Unseasonably warm, quiet weather along the West Coast is drawing to a close as the dominating high pressure begins to dissipate and pave the way for cooler, wetter, and possibly stormier conditions.

Throughout the last week, the West Coast has experienced abnormally warm, dry weather, with afternoon highs 10 to 15 degrees above the norm for March. This warm spell has been especially pronounced across the Pacific Northwest, where several record highs were broken in Washington.

Although the recent conditions offered a taste of summer, shifts in the upper atmosphere signal significant weather changes are on the horizon. As the aforementioned high-pressure system weakens, it will open the doors to a moisture-laden Pacific storm, bringing cooler and wetter conditions this week.

Starting Wednesday, the Pacific Northwest will see an uptick in rain chances, spreading to Northern California by Thursday. This pattern will persist, and by Friday evening, the low-pressure system will have settled over the Pacific Northwest, bringing more widespread rainfall from Washington to northern California.

Moreover, the forecast includes a potential for valley thunderstorms, particularly affecting areas like Sacramento by Saturday. Speaking of potentially impactful weather, the Cascades and Sierra will see additional rounds of heavy snow through the weekend, making travel in and out of the region difficult at times.

With little change in the atmospheric pattern, the cool and wet conditions are expected to continue through the weekend. Additional rounds of showers will gradually increase the risk of isolated flash flooding in the valleys. Meanwhile, mountain areas could accumulate 1 to 2 feet of snow above 6,000 feet by Monday.