An unusually strong weather system will move across the area tonight into Saturday. It will bring much cooler temperatures, rain (mainly north of I-80) with isolated thunderstorms with small hail and lightning and gusty winds. Temperatures will warm up quickly after this system early next week with 90s to near 100 degrees.
Discussion
Key Points
- Robust weather system impacting the area Thursday into the early weekend.
- A Flash Flood Watch has been issued for the Park Fire Burn Scar from 11 AM Friday to 11 AM Saturday for possible debris flows within and downstream of the burn scar.
- Isolated to scattered showers/t-storms with 15-30% chance of thunderstorm development mainly north of I-80 Thursday into early Saturday.
No real changes to the forecast with a strong unusual storm system to move across the area tonight into Saturday. The upper trough is already digging into northwest NorCal. Some energy moving around the trough and overall lift from the upper low will bring showers and a few thunderstorms to far northern counties…mostly confined to Shasta county. Not expecting anything of significance south towards the Park Fire burn scar.
Friday, the first main chunk of energy will push across NorCal. The timing of this energy moving across has been advertised well by the models. As it does, will be lots of clouds around to limit daytime heating and also the main cold part of the upper low will remain in Oregon. This will limit the chances of stronger thunderstorms in northern counties. That being said, overall expected a larger area of rain showers and rain with isolated thunderstorms to push across basically the northern half of the forecast area Friday afternoon through the night. Rainfall rates on the Park Fire burn scar will be tested as rainfall rates are very low there right now. Too close to call at this point but nearly all convective allowing models and ensembles not pointing to much organized convection which makes sense given the timing of the wave and lack overall of much instability. For that reason we will keep the Flash Flood Watch for the Park Fire burn scar going.
Last chunk of the upper low push out of the are Saturday morning. It may linger a bit into Saturday afternoon which may extend the risk of heavier showers over the burn scar but for now looks to be pretty good subsidence behind the energy for general less chances by Saturday afternoon.
Extended Discussion (Monday through Thursday)
Good ensemble agreement that the warm up for the start of the week next week. By Tuesday probabilities increasing for most areas to be in the upper 90s to around 100. Some uncertainty in the strength and timing of next chunk of weaker energy later in the week but at this time doesn’t appear to be very impactful.