bluewave

If go back a day and read the posts you will see that there is no mention of any silver bullet in regard to the forecast going forward. We were discussing the competing influences that we are seeing in the modeling. On one hand we had the strong +AAM rise leading to the blocking across the North Pacific. But the Pacific Jet is much stronger than when we had this pattern back in 13-14 and 14-15. So the upper low is much closer to Aleutians eroding the block from the west and displacing the ridge axis further east limiting the cold air production over North America relative to those years so far. As the influence to the +AAM begins to fade the continuing forcing near the Maritime Continent will start to have more influence leading to a moderation in the pattern by mid-December with more ridging near the East Coast.

Noisy is a term frequently used in the CPC MJO discussions when dealing with the RMM plots. So there is nothing unusual about the term. The key for us won’t necessarily be a specific RMM index value but where the actual forcing is located. The VP anomaly forecasts have been very steady in the MJO 5 for early December. Then they slowly propagate the wave closer to MJO 6 by mid-December. Forcing in that region in December usually results in a ridge developing near the East Coast. This is why the models have been showing more ridging near the East Coast in recent runs after early December. The only reason we are starting December colder than average is due to the +AAM spike boosting heights over the NPAC. Models have been indicating that this influence will gradually wane allowing more in the way of the Maritime Continent forcing influence to take over.

We had this same discussion back in November. The VP anomalies remained constant in MJO 2-3. Remember when the forecast by some models was to stay in the circle using the RMMs? But it came out above a +2.0 amplitude. The RMM amplitudes can vary quite a bit from run to run but the actual forcing as per the VP anomaly charts didn’t change much. Now as we head into December the RMMs are changing amplitude again but the location of the forcing is constant near phase 5 early in the month with a slow progression toward phase 6 by mid-December.

This is par for the course for the RMM charts which can be very noisy. The actual forcing on the VP anomaly charts is headed into the MJO 5-6 regions in December. This has been a steady forecast for weeks now. What has changed in the long range outlooks is that the +AAM influence is starting to wane allowing the more MJO 6 look for Mid-December to have more influence.

Yeah, this is why we are seeing these much stronger jet extensions than we saw in the past with these ABNA patterns. We get the strong +PNA -WPO block for a time before the Pacific Jet eventually pushes through. You can see the October SSTs in that tropical region around MJO 5-6 were near the warmest on record. 2010 28.957 2011 28.645 2012 28.604 2013 28.959 2014 28.778 2015 28.220 2016 29.360 2017 29.024 2018 28.820 2019 28.867 2020 29.208 2021 29.414 2022 29.298 2023 28.735 2024 29.312

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