January PDO Goes Positive

[donsutherland1]

The January PDO figure just came out: +0.44. As noted in the past, the PDO generally varies directly with the PNA. Hence, when the PDO is positive, the PNA is more likely to be positive and vice versa.

Further down the road, should the PDO+ be sustained, this could have big implications for March.

[Tip]

Don

I have a question for you when you get the time. It is evident this year that most storms have trended north as the event approaches. But with the upcoming overrunning storm for 2-20 to 2-22 I thought the very negative NAO would suppress storms further south. However, with this President Day event the trend of the models has again been north to the point where originally precip barely made it to C Jersey and now both the GFS and Euro have the freezing line racing north into NY during the event. This is happening because the polar high over Quebec is diplaced east even though the NAO remains very negative. The only thing I can think of is that the axis of the -NAO is too far east and or the influence of a SE ridge. Thanks for any help.

[donsutherland1]

Tip,

You raise an important point about the effects of blocking.

First, I think it's a little soon to commit to any track on the possible 2/20-21 event. At this time, the modeling is still catching up to the major pattern change that appears to be starting to unfold. Thus, there is substantial variability in the solutions that are being advanced.

Second, I believe that there will be a period of suppression. Whether the first storm is farther north remains to be seen. The suppression might follow when the blocking reaches its maximum extent.

Third, given past analogs, weak El Niño climatology and the pattern change now taking place, I believe there is a higher than average possibility of a good storm for the MA and NE. While a "Kocin-Uccellini-type" storm is not guaranteed, there are at least three that might deserve further examination at some point depending on how the pattern specifically evolves:

• March 1956
• January 1961
• February 1967

No such storm is guaranteed. However, there might be at least something to the 6z GFS run's extended range "madness" albeit in scaled-back fashion. After all, the signal for such a late-month major event has been on the ensembles for sometime, now.

For now, I believe the MA remains in the game for at least some accumulating snow during the 2/20-21 timeframe. The details concerning amounts/changeover, etc., remain to be resolved.

[Tip]

For the 2-20 to 2-21 storm, the pattern is shaping up to be a battle between two atmospheric giants - the negative NAO and a building SE ridge. Latest model guidence shows the season=long northward trend of the overrunning event even on the usually reliable Euro while the GFS is trending towards a stronger and stronger SE ridge. Four rounds/days left in the fight and the SE ridge is ahead on all cards, but the negative NAO still has a puncher's chance left. In any event, I still think there will be a signifcant storm down the road.

Thanks for answering my inquiry.

[donsutherland1]

Tip,

The NAO should begin to fall sharply over the next few days (GFS ensembles) and I would not be surprised if the northward trend stops over the next day or two and then the models turn back somewhat farther to the south.

I don't believe the weekend event is the strongest candidate for a KU storm. So far, no changes in my thinking as far as that event is concerned.