bluewave

The Nino-like influence is why the EPS is going +6C to +10C in Canada around Christmas which is usually much colder during La Ninas.

While there is forecast to be a weak low level inversion tomorrow, the models have 50 KT down to 975mb. So any convection could mix down 60 mph+ gusts on Long Island. Also our best rain event probably since last summer. Good low topped squall line potential with plenty of moisture available and highs in the low 60s. GFS Text Sounding | 21 UTC Wed 11 Dec 2024 | Latitude: 41.0000 | Longitude: -72.0000 PRES HGHT TEMP DWPT RELH MIXR DRCT SKNT TWTB TVRT THTA THTE THTV 1002.8 0 14.9 12.9 87 9.4 178 37 13.7 16.5 287.8 314.2 289.4 1000.0 24 15.9 13.6 85 9.9 179 40 14.6 17.7 289.1 317.0 290.8 975.0 240 15.7 14.1 90 10.5 181 56 14.7 17.5 290.9 320.7 292.8 950.0 460 14.5 14.0 97 10.7 184 64 14.2 16.3 291.9 322.4 293.7

My guess is that the Aleutian Low showing up in all the guidance is a response to the forcing developing near 120W to 150W next few days which is classic El Niño. So we will have dual EPAC and WPAC forcing. The WPAC forcing is probably enhancing the Pacific Jet leading to such a dominant northern stream and weaker STJ.

While the forecasts beyond 2 weeks don’t have that much skill, both the EPS and GEFS are trying to show a more Nino-like WWB pattern by early January.

I understand the sentiment when we use terms like luck when dealing with weather patterns. I even used the term the other day when I stated that we got lucky when the MJO went into phase 8 during January 22. But there are mechanisms driving the weather patterns with reasons behind our sensible weather outcomes. From 2010 to 2018 we were in a fantastic pattern for snow along the East Coast. It came down to the Pacific Jet not being overpowering allowing frequent Benchmark storm tracks. There was no shortage of record warmth in snowy winters like 12-13, 15-16, 16-17, and 17-18. But we were able to get cold and snowy storm tracks in warm patterns. Something changed with the Pacific Jet during the 18-19 winter. We started to get stretches when it became overpowering with primary low tracks through the Great Lakes and hugging the East Coast. So we started to see that even during cold patterns the storms were taking warmer tracks for the East Coast. Fast forward to this December and we have been seeing a similar pattern. Great snowfall outcomes for the lake effect zones and much less along the East Coast. Same old pattern of cold arriving after the storms and not being place ahead of the storms. When we are able to get some development near the Benchmark, there is often a low in the lakes forcing the baroclinic zone too far north. So this month so far is featuring a series of ridges and troughs crossing the country with alternating warm ups and cool downs. But the faster Pacific Jet is the underlying pattern leading to less snow along the East Coast even with the windows of cold we have been getting. So we don’t need a sustained much warmer than average pattern for below normal snows. if we take a look at the Pacific Jet anomalies since 2010, there has been an increase since the 18-19 winter. Plus we just saw the models greatly underestimate the Pacific Jet the closer in time we got to the forecast period last few days. December 2022 had one of the greatest December -AO blocks on record with well below normal snowfall. Many places even had a small cold departure for the month.

Going to need to slow the Pacific Jet down in order to see decent snows near the coast. Notice how even in the short term we warm up ahead of the storms and the cold comes in behind the lows. This is a great pattern for the lakes and higher elevations. Fast Pacifc flow features alternating ridges and troughs

The one constant is that the Pacific Jet has been verifying stronger than forecast leading to cutter and hugger storm tracks. So we get warm ups ahead of the lows with mostly rain at the coast. The cold comes in behind the storms instead of being in place ahead of the lows. The LES areas and higher elevations get the bulk of the snows. What you want to see is cold in place ahead of the storms with a clean BM storm track. But the fast Pacific flow has been working against the BM track for years. When we do get BM tracks there is usually a primary low running to the Lakes forcing the baroclinic zone too far north.

I was discussing the possibility of a La Niña mismatch for December back in this thread during October. Past instances of this occurrence featured +PNA patterns during La Niña Decembers. But there were other factors which I noted may not be in full agreement with the past years. One of those is that the La Niña 3.4 STS are much warmer than last mismatch Decembers. So we were able to get that +SOI spike and the potential strong Aleutian low by mid-month. But as I have been noting in this thread, the Pacific Jet is much faster than those mismatch years. This has resulted in the warmer storm track for the East Coast last week while the Great Lakes cashed in. Now we see another warmer track coming up for this week along the East Coast as the Southeast Ridge developed in the shorter range modeling. The fact that the models have been underestimating the Pacific Jet beyond a week out doesn’t boost our confidence that todays solutions for a trough returning in the week 2 period near the East is going to have any staying power. Since the flow is so fast that the ridge axis may eventually shift east again in later runs should the heights falls near Alaska prove stronger than forecast with the potential Aleutian low. Whatever happens later this month it will prove to be an interesting contrast in competing influences which we have rarely seen during past Decembers.

While we can definitely see the La Niña background influence, that strong Aleutian Low showing up for mid-December is an El Niño feature with many Nino years in the current CPC forecast D11 composite. 20061209….El Nino 19941219….El Nino 19861222..El Nino 19661214..cold neutral 20051226….La Nina 20061221….El Nino 19861227..El Nino 19721222….El Nimo 20061226….El Nino 20021211..El Nino

You have to wonder what is going in with the WPO since we usually don’t see such dramatic reversals this time of year like the EPS, GEFS, and GEPS are showing.

It wast that cold around NYC with may averaging -0.5 and June -1.1 against the warmest 30 year means on record.

While it wasn’t cold enough to average below freezing like 2007, this was the coldest start to December since then before the pattern warms up. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending 12-01 to 12-07 average temperature 2024-12-07 34.7 0 2023-12-07 44.7 0 2022-12-07 45.7 0 2021-12-07 45.1 0 2020-12-07 42.1 0 2019-12-07 36.0 0 2018-12-07 40.0 0 2017-12-07 46.6 0 2016-12-07 44.1 0 2015-12-07 47.8 0 2014-12-07 42.4 0 2013-12-07 45.6 0 2012-12-07 45.1 0 2011-12-07 49.1 0 2010-12-07 36.9 0 2009-12-07 43.6 0 2008-12-07 38.1 0 2007-12-07 31.3 0

The first week of December was the coldest back to 2010. But it was more of a short term cold pattern similar to recent years. The cold in early December 2010 extended right through January. It was a fantastic pattern for LES snows due to the block near Seattle and the record warmth in the Lakes. But those factors moderated the cold in the Northeast so the coldest relative to the means went to the south. These quick warm ups after cool downs have become the norm for the East. Our last extended cold month was January 22 in the East courtesy of the MJO 8 pattern.

Unfortunately, we have still been getting warmer storm tracks even during cold patterns like we just had due to how overpowering the Pacific Jet has become in recent years.

The EPS is probably rushing the retrograding ridge since the axis has been ending up further east due to it underestimating the Pacific Jet longer range.

With the strength of that Pacific Jet it could take until the start of January to see cold departures like the first week of December.

You aren’t going to get any sustained cold next few weeks with that big +EPO vortex and fast Pacific flow.

The 2”+ potential on 12Z CMC would be a good news for some of the reservoirs that are running low.

It will be interesting to see if those IO WWBs can shift east of the Dateline by March leading to El Niño development in 25-26. The other possibility is that this La Niña is a late blooomer and we see renewed strengthing next few months and the La Niña next winter is stronger. So many competing influences can make the really long range even more challenging to figure out.

My guess is that we are seeing an interaction between competing influences. The big Southeast Ridge amplification this week is classic La Niña and MJO 4-6. But the stronger Aleutian Low longer range is more Nino-like. The faster Pacific Jet isn’t allowing the -EPO to lock in for very long. Niña-like pattern coming up Pattern becoming more Nino-like

The good news is that the rainfall is slowly starting to recover a bit after one of our driest falls which have left some reservoirs near record lows.

Several of the MJO composites which can have lags for where the forcing has been recently also have a very strong Aleutian Low. Especially given how strong the Aleutian Ridge was recently would take longer to reverse. So we could be seeing an odd mix of competing influences that we normally don’t see in December together. I guess the bottom line is that both the MJO and Nino 1+2 composites are warm this time of year.

Maybe that very strong Aleutian Low which both the EPS and GEFS have is a delayed response to the quick Nino 1+2 warming and record EPAC WWB back in late November. Notice how many of the CPC day 8-14 analogs are El Niño Decembers. That is a very strong El Niño look.

That’s not correct since we really need the rain for water supplies and not just vegetation concerns which are lesser this time of year. It’s important to start making up the fall precipitation deficit during the winter months so water restrictions don’t occur during the growing season. The last thing we want to see is a drought pattern go into the summer in a much warmer world than last droughts over 20 years ago.

It really makes you wonder whether study back in 2020 was onto something. https://e360.yale.edu/features/why-clouds-are-the-key-to-new-troubling-projections-on-warming Others soon followed. Last month, American and British researchers, led by Zelinka, reported that 10 of 27 models they had surveyed now reckoned warming from doubling CO2 could exceed 4.5 degrees C, with some showing results up to 5.6 degrees. The average warming projected by the suite of models was 3.9 degrees C (7 degrees F), a 30-percent increase on the old IPCC consensus. French scientists at the National Center for Scientific Research concluded that the new models predicted that rapid economic growth driven by fossil fuels would deliver temperature rises averaging 6 to 7 degrees C (10.8 to 12.6 degrees F) by the end of the century. They warned that keeping warming below 2 degrees C was all but impossible. ALSO ON YALE E360 Can artificial intelligence help build better, smarter climate models? Read more. Zelinka said the new estimates of higher climate sensitivity were primarily due to changes made to how the models handled cloud dynamics. The models found that in a warmer world clouds would contain less water than previously thought.