structures would be favored in South
Dakota given the deep-layer flow orientation. A supercell or two
could occur in western Nebraska, should storms form.
...Southern High Plains into Western Kansas...
With the synoptic trough lagging to the west, mid-level height falls
will be very weak during the afternoon. The dryline/surface trough
will be the focus for storm development. Temperatures nearing 90 F
behind the dryline appear sufficient for an isolated storm or two to
develop. That said, some guidance does not develop any convection.
Deep-layer shear will be roughly perpendicular to the surface trough
and mid-level lapse rates will be steep. Storms that can develop
will be supercellular. Large hail would be the main concern with
this activity.
...Eastern Montana...
High-based convection is possible in association with the deepening
surface low. Dewpoints will not likely reach 40 F. Gusty outflow
winds are possible, but potential for severe gusts is low.
..Wendt.. 04/21/2026
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SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0237 PM CDT Tue Apr 21 2026
Valid 231200Z - 241200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF THE
MID-MISSOURI VALLEY VICINITY INTO SOUTHERN KANSAS AND NORTHERN
OKLAHOMA...
...SUMMARY...
Severe thunderstorms will be possible from northern Oklahoma into
southern Minnesota on Thursday. Large hail to very large hail,
damaging winds, and a few tornadoes are possible.
...Synopsis...
Two shortwave troughs within a larger-scale trough over much of the
Rockies will pivot northeast on Thursday. The initial shortwave will
impact parts of the central Plains and mid-Missouri Valley. A
second, compact shortwave will pivot into parts of Oklahoma and
Kansas. At the surface, moisture return will continue ahead of a
Pacific cold front in the central Plains. A weak surface low is
expected to develop along the Oklahoma/Kansas border and track
eastward. Attendant to this low, a dryline will drape southward into
the Permian Basin.
...Central and southern Kansas...Oklahoma...
With mid-level ascent arriving mid/late afternoon, storms are likely
to initiate along the cold front as well as near the triple point
associated with the weak surface low along the KS/OK border.
Supercells are most likely near the triple point and could persist
so long as storm interactions remain minimal. 40-45 kts of shear and
2000-3000 J/kg MLCAPE will promote storms capable of all hazards,
including tornadoes and very-large hail. A strong low-level jet will
develop ahead of this activity during the evening. The tornado
threat could increase for storms that can remain discrete.
In Oklahoma, if and how many storms develop remains uncertain along
the dryline. Northern portions of Oklahoma are more likely to have
severe storms given the proximity to the surface low. A similar
environment will exist east of the dryline as does farther north
into southern Kansas. There is a conditional threat for all severe
hazards.
...Mid-Missouri Valley...
Storms are expected to develop along the cold front potentially as
early as mid afternoon. However, capping appears strong enough in
forecast soundings that initiation could delay until late afternoon.
Steep mid-level lapse rates will be in place along and ahead of the
front. Deep-layer shear will be 30-40 kts, but generally parallel to
the front. Initial storms could be supercellular and produce large
to very-large hail early in the convective cycle. Upscale growth
appears likely to occur rather quickly. Damaging/severe winds would
become the primary risk at that point. Tornadoes are also possible
given the low-level shear, both with initial supercells and perhaps
with QLCS circulations.
..Wendt.. 04/21/2026
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