April 30, 2018 – Drier and warmer this week except for scattered mountain showers and thunderstorms over the Sierra through Wednesday.
Clear to partly cloudy skies across interior NorCal early this morning. It will be a chilly start to the last day in April as current temperatures are in the upper 20s to lower 30s in the mountain valleys, and in the upper 40s to lower 50s across the Central Valley.
It will be another day of cool and unsettled weather as the upper trough continues to dig toward SoCal. Highs today are expected to be a little milder across much of the area compared to Sunday, but will still be around 5-10 degrees below average for late- April. Scattered showers and a few thunderstorms will likely redevelop this afternoon over the northern Sierra, and a few may develop along the Coast Range and foothills.
Northerly flow is expected to increase across the area on Tuesday as we’ll be on the backside of the trough. Locally breezy conditions are expected through the Central Valley. A last batch of short-wave energy is forecast to slide southward keeping a chance for a few showers in the Sierra south of Lake Tahoe. Temperatures will warm around 5-10 degrees as the airmass begins to moderate.
Further warming and drying takes place Wednesday and Thursday as ridging from the eastern Pacific takes hold. Highs on Thursday are expected to be in the 80s through the Central Valley.
Extended discussion (Friday through Monday)
Upper ridging remains in control of the region with dry conditions and above normal temperatures on Friday. The ridge flattens as an upper trough pushes into the West Coast next weekend. The GFS quickly ejects the trough to the east by late Sunday, while the EC keeps troughing over the forecast area through early next week. The upper trough could bring increasing cloud cover and possible mountain showers but specific details remain uncertain this far out. Have decided to keep the forecast dry until model differences are resolved. A lot of differences in models over the weekend, but there would likely be some cooling if trough solution is accurate.