The active weather pattern that we’ve experienced will be coming to an end this week. However, before it does, we will see more rain and snow. An upper level low is dropping a cold front into our area and it will move onshore into the evening hours tonight. Ahead of this front, a line of showers that is tracking along the I-5 corridor at the moment. Showers will begin increasing along the Cascades and the Basin will see these showers overnight. Behind the line, post-frontal showers will stick around throughout Sunday afternoon. So expect light, isolated showers in all areas throughout the day tomorrow.
Cooler air is behind the front and will move in tonight. Snow levels at the moment are around 5,000′ and will drop down to 4,000′ overnight. The Cascades and Siskiyous will see fresh snowfall of anywhere from 2″-4″ of accumulation over the next 24 hours. Daytime temperatures will get above freezing and cause some melting through the day. Mountain passes above 4,000′ will be impacted by snow overnight and then slush during the day. The snow levels in the Basin will start out at 4,300′ Sunday morning and will rise through the day. Less than an inch of snow accumulation is expected in the Basin.
Instability will be a factor through tomorrow causing a slight chance for thunderstorms. Because of this we could also see hail and graupel form and fall in some areas. This will depend on the updrafts of these storms. Mountain locations could see hail due to orographic lifting. Fog will also be seen in areas that are prone to it. The saturated air mass will cause clouds to lower overnight and mountain fog will not be out of the question.
Shower activity will decrease and fizzle out by the late afternoon on Sunday. A high pressure ridge will move into the area after that. As the ridge is strengthening, a warm front offshore will be passing us and this could bring a chance for shower activity to the area. The only issue is that models are in extreme disagreement in exactly if and when we will get showers. As for now I decided to put a small chance in the forecast. Mostly cloudy skies are expected. As we move closer to the event, we will have a better understanding of where the rain will end up. This is the last chance for precipitation before the high pressure ridge dominates the area. Mostly sunny skies and warm temperatures are in the forecast for the week ahead. When the ridge gets far enough inland, winds will shift to the east and this will set up a Chetco Effect for the Coastal regions. Temperatures will get warm with the offshore flow and the lower 70s are expected on Tuesday and Wednesday. Temperatures in all regions will warm up above average for the rest of the week. The next chance for precipitations will not be until the weekend.
Thanks for logging on and enjoy your weekend.
Meteorologist Seth Phillips