May 4, 2018 – Dry and warm through early next week with above normal temperatures. A slight chance of light showers for the northern California mountains the middle of next week.
Discussion
Upper level high pressure ridge remains over the west coast for fair skies over the CWA this morning. Fort ord profiler showing recent marine layer depth at below 1000 feet which is significantly more shallow than 24 hours ago. Delta breeze is similar to 24 hours ago but with shallow marine layer there should not be a significant intrusion of coastal stratus into the delta and valley. Overall airmass a little warmer today so should see a little warming most areas. Delta breeze is expected to drop off this afternoon so will likely see more warming over the delta region. Upper ridge axis shifts eastward into the Great Basin on Saturday allowing for some cloud cover over NorCal.
Overall airmass should remain similar to today however so not expecting much change in daytime highs. Models consistently move a shortwave trough over the ridge and into the Pacific Northwest on Sunday. Latest models appear to be weaker with this disturbance than previous runs and as a result, any precipitation produced by this system would remain north of the CWA. Have bought into this trend and have removed precipitation threat over the northern portions of the forecast area for Sunday. Upper ridge rebuilds over the west coast on Monday bringing still warmer temperatures. Daytime highs in the valley will push up into the mid 80s to near 90 in the northern Sacramento valley.
Extended discussion (Tuesday through Friday)
Ridge of high pressure will shift eastward Tuesday as the next weather making system moves toward northern California. Upper level trough takes a negative tilt as height falls occur towards Tuesday afternoon/evening. Lapse rates aloft will be steep enough to bring some instability over the mountains, bringing chances for showers and thunderstorms over the northern mountains into Tuesday night. Latest model runs have backed off the chances for precipitation in the northern Sacramento valley, so removed precipitation chances for the valley.
Model trends have shifted for the upper flow pattern for the endof next week. Previous runs had another disturbance moving to the north of the forecast area, but latest trends have a more gentle zonal flow pattern over the region. A stray shower or two cannot be ruled out for the coastal mountains, but chances for precipitation are looking more unlikely at this point.
Afternoon high temperatures will be warmest on Tuesday but will decrease to near normal on Wednesday as trough aloft passes.Temperatures will tick up a few degrees each afternoon toward the end of next week.