bluewave

I like to look at the 500 mb composites. A strong -EPO is a classic El Niño response in October. But the ridge NW of Hawaii is more La Niña or -PDO. So far we are getting a blended composite telling us the El Niño is battling with the -PDO. This is why we are seeing the EPO fluctuations. Most other months of the year the PNA is the prime index that gauges how well El Niño or La Niña are doing.

The interaction with the coupled -PDO is what’s giving us the blended El Niño and La Niña October 500 mb composite.

Getting close to the all-time weekly record of +1.7 set in November 2015. But not sure what the daily record was back then. These WWBs displaced so far west instead of over Nino 3.4 are really putting a west lean on the most anomalous SSTs and forcing. +30C is the real deal.

The warm blob and NPAC ridge was displaced too far west last winter from the 13-14 more optimal position. Once that warm pool and ridge position pulls to the north and Northwest of Hawaii it becomes a problem for us. We need it closer to the West Coast for a better winter experience here.

Sometimes you just have to laugh.

It kind of looks like the WWBs so far west mostly allow Nino 4 to warm more while all the other regions stagnate or move sideways.

While the OP Euro is probably overamped at 500 mb in the SE, it’s still a good signal in the ensemble mean.

Pretty good ensemble support for another storm next weekend.

The Euro generally had the 500 mb pattern correct last winter. Notice how the ridge and trough axis longitudes worked out. But it underestimated the depth of the trough in the West. The East was particularly a good forecast indicating that the south based Greenland block would link up with the SE Ridge.

Yeah, unusually early and extreme. Plus a much weaker El Niño than 15-16.

Yeah, I will defer to the BOM since the IOD has a very big impact on their weather.

The south based blocking down into Northern New England has been very impressive since the summer.

Yeah, most of the DMI posts on twitter follow the one from the article and link I posted.

It was according to the DMI index used in the NOAA article a few years ago. https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php https://www.climate.gov/news-features/blogs/enso/meet-enso’s-neighbor-indian-ocean-dipole Typically, the strength of the IOD is monitored with the so-called Dipole Mode Index, which is a measure of the surface temperature difference between the western and eastern tropical Indian Ocean. The monthly Dipole Mode Index time series reveals other extreme positive phase IOD events, like in 1994 and 1997, but 2019 brought the most extreme event over past 40 years, at least according to this particular index. This event reached its peak in October and November before rapidly weakening in December—a rather typical seasonal evolution for an IOD event. According to the Australian Bureau of Meteorology, which regularly monitors the IOD, the current Dipole Mode Index is near zero (3), indicating that the IOD has returned to neutral conditions. The Dipole Mode Index measures the strength of the Indian Ocean Dipole, with positive values indicating the positive phase and negative values indicating the negative phase. The index is calculated as the monthly difference between the western (10°S-10°N, 50°-70°E) and eastern Indian Ocean (10°S-0°, 90°-108°E) sea surface temperature departures from average. The index value in October 2019 is the highest value since at least 1979, indicating that the recent positive event was quite extreme. Climate.gov figure from ERSSTv5 data.

This is actually a pretty strong blocking pattern for a October.

Yeah, Gavin Schmidt brought up that point in a recent tweet.

We won’t know any of this for sure until the winter is over. If we have a dominant -PDO with Aleutian ridge north or northwest of Hawaii, then this raises the prospects of a trough near or over the Western US. The Nino influence could pump the +PNA ridge in Canada. But combined with a trough in the West could push the ridge into the Northeast. Also remember absolute PDO values are less important when they don’t match what is happening north of northwest of Hawaii. So this is why using raw PDO values doesn’t always work out. Plus we do have intervals when the PDO can’t couple. That is probably what we would like to see. Most Nino winters are judged by what happens after January 15th or 20th so we have plenty of time to evaluate.

There aren’t enough superlatives to describe 09-10 for you guys. Just like 95-96 around NYC and 14-15 near Boston. I just feel fortunate that the best winters for snowfall were in our lifetimes. This makes the winter warming trend easier to take.

Especially if this El Niño continues to underperform and we hold onto the warm pool and Aleutians Ridge north and northwest of Hawaii.

It’s impressive how big an influence the PDO has for us. Our last really cold winter in 14-15 was a solid +PDO combined with a weak Modoki. We got lucky during the first half of 20-21 when the -PDO couldn’t couple and the +PNA emerged. Same went for January 2022. The 20-21 non-canonical -PDO +PNA may have had its roots in the October 2020 MJO.

14-15 was in the 81-10 climate normals period which went into effect in the spring of 11. 09-10 was still in the 71-00 climate normals period which began in the spring of 01 like 04-05 and 02-03. The 94-95 winter was the 61-90 period. The only complete winters so far in the warmest 91-20 climate normals period so far were 21-22 and 22-23. But we can use the 91-20 normals period if you like and the outcome is the same.

Of course. But each composite has a single climate normals period. Notice how the outcome is the same if you use 71-00 or 81-10 climate normals periods.

You can only use one climate normals period for a single composite and 4 of those 5 winters were after 2000 when the period began. There is no difference if we use 1981-2010 climate normals period.

The -PDO Modoki composite is drastically warmer in the East than the more +PDO-like Modoki composite.

For the entire CONUS, the 04-05 winter was 12th warmest and 94-95 was 10th warmest.