The short-term forecast continues to be really easy with the weather pattern solidly locked in, and perfect model agreement over the last few weeks on this dry pattern for the first half of December.

Monster ridge in the West!

Or some sort of kryptonite like phenomenon scaring all storms away from CA...

If you really need to satisfy your fresh snow hunger you could take a trip to Mexico or Louisiana this weekend...

I think that I pretty covered everything else in the Summary.

The pattern looks to remain dry until mid-month.  The first sign of a pattern change for me is usually when the forecast models start to disagree or become inconsistent in the long-range.  In the last post we showed that starting to happen as about 1/3 of the ensemble members on the models were starting to show a breakdown or shift of the ridge around the 20th.

The inconsistencies and disagreements continue today.  We have no clear picture of when storms may return, but the models not in perfect harmony on a solution of ridge in the West beyond mid-month is better than when they were for the first half of the month.  We can grasp at a few more straws today and look at what some of the runs are showing.

The GFS ensemble mean today is showing a weaker ridge from the 20th-25th, but still has the deep trough in the East.  It no longer shows a stronger ridge up near Alaska with storms possibly cutting underneath.  Remember that deep trough for my final comments.

The strong jet stream could break over the West Coast ridge into the Pacific NW though with this pattern.  The operational run shows this possibility in the precip forecast today.

That is closer to the forecast for the season I had earlier in the Fall.  The storm track is into the Pacific NW, and Northern Rockies, and we are on the Southern edge most of the season.  

The GFS ensemble control run still shows a stronger high pressure near Alaska, the ridge over the Southwest, and the trough closer to the West Coast, but still a deep trough in the East hold that Western ridge in place.  This as well could setup for the Pacific NW to start getting storms again around mid-month.

The European ensemble control run is showing something completely different with a trough from Alaska into Canada, and a ridge in the Eastern U.S. by the 18th, and a ridge off the coast.  

For us that may mean the same as the models above with the storm track back into the Pacific NW around mid-month, as the European deterministic model run shows for precip through the weekend of the 16th.

The European ensemble mean run is almost identical to the GFS ensemble mean run above.  Both have a weaker ridge over the West that could allow storms into the Pacific NW, and a deep trough in the East still 2 weeks from now.

what is interesting today is the forecast for the PNA, EPO, and WPO.  The PNA (pacific north american) pattern forecast is similar on both the GFS and Euro models in showing a switch to a negative PNA pattern mid-month.

Positive phase as we are seeing now...

Negative phase...

The EPO and WPO(east and west Pacific oscillations) are forecast to go postive...

Negative phase...

Positive phase...

The forecast for negative PNA/postive EPO/WPO would argue that we see a pattern of a trough in the North Pacific up near Alaska and a trough near the West Coast, at least into the Pacific NW.  The ridge off the coast and in the EASt.  That is most similar to the European ensemble control run forecast above.  The one that is most different from the others, but seems to line up closest to the teleconnection forecasts.

What does all that mean?  It means the models are all over the place beyond mid-month that could mean some sort of pattern change is coming.  We just don't know exactly what yet.  I do know two things from experience.  1:  Deep cold troughs in the East don't easily shift off the coast.  2:  The pattern change for the West Coast after a prolonged dry spell tends to show up a little too fast on the forecast models.

For now I would watch the possibility of storms returning to British Columbia and the Pacific NW around/beyond mid-month.  For now we are dry through the next 2 weeks in CA.  If we do see a pattern change to storms returning I would watch the forecast for the trough in the East, and I would delay it a bit at first.  So for now we will keep an eye on the last week of December 22nd-31st.  

Stay tuned...BA

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