Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Thu May 28 2026
Valid 281200Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE PACIFIC NORTHWEST...
...SUMMARY...
Thunderstorms with severe wind gusts, large hail and an isolated
tornado threat are expected across parts of the Pacific Northwest
this afternoon and evening.
...Pacific Northwest...
An upper-level low will remain over central California today. On the
northern periphery of the system, bands of large-scale ascent will
move westward across the Pacific Northwest, providing support for
thunderstorm development. At the surface, a low will deepen and move
northwestward from eastern Oregon into southern Washington. A
surface trough will extend southward from the low into north-central
and west-central Oregon. Thunderstorms are forecast to first develop
across southern Oregon around midday, with convective coverage
gradually increasing over much of Oregon during the afternoon. A
larger-scale line segment is expected to organize and move
northwestward across Oregon late this afternoon and into southern
Washington early this evening.
As surface temperatures warm today, instability will increase along
the surface trough with MLCAPE expected to peak in the 1200 to 1500
J/kg range. The instability combined with 30 to 40 knots of
mid-level east-southeasterly flow, along with low to mid-level lapse
rates in the 8 to 8.5 C/km range, will support severe thunderstorm
development. This environment will be favorable for severe wind
gusts and isolated large hail within the stronger parts of an
extensive line segment. Near the surface trough, 0-3 km
storm-relative helicity is forecast to increase into the 200 to 250
m2/s2 range by late afternoon, which could also support an isolated
tornado threat. Any tornado threat would mainly be associated with
rotating elements embedded in the line. As the line moves
north-northwestward and expands, a severe threat is expected to move
into southern Washington by early evening. A marginal severe threat
could impact parts of central and northern Washington later in the
evening.
...East-central Colorado...
A mid-level trough will move northward across the central Plains
today. At the surface, upslope east-southeasterly flow will be in
place across eastern Colorado. Along the Front Range, the Denver
Cyclone is expected to develop by afternoon. Topographic lift and
increasing low-level convergence will result in scattered
thunderstorm development from the Palmer Divide northward into
north-central Colorado. Forecast soundings along this corridor by
late afternoon have 0-6 km shear in the 20 to 30 knot range with
700-500 mb lapse rates around 8 C/km. This should support a hail
threat with the stronger cells.
..Broyles/Chalmers.. 05/28/2026
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