A combination of two separate storms will bring much of the West a round of wet, cool weather for Wednesday into Thursday.
The first storm is located west of California and is cut off from the overall jet stream. This low is about at 35N and 135W on the satellite picture below.
The second storm is just off the picture in the western Aleutians and Bearing Sea and will move southeast across the Gulf of Alaska and north Pacific the next couple of days. The southern low is still headed south and that motion continues tonight before stalling, and then moving east slowly Tuesday night through Thursday. The track of that low takes the greatest amount of energy across Southern California late Wednesday into Thursday morning. The northern storm spreads rain into the western Northwest Wednesday with the southern end of the rain filling in the gap the southern storm left across northern and central California. The interior Northwest and into Idaho and Utah has the greatest amount of precipitation late Wednesday night and Thursday. Meanwhile in the south, the rain will tend to end in most places in California by Thursday afternoon. Farther east, even Arizona will see some precipitation late Wednesday night and Thursday.
Snow will fall but snow levels will not be especially low, generally in the 6,000 foot range or slightly above in the Sierra and a little higher than that in the Arizona Mountains. Snow will also fall in the Cascades, but roads through the passes should be okay.
As of the end of June there had been no named storms in the Eastern Pacific basin.
This is some serious and dangerous heat. Outdoor activity is just not at all recommended during the daytime.
A strong ridge of high pressure in the West brings the highest heat of the season so far to a large area.
Combine the cold with the wind and some precipitation and there is a real danger of hypothermia.
Any shower and thunderstorm can contain heavy downpours, heavy enough to cause temporary, low-lying ponding.
According to all long-range models, the warmest area in North America compared to average will be over the Northwest.