bluewave

The entire snowfall distribution near the coast has dramatically shifted since the 1990s. I will just use NYC as an example but all the other coastal sites have experienced the same pattern change. So we have 60+ years of data divided into 2 climate normals periods spanning 30 years each. The mid range seasonal snowfall range has greatly diminished and been replaced by all or nothing type years. Meaning well above or well below normal snowfall. This has become an issue as the climate continues the rapid warming since the 1990s. So the risk is that we continue to see this pattern increase going forward leading to the average coastal snowfall falling to around 15” or less from the 2020s into the 2040s. 1960-1961 to 1992-1993 NYC snowfall distribution 19” to 30”……17 seasons Under 15”…..5 seasons Over 31”……4 seasons 1993-1994 to 2023-2024 19” to 30”……4 seasons Under 15”……11 seasons Over 31”……..14 seasons

The difference back in that era was that we didn’t have the persistent have cutter, hugger, and suppressed Southern Stream storm tracks like since 18-19. We would get clippers dropping south of us for snow. Plus we often get coastal tracks near the BM which weren’t KU events but more moderate events. Then there were the KU years sprinkled in but not of the 2010 to 2018 frequency and magnitude. So we had more options for NYC to get to within the 19” to 29” range which was very common. These days we need a major snowstorm or multiple ones for NYC to approach the 24” to 25” range. So there was more variety to get the job done instead of having to rely exclusively on KU NESIS events since the 1990s.

Exactly since it’s the storm track which is necessary to getting NYC close to 25”.

Jan 21, 2001 was a cat 1 KU event due to how extensive the 6-9” area was.

The statistically objective metric is that NYC hasn’t had an average to above average snowfall season in over 30 years without a major coastal snowfall event ranking somewhere on the NESIS KU BM track. Many of these storms had 10”+ and 20”+ amounts somewhere in the OKX forecast zones. There were several winters during the 30 years from the 60s to 90s within around 3” of the long term 24” to 25” range that didn’t have such heavy snowstorms. So in the colder era we were able to break even just on small to moderate events. These days we need major to historic snowstorms to achieve this outcome. So we have fewer ways to do it than in the old days. Since there were several years with and without KUs which go there.

Yeah, the risk around the 20th is the -AO linking up with the Southeast Ridge again. This would result in the low hugging the coast. So the inland regions could really cash in while the coast gets another mixed precipitation event. Still too early to be sure since it’s outside the model reliable range. Just about every other February -AO in the -4 to -5 range had a KU within about a week or so of the occurrence. Like in February 2021, 2010, 1978, and 1969. So it would be very disappointing if we get 3 -AO link ups with the Southeast Ridge. I posted the other day how this has become a frequent occurrence in the 2020s. The last -4 AO link up was only a little over 2 years ago in December 2022. Prior to that we had one near -4 in December 2012. Then before that it was in January 1998. So this has become a much more frequent occurrence. Hopefully, we can find a way to buck the trend around the 20th to avoid the cutter, hugger, and suppressed Southern Stream pattern we have been in since 18-19. 2 Southeast Ridge link ups in near term Third one possible around the 20th

Snowfall can vary quite a bit over short distances. https://www.raymondcmartinjr.com/weather/2001/05-Mar-01.html

It’s in the official monthly climate report for March 2001. https://www.ncei.noaa.gov/pub/orders/IPS/IPS-B4467854-7C53-42F0-88D4-3798355E3BA8.pdf

Every weather event that occurs is in some way influenced by the average global temperatures around the time of the event. You wouldn’t expect the real world weather events to be the same during an ice age as they were during the PETM. So the background climate temperatures during each era sets the parameters or range of possibilities for the individual weather events.

The most memorable storm that winter closer to NYC was the 12-30 event which broke the slump we were in since after the 95-96 winter. Data for December 30, 2000 through December 30, 2000 Click column heading to sort ascending, click again to sort descending. NY PORT JERVIS COOP 16.8 NY DOBBS FERRY-ARDSLEY COOP 14.0 NJ NEWARK LIBERTY INTL AP WBAN 13.9 NY MINEOLA COOP 13.6 CT DANBURY COOP 13.4 NY LAGUARDIA AIRPORT WBAN 13.3 CT STAMFORD 5 N COOP 13.0 NJ HARRISON COOP 12.8 NY NEW YORK AVE V BROOKLYN COOP 12.7 NY NY CITY CENTRAL PARK WBAN 12.0 NY JFK INTERNATIONAL AIRPORT WBAN 10.3 CT IGOR I SIKORSKY MEMORIAL AIRPORT WBAN 10.0 Data for January 20, 2001 through January 21, 2001 Click column heading to sort ascending, click again to sort descending. NY WEST POINT COOP 7.5 NY GARDNERVILLE COOP 7.3 NJ WANAQUE RAYMOND DAM COOP 7.0 NY WALDEN 1 ESE COOP 7.0 NY PORT JERVIS COOP 6.7 NJ CHARLOTTEBURG RESERVOIR COOP 6.5 NY SEA CLIFF COOP 6.5 CT DANBURY COOP 6.3 NY NY CITY CENTRAL PARK WBAN 6.0 NJ ESSEX FELLS SERVICE BLDG COOP 6.0 NJ GREENWOOD LAKE COOP 6.0 NY JFK INTERNATIONAL AIRPORT WBAN 6.0 CT IGOR I SIKORSKY MEMORIAL AIRPORT WBAN 6.0 NY WESTCHESTER CO AP WBAN 6.0 CT JEWETT CITY COOP 6.0 Data for February 22, 2001 through February 23, 2001 Click column heading to sort ascending, click again to sort descending. NJ CANOE BROOK COOP 6.5 NJ CRANFORD COOP 6.2 NJ PLAINFIELD COOP 6.0 NY LAGUARDIA AIRPORT WBAN 6.0 NJ HARRISON COOP 6.0 NY NY CITY CENTRAL PARK WBAN 5.8 NJ NEWARK LIBERTY INTL AP WBAN 5.7 Data for March 5, 2001 through March 6, 2001 Click column heading to sort ascending, click again to sort descending. NY RIVERHEAD RESEARCH FARM COOP 14.5 CT DANBURY COOP 14.3 CT IGOR I SIKORSKY MEMORIAL AIRPORT WBAN 13.5 NY BRIDGEHAMPTON COOP 13.3 NY WEST POINT COOP 13.0 CT JEWETT CITY COOP 10.0 NY WALDEN 1 ESE COOP 9.0 CT ANSONIA 1 NW COOP 9.0 CT NORWICH PUBLIC UTILITY PLANT COOP 8.5 CT GROTON COOP 7.5 NY ISLIP-LI MACARTHUR AP WBAN 7.0 NY DOBBS FERRY-ARDSLEY COOP 6.5 NY MINEOLA COOP 6.2 NJ NEWARK LIBERTY INTL AP WBAN 6.1 NJ GREENWOOD LAKE COOP 6.0 CT STAMFORD 5 N COOP 6.0

Remember that NYC doesn’t always jackpot when we have an active KU BM storm track regime. Sometimes the coastal storm tracks are inside the BM like December 2020 favoring the interior like BGM. Other times coastal storm tracks are just wide of the BM favoring Suffolk County like in January 2022. And other times we get more of a goldilocks track like in January 2016 with the jackpot in the middle near NYC. So the common denominator for all NESIS snowstorms is generally someone around the region getting a 10”+ snowfall max. This type of major coastal snowstorm track has become a prerequisite for NYC to reach within a few inches of the longer term mean in the 24” to 25” range. All the seasons since 93-94 with near to above this range featured KU NESIS snowstorms. From the 1960s to the 1980s NYC could get to within a few inches of the 24-25” snowfall range with numerous smaller to moderate events and no major KUs. But obviously the much higher years such as 77-78 featured major KU events. So there were multiple ways to get close to the 24-25” range.

We had the -EPO +PNA which was able suppress the Southeast Ridge.

-PNA -AO intervals back in the much colder era didn’t regularly feature a Southeast Ridge linking up with the -AO Greenland blocks. This is more of a recent occurrence during the 2020s. Notice back in the 1950 to 1970 era when we had frequent -PNA and -AO patterns there was usually a trough in the East. My guess is this recent alteration of that past pattern is related to our much warmer climate including land areas, SSTs, and a faster Pacific Jet. I complied 15 separate such months from that era as a comparison. 1950 to 1970 colder era winter -PNA -AO patterns across 15 different months

The Southeast Ridge wouldn’t have linked up with a -4 to -5 -AO block in that much colder climate era.

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.