This winter for California was chugging along to be one of the driest in recent years. The snowpack in the Sierra by early March was puny compared to normal, and rainfall was up to 70% lower than normal in many places in the state. This was at least partially due to a pretty decent La Nina for much of the time from November through February. However, the La Nina was weakening and that continued over the following weeks. This, at least in part, may have helped along the rather stormy weather pattern of the last month. While precipitation levels, and most importantly the snowpack, have not recovered to normal in many areas (there is an exception) the current water situation is far better than it was just a little over a month ago.
To show this I have a few charts for you. The first shows precipitation amounts accumulated over two separate time periods for select cities from north to south. The first time block is from Nov. 1 through March 14, the second is from March 15 through midnight last night. In each column is the amount of rain that has fallen and in parenthesis the percentage of normal for the time period listed.
It is easy to see two things. The first is how wet the last month has been and the second is how dry the previous four and a half months were. Also note that a few cities had nearly as much, or more, rain in the past month than they did in the previous four and a half months.
The next two charts show the snow water equivalent in the snowpack in the Sierra. The first was on March 14 and the second was this morning.
There was considerable recovery here too, especially in the northern and central Sierra with the northern Sierra getting back to what is normal. The average statewide has more than
doubled in the last month.
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.