Big Picture: Dry now, but much wetter to end the month of January.

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As we enter a period of dry weather, the Pacific storm track remains well to our north. Still, clouds and an occasional shower may reach us in the North Bay through Wednesday. As the week goes on however, the jet stream will begin to push storms further north into Canada. (Image 1)

As this happens, the high pressure ridge sitting over the West Coast will strengthen and push north, leaving us dry with warming temperatures. (Image 2)

However even as all of this is underway, a subtle shift in the position of the high pressure center is forecast. This so called “retrogression” or westward movement of the high will increasingly allow low pressure to become established over California and the Pacific Northwest by the 20th of January. (Image 3)

As this happens, the low pressure trough is forecast to deepen, and allow first cold air and then storms to penetrate south into California. (Image 4)

Most ensemble forecasts (average of many model runs) now show the last week of January will bring us some much needed rain. (Image 5)

At the same time, the Pacific North American pattern goes negative, which is generally associated with a southward dip in the jet stream. (Image 6)

The models have been signaling a pattern shift around the 20th of January. This appears to be what will happen. In fact the long range forecasts of both the GFS and European models see rain returning the last week of January. (Images 7 and 8)

And continuing into the first week of February. (Image 9)

And the forecast position of the jet stream by the last week of January provides additional evidence a change is coming. (Image 10)

Yes, we’ve heard this all before. In a La Nina year the difference between wet and dry is a fine line. A subtle shift in the storm track can mean the difference between a drenching and a dry period.

However we remain hopefully optimistic that we will soon enter a period of two weeks of wet, occasionally stormy, winter weather.