Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0753 AM CDT Thu May 28 2026

Valid 281300Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR WESTERN IDAHO
INTO CENTRAL AND EASTERN PORTIONS OF OREGON AND WASHINGTON...

...SUMMARY...
Scattered severe thunderstorms are possible over western Idaho and
east of the Cascades in Washington and Oregon.  Severe gusts (60-85
mph), large hail, and perhaps a tornado are the forecast hazards
this afternoon through the late evening.

...Columbia Basin vicinity into ID/northern NV...
A mid- to upper-level low over the Sierra Nevada will move little
during the period.  Water-vapor imagery this morning indicates a
disturbance over NV will move north and northwestward through
eastern NV into eastern OR by early evening.  In the low levels, an
area of low pressure is forecast to develop by late afternoon and
migrate from the ID/OR border into the Columbia Basin.  

A plume of steep 700-500 mb lapse rates arc around the northern
periphery of the western U.S. low and extend from the Snake Valley
westward into OR/WA.  As heating of a seasonably moist airmass
occurs, initial thunderstorm activity will gradually shift from
south to north from northern NV/southern ID and southern OR.  Model
forecast soundings show steep low to mid tropospheric lapse rates
favorable for evaporative cooling and the development of strong to
severe downdrafts.  Slightly greater buoyancy is shown in model
guidance farther north in northern OR into western ID (1500 J/kg
MLCAPE).  As storms move into this region during the late afternoon
to evening timeframe, it is possible a more extensive threat for
severe gusts develops.  Regardless, severe outflow both with the
stronger cores and linearly oriented clusters appear to be the main
hazard.  Large hail may accompany the stronger cells.  A continued
threat for scattered severe gusts may occur into the late evening as
this activity shifts northward into interior portions of WA.

...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.

..Smith/Weinman.. 05/28/2026