May 30, 2019 – Mainly late-day and evening mountain showers and thunderstorms through the weekend as an upper low drops slowly south through the region. Temperatures remaining a little above average. Temperatures warming to well above normal early next week with a slight threat of Sierra afternoon thunderstorms continuing.
Showers have ended for tonight as more stable nighttime conditions prevail and skies have cleared most areas. No significant change in the forecast as an upper low now centered over southwest Oregon continues to track southward. Showers and thunderstorms a good bet to return again later today as the upper low drops into NorCal.
Cape values over NorCal are expected to be similar to Wednesday with PW values similar as well as around an inch layer precipitable water lingers over the region. Most thunderstorm activity will be over the mountains but solar heating will allow for a thunderstorm threat over the valley as well.
The southwestern CWA may remain clear of any shower activity under the more stable conditions farthest from the low center. Daytime highs today should come in a little cooler as the cool upper low drops into the region falling to just above season normals. Snow levels will remain high and above pass levels, however, so the thunderstorm activity remains the main hazard today.
Models in good agreement in continuing the low southward on Friday placing the center over northern SoCal by the end of the day. Moisture and instability will still be in abundance so mountain thunderstorms a good bet again in the afternoon. Temperatures are forecast to warm most areas moving upwards to a few or several degrees above normal. Only minor changes are expected on Saturday with the upper low only expected to move slightly southward. This will mean yet another day of afternoon mountain showers or thunderstorms with daytime highs warming slightly more. Only minor changes continue on Sunday as the upper low remains over SoCal.
Extended Discussion (Monday through Thursday)
Upper low centered near KSAN Monday will keep a threat of afternoon showers or thunderstorms over the higher terrain of the Sierra Nevada. Upper ridging then becomes main synoptic feature over NorCal with dry weather and high temperatures 5 to 15 degrees above normal.