April 5, 2017 – Dry and warm weather continues today. Showers return Thursday, mainly for areas north of Sacramento. Stormy weather is expected to arrive on Friday with strong gusty winds, heavy rain, heavy mountain snow and thunderstorms. Showers are forecast to taper off by Sunday.
Winter Storm Watch from Thursday afternoon through Saturday evening. High Wind Watch from Thursday evening through Saturday afternoon
Discussion
Lots of cloudiness continues to stream up into NorCal from the southwest ahead of the approaching trough now over the eastern Pacific. All the cloud cover is resulting in mild early morning temperatures with current readings ranging from the 30s and 40s in the mountains to mainly the 50s elsewhere.
Today is expected to be the last dry day with mild temperatures for awhile. The upper ridge is shifting east, but should hold long enough to give the valley another day of high temperatures in the 70s to lower 80s.
The end-of-week forecast continues on track with relatively few changes. Still looks like some light showers later tonight and Thursday for areas north of Sacramento as the initial short-wave lifts out ahead of the main trough.
The main event for interior NorCal is still expected later Thursday night into early Saturday as the main upper trough pivots toward the PacNW while a couple strong waves moves across NorCal tapping deeper moisture to our west.
Heavy rain at the lower elevations, heavy snow in the mountains, strong gusty southerly winds and thunderstorms will affect the region before showers taper off later Saturday and Saturday night.
Still looks like several feet of snowfall accumulation will be possible along the crest of the southern Cascade Range/northern Sierra Nevada with two waves of heavier snowfall (late Thursday night into midday Friday, and Friday night into midday Saturday) impacting the higher mountain passes including I-80 and US-50.
The valley may see an inch or two of rain from this event while the foothills and mountain are expected to see around 3-6 inches.
Strongest winds will likely develop later Thursday night and continue Friday as a surface low deepens as it moves northward off the coast of Oregon resulting in tightening pressure gradients over NorCal. More wind may occur Friday evening as another surface low deepens and moves onshore across NorCal associated with the second short-wave moving inland.
Extended discussion (Sunday through Wednesday)
Sunday morning starts off on the chilly side with early morning temperatures ranging from the mid 30s to low 40s. Shortwave ridging develops over NorCal on Sunday so much of the valley should be dry with light lingering snow showers over the mountains. Cold air behind the Friday-Saturday storm will cause snow levels to drop into the foothills between 2500 to 3000 ft. However, with little moisture, any additional snow accumulations will be very light.
A weak system is expected to brush NorCal sometime late Sunday night into Monday. This system’s more northern track means that any precipitation that occurs should stay well north of I-80 and be mostly limited to higher terrain. Mostly dry on Tuesday, but it looks like another storm could move into our region sometime Wednesday or early Thursday.
So far this season Downtown Farm in Colfax has recorded 87 inches of rain, in an area where a mid-to-high 40s average has been the norm for the last decade. If the rain totals predicted for this storm come to pass, we will be within 10 inches or less of 100 inches for the season by the end of the weekend. Amazing.