A pattern change?

The prevailing rex-blocky flow regime that has persisted for some time now in the eastern Pacific and has brought rather warm and dry weather to the West may be beginnning to break down this week. As there always is in dealing with complex blockign patterns, the models are having difficulty resolving mean flow anomalies in the 5-10 day period. As a result, forecasts will change quite a bit over the next few days. There are a few considerations:

1. La Nina has reached a solid moderate state and is continuing to have an influence on the position and amplitude of the jet stream. Negative SST anomalies extend into the West Pac. attm, decreasing tropical convective forcing.

2. Northern Hemisphere fall transition regimes are notoriously hard to predict and tend to be more resistent to change than the long range models are apt to indicate.

3. A Kona Low has developed near the west side of the Hawaiian island chain. This is usually a telltale precursor to a more highly amplified flow regime downstream (West Coast).

With this in mind, I expect the jet to sag south far enough to bring rain to NorCal from about the Bay Area northwards in the next 5-7 days. More southward extension is possible after that, but this remains to be seen. Stay tuned…it’s that time of year again…

And another weather-related note: the Army Corps of Engineers has recently announced that it estimates that the Atlanta, GA metropolitan area will run out of potable water in about 100 days. Reservoir levels are approaching critical values, and the resource draw on a daily basis is dropping the remaining water levels by nearly 1 foot per week. This could be a fairly dramatic scenario to watch unfold over the next few months. Exceptional drought is occurring in the region at this time, but the main reason the water crisis exists is the unsustainable growth the area has experienced over the last decade. People in CA and other Western states should watch the situation in Atlanta with great concern–another dry winter here and we may be in the same boat. So to speak.