Dealing with closed lows is always fun. Of course, I am being sarcastic, but rarely do the computer models get it right days ahead, and sometimes just a day ahead. Since the middle of last week, I have gone out and said that the current closed low sitting west of northern California would bring the possibility of showers and thunder to portions of California this week. I still think that is going to happen, though with some modifications.
The low is still devoid of any important moisture and is more easily apparent on water vapor satellite pictures than on more conventional infrared or visible pictures.
This is problem one and two. When does the low moisten, and how much moisture will there be? The low is also sitting a little farther off the coast and is now expected to move farther south than southeast. This is problem number three. A more westerly track would keep what moisture, and instability, it had more along the coast and offshore through Wednesday, and it would take longer to work its way into southern California.
To help you visualize this, the GFS 500 mb charts for Wednesday morning and Thursday morning are below. Again, just so you know the European is pretty much in the same camp.
Taking this track, there might be a shower in spots around the Bay Area tomorrow, but it could as easily be rain-free, and I would classify the chance of no better than 20 percent. By Wednesday, it seems a shower, perhaps a thundershower, can occur along the Central Coast and maybe to just south of Pt. Conception in the afternoon. Odds are increasing that it does not rain in the Los Angeles and San Diego area during the day Wednesday. The best chance for precipitation in southern California comes Wednesday night through Thursday evening as the low heads east across the area. Here the European is a little slower than the GFS. Still of concern is how much moisture there will be. Instability will be pretty good, especially during the day Thursday, so it seems pretty likely there will be at least scattered showers and a thunderstorm. How far north will the showers occur Thursday? I think Central California from San Luis Obispo to the San Joaquin Valley on south may have a shower or thundershower is about as far north as they will be with the chances increasing as one heads south.
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.