bluewave

Multiple KUs that winter with one on 12-30 and another 1-19. https://www.ncei.noaa.gov/access/monitoring/rsi/nesis

Normals and averages can be used interchangeably in describing climate means. From 49-50 to 08-09 NYC averaged 24.4”. But the shift to a record number of BM KUs from 09-10 to 17-18 resulted in the 2010s averaging 37.9”. The lack of BM KUs during the 2020s has dropped the decadal average down to 13.6” through today. So all NYC needs to do is get a few more inches to break even for the 2020s snowfall averages. But needs significantly more to get back to the 60 year average of 24.4” from the 1950s through 2000s.

Unfortunately, the waters near Indonesia were the warmest on record for January along with east of Japan.

It could be the rapid SST warming near Japan and acceleration of the Pacific Jet leading to the cutter, hugger, and suppressed Southern Stream tracks since 18-19.

They can do well with suppressed Southern Stream tracks but we can’t.

NYC hasn’t had a normal snowfall season since the 1990s without some portion of the area from EWR to Eastern LI experiencing a KU BM snowstorm with 10”+ totals. So this persistent cutter, hugger, and suppressed Southern Stream storm track is working against normal snowfall seasons. In the colder era before the 90s, NYC could approach 25” inches with out BM KUs during seasons like 73-74, 76-77, 83-84, and 84-85. So these days a major KU snowstorm is the prerequisite for NYC getting near or over 25”.

The Southeast Ridge would link up only sporadically with weaker to moderate -AO events from the 1950s through the 1990s .The best known stronger event from that era was 1-9-98. It could be related to the stronger Pacific Jet and the record warm Atlantic SSTs. So it’s the frequency and intensity which has been something new during the 2020s. The coming event this week will be the 2nd -4 link up in just a little over 2 years. The south based block in December 2020 allowed BGM to get the 40” jackpot instead of closer to NYC. It lead to the first snowfall shut out for us back in December 2022 with similar past La Niña and -AO levels. Then the March 2023 pattern followed a similar script. Now we are getting mixed precipitation events with this present south based -AO block. The 11-12th event may be one of the few events without mixing issues in NYC. Interior spots that build up a big enough snowpack could become susceptible to flooding if one or more of the coming storms rides too far north. 2nd -4 -AO in only a little over 2 years this week linking up with the Southeast Ridge -4 -AO December 2022 linking up Southeast Ridge 2022 12 18 -4.151 2022 12 19 -3.671 2022 12 20 -3.326 Earlier era linkage during 97-98 super El Niño 1998 1 9 -3.987 1998 1 10 -4.269

I searched the 500 mb database and only found weaker -AO examples before 2020 with the -AO linking up with the Southeast Ridge. A handful of less intense instances in the 1950s and late 1990s. But no strong -AO link ups with the Southeast Ridge like December 2020, December 2022, and now this week coming up. So we are getting multiple ways to mix with rain these days around NYC which weren’t present in the past. Plus with the much stronger Northern Stream of the Pacific Jet has lead to suppression when we had troughs in the Northeast this winter so far. This makes it harder to get the classic BM track since cutters, huggers, and suppressed Southern Stream storm tracks dominate. It’s why just looking at the strong -AO this week in isolation of these other factors won’t give us the complete picture. Past instances with such strong drops to near or below -4 didn’t have these headwinds working against getting a solid BM track. So any snowfall expectations for this week based on past big -AO drops need to be filtered through the newer framework. It also raises the potential for interior locations that get a decent snowpack in the coming weeks could be open to flooding when one of these systems rides too far north.

Another case of a -4 or lower -AO linking up with the Southeast Ridge which didn’t happen before 2020.

4” here just to the east of KHVN.

This is a much different storm track pattern than was the case from 1970 through 1999. Places like NYC would usually average somewhere in the 19” to 30” for seasonal snowfall with just a few years above and below that range. During the 2020s NYC has been averaging closer to 14” to 15”. So we need a big return to benchmark KU snowstorms ASAP next 3-4 seasons for NYC to avoid having a permanent shift under 20”. But the good news so far is that even with the less snowy seasons, NYC has still avoided getting close to shut out and an under 1” season.

The first example of this cutter, hugger, and suppressed Southern Stream storm track became evident during the 18-19 DJF period when we only had a single snow squall at the end of January even with the cold pattern in January. All our snow that year was one SWFE in November and a brief period in early March where areas further north did OK. Then this was followed by disappointing 19-20 season. The overpowering Northern Stream of the Pacific Jet began to become a big factor. While the BM KU tracks made a return for 20-21, even in that season there were some notable differences. The December event tracked very close to ACY so BGM got the 40” jackpot. Then the damaging flood cutter on Christmas. The early February event was the only traditional BM KU of this decade where points west to NYC and LI cashed in together. The BM tracks in 2022 were shifted further east so Suffolk did great and areas further west were left out. Of the best results. December 2022 featured the best December AO blocking since 2010 but we didn’t get another Boxing Day Blizzard with 30” around Newark. The hostile Pacific ran the table and even the MJO 8 and -AO pattern in March couldn’t produce. Then in 23-24 we got the one week window in February with the record STJ and the Northern Stream briefly relaxing. Mostly Central Jersey was favored for the best results. Then we had the great -EPO and +PNA from this December into January being joined by the -AO and colder than average temperatures. Very little snowfall to show for it over those two months vs past La Niña mismatch with 10-20”+ in NYC for similar past patterns. One of the most extreme Southern Stream suppression events of all-time with the Gulf Coast getting the record snows. Now this February we have been getting hugger tracks with front end thumps and then mixed precipitation closer to the coast. So while the retrogression pattern following the big -AO block forecast for mid-February has produced KU BM tracks in the past, it’s very uncertain if the storm track will cooperate this time around. Hopefully, we can out something together during that retrogression interval around or after the 20th. While it’s always possible we could see a better March this year than the last 5, I wouldn’t want to have to rely on March if this pattern continues to underperform. Not seeing the big SSW signal like in 2018 and strat coupling which lead to the 30” March on LI and locked in -AO for the whole month. Since it looks like the -AO will start weakening later in February as it retrogrades back into +PNA.

This time around we are still contending with the much faster Northern Stream of the Pacific Jet since 18-19. That winter had the great STJ to go with KB block retrograde back across the North Pole. So we are still dealing with the cutter, hugger, and suppressed Southern Stream storm tracks which make 30” snowstorms in NYC harder to come by.

That KB block shifted the whole pattern across the Northern Hemisphere this month. It’s forecast to retrograde back to near the North Pole over the next week. Notice how this is causing the global temperatures to finally drop below the record levels.

The KB block is definitely the reason we saw the shift on model forecasts for February. The wave break which just occurred with the record low east of Hudson Bay wasn’t forecast very well back in late January. So this record block is forecast to retrograde back into the AO region.

We are just following model forecasts which have improved greatly since the 70s and 80s. Then we take into account what the recent model biases have been. But no matter how much long range model forecasts improve, a 10 to 15 day forecast is always going to have some errors due to the nature of modeling. We live very close to where continental air masses interact with the Gulf Stream to our Southeast. So my guess is that this is one reason snowfall details usually have to wait with snowfall until the short term. Models just can’t pin down snowfall details over a 240 or 360 hr forecast period. So the best we can do is identify patterns would could potentially produce snow. It’s even harder with a rapid succession of systems like we are getting this month. Most 360 hr surprises in the 2020s have been toward warmer and less snowy as the time period approached. So this near record block forecast for mid-February wasn’t showing up on the models back on January 30th. But the general 500 mb longwave pattern will turn out to be correct. It’s always the nuisances and details within a pattern will vary. So while we can get excited about snowfall potential in a general pattern, it’s always going to come down to the shorter range details as to how much snow we get. Old 360 hr forecast had correct longwave 500 mb pattern but missed the record block near Greenland and the North Pole New forecast Old forecast

The record KB block driving the Siberian Airmass SE along with the record SSTs near Japan.

2002-2003 was the last time that all of our climate sites had all 3 winter months with a negative temperature departure. But that was during a much colder climate normals period. So it’s easier to get a cold departure now with the much warmer normals. Since a cold departure now like during December would have been warm using the older climate normals period. Some of our stations had 3 in a row during 09-10 and others like Newark didn’t. This winter JFK finished above average back in December and Newark just managed a slight negative departure of -0.1. So nothing like the magnitude experienced in 2002-2003.

That was based on the modeling at the end of last week before the -AO block started showing up. The first week of February so far has indeed been warmer than average and followed the La Niña script. But the wave break with the record low east of Hudson Bay shifted the whole pattern going forward. Models still have the -AO block peaking next week and gradually weakening later in the month as the block retrogrades back into +PNA.

This looks like the first 5 SD 500 mb block near Greenland during the winter since February 2021. So the million dollar question is whether our best snowfall opportunities will occur prior to and around the peak in mid-February or after. Back in 2021 when the AO went -5 the best snows came in before the block and not after it peaked. This is pretty much unknowable at this point. But at the very least the magnitude of the block now argues for a colder than average February. Before the models started showing the block they were going for +1 to +2 pattern in the means for February. So this could be the first winter since 2002-2003 with all 3 winter months having a cold departure. We are now pretty much assured of having our first colder winter here since 2014-2015. Regardless of the snowfall outcome, this block will be impressive even if doesn’t couple with the stratosphere. So more of a bottom up event. Longer range the models have the AO block weakening in later February and giving way to more of +PNA which is pretty rare for a La Niña February. 5 SD 500 mb anomaly one of the most impressive of 2020s so far

It’s a new 500 mb record for this time of year. Mika Rantanen ‪@mikarantane.bsky.social‬ Follow That is a huge blocking predicted to form over NW Russia. Record-breaking in intensity (for the time of the year), with 500 hPa levels half a kilometre higher than normal. It's like a stone in a river that directs the warm, moist air flow from the North Atlantic towards the Arctic. ALT ALT February 4, 2025 at 8:36 AM Everybody can

New lowest extent record for 2-5 by 500k.

Arctic sea ice thickness and extent at record low levels for this time of year.

This month could be the end of the drought here as the Euro seasonal is wet right through the summer. https://charts.ecmwf.int/products/seasonal_system5_standard_rain?area=GLOB&base_time=202502010000&stats=tsum&valid_time=202506040000