RSS Mesoscale Discussions from Storm Prediction Center
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0251 PM CDT Wed May 27 2026
Valid 272000Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
OHIO VALLEY AND MID ATLANTIC...
...SUMMARY...
Scattered severe thunderstorms remain possible across parts of the
Ohio Valley and Mid-Atlantic this afternoon and evening. Strong to
severe gusts capable of producing wind damage should be the primary
hazard, but isolated hail may also occur.
...20Z Update...
The previous forecast (see below) remains generally on track (please
see MCD 876 for short-term severe trends in the Mid-Atlantic
region). The primary change to the outlook was to drop severe wind
and hail probabilities across the TX Panhandle. Here, convection has
failed to deepen, with widespread cloud cover becoming more
prevalent during the diurnal heating maximum. It is unclear if cells
can congeal into larger storm cores capable of producing severe wind
and hail. However, enough overlapping vertical oriented low-level
vorticity and 0-3 km CAPE exists to support a landspout, so 2
percent tornado probabilities have been maintained given the
presence of convective updrafts.
..Squitieri.. 05/27/2026
.PREV DISCUSSION... /ISSUED 1120 AM CDT Wed May 27 2026/
...Ohio Valley/Mid-Atlantic...
30-40 kt of mid-level westerly flow will be present today across
parts of the OH Valley and Mid-Atlantic, sandwiched between an upper
trough over Ontario/Quebec and a mid-level anticyclone centered over
the western Atlantic. A west-east oriented front, modulated by
ongoing convection, will serve as a focus and northern limit for
severe potential. Latest surface observations show a rather moist
low-level airmass present along/south of this boundary (also
reference the 12Z observed soundings from IAD/RNK), with surface
dewpoints generally in the mid 60s to low 70s. Lapse rates aloft are
expected to remain poor, and persistent cloud cover will slow
daytime heating.
Still, weak to moderate instability (MLCAPE 500-1500 J/kg) coupled
with 30-40 kt of westerly deep-layer shear will support organized
thunderstorms this afternoon and early evening as a weak mid-level
shortwave trough moves eastward across the OH Valley/Mid-Atlantic. A
mix of multicells and marginal supercell structures is anticipated
along/south of the front, with scattered damaging winds the main
severe risk. Some hail could also occur with the strongest cores.
The Slight Risk for severe/damaging winds has been expanded westward
into parts of WV and vicinity, where a favorable
environment/convective evolution should occur, similar to locations
farther east in VA/MD along/south of ongoing precipitation.
...Pacific Northwest/Northern Rockies...
A closed mid/upper-level low is not expected to move much over CA/NV
today. Enhanced east-southeasterly mid-level flow and modest
large-scale ascent to the north of this cyclone will likely support
isolated to widely scattered thunderstorms this afternoon and
evening across parts of OR/ID and western MT. Cool temperatures
aloft and adequate low-level moisture should support at least weak
instability as filtered daytime heating occurs. As low-level lapse
rates steepen with the well-mixed boundary layer, isolated severe
gusts appear possible with the high-based convection that develops
and spreads west-northwestward through the afternoon/evening. Some
gusts may reach up to 70-75 mph on a localized basis, but confidence
in a more focused corridor of severe winds remains too low to
include greater probabilities at this time. Isolated hail may also
occur.
...Coastal Texas to the ArklaTex...
An expansive MCS has moved offshore from coastal TX into the western
Gulf late this morning. A leading MCS/outflow is also present across
parts of southern/central LA. Current expectations are for limited
redevelopment and severe risk through the period in the wake of this
ongoing activity across coastal TX/southern LA. However, there may
be an opportunity for modest destabilization near an MCV across the
ArkLaTex vicinity this afternoon. Favorable/veering wind profiles
with height through mid levels and related deep-layer shear (see
recent VWPs from KSHV) would conditionally support organized
thunderstorms this afternoon, assuming sufficient instability can
develop amid widespread cloud cover. Have opted to add a focused
Marginal Risk across portions of the ArkLaTex and vicinity for this
potential, with both occasional damaging winds and a tornado or two
possible with the stronger cells that develop.
...Upper Midwest/Western Great Lakes...
Modest north-northwesterly mid-level flow should exist today across
the Upper Midwest and western Great Lakes. With continued daytime
heating, moderate instability should develop along/south of a weak
surface front. Thunderstorms that initiate along/near the front this
afternoon could pose an isolated threat for severe hail and damaging
winds, particularly across parts of WI where the best convective
signal exists in various short-term model guidance. However, overall
convective coverage is uncertain, as large-scale ascent should
remain fairly weak.
...Southern High Plains...
Cool temperatures aloft in association with a weak mid-level trough
over the southern High Plains should aid at least weak
destabilization this afternoon across parts of northwest TX into the
TX Panhandle and far western OK. While low-level moisture will
remain fairly muted and deep-layer shear rather modest, a few
stronger thunderstorms capable of producing isolated hail/gusty
winds and perhaps a landspout may occur.
Read more
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1230 PM CDT Wed May 27 2026
Valid 281200Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE COLUMBIA BASIN...
...SUMMARY...
Scattered severe storms are possible on Thursday over portions of
the Columbia Basin with more isolated storms across the broader
Northwest region. Damaging winds will be the primary threat, with
some threat for large hail.
...Synopsis...
A mid-level shortwave trough currently on the western periphery of
the broader mid-level low across California at mid-day Wednesday
will move around the low-pressure center and emerge across the
Northwest on Thursday. East of this low, a strong mid-level ridge
will be maintained across the central CONUS with a mid-level trough
in the east. This pattern will result in a mostly nebulous surface
pattern other than a more defined area of high pressure across the
Great Lakes.
...Northwest...
Low-level moisture will increase across the Columbia Basin Wednesday
and Thursday, primarily from the northeasterly surface flow. This
moisture, combined with cooling air aloft and robust surface
heating, will result in abnormally large instability across the
region. In fact, the GFS/NAM/RAP forecast soundings show record-high
MLCAPE values at OTX tomorrow afternoon. Given the climatological
extreme of these values, it seems unlikely to be as high as forecast
(1500-2000 J/kg). However, even 750-1000 J/kg MLCAPE would result in
an environment favorable for severe storms, particularly across
northern Oregon and south-central Washington where even the HRRR
shows 1000 to 1200 J/kg MLCAPE. Very steep mid-level lapse rates
(near 9 C/km) and moderate shear will also support organized severe
storms.
The timing of the mid-level shortwave trough emerging across Oregon
appears to be well-timed with afternoon peak heating. Therefore,
expect storms to initially form across east-central Oregon and move
north-northwestward through the evening. Most 12Z CAM guidance shows
upscale growth into a linear segment which would likely support a
damaging wind threat, particularly given the steep lapse rate
environment. For these reasons, have upgraded to a Level 2 Slight
Risk across portions of the Columbia Basin.
Expanded the wind probabilities across the Cascades slightly as the
environment appears to be favorable to the west of the crests.
However, it appears the marine layer should move into areas such as
Portland prior to the arrival of the storms. Therefore, have kept
severe probabilities east of this zone where the marine layer will
likely have a stabilizing effect.
..Bentley.. 05/27/2026
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SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 PM CDT Wed May 27 2026
Valid 291200Z - 301200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN
MONTANA...THE CENTRAL HIGH PLAINS...AND THE SOUTHERN HIGH PLAINS
INTO SOUTHERN ARKANSAS AND NORTHERN LOUISIANA....
...SUMMARY...
Isolated to scattered storms may produce large hail from eastern New
Mexico and western Texas into southern Arkansas and northern
Louisiana on Friday. Strong to severe storms may also occur across
western Montana with gusty winds and marginal hail. Damaging
thunderstorm wind gusts are also possible across portions of the
central High Plains.
...Synopsis...
A closed low across the Great Basin will become an open wave and
start to advance northeast toward the central Rockies. As this
occurs, lee troughing will begin across the southern and central
High Plains and into eastern Montana. A strong mid-level trough will
move southward across eastern Canada into the Northeast.
...Western Montana...
Weak to moderate instability will build across western Montana on
Friday as dewpoints increase into the mid 50s and mid-level
temperatures cool. Mid-level flow is forecast to increase to 30 to
40 knots across western Montana which will provide sufficient shear
for storm organization. The Marginal Risk was expanded slightly to
account for the likely extent of the threat given the 12Z guidance.
...Central Plains...
Surface moisture is forecast to back up near the terrain across
northern Colorado and southeast Wyoming. This will lead to weak to
moderate instability across the region. In addition to typical
terrain circulations, guidance suggests a weak mid-level shortwave
trough may emerge across the region and provide additional support
for storm development. Shear is forecast to remain relatively weak,
but weak to moderate instability, and steep lapse rates will support
some threat for severe wind gusts.
...Southern Plains into southern Arkansas and northern Louisiana...
A southern stream mid-level jet streak is forecast to emerge from
northern Mexico into the southern High Plains. This ~40 knot jet
streak will overspread portions of the southern High Plains and the
dryline. This should provide ample shear for storm organization
during the afternoon/evening. Greater storm coverage and severe
potential may exist between Midland and Lubbock at the nose of this
stronger mid-level flow. However, there is still some uncertainty
with the timing/location of this jet streak, so will not add higher
probabilities at this time.
Added 5% probabilities farther east across Oklahoma and into
southern Arkansas and northern Louisiana. Moderate instability is
expected south of a frontal zone in this general area. This may be a
focus for storm development Friday afternoon/evening. Shear may be
somewhat weak, but the instability and frontal focus could support a
few strong to severe storms.
..Bentley.. 05/27/2026
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