Chris Fontana, "The Old Forecaster" 5/21/2013
This morning's satellite picture (below) shows the cold low pressure area dropping southward along the Canadian Coast. This system will move inland over the Pacific Northwest tonight and early Wednesday and will remain there Thursday. The low has cold air...for this time or year...associated with it, but not a lot of moisture.
Today there will be increasing clouds across the north coast, Trinity, Siskiyou, northern Shasta and Modoc counties with isolated showers over the northwest corner of the state. The rest of Northern California will be mostly sunny with a few clouds in the afternoon. Temperatures today will drop 6 to 12 degrees. Gusty southwest to northwest winds will occur with gusts 35 to 45 mph over eastern Siskiyou and Modoc counties.
Wednesday and Thursday the north coast, Trinity, Siskiyou, northern Shasta, and Modoc counties will be partly cloudy with isolated light showers. Snow levels will be 5000 to 6000 feet. Lassen, Plumas and the higher elevations of Nevada county will see some afternoon clouds with the chance of a light shower. The valley will be sunny with some afternoon clouds. Temperatures will be 15 to 25 degrees below normal in the north where the clouds are and 8 to 14 degrees below normal elsewhere. The valley will be in the low to mid 70s Wednesday and Thursday. Gusty southwest to northwest winds will continue in the afternoon and evening.
Friday the low will begin to move eastward. There will still be a few clouds near the Oregon border but for the most part the state will be partly to mostly sunny. Temperatures will normal or a few degrees below normal. Saturday and early Sunday another low pressure area will be off the coast. This is a weak system and not as cold as the current one. However, it will have a few more clouds with it. Saturday and early Sunday there will be partly cloud skies across the north state with a few light showers over the foothills and mountains. Temperatures will continue normal or a few degrees below.
This low will move east of our area Sunday afternoon. A weak high pressure ridge will rebuild along the coast. Monday and Tuesday will be mostly sunny with temperatures near or a little above normal.