June 6, 2020 – A cooldown is expected through the weekend, with chances for showers, thunderstorms, breezy winds, and light mountain snow. Dry weather is expected to return Monday, with a warming trend bringing above normal temperatures by mid-week.
Discussion
Satellite imagery this morning depicts a general broad trough over the region. To our south, a trough has dug into souther CA and NV, which helped usher in cooler weather yesterday. Farther north, a stronger through exits and will influence our weather today. Most notably, temperatures will be substantially cooler and there will be slightly higher chances for precipitation for the mountains, foothills, and northern Sacramento Valley this afternoon and evening. Soundings indicate the main hazards with any storm that develops would be locally strong winds, small hail, and lightning. On top of the cooler weather and precip chances, winds are forecast to increase. Right now the strongest winds are in the Delta and northern San Joaquin Valley, where westerly winds are forecast to be around 20-30 mph and gusts could peak up to 40 mph. A Wind Advisory has been issued for these areas from 5PM to 11PM; however, the end time may need to be changed to earlier in the evening. Pending how the morning model runs come in, the Wind Advisory may need to expand northwards into portions of the Sacramento Valley. Winds are currently below advisory thresholds, but some of the hi- res guidance highlighted stronger winds along the west side of the Valley and from Sacramento to Red Bluff.
Tonight, light snow is also expected over the mountains and will continue into Sunday as snow levels fall. Snow levels around 5kft will be seen Sunday morning, rising slightly though the afternoon. The highest peaks may see some accumulation up to 4 inches, with only very minor accumulations at pass levels. Impacts are expected to be on the lower end. Slippery roads will be possible and recreational hikers or campers at the higher elevations may be affected by adverse weather. Cold overnight lows will be seen in the mountains Saturday night falling into the 20s in most locations.
Mountain and foothill showers continue through Sunday evening before clearing out late Sunday night as a ridge builds in over the area. An isolated thunderstorm will also be possible mainly over Shasta County Sunday as the trough moves out. Warmer and drier weather begin Monday and continues through midweek.
Extended Discussion (Wednesday through Saturday)
For the extended, the repetitive pattern of mid-week heating and weekend cooling continues as a ridge is dislodged by yet another a cool Gulf of Alaska low.
Upper level ridging will bring very warm temperatures to the region mid week, with Valley highs making it back into the 90s. Wednesday will be the warmest day of the week with highs roughly 5 to 10 above average, meaning mid 90s for the Valley. Slightly cooler temperatures expected on Thursday as an upper level trough from the Gulf of Alaska approaches. This will be the start of a cooling trend with Valley temperatures back into the 80s by Friday.
The trough will be just off the West Coast Friday bringing cooler onshore flow and shower chances back to the forecast for the northern mountains. Precipitation potential spreads further south into the northern and central Sacramento Valley and the Sierra by Saturday.