SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1246 AM CDT Wed Mar 26 2025 Valid 261200Z - 271200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE PACIFIC NORTHWEST... ...SUMMARY... Severe thunderstorms are forecast across parts of the Pacific Northwest this afternoon and evening. Supercells are expected west of the Cascades across Oregon into Washington. These may produce large hail, perhaps a brief tornado, and locally strong gusts. ...Pacific Northwest... Seasonally strong upper low off the Pacific Northwest Coast will shift east today as a 100+kt 500mb speed max translates toward the OR Coast by late afternoon. Strong 12hr height falls will spread across this region and the associated synoptic cold front should arc from off the WA Coast-south along the OR Coast by 27/00z. Upper ridging has permitted boundary-layer moisture to increase/hold across both the interior Northwest, and west of the Cascades where surface dew points are currently in the mid 50s. While PW values are not forecast to be particularly high across this region, large-scale forcing will contribute to moistening profiles and PW values may approach 1 inch prior to convective initiation. Of particular concern are the cold mid-level temperatures, and the steep lapse rate plume that will overspread this region. Forecast soundings suggest convective temperatures should be breached by 21-22z west of the Cascades, and surface-based CAPE should approach 1000 J/kg within a favorably sheared environment for organized, rotating updrafts. Latest thinking is isolated-scattered robust convection will develop by 21-22z across western OR, immediately ahead of the strong forcing. This activity should grow upscale and lift north-northeast ahead of the approaching speed max. Profiles favor supercell development and latest HREF guidance supports this scenario. Hail should be common with this activity and the strongest updrafts may generate quite large stones, possibly exceeding golf ball size, or even larger with the strongest storms. While a brief tornado can not be ruled out, low-level shear does not look particularly favorable for more than an isolated report. Damaging winds are also possible with any of these supercells. Strongest storms should spread into WA during the early evening as the short wave ejects northeast. ...Lower Rio Grande River Valley... Water vapor imagery depicts a substantial sub-tropical cirrus plume from the southern Baja Peninsula, across Mexico toward the lower Rio Grande Valley. Latest model guidance suggests a weak disturbance will approach the international border by mid day and this will draw a substantial moisture plume into south TX. Forecast soundings exhibit modest lapse rates despite the moistening profiles. While forecast shear is not particularly strong, some organization is possible and this activity could generate gusty winds or perhaps some hail. Otherwise, a considerable amount of convection/precip is expected across this region which may disrupt/limit organizational potential. ..Darrow/Lyons.. 03/26/2025