RSS Mesoscale Discussions from Storm Prediction Center
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Sun Jun 21 2026
Valid 212000Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE CENTRAL HIGH PLAINS TO THE MISSISSIPPI AND LOWER OHIO VALLEYS...
...SUMMARY...
Scattered severe thunderstorms should occur from the central High
Plains into the mid Mississippi and lower Ohio Valleys, mainly this
afternoon into tonight. Large to very large hail, severe/damaging
winds (some 75+ mph), and tornadoes will all be possible. Some
potential for strong tornadoes may develop across parts of Illinois,
and Indiana during the afternoon and evening.
...20z Update Mid MS Valley and lower OH Valley...
Minimal changes were made to the prior outlook given the latest
observational trends. Several clusters of strong thunderstorms are
ongoing ahead of an MCV across the mid MS Valley. An observed messy
convective mode should persist with a mix of bowing structures and
transient supercells likely ahead of the MCV, and near the effective
warm front from eastern IL into IN. Additional storm development is
also possible behind the MCV along the remnant boundary into MO and
eastern KS. This will support a risk for damaging gusts and perhaps
a couple of tornadoes where low-level flow is backed and hodographs
are larger. Eventually upscale growth into one or more bowing
clusters is likely later this evening/overnight into the OH valley
with a continued risk for damaging gusts and embedded tornadoes.
...KS/OK this evening/tonight...
Severe storm development appears probable along the modified
trailing outflow across northwest OK and southwest KS this afternoon
into this evening. Sufficient vertical shear exists for supercells
and organized clusters. With large buoyancy and steep low/mid-level
lapse rates, large hail is likely with these strong updrafts. A
brief tornado or two is also possible, owing to storm interactions
and ambient vertical vorticity along the outflow boundary.
Damaging wind potential will likely increase with storm
consolidation, though the more cellular initial mode suggests this
maybe somewhat gradual. These storms, and additional convection
originating further north from the central High Plains, should
persist overnight into central and southern OK, reaching the Red
River Valley by 12z tomorrow morning with isolated severe potential.
..Lyons.. 06/21/2026
.PREV DISCUSSION... /ISSUED 1110 AM CDT Sun Jun 21 2026/
...MO/IL/IN/KY...
A long-lived band of thunderstorms currently extends from
east-central MO into southwest MO/northeast OK. This activity is
tracking into a region of increasingly warm/moist air where
dewpoints are rising to near 70F and breaks in the clouds are
contributing to moderate CAPE values. All CAM guidance suggests
that storms along the line will intensify this afternoon and track
eastward across southern IL/southern IN and northern KY. Low-level
shear is quite strong, but somewhat veered. This increases
uncertainty of storm mode between discrete supercells or bowing
structures. It appears there will be a period of risk early in the
event for tornadic supercells, followed by multiple linear storm
segments capable of damaging wind gusts. Storms may remain severe
as far east as southern OH and eastern KY overnight. Refer to MD
#1228 for further short-term details.
...MO/KS/OK/AR...
In the wake of the aforementioned convection, an outflow boundary
extends southwestward into central OK. Rapid clearing is occurring
north of the boundary, where residual moisture and steep lapse rates
will quickly destabilize the area. Scattered thunderstorms are
expected to form by late afternoon in this zone and track slowly
southeastward. Sufficient deep-layer shear and high CAPE will
promote the risk of a few supercells capable of large hail and
damaging winds. A tornado or two might also occur.
...NE/CO/KS...
Low clouds are eroding across the NE Panhandle southward into
eastern CO/western KS, where rapid afternoon destabilization should
occur. A weak shortwave trough over eastern WY will rotate into the
region this afternoon, helping to initiate scattered thunderstorms.
Supercells capable of very large hail appear possible, tracking
southeastward across the risk area through mid-evening.
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1221 PM CDT Sun Jun 21 2026
Valid 221200Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MID-ATLANTIC INTO SOUTHERN APPALACHIANS...AND OVER PARTS OF THE
NORTHERN AND CENTRAL HIGH PLAINS...
...SUMMARY...
Scattered severe storms appear possible across portions of the
Mid-Atlantic into the Southern Appalachians Monday afternoon and
evening. Widely scattered severe storms are expected across the
northern and central High Plains, with more isolated severe weather
possible from the southern Plains into the lower Mississippi Valley.
...Synopsis...
A series of perturbations, embedded within broadly cyclonic
mid-level flow, will progress eastward to the Atlantic Coast, to the
south of an upper low tracking from eastern Ontario into southern
Quebec. Farther west, separate vorticity maxima will overspread the
northern and central High Plains, in tandem with a belt of
strengthening mid-level winds.
In the lower levels, a 40-50 kt low-level jet (LLJ) is forecast to
migrate from the Allegheny Plateau into the lower Hudson and DE
River Valleys Monday afternoon, ahead of a surface low developing
toward those same areas. Meanwhile, a trailing cold front will
advance south through the central Appalachians, TN Valley, and Ozark
Plateau, with the western extension of the boundary linking with a
secondary low over western TX. Elsewhere, a lee cyclone is expected
to deepen over eastern WY, along a weak front settling southeast
through the northern High Plains.
...Mid-Atlantic into the southern Appalachians...
12Z CAM guidance is in relatively good agreement in depicting the
remnants of an overnight (Sunday night/early Monday morning) MCS
overspreading NY and PA, within a zone of warm air and moisture
advection occurring with the terminus of the LLJ. To the
south/southeast of that convection across the lower Hudson and DE
River Valleys, modest air mass destabilization is expected, with
comparably stronger instability with southward extent into the
central/southern Appalachians and Piedmont. Deep-layer shear is
forecast to strengthen through the day as a belt of 40-50 kt winds
at 500 mb overspreads the region from the west.
Thunderstorms are expected to increase in areal coverage and
intensity during the afternoon from the vicinity of the outflow or
differential heating boundary in eastern PA south/southwest into the
southern Appalachians and Piedmont. Damaging winds will be the
primary hazard owing to steepening low-level lapse rates and high
moisture content, which will enhance wet-microburst processes. A
relatively narrow corridor of potentially greater tornado potential
may materialize from the DelMarVa into the DE River Valley, where
stronger low-level shear is forecast. However, given uncertainties
in the degree of air mass destabilization in the northern extent of
that area, the 2% unconditional tornado probability will be
maintained. A separate area of tornado potential may materialize
Monday afternoon across parts of the southern Appalachians within
the southwest extension of the LLJ, where a number of the 12Z CAMs
indicate updraft-helicity swaths embedded within a linear complex of
storms.
...Northern and central High Plains...
The deepening lee cyclone will enhance the flux of an increasingly
moist low-level air mass into the high terrain, beneath a plume of
steep mid-level lapse rates, supporting moderate afternoon
instability. Greatest storm coverage is expected across portions of
eastern MT and western ND Monday afternoon within the northern
extent of the instability axis, where the strongest forcing for
ascent is expected. Weaker forcing with southward extent is expected
to lead to more widely spaced storms in eastern WY and CO. Here,
comparatively stronger instability and vertical shear will support
supercells capable of large to very large hail and perhaps a brief
tornado or two during the afternoon and evening hours.
...Southern Plains...
Areas of storms ongoing Monday morning across parts of the Red River
Valley into the ArkLaTex region are expected to gradually weaken by
midday, owing to rising mid-level heights across the region. In the
wake of that activity, moderate to strong instability is forecast by
afternoon in the vicinity of the stalled synoptic front and any
remnant outflow boundaries. However, considerable uncertainty
remains in surface-based storm development given the absence of
appreciable forcing for ascent. As such, the low unconditional
probabilities will be maintained with this forecast update. On the
condition surface-based storms develop and are sustained, the
parameter space would support intense supercells capable of large to
very large hail and some tornado threat.
..Mead.. 06/21/2026
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SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0216 PM CDT Sun Jun 21 2026
Valid 231200Z - 241200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE CENTRAL
HIGH PLAINS...
...SUMMARY...
Scattered severe storms are expected across the central High Plains
on Tuesday with isolated severe storms possible into the Upper
Mississippi Valley. Large to very large hail and damaging wind gusts
will be the primary threats.
...Synopsis...
An upper low initially over Saskatchewan/Manitoba will drift
southeast to along the international border with an attending belt
of 40-50+ kt mid-level flow forecast across the northern and central
Plains into the upper Midwest. Farther east, a short-wave trough
trailing an upper low over Ontario will move through the
Mid-Atlantic. In the low levels, an area of low pressure is forecast
to develop from the northern Plains into upper MS Valley with a
trailing boundary extending southwest into the central High Plains.
Elsewhere, a cold front will move off the Mid-Atlantic Coast with
the trailing extension of the boundary moving into the Southeast.
...Central and southern High Plains...
Despite the potential for early-day storms across portions of NE,
TX, and OK, the EML is expected to remain intact over the central
High Plains. When coupled with an increasingly moist upslope air
mass in the vicinity of the front, moderate to strong instability is
forecast by afternoon. Diurnally enhanced thunderstorms are expected
to form along favored terrain and pre-existing surface boundaries
amidst a kinematic environment featuring vertically veering winds
with height with sufficient vertical shear to support supercells
capable of large to very large hail. The nocturnal strengthening of
a low-level jet over western parts of KS, OK, and TX may favor
upscale growth of storms into a forward-propagating MCS Tuesday
evening with an associated increase in severe-wind-gust potential.
...Upper Mississippi Valley into the mid Missouri Valley...
Latest model data are in good agreement in depicting areas of
showers and storms lingering through much of the day across the
pre-frontal warm sector. Vertical shear is forecast to be
sufficiently strong to support organized storm modes, especially
across the upper MS Valley. However, the potential for clouds and
precipitation to limit air mass destabilization leads to uncertainty
in the extent of the severe-weather threat. As such, the low
severe-weather probabilities will be maintained with this forecast
update.
...Middle and southern Atlantic Coast into the central Gulf Coast
States...
A few strong storms capable of gusty winds appear possible Tuesday
afternoon along and ahead of the synoptic front. While poor
low/mid-level lapse rates are expected to limit a more robust
damaging-wind threat, low severe-weather probabilities may
eventually be added once details in storm evolution become more
clear.
..Mead.. 06/21/2026
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