The weather pattern we have been in the past 3 or 4 days has been very typical for a La Nina season. It's been very wet in the Northwest with streams and rivers being pushed to flooding levels in spots. Meanwhile, Southern California has been having a taste of summer in December with 80s widespread yesterday and today.
The weather pattern looks like it is certainly is changing and is one that could eventually spread large amounts of rain much farther south through California, by the end of the week through the middle of next week.
The overall pattern change will come about when a cold vortex develops west of the Pacific Northwest sending a strong, zonal jet stream from the sub tropical central Pacific right into California. Does this pattern sound familiar? It should since it is very much like the Pineapple Connection one would see more in an El Nino winter season than La Nina year. Take a look at a satellite picture in the central Pacific that already shows considerable amount of moisture gathering.
Look at all the clouds (moisture) out to the north and west of the Hawaiian Islands that extends west beyond the dateline.
The wettest time period seems to be from this coming Saturday through the following Wednesday. There is absolutely no use this far out trying to decide when the heaviest precipitation would occur in any particular area. Heck, this pattern is not even a guarantee this far out. However, both the European and GFS are singing the same wet tune today and the Canadian seems to be harmonizing along as well. Initially, the heaviest rain may fall in the northern half then move farther south over time. But all these details will have to wait. For snow enthusiast this would not be a cold pattern with low snow levels but at ski elevations there still could be a lot of snow.
Here are a couple of maps from the GFS to give you some idea of how wet the models are looking. Below are two plots of total precipitation for the Southwest. The first is from this morning at 12Z through next Tuesday at 12Z.
The second is additional precipitation from 12Z Tuesday through 12Z Thursday.
Most of my readers are savvy enough to know that if we really set up a Pineapple Connection these precipitation amounts would not be high enough, especially on west facing mountains.
It is going to be very, very interesting to see how all this pans out and you can be sure that I will be all over this as the week progresses.
A rather extended period of unsettled weather will be occurring over parts of California and the Southwest
The remainder of the week a large building ridge of high pressure takes over
There will be more showers and thunderstorms are likely that can produce very heavy downpours in Arizona.
This rain caused problems with flash flooding producing some damage and there were a few swift water rescues.
Computer models are insistent that a rather strong piece of energy will move through California Tuesday, bringing more widespread rainfall.