For much of the last week, the monsoon moisture flowing into the Southwest has been completely shut down by dry westerly winds. This is about to change.
High pressure aloft that has been centered to the south will move east, and this will turn the flow to the south over the next few days. There is plenty of moisture to the south over Mexico. Some additional moisture may be coming in thanks to Dolly, and its remains, moving inland across Mexico. It is even possible newly formed Norbert could add some moisture to the mix (though this is far less certain). Whatever the source I am looking for a big change in the weather by the end of the week and over the weekend.
To demonstrate this, let's first look at how much water is in the air, precipitable water, from now and into the weekend.
This is a big increase in moisture to aid in the development of showers and storms.
The following is how much TOTAL rain falls is expected from today through the time period indicated.
These maps are from the GFS. Don’t necessarily look at the amounts predicted and where the heaviest rainfall is forecast to be. In the first place, the GFS just doesn’t have the kind of refined grid to be precise like that this far out. Second, we are dealing with showers and thunderstorms, small-scale features that can bring highly variable rain amounts over very small differences in area. The main purpose of the last two graphics was to show this big increase in the overall rain fall pattern from Thursday to Saturday.
I expect that it will shower or thunderstorm at least somewhat farther west, into southeast California and north into southern Nevada. With the arrival of showers and thunderstorms, high temperatures will be coming down.
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The pattern next week will favor unsettled and cool weather for the Northwest.
Rain and mountain snow will highlight just about every day this week in the Northwest.
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