Yesterday a wave of cold air from British Columbia and Alberta blew down straight north to south, bringing colder, drier air to all the West Coast. The wind blast of Saturday morning was once a big rain and snow maker in Seattle, but was bone dry before even reaching southern Oregon. Airflow that goes north to south makes precipitation bands die.
Next, a strong storm center drifted south behind the blast front, moving much more slowly. The strong center was able create winds from the southeast that were stronger and faster than the northwesterly direction it was traveling, producing a healthy rain band that had great hang time, while working its way south down the entire length of California. In fact, it became stronger the farther south it got. The San Joaquin Valley got its first soaking rain session, the Sierra the storm that possibly started the ski season. Hopefully. We'll know for sure by tomorrow if it was enough snow.
Meanwhile, very active weather over the pacific. A Rossby Wave, waves of cold low pressure toughs essential for winter storm building, dropped so low, it spawned a "cutoff low" that drifted down to Hawai'i, an event called a "Kona Low." The cutoff low has produced heavy rains and flooding in Hawaii. These cutoff lows can save a rainy season when they drift Northeast to California. The fact that Hawai'i is having extreme weather at all may eventually bode well for California.
