Weekend Southwest Tropical Moisture?

Today, I want to talk briefly about an interesting scenario the GFS has been hanging its hat on for the weekend, especially the latter half of the coming weekend.

First, a look at the Pacific satellite picture to help explain things.

Two things to note. First is an area of moisture that originates from around 10N and 130-135W to the east and northeast toward central Mexico. The second feature is a north-south band of clouds out around 150W north of the Hawaiian islands.

The GFS takes the second feature and pushes it southeast, forming a closed low by Saturday between 130 and 135W. As that happens, it ejects the moisture in the tropics to the northeast, aiming it at Southern California and Arizona. While it does not show a lot of rain falling from that moisture, it does bring a lot of clouds and a little rain. Knowing that the model performance on these features is less than stellar in figuring out how much it rains (for instance last weekend), I would not trust the small amount of precipitation it has. This scenario is a rather rare one and I have not seen many patterns like this in the winter bringing moisture from this far south in the Pacific. It will be interesting to see how this all evolves. Of course, the European has no such feature, which is a possibility as well. While it develops the closed low, it does so much farther west than the GFS.

This is something I am going to watch over the next couple of days to see if the GFS is as consistent as it has been the last two days.