WeatherWatcher: Rain returns, warm winter

• Rain returns
• Warm temperatures

The rain will return this week about Wednesday afternoon. In the meantime, expect some patches of low clouds, fog, giving way to a mostly sunny afternoon for Tuesday. Highs will probably be in the low 50's as they were today. Wednesday will be mostly cloudy as a storm front moves in to bring us rain Wednesday night and Thursday. Cooler temperatures will arrive with the rain, temperatures in the upper 40's and low 50's for highs. Friday will clear up a little bit before another front moves in Saturday for some more rain. These storms are nothing really serious, I don't expect very heavy rain, at most half an inch out of each system. After Sunday longer range points to more dry weather such as the stuff we've been getting last weekend.

Warmer temperatures:

February has come and gone with more of the winter trending the same way, warmer than normal, and about normal precipitation. The reason for our warm weather? A very warm spike in what is called the PDO, (Pacific Decadal Oscillation). This pattern causes warmer than normal weather, kind of like El Niño, except the precipitation remains near normal if not towards the wetter side. Typically the warm phase and cold phases of this oscillation last 20-40 years, but sometimes there is a warm spike in the middle of a cold phase, and a cold spike in the middle of a warm phase.  Such a cold spike in the warm phase occurred in the winter of 1990-1991. Some may remember the nasty winter snow and cold we had that December. 

We switched into a cold phase PDO around 2006-2007. The warm spike started last winter and appears to be peaking right now. Usually the warm spikes happen right about when a weak or moderate El Niño develops. We skirted right on the border of a La neutral to an El Niño all winter long. Long story short, an interesting combination of naturally occurring patterns have combined to give us this warm and wet winter, leading to one of the lowest mountain snow packs on record.

Thankfully water management is much better than it was in past years and most utilities have been saving the rainwater, realizing we do not have the snow runoff available this summer. So with some luck we may not run into any shortages for the summer/ fall seasons of 2015.

I put up a graph of the average temperatures for January and February 2015 compared to the weather station's average. You can click on the graph to view a larger version.

January 2015:

February 2015:

 March 2015:

As you can see, low temperatures and high temperatures have all been almost universally higher than the average. February really shows it the most, with January having a few days where the low temperatures reached near normal. There were many nights where the low temperature was the normal high temperature for the day.

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