PNA Flip in December?
Back on the road today but a quick post before heading home from the in-laws. On the way down it was night and the kids were asleep, but today it will be daytime so I’m looking forward to the exciting 7 hour trip with the 1 and 3 year old.
Checking the forecast icon above for the PNA should be one of your daily tasks. As long as we are in the +PNA our chances of big snow are pretty low. The AO above and NAO which you can see if you click one of them are both still positive. That means a negative PNA would reverse the dry pattern for CA. When there is a positive PNA there is a ridge over Hawaii and a ridge over the West with a trough near the Aleutians and over the Southeast.
As you know if you have been following the blog the past few years we like to see a ridge near the Aleutians and a trough in the West. The +PNA pattern is a good one for Alaska and a lot of times for British Columbia but a dry one for us down in CA. The forecasts were showing a continued +PNA through December but they have flipped a little and now show it possibly going negative mid-month.
That can change but I think it is still a little early and that we don’t start getting back into the -PNA pattern until later in the month. This dry pattern for December has not been a secret as the analogs with previous second year La Nina Decembers showed it. That is what had me talking about the flip to dry throughout December. Those same analogs flip to cold and snowy in January and February.
La Nina favors the -PNA so it will be back. Also watch the MJO as it continues to really get strong heading into the Maritime Continent. That could get things interesting later in December as well. There is a lot of cold up in Alaska and building in Canada, so that will at least try to push South over the next couple of weeks.
The forecast models are still struggling with how to handle the cold trough dropping down across the West later this week. One thing is for sure, it will be colder with highs only in the 30′s for Thursday and Friday. There is still the possibility though of a piece of energy splitting off into a cut-off low that stalls over CA/NV. That could bring some light snowfall and the low could stall out but it looks like the bulk of the precip once it stalls would stay to our South.
After that it looks like possibly another shot of cold air to start the following week. Still no break through of the Westerlies or big storms in sight. Stay tuned…BA
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