April 18, 2021 – Dry and well above normal temperatures through Monday. Cooler Tuesday with the chance of mainly mountain showers and isolated thunderstorms. Slight chance of showers Wednesday before returning to dry weather for the mountains.
Discussion
High pressure will continue through Monday. Light winds with little change to some minor cooling for the daytime high temperatures are expected on Monday. We should see an increase in winds late in the day in the Delta that should persist through at least the evening hours as well.
Early Tuesday a low pressure system will begin to move into the far part of the state. Some showers and maybe a few mountain thunderstorms may be possible with the best chances around I-80 northward during the day. As the low shift southward in the evening hours chances of showers and thunderstorms shifts southward from around Alpine County north through Plumas County. Snow levels will be around 7500 feet with 1 to 3 inches of snow possible over the peaks. The pace of the low moving southward has increased from yesterday as a result there are increased areas further south with chances of precipitation. The other notable change is winds will shift northerly during the afternoon in the valley but do not look to be strong.
Wednesday there is low confidence in continuing mountain showers. Models in disagreement on the placement of the low either well east of the region or remaining over California. Clusters have shifted the trough axis south into Southern California compared to yesterday when it was over Central California so the trend is toward less of a chance for precipitation.
Extended discussion (Thursday through Sunday)
A ridge of high pressure will return for this Thursday and Friday with drier and warmer conditions returning. Temperatures remain roughly 10 to 15 degrees above normal during this time.
A pattern change may be seen over the weekend into next week, although cluster analysis still indicates considerable timing issues on when a trough will move over area currently keeping the trough off the coast next Sunday. The deterministic European and GFS models are in good agreement indicating the potential for a decent late season storm moving into the region next Sunday. Uncertainty continues that far out.