The heat wave that has been affecting California of late has given way to noticeable cooling starting today in a lot of areas. More cooling is likely tomorrow.
However, the most interesting thing on the weather maps is what the models have for next week. Currently, there is a closed 500 mb low sitting well west of northwestern Mexico and Southern California around 35N and 138 west.
This low has been sitting out in the Pacific since the start of last weekend. Over the next several days, the low will slowly move north-northeastward to the west of northern California by Friday, then it will inch toward the northern California coast by Sunday. This low has limited moisture with it right now, but these kind of systems can change character quite a bit over time. The low is trapped below what is a REX block which is a high-latitude high that develops in the Gulf of Alaska. These blocks are notorious for being long-lasting and slow to break down. For the first time this week, the computer models are in very good agreement in where the low moves to next week. Here is what the GFS has for 12Z Monday, pretty close to the European.
And by Tuesday, the low is just a little more south and east.
After Tuesday, this low will only very, very, very slowly move east or east-southeast and may take until Friday to be over southeastern California.
While it's a dry storm right now, this low will bring with it the chance of rain showers at any elevation as it moves inland and through central and Southern California. A deep marine layer by Tuesday could mean some light rain being squeezed out from the south-central coast into Southern California. Temperatures will also be pretty darn cool, well below normal for the time of year. This will especially be noticeable after all the heat of late.
More on all this as it evolves.
These is the possibility that another surge of tropical moisture could move into Arizona and Southern California by the middle of next week.
I still believe the greatest amount of rain, at least partially relating to Norbert, occurs from southeast California to Arizona
The effects on Southern California are very much in question.
With low wind shear and warm water in its path for a while longer, it is likely that Norbert intensifies into at least a Category 2 storm.
For much of the last week the monsoon moisture flow into the Southwest has been completely shut down by dry westerly winds. This is about to change.
A big pattern change is underway, one that will completely shut down any chance of showers and thunderstorms for an extended time period.