bluewave

That’s why the extended EPS just joined the milder GEFS for mid to late December with the MJO 6-7 look due to the near record SSTs in those areas. Dec 16-23 Dec 23-30

The storm is moving very fast so we should dry out by later in the day with a gusty westerly flow developing.

Yeah, it’s always more straightforward when the MJO is dominating the pattern. Then we just look up the composites on the various sites and see which ones fit the pattern better. I have seen intervals when the one site works better than the other and it can really vary at times. Then we have the additional challenge of figuring which way the pattern is going when the MJO isn’t quite as dominant and is competing with other influences. The good thing is that when one set of composites starts working, it will often follow the composites during the future MJO progression. Then sometimes the models don’t really agree on where the MJO is headed or how dominant it will become. So different models can have different outcomes. Many times the EPS has issues with the barrier effect and tries to stall the MJO before getting to the Maritime Continent phases. The GEFS had more of a MJO 6 look from the JMA site at 12z. Will it be correct? Who knows for sure with the recent model forecast volatility. But it’s just something to be aware of in order to see where one individual model is headed. Nothing is set in stone and there can be plenty of long range model volatility this time of year due to the change of seasons as the means are falling a a fast rate from fall into winter along with the attendant wavelength changes. 12z GEFS mean had a MJO 6 look in mid-December using the JMA composites with 57 date composite

The tabelle site states that many of their composites are based on low sample sizes. JMA has a much larger number of cases. But the point may be moot if we see competing influences between the +AAM and MJO. In that case the resultant pattern may not look like any specific composite in either site but a blending of several. We usually have to wait and observe what the MJO actually does and then browse both sites to see which composites are doing better with the actual verifying pattern. So the model trends into early next week will be key in determining what the actual December pattern looks like.

The sample sizes on that site are very small and the JMA has a different look with their much larger sample sizes for MJO 5 and 6. The model trends next several days will be very important. If the +AAM and MJO start to produce an interference pattern, then we could see a series of ridges and troughs traversing the country with a very fast Pacific flow in December.

It could also be the GEFS showing the MJO emerging from the circle on the RMMs with increasing Maritime Continent forcing.

The GFS finally came north and is more consolidated with the low on Thanksgiving. New run Old run

We’ll need the Pacific Jet stream and Aleutian Low to back off enough got get a pattern like 13-14 or 14-15. Notice how these features are eroding the western edge of the ABNA pattern. So the ridge axis is getting pushed further east with warmer conditions over NA than during those two winters. It’s still early so there is time for things to change later on. 13-14 and 14-15 winters weak Pacific Jet and Aleutian Low Early December forecast stronger Pacific Jet and Aleutian low tucked in near Alaska and ridge axis further east.

The only good thing about a rainy Thanksgiving is that it will help some spots avoid their driest fall on record.

The Tug Hill may have a small edge but it could be impressive for both locations.

While the record warm lakes will modify the air mass when it gets to our area, it’s a great set up for heavy lake effect snow.

Nice pattern for lake effect snow.

Top 5 warmest fall for many spots across the region through the 24th.

Because as we saw last winter, the 500mb Nino ridge over Canada which drove the record warmth was actually more expansive than much stronger El Niño events like 1997-1998 and 1877-1878. The event was a full fledged super El Niño if you take into account the westward extension of the warmest SSTs near and west of the Dateline and record Nino 4s. This essentially rendered the RONI ineffective last winter as a metric for El Niño strength. We got a super El Niño 500 mb and temperature response over North America and globally. The one possible way RONI worked out was the lower number was reflective of the Niña background which helped to boost the ridge in the East much stronger than past El Niños.

It’s like using temperature departures which keep rising every 30 year period. An equally warm month now as many years ago will have a smaller departure relative to the new warmer 30 year baseline. But the actual temperature will be the same. So RONI is more of a relativity index like 30 year climate normals. To me it’s actual temperatures like the Nino 3.4s which have more weight as the means and departures are more relative metrics like RONI. That why I frequently use rankings vs departures. So departures and RONI still have place when weighed against the actual temperatures.

RONI is not meant to rate the actual El Nino intensity only what the SSTs in other regions were relative to Nino 3.4.

I was discussing the strength of the Pacific Jet and the ridge axis ending up well to the east of the old EPS run. So the pattern is different from what the model was originally showing. More amplified ridge out West and deeper trough in East is why the East is forecast to be colder and the West warmer than the earlier runs.

While the early December pattern will be colder than normal, it really isn’t that cold by early December historical standards. The slightly lower heights near Alaska are allowing some Pacific air mass moderation. Plus the record fall warmth and low snow cover are having an influence.

It was a borderline super event with one ONI reaching +2.0. A lower RONI doesn’t diminish the actual Nino 3.4 SSTs. So it’s not a metric used to evaluate the El Niño strength.

Right now we are seeing a constructive interference pattern with the Pacific Jet extensions enhancing the ridge position. Though the position is further east than forecast due to the stronger Pacific Jet influence. My guess is that it will be a battle between those forces for December. If the constructive interference wins out ,then the ridge will stay out West for all of December and only slightly drifting into the Plains at times. But if the the Jet stream disturbances can push through due to the stronger Pacific Jet, then the ridge will shift East by mid to to late December and the whole pattern will relax. So a small difference between the forces can tip the scales one way or another. You can see the older run of the EPS underestimating the Pacific Jet. New run stronger Pacific Jet with lower heights near Alaska Old run EPS weaker jet

The Pacific Jet is still Niña-like in strength. Notice the trough correcting closer to the Aleutians for the start of December. If the models continue to underestimate it, then the ridge axis will gradually start drifting east in later runs. So it will be a battle between the jet extensions enhancing the ridge and trying to weaken it. Modeling by next week will probably give us a more definitive answer as to where that ridge axis ends up in mid to late December. New run stronger jet carving out trough near the Aleutians with ridge axis into the West Old run jet was weaker with ridge axis further west

1989 was the last white Thanksgiving but we have warmed up quite a bit since then.

It’s interesting that we may have both found our way to the Pacific blocking through different means. I was mentioning the mismatch potential back in October with the high amplitude MJO 5 leading to less MJO influence early on in December like we are seeing now. But I wasn’t sure whether it would manifest in December as +PNA, -EPO, or -WPO. It’s good that we can use different approaches and come to a roughly similar conclusion of more blocking on the Pacific side to start December than recent years. The complicating factor I mentioned is that the mismatch is occurring against a much weaker La Niña state than 2020, 2017, and 2010. So we may see more of a competing influence going foreword than those stronger La Niña years. It’s possible we may see a stronger MJO influence later on which would add another competing influence to the mix. It will be fun to see how it goes.

Yeah, if the +AAM influence starts to wane with a resurgent La Niña cooling and EWBs then we could see this pattern start to shift by mid-December as the Pacific Jet tries to intensify.

Probably due to the actual temperatures being cold but nothing too extreme for the first week of December. It’s still early in the season and we are starting from a very warm base state this fall. So it will take time to build more impressive cold. We usually have to wait until we get further into the winter like in 20-21 to generate a more impressive Arctic outbreak. 2021 record Arctic outbreak