bluewave

In terms of temperatures we were colder than December 2023 and 2021 and not that much colder than 2022. Even though snowfall has been better than December 2021 to 2023, the snowfall has been well below what past La Niña +PNA Decembers had. This has been due to the faster Pacific Jet causing the +PNA ridge to drift further east at times. Our past +PNA La Niña Decembers were also mostly colder than this year with 7”-14” at Newark. The ridge also stayed anchored further west allowing better December very snowy benchmark storm tracks. So far from the very low bar of the last few Decembers were are doing better which is good. But very strong Northern Stream of the Pacific Jet didn’t relax enough for the colder and snowier outcomes in the other +PNA Decembers in 2020, 2017, 2005,2000, and 1995.

The 16-17 La Niña was one of the more unique that we have seen. It was our first La Niña winter around NYC averaging near 40° with many stations going over 30” on the season. We had a great benchmark storm track even when there was record warmth in the 60s within a day or two of some of the best snowstorms. It was also a snowy December for our area here in Southern CT. Many stations finished that December with 6” to 9”. Monthly Data for December 2016 for Fairfield County, CT Click column heading to sort ascending, click again to sort descending. DANBURY COOP 9.2 BROOKFIELD 3.3 SSE CoCoRaHS 7.8 BETHEL 3.5 NNE CoCoRaHS 7.8 NEWTOWN 4.3 E CoCoRaHS 7.8 BETHEL 0.5 E CoCoRaHS 7.4 SHELTON 1.3 W CoCoRaHS 6.7 IGOR I SIKORSKY MEMORIAL AIRPORT WBAN 6.0 TRUMBULL COOP 6.0 Monthly Data for December 2016 for New Haven County, CT Click column heading to sort ascending, click again to sort descending. PROSPECT 1.5 NW CoCoRaHS 9.9 CHESHIRE VILLAGE 2.2 SE CoCoRaHS 6.9 PROSPECT 0.5 SW CoCoRaHS 6.7 SOUTHBURY 2.0 NNE CoCoRaHS 6.2 MOUNT CARMEL COOP 6.0 HAMDEN 3.0 WSW CoCoRaHS 5.9 MILFORD 1.8 E CoCoRaHS 5.7

The actual cutoff value is closer to 4” like Newark since they measure later in NYC after the snow has had time to melt or settle since the airports measure more frequently. The official NYC values have been too low compared to the airports since the 1990s. Many times the measurement at the park occurs hours after the snow has stopped yielding a lower value than at the airports that measure when the snow stops. The December La Nina cutoff for above average seasonal snowfall at Newark is closer to 4”. It’s probably a little higher than the 3” at NYC since they measure more frequently than NYC before the snow has a chance to melt or settle. So the 3” measurements are actually closer to 4” in NYC if they measured at the end of the snow instead of waiting up to 6 hours. The only time that a lower December snowfall total worked out at Newark last 30 years was the 16-17 La Nina. The reason this works out for our area is due to La Ninas being frontloaded by nature. So the above average La Niña snowfall winters have a snowy start. Newark December La Nina snowfall and seasonal totals 2024….2.5”……? 2022….0.1”…..2.7” 2021…..0.1”….17.9” 2020…11.9”….45.7” 2017….7.7”…..39.4” 2016….3.4”….30.0” 2011…..0……..8.8” 2010….24.5”….68.2” 2008….8.3”…..27.1” 2007…..3.9”….14.6” 2005….11.0”….37.9” 2000….14.9”….39.3” 1999……T……..18.4” 1998……1.2”…..12.8” 1995……12.8”….78.4”

The timing worked out very well this year for the coldest and snowiest part of the month close to Christmas before we warm back to the 50s to close out the year.

This is why we should probably think about adjusting the snowfall measurements higher prior to 1990 since they measured less frequently. So snowfall during the older era was underestimated compared to today. While it doesn’t take away from the 2010s, the older era storms would be heavier if measured the same way. https://news.ucar.edu/14009/snowfall-measurement-flaky-history Many pre-1990 numbers would be higher using current methods Earlier in our weather history, the standard practice was to record snowfall amounts less frequently, such as every 12 or 24 hours, or even to take just one measurement of depth on the ground at the end of the storm. You might think that one or two measurements per day should add up to pretty much the same as measurements taken every 6 hours during the storm. It’s a logical assumption, but you would be mistaken. Snow on the ground gets compacted as additional snow falls. Therefore, multiple measurements during a storm typically result in a higher total than if snowfall is derived from just one or two measurements per day. That can make quite a significant difference. It turns out that it’s not uncommon for the snow on the ground at the end of a storm to be 15 to 20 percent less than the total that would be derived from multiple snowboard measurements. As the cooperative climate observer for Boulder, Colorado, I examined the 15 biggest snowfalls of the last two decades, all measured at the NOAA campus in Boulder. The sum of the snowboard measurements averaged 17 percent greater than the maximum depth on the ground at the end of the storm. For a 20-inch snowfall, that would be a boost of 3.4 inches—enough to dethrone many close rivals on the top-10 snowstorm list that were not necessarily lesser storms! Another common practice at the cooperative observing stations prior to 1950 did not involve measuring snow at all, but instead took the liquid derived from the snow and applied a 10:1 ratio (every inch of liquid equals ten inches of snow). This is no longer the official practice and has become increasingly less common since 1950. But it too introduces a potential low bias in historic snowfalls because in most parts of the country (and in the recent blizzard in the Northeast) one inch of liquid produces more than 10 inches of snow. This means that many of the storms from the 1980s or earlier would probably appear in the record as bigger storms if the observers had used the currently accepted methodology. Now, for those of you northeasterners with aching backs from shoveling, I am not saying that your recent storm wasn’t big in places like Boston, Portland, or Long Island. But I am saying that some of the past greats—the February Blizzard of 1978, the Knickerbocker storm of January 1922, and the great Blizzard of March 1888—are probably underestimated. So keep in mind when viewing those lists of snowy greats: the older ones are not directly comparable with those in recent decades. It’s not as bad as comparing apples to oranges, but it may be like comparing apples to crabapples.

Probably a quick coating to 1” where the best snow bursts occur.

The December La Nina cutoff for above average seasonal snowfall at Newark is closer to 4”. It’s probably a little higher than the 3” at NYC since they measure more frequently than NYC before the snow has a chance to melt or settle. So the 3” measurements are actually closer to 4” in NYC if they measured at the end of the snow instead of waiting up to 6 hours. The only time that a lower December snowfall total worked out at Newark last 30 years was the 16-17 La Nina. The reason this works out for our area is due to La Ninas being frontloaded by nature. So the above average La Niña snowfall winters have a snowy start. Newark December La Nina snowfall and seasonal totals 2024….2.5”……? 2022….0.1”…..2.7” 2021…..0.1”….17.9” 2020…11.9”….45.7” 2017….7.7”…..39.4” 2016….3.4”….30.0” 2011…..0……..8.8” 2010….24.5”….68.2” 2008….8.3”…..27.1” 2007…..3.9”….14.6” 2005….11.0”….37.9” 2000….14.9”….39.3” 1999……T……..18.4” 1998……1.2”…..12.8” 1995……12.8”….78.4”

With the consistent undermeasurement of snowfall there since the NWS left in the early 90s, maybe the actual December cutoff for above or below seasonal snow during a La Niña is somewhere between the 3”-4” range. I have been using 3” since that is how the measurements have gone in the official records. So the actual level if there was correct measurement would probably be somewhere in the 3.0” to 4.0” range.

While the long range ensemble forecasts beyond a week can vary quite a bit, the model error has been very consistent. The December long range forecasts issued back on December 1st underestimated the strength of the Pacific Jet. This lead to the 500 mb heights verifying lower than forecast over the EPAC south of Alaska. This allowed the ridge to drift east at times instead of staying anchored out West. We have seen some version of this model error every winter in the Pacific since 15-16. So now if the models are showing lower heights over Western NA than there were from earlier runs, it’s possible we see some version of this pattern repeat heading into January. The other issue has been the tendency for long range -AO forecasts to link up with the Southeast Ridge at least transiently when lows are ejecting from the trough which has been so frequent in the West. Just hoping we can get enough overlap between the fading +PNA and the emerging -AO to at least get a shot at a 4” snow event for NYC. But there are no guarantees with the way the Pacific has been acting as the spoiler since 18-19.

The closest wall to wall winter for snow and cold in the East at under at under 1000 feet elevation would probably be Caribou, Maine in 76-77. Every day from 12-1-76 to 2-28-77 had at least 1” of snow on the ground. The highest temperature over that stretch was only 37°. With a total of just 6 days going above 32° for a high.

It would be nice to see snow on a SW flow which we haven’t had in a while.

Hopefully, NYC can get it done this winter so they don’t challenge 1932. Number of Consecutive Days Snowfall < 4 for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. 1 1394 1932-12-16 2 1063 1952-01-27 3 1058 2024-12-22 4 1051 1963-12-22 5 794 1956-03-15

The trough showing up at the end of the runs is the same long range Pacific bias we have seen all winter. Heights over the EPAC and WNA have been verifying lower than forecast beyond 10 days. So this is nothing new since it’s the seasonal pattern so far. The one change we have seen in the models due the Hudson Bay warming event has been more blocking east of Hudson Bay. So at least we will get some blocking help from the Atlantic side in early January. The big question is how long does the early January window last? So far this winter is staring out on the La Niña temperature path of colder December 1 to estimated January 15th. Most of the time in this progression we see a warmer back half of winter on the La Niña progression path. Its also typical for mismatch December La Niñas with a +PNA to become more -PNA over time. My hope is that the Pacific can back off enough with some help from the Atlantic blocking to allow NYC to break the 4” snow losing streak in early to mid-January. I wouldn’t put it past the Pacific to spoil things again so there are no guarantees.

The global average temperatures are based on the older averages. This makes more sense for keeping track of long term trends. 30 year climate normals are great in a stable climate. But they mask the warming when they update every 30 years in such a rapidly warming climate. Now that the climate normals are so much warmer, the bar is lower to get a colder than average winter. So it’s possible we could eventually get a colder than average winter in the 91-20 normals, but it could still have been a warmer winter using 81-10 normals.

I said a while back in one of our great discussions that these next 5 winters would probably determine whether we could at least see one colder winter for a change after the 9 winter warmer streak. You would think after 9 years that even in a warming climate we could at least manage one colder winter every now and then. This winter will be a test case for us since we will carry a small cold departure into the start of January.

First time that Sussex, NJ got down to -4 since 18-19. Time Series Summary for SUSSEX AIRPORT, NJ - Jan through Dec Click column heading to sort ascending, click again to sort descending. 2024 -4 9 2023 -1 6 2022 -3 11 2021 3 0 2020 -2 2 2019 -15 2 2018 -4 2 2017 4 1 2016 -6 9 2015 -16 0 2014 -13 0 2013 0 5 2012 -1 6 2011 -15 10 2010 3 2

So far this winter isn’t as cold or snowy as 2017 was during the first half. So we wouldn’t need that type of warmth for the winter to still finish above average. All we know so far is that we are starting with a typical frontloaded La Niña cold scenario.

All we can say is that the temperature departures are following a frontloaded La Niña seasonal progression with December 1st through January 15th probably averaging colder than normal around NYC.This would be the first time for NYC since the 17-18 La Niña.The big question is if January 16th to February 28th second half will follow the warmer shift we saw in 17-18 which tilted the whole winter warmer than average. But if we can maintain some Nino influences in February such as we saw with the +AAM rise, then we could have our first colder winter since 14-15. We probably won’t know for sure which way it will go until we get further into January.

Coldest December day in 2 years. But not quite as cold as 2022. The timing was really close right before Christmas both years. 12-22-24…21/15….-19.0 12-24-22….15/7…..-25.9

You can see the ripple effect it having on the modeling going forward. The extended EPS runs from a week ago had stronger Pacific blocking and weaker Atlantic blocking. Now the Atlantic blocking is forecast to be stronger January 6th to 13th and the Pacific a little weaker. Notice the narrower ridge over Western North America and stronger and more expansive from Eastern Canada through Iceland. New EPS weekly run for January 6th to 13th Old run

NYC briefly got down to 3° in February 2023 but it was in a sea of warmth. Climatological Data for NY CITY CENTRAL PARK, NY - February 2023 Click column heading to sort ascending, click again to sort descending. Sum 1360 942 - - 665 0 1.28 2.2 - Average 48.6 33.6 41.1 5.2 - - - - 0.1 Normal 42.2 29.5 35.9 - 816 0 3.19 10.1 2023-02-01 38 26 32.0 -1.7 33 0 0.02 0.4 T 2023-02-02 40 29 34.5 0.7 30 0 0.00 0.0 0 2023-02-03 35 11 23.0 -10.9 42 0 0.00 0.0 0 2023-02-04 27 3 15.0 -19.0 50 0 0.00 0.0 0 2023-02-05 49 27 38.0 3.8 27 0 0.00 0.0 0 2023-02-06 52 34 43.0 8.7 22 0 0.00 0.0 0 2023-02-07 43 30 36.5 2.1 28 0 0.02 0.0 0 2023-02-08 53 39 46.0 11.4 19 0 T 0.0 0 2023-02-09 55 42 48.5 13.7 16 0 0.00 0.0 0 2023-02-10 61 45 53.0 18.1 12 0 0.00 0.0 0 2023-02-11 46 36 41.0 5.9 24 0 0.00 0.0 0 2023-02-12 48 38 43.0 7.7 22 0 0.01 0.0 0 2023-02-13 57 41 49.0 13.6 16 0 0.00 0.0 0 2023-02-14 54 40 47.0 11.4 18 0 0.00 0.0 0 2023-02-15 67 47 57.0 21.2 8 0 0.00 0.0 0 2023-02-16 70 56 63.0 27.0 2 0 0.07 0.0 0 2023-02-17 61 32 46.5 10.3 18 0 0.18 T 0 2023-02-18 43 27 35.0 -1.4 30 0 0.00 0.0 0 2023-02-19 50 37 43.5 6.9 21 0 0.00 0.0 0 2023-02-20 61 47 54.0 17.2 11 0 0.00 0.0 0 2023-02-21 50 37 43.5 6.5 21 0 0.27 0.0 0 2023-02-22 44 37 40.5 3.3 24 0 0.14 T 0 2023-02-23 44 38 41.0 3.6 24 0 0.02 0.0 0 2023-02-24 45 25 35.0 -2.6 30 0 0.00 0.0 0 2023-02-25 33 23 28.0 -9.9 37 0 T T 0 2023-02-26 50 30 40.0 1.9 25 0 0.00 0.0 0 2023-02-27 46 33 39.5 1.2 25 0 0.21 0.9 0 2023-02-28 38 32 35.0 -3.5 30 0 0.34 0.9 2

The biggest shift we have seen in recent days modeling is the much stronger 500 mb blocking forecast east of Hudson Bay. This feature wasn’t showing up on the older runs. You have to wonder if the record warmth that Hudson Bay absorbed during the summer leading to the current delayed free up is playing a role. A +500 meter anomaly would be one of the strongest on record for this time of year. Even before the record warmth for next week, the Hudson Bay Area has been much warmer than normal this month. https://nsidc.org/sea-ice-today/analyses/sluggish-freeze-warming-north

Yeah, November 2018 had impressive snow and cold for so early in the season. It was the 5th earliest date that NYC dropped under 20°. While the winter still averaged warmer than normal, NYC almost made it to 0° in late January. Frost/Freeze Summary for NY CITY CENTRAL PARK, NY Each section contains date and year of occurrence, value on that date. Click column heading to sort ascending, click again to sort descending. 1933 03-11 (1933) 16 11-16 (1933) 17 249 1924 02-24 (1924) 14 11-17 (1924) 19 266 1936 03-07 (1936) 17 11-18 (1936) 18 255 1879 03-01 (1879) 18 11-21 (1879) 16 264 1987 03-11 (1987) 16 11-21 (1987) 18 254 1880 03-25 (1880) 14 11-22 (1880) 13 241 2018 02-03 (2018) 16 11-22 (2018) 17 291 1888 03-25 (1888) 16 11-23 (1888) 17 242 1938 03-04 (1938) 9 11-25 (1938) 19 265 1932 03-16 (1932) 19 11-26 (1932) 19 254 1903 02-21 (1903) 19 11-27 (1903) 19 278 1917 02-13 (1917) -0 11-27 (1917) 19 286 1871 02-23 (1871) 15 11-28 (1871) 16 277 1890 03-09 (1890) 18 11-28 (1890) 19 263 1901 03-07 (1901) 16 11-28 (1901) 19 265 1930 03-03 (1930) 18 11-28 (1930) 15 269 1872 03-22 (1872) 17 11-29 (1872) 15 251 1875 03-23 (1875) 13 11-29 (1875) 14 250 1891 03-17 (1891) 19 11-29 (1891) 17 256 1929 03-10 (1929) 12 11-29 (1929) 18 263 1955 03-08 (1955) 19 11-29 (1955) 16 265 1876 03-20 (1876) 15 11-30 (1876) 19 254 1887 03-30 (1887) 16 11-30 (1887) 17 244 1958 02-19 (1958) 12 11-30 (1958) 18 283 1976 03-18 (1976) 19 11-30 (1976) 17 256 NY WEST NYACK 1.3 WSW CoCoRaHS 6.7 NJ MAPLEWOOD TWP 0.9 SE CoCoRaHS 6.5 NJ WESTFIELD 0.6 NE CoCoRaHS 6.5 NJ OAKLAND 0.9 SSE CoCoRaHS 6.5 NJ HAWTHORNE 1.0 SSE CoCoRaHS 6.5 NY PEEKSKILL 0.4 N CoCoRaHS 6.5 CT WESTBROOK CENTER 1.5 NE CoCoRaHS 6.5 CT MADISON CENTER 4.1 N CoCoRaHS 6.5 CT NAUGATUCK 1.7 NNE CoCoRaHS 6.5 NJ NEWARK LIBERTY INTL AP WBAN 6.4 NY NY CITY CENTRAL PARK WBAN 6.4 CT NEW CANAAN 1.9 ENE CoCoRaHS 6.4 CT MADISON CENTER 1.6 W CoCoRaHS 6.4 CT MONROE 0.1 SE CoCoRaHS 6.3 NJ HAWTHORNE 0.4 S CoCoRaHS 6.2 NY ARMONK 0.4 E CoCoRaHS 6.2 NJ TETERBORO AIRPORT WBAN 6.0 NJ NORTH ARLINGTON 0.7 WNW CoCoRaHS 6.0 NJ WAYNE TWP 0.8 SSW CoCoRaHS 6.0 NJ MONTCLAIR 0.7 N CoCoRaHS 6.0 CT NORWALK 2.9 NNW CoCoRaHS 6.0 CT HIGGANUM 0.7 N CoCoRaHS 6.0 CT MYSTIC 0.9 W CoCoRaHS 6.0 CT NORWICH 2.5 NNE CoCoRaHS 6.0 NJ HARRISON COOP 5.8 CT IGOR I SIKORSKY MEMORIAL AIRPORT WBAN 5.8 CT RIDGEFIELD 1.9 SSE CoCoRaHS 5.8 NJ NEW PROVIDENCE 0.8 ESE CoCoRaHS 5.5 NY BRIGHTWATERS 0.7 NNW CoCoRaHS 5.5 CT DARIEN 2.8 NW CoCoRaHS 5.5 CT DURHAM 1.2 W CoCoRaHS 5.5 NY SYOSSET 2.0 SSW CoCoRaHS 5.4 CT PAWCATUCK 1.8 SSE CoCoRaHS 5.2 CT IVORYTON 0.9 WSW CoCoRaHS 5.1 NJ CANOE BROOK COOP 5.0 NJ WANAQUE RAYMOND DAM COOP 5.0 NY WANTAGH 0.3 ESE CoCoRaHS 5.0 CT STAMFORD 5 N COOP 5.0 NY NESCONSET 1.4 SSW CoCoRaHS 5.0 CT MONROE 0.8 W CoCoRaHS 5.0 CT KILLINGWORTH 2.6 ESE CoCoRaHS 5.0 CT WALLINGFORD CENTER 3.3 NNW CoCoRaHS 5.0 CT GROTON COOP 5.0 CT NEW LONDON 1.0 NNW CoCoRaHS 5.0 NY MIDDLE VILLAGE 0.5 SW CoCoRaHS 4.9 NY JFK INTERNATIONAL AIRPORT WBAN 4.8 NY LAGUARDIA AIRPORT WBAN 4.7 NY UPTON COOP - NWSFO NEW YORK COOP 4.6 NY WANTAGH 1.1 NNE CoCoRaHS 4.5 NJ HARRISON COOP 0 NJ CALDWELL ESSEX COUNTY AP WBAN 0 CT STAMFORD 5 N COOP 0 NY WESTCHESTER CO AP WBAN 0 NY SHRUB OAK COOP 0 NY MOUNT SINAI COOP 1 CT GROTON NEW LONDON AP WBAN 1 CT GROTON COOP 1 NJ NEWARK LIBERTY INTL AP WBAN 2 NJ CANOE BROOK COOP 2 NY NY CITY CENTRAL PARK WBAN 2 NJ TETERBORO AIRPORT WBAN 2 NY FARMINGDALE REPUBLIC AP WBAN 2 CT NEW HAVEN TWEED AP WBAN 2 NY WESTHAMPTON GABRESKI AP WBAN 2 CT NORWICH PUBLIC UTILITY PLANT COOP 2 NY LAGUARDIA AIRPORT WBAN 3 NY JFK INTERNATIONAL AIRPORT WBAN 3 CT IGOR I SIKORSKY MEMORIAL AIRPORT WBAN 3 NY CENTERPORT COOP 3 NY ISLIP-LI MACARTHUR AP WBAN 3 NY MATTITUCK COOP 3 NY BAITING HOLLOW COOP 3 NY UPTON COOP - NWSFO NEW YORK COOP 3 NY ORIENT POINT STATE PARK COOP 3

Yeah, I agree. That’s why my posts often take in regional, national, and global influences to add context. Since the local forecasts are heavily influenced by the larger patterns. Never understood why anyone would want to define the geographic range of this forum so narrowly as to ever state that your obs don’t matter. I appreciate what the people in your area of the forum add to the discussion. I like to think that anyone in the OKX, PHI, BGM, ALB, or even the bordering BOX NWS forecast zones should be able to feel at home in the forum and that their posts add value.

The reason I posted the original map last week was to highlight this very point. It’s a very big news story for North America at any time of the year when even a 1 week pattern is this anomalous. At no point did I mention the term torch for our area. Plus I didn’t even use that term to describe a month like December 2015 that went +13.3° or when we hit 80° in February 2018. I tend to stay away from emotionally charged terms even if they are warranted in cases like those months. In our immediate area I can think of several reasons why it’s pertinent to our discussion. Whether we top out in the 40s or 50s close to New Years isn’t really that important in the larger scene of things. But how much of a lingering effect the pattern has going forward could be critical at least last near and just after the New Years. It could have an influence early on for P-Types near the immediate coast. The pattern will not cool down instantly. The other issue that I highlighted yesterday was how much this will influence the blocking Northeast of Hudson Bay. This is a feature which could potentially work to our advantage for storm tracks once colder air makes it back into the pattern. So it could be a potential plus for us. But the Pacific pattern has still been a net minus for our snowfall. Hopefully, we can get some Atlantic side push back to help out some snowfall points on the board in January.