bluewave

Yeah, such a fast and active Northern Stream of the Pacific Jet and record Great Lakes warmth gave your area very impressive snowfall totals.

This 7 year data conforms to what has been happening over the last 30 to 60 years. So you make an error when saying it’s only 7 years and arbitrary. It’s not singling anything out but rather it’s matching the longer term existing trend. From the 60s into the early 90s my area had a cold and stable temperature pattern. So the areas around NYC had mostly mid range snowfall seasons. Very few much above normal and much below normal snowfall. Since the 90s we have shifted to an all or nothing snowfall distribution pattern with hardly any snowfall seasons near the middle of the distribution. So our snowfall has become much more extreme with well below and well above dominating. This 30 year shift has occurred against the backdrop of rapidly warming temperatures. The record snowfall highs from 09-10 to 17-18 and the record lows since 18-19 perfectly conform to this 30 year snowfall distribution shift. In the colder era before the mid 90s, the NYC area could reach the middle range of 19” to 31” seasons without historic KU benchmark NESIS storms. So a colder climate provided more options of reaching this mid range.Obviously, the KU seasons were the ones which finished well above the mean. So NYC Metro and other locations have fewer options of reaching this middle range. Many seasons jumped above this range from 09-10 to 17-18 relying exclusively on a 1 in 100 year phenomenal concentration of Benchmark storms with a significantly higher concentration of NESIS events experienced in the past. So my guess is that relying on a another 9 year run like that is probably a low probability chance of reoccurrence. Now we are left with the current all or nothing pattern where the higher and middle range distributions seeing smaller probabilities. So it’s no surprise when we lost the benchmark tracks for much of the time since 18-19 ,that the region is at the all-time record lows for snowfall. Past lows near this range over 7 year periods were primarily a result of drier conditions and not record warmth. These were followed by numerous 50” + seasons which were easier to come by in a colder climate. So as we continue to warm, both storm tracks and the seasonal background temperature warming provide less opportunities for snow. Having to rely so heavily on just one type of storm track has left us open to repeated well below normal snowfall seasons last 7 years. Since the Great Lakes cutters, I-78 to I-80 hugger tracks, and suppressed Southern Stream lows with the faster Northern Stream of the Pacific had lead to record low snowfall. The data suggests a few ways this could go in the coming years. First, my guess is that the longer term snowfall peaked in 17-18 around NYC .Then 18-19 began the decline that has been expected in a warmer climate reducing snowfall chances. Option one is that the last 7 years continues and represents the new normal for snowfall. Option two is a return to occasional benchmark storm tracks with an uptick in snowfall next several seasons but coming up well short of 09-10 to 17-18. This would be followed by another downtown in the 2030s if it did occur as temperatures continue to warm. Option 3 is a return to the 09-10 to 17-18 benchmark era which I give the smallest chances to.

The most significant snowfall metric for NYC and the whole area near the coast is the 7 year snowfall running mean. This is at record lows for any 7 year stretches on record. The major issue going forward is that those were all in the colder era and were mostly the result of dry conditions. So it was much easier to end a snow drought since the moisture always returned and it was colder. It’s more challenging to end a snow drought based on too warm for heavy snow like we have seen in the last 7 years as the background climate warms. This winter was a great example of too warm for heavy snow since the storm tracks were so warm. The average winter temperature on the precipitation days above .25 of liquid was 41.0°. That is way too warm for heavy snows as the under 4” run continued in NYC. This wasn’t the case in the past when it was too dry for heavy snows. All the previous snow droughts ended with very big 50”+ seasons in the following years. But that is going to be a a significant challenge in this much warmer climate. Lowest NYC 7 year snowfall totals and the big seasons which followed 2019 to 2025……14.9” 1986 to 1992……16.3”…..93-94….53.4”…..95-96…75.6” 1970 to 1977…..…17.1”……77-78…50.7”….78-79….29.4” 1950 to 1956…….17.0”…..57-58….44.7”….60-61…..54.7” 1927 to 1933……15.4”……33-34….52.0”…..34-35….33.8”….35-36….33.2”

The model bias has been remarkably consistent this winter and since 18-19. Constant underestimating of the strength and effects from the Pacific Jet beyond 120hrs and especially from 168hrs and after. This has lead to the big modeled snowstorm always remaining a week or more out in time. So the closer in time we get the models figure out that the fast Pacific flow will play the spoiler. The original model run from 168hrs and beyond shows a big snowstorm coming up the East Coast. But there is questionable wave spacing in the West. Shorter term runs show that low out West becoming the kicker as the faster flow than forecast leads to the modeled lead low getting suppressed south and our area missing the snows. The next error was the way overdone EPS snow means showing the best overrunning gradient closer to NYC. But as the storm time approaches, there is a little too much wave spacing between lows and the storm digs too much to our west pumping the Southeast Ridge. So the best overrunning snows go north of NYC. Another common track is a well spaced low to our west with no kicker at all behind it. So this long range forecast starts out as a cutter track and even ends up further west so interior portions of the Northeast end up with P-type issues. It leads to the saying that the one storm track forecast from more than a week out that the models can get right is a cutter. Since it can go 50 miles west of NYC or 500 miles west with a similar outcome for us along the coast. But areas further west can start out more snowy and end up with mixing or just mostly rain.

The WWB we just got in the EPAC during February was the strongest on record for just north of the equator. So this is why we have seen the sudden jump in surface warming near SA. We would probably need a follow up WWB back a little closer to and east of the Dateline in late March into April to tip the system back into El Niño again. Still plenty of time to observe since the spring forecast barrier makes ENSO outlooks tricky this early on.

No shortage of overperforming wind events this year.

We would want to see the shallow surface warm pool near SA link up with the the one at greater depth closer to the Dateline as was the case in March and April 2023 to have a shot at El Niño development this year.

You just have to laugh at how predictable these storm tracks have become. When the faster flow results in smaller wave spacing, then the low coming into the West acts as a kicker and the low further east gets suppressed to the Mid-Atlantic or Southeast. Then when the lows are further apart, the low out West amplifies too much pumping the Southeast Ridge and the low cuts to the Great Lakes. The third scenario is a compromise between these previous two tracks and the low tracks right across the I-84 I-80, I-78, or I-95 corridors hugging the area. Bottom line is the localized snow belts in the Great Lakes and Northeast higher elevations really do great in this type of pattern.

You can see how much faster the Northern Stream of the Pacific Jet has become from near Japan right across the Pacific into the U.S. since 18-19. This has lead to storm tracks cutting through the Great Lakes, hugging the I-78, I-80, and I-95 corridors. Then other storms getting suppressed to our south with kicker lows coming into the West. It has left very little room for the benchmark tracks which reached record numbers from 09-10 to 17-18.

The faster flow is the reason for the strong storm tracks through the lakes instead of relaxing and giving us a quiet ridging pattern.

Not an easy feat with such a fast Pacific flow and storms racing through the Great Lakes.

I agree with this. The much faster Northern Stream of the Pacific Jet since 18-19 is the primary reason that we had such low snowfall from Philly to Boston. Warmer overall winter temperatures and especially the warmer storm tracks. The warmer storm tracks have prevented us from having a snowy winter in a warmer pattern like we often got back during the mid to late 2010s. So we finally got a winter near with near average temperatures this year. But the best we could do is a reversion to the much lower recent 7 year mean for snowfall. So the Pacific overpowered what used to be colder and snowier teleconnections as recently as last decade. Reversion to the 7 year snowfall mean in 2025 from Philly to Boston Monthly Total Snowfall for Philadelphia Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Mean T 0.5 1.0 4.4 4.0 0.6 0.0 10.5 2024-2025 0.0 T 0.3 4.6 3.2 0.0 M 8.1 2023-2024 0.0 T T 8.0 3.2 0.0 0.0 11.2 2022-2023 T 0.0 T T 0.3 T 0.0 0.3 2021-2022 0.0 0.0 T 12.1 0.4 0.4 0.0 12.9 2020-2021 0.0 0.0 6.6 3.0 14.3 0.0 0.0 23.9 2019-2020 0.0 T 0.1 0.2 T 0.0 0.0 0.3 2018-2019 0.0 3.6 0.3 2.6 6.6 4.0 0.0 17.1 Monthly Total Snowfall for New York-Central Park Area, NY (ThreadEx) Click column heading to sort ascending, click again to sort descending. Mean 0.0 0.9 2.3 3.7 6.4 1.6 T 14.9 2024-2025 0.0 0.0 2.8 3.0 7.1 0.0 M 12.9 2023-2024 0.0 T T 2.3 5.2 T 0.0 7.5 2022-2023 0.0 0.0 T T 2.2 0.1 0.0 2.3 2021-2022 0.0 T 0.2 15.3 2.0 0.4 0.0 17.9 2020-2021 0.0 0.0 10.5 2.1 26.0 T 0.0 38.6 2019-2020 0.0 0.0 2.5 2.3 T T T 4.8 2018-2019 0.0 6.4 T 1.1 2.6 10.4 0.0 20.5 Monthly Total Snowfall for Boston Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Mean 0.6 0.0 4.6 10.2 8.7 2.4 0.2 26.6 2024-2025 0.0 0.0 5.7 8.2 14.2 0.0 M 28.1 2023-2024 0.0 T 0.2 9.0 0.5 T 0.1 9.8 2022-2023 0.0 T 1.0 6.9 3.6 0.9 0.0 12.4 2021-2022 0.0 T 0.4 36.2 15.3 2.1 T 54.0 2020-2021 4.3 T 13.0 5.8 15.3 0.1 0.1 38.6 2019-2020 0.0 T 11.5 3.1 0.5 T 0.7 15.8 2018-2019 0.0 0.1 0.1 2.1 11.6 13.5 T 27.4

No snow is the new normal for March in the 2020s. Monthly Total Snowfall for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Mean 0.1 0.1 2025 0.0 0.0 2024 T T 2023 0.1 0.1 2022 0.4 0.4 2021 T T 2020 T T

But January 2021 was our most negative NAO winter month of the 2020s so far both at 500 mb and the surface. And it was still a mild January in the Northeast. Caribou finished at +7.9 and had their 10th warmest January on record. So such a strong -NAO in an earlier era in January was much colder in the Northeast even if there was also a trough near the Pacific NW.

We had a big divergence between the CPC PNA and the 500 mb PNA especially in February which had the classic 500 mb -PNA vortex in the PACNW even though CPC index was +PNA. I liked your old idea of creating custom 500mb indices. I think the divergence between the AO and NAO is less if we just used the 500 mb composites and didn’t use the CPC. My guess is the 500 mb NAO would be negative more often than we have been getting from the CPC. So the NAO and AO would align more at the 500 mb level.

The specific phenomenon are strongly influenced by the global temperatures at any given time. This is why teleconnections which were cold in the 70s to early 90s haven’t been as cold anymore. Plus the coldest recent month in the Northeast was during one of the strongest +NAO winters on record in February 2015. January 2021 was the most negative 2020s winter NAO month and it was mild in the Northeast. So other teleconnections and patterns have a much bigger influence than the NAO in the Northeast.

The state of the NAO whether positive or negative doesn’t cause the Northern Hemisphere cold pool to get smaller like we have been seeing resulting in the limited area of these Arctic outbreaks.

Montana has been one of the small areas in North America with 4 top 10 coldest Februaries since 2018. So these Arctic outbreaks have been focusing in smaller geographic regions. In the old days the cold dropping down the Plains would spread out to the East Coast. Now the core of the cold stays in a narrower corridor closer to the Plains and Midwest. Time Series Summary for Great Falls Area, MT (ThreadEx) - Month of Feb Click column heading to sort ascending, click again to sort descending top 10 coldest Februaries since 1892 1 1936 -5.2 0 2 2019 -0.2 0 3 1922 9.0 0 4 1989 10.3 0 5 1899 11.0 0 6 2025 11.3 0 7 2018 11.8 0 8 2021 12.4 0 9 1975 13.1 0 10 1978 14.4 0

Maybe the higher 500mb heights near the East Coast are influencing the location of the wave breaks which have been leading to the orientation of the -AO and -NAO blocks during the 2020s.

It hasn’t made a difference whether it was a -NAO or -AO during the 2020s. March 2023 was one of the most negative NAO months of the 2020s so far. We still got the Southeast Ridge link up which forced the storm on the 13 to 15th too far north for my area. So it turned into an higher elevation special. 2023 1.25 0.92 -1.11

There are probably multiple factors contributing to the more +NAO winter trend and -NAO summer trend.

That’s the point. Even when we had strong -PNA -AOs in recent years, the actual 500 mb heights weren’t as low near the Pacific NW as there were in the 1950s to 1970s. So deeper troughs digging into the West during that colder era didn’t pump the Southeast Ridge. During the 2020s all it takes are relatively weak lows coming into the West and we get a big 500mb ridge amplification in the East.

Back in the 50s to early 70s we seldom had a Southeast Ridge when there was a strong -PNA -AO pattern. So the Southeast Ridge becoming such a big player in our sensible weather is a more recent phenomenon. My guess is that it’s a function of the much warmer global SST and land temps along with the warming at 500mb.

I think the more +NAO could be a function of the increased KB blocking low sea ice feedback. We used to get a much stronger vortex in Europe when there was such strong blocking across the Arctic in the old days. Instead the KB block build down into Europe preventing the usual cold trough development. So this is also contributing to the Southeast Ridge which has been increasing over the years. But even past instances of a very deep vortex centered south of Greenland like this year didn’t have as strong of a Southeast Ridge. The vortex out there this month was among the strongest that was observed in the February when compared to the other strong years in the composite. But the Arctic blocking was more intense this February than in the composite.

We have been seeing the -AO decouple from the -NAO. We used to get both falling in tandem more often. Now we get -AO and +NAOs more often.