bluewave

The AO has had a much bigger influence this winter than the MJO. We got our biggest snowstorm of the winter in early February when the MJO was in an amplified +2 phase 6. The AO was the more dominant force. Now that we are finally getting a MJO 8, the AO is spiking to +2 or +3 becoming the greater factor next week.

Yeah, the GEFS is coming in even stronger with the AO rise. So it looks like we have a shot at our first 60°+ of the year sometime during the 2nd week of March. The ridiculous AO volatility since the February record rise continues.

This is the summary from NOAA: https://www.ncei.noaa.gov/news/Upcoming-NOAA-2020-Climate- Calculating the New Climate Normals Palecki emphasized that NOAA’s Normals are rather complicated sets of calculations, not just simple averages. These calculations fill in missing data using surrounding weather stations and ensure that daily Normals match monthly Normals. They also remedy discrepancies that might arise when stations change locations. In this next round of Climate Normals, new things will be added—including several small changes to how NCEI calculates them. “Our main methodologies have not changed since the last Normals cycle,” Palecki said. “But minor improvements have been made in how we round numbers, calculate percentiles, count the numbers of days exceeding thresholds, and format output.” todayAlso, for the first time, this updated batch of Normals will include 15-year Normals for those needing a climatology representing a period closer to today. NOAA will also release high spatial resolution monthly Normals data for the conterminous U.S., as well as develop new tools and methods to access the data. These new Normals are a better baseline for today’s climate, helping inform activities in many economic sectors,” Palecki added. “Interestingly, this shift will result in there being fewer ‘above normal’ temperature days in most of the U.S. at the start of this decade compared to recent years that used the previous Normals cycle. Climate will continue to change in the U.S. during this decade, however, so we will need to do this again in 2031.” Once the new NOAA Normals are released in May 2021, they will be available to the public from NCEI.

Based on the raw numbers it’s this last decade. Looks like December will see the greatest temperature rise. But the exact numbers will have to wait until the raw data goes through quality control. https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data Procedures are put in place to deal with missing and suspect data values. In addition, Climate Normals include quantities other than averages such as degree days, probabilities, standard deviations, etc. Climate Normals are a large suite of data products that provide users with many tools to understand typical climate conditions for thousands of locations across the United States.

The new 30 year climate normals are scheduled to come out this spring. It looks like the NYC 1981-2010 DJF average of 35.1° is set to rise closer to 36.0° for 1991-2020. But the NCDC has the final say since they look for any possible errors in the raw data.

It took an AO drop under -5 to get only the 4th colder winter month since December 2015. This was the first 6 winter stretch with an average temperature of 36.0° or warmer. So the warmer than average winter run since 15-16 continues. NYC Dec 15....+13.3 Jan 16....+1.9 Feb 16....+2.4 Dec 16....+0.8 Jan 17....+5.4 Feb 17....+6.3 Dec 17....-2.5 Jan 18.....-0.8 Feb 18....+6.7 Dec 18....+2.6 Jan 19....-0.1 Feb 19....+0.9 Dec 19....+0.8 Jan 20....+6.5 Feb 20....+4.8 Dec 20.....+1.7 Jan 21.....+2.2 Feb 21.....-1.1 Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Season Mean Avg Temperature Departure 2020-2021 36.1 +1.0 2019-2020 39.2 +4.1 2018-2019 36.3 +1.2 2017-2018 36.2 +1.1 2016-2017 39.3 +4.2 2015-2016 41.0 +5.9

We’ll probably see a warm up during the 2nd week of March as there is another big AO rise forecast.

Colder start to March on the 12z EPS.

This is also the first time that Allentown had nearly 25” more than Suffolk since the snowfall increase in 2002-2003. Islip snowfall 2010-2021 and BNL 2003-2009 Time Series Summary for Allentown Area, PA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Ending Date Total Snowfall Oct 1 to Apr 30 ISP/BNL 2021-04-30 58.1 33.5 2020-04-30 5.3 6.8 2019-04-30 32.1 12.8 2018-04-30 49.9 65.9 2017-04-30 28.3 39.3 2016-04-30 36.2 41.4 2015-04-30 50.1 63.7 2014-04-30 68.1 63.7 2013-04-30 21.4 46.9 2012-04-30 12.0 4.7 2011-04-30 38.9 55.3 2010-04-30 59.8 53.8 2009-04-30 24.1 43.0 2008-04-30 21.2 11.5 2007-04-30 23.0 9.5 2006-04-30 32.5 30.5 2005-04-30 42.3 78.5 2004-04-30 39.3 66.2 2003-04-30 54.4 62.1

This was a really unusual winter with the strong blocking displaced so far south. You can see how much warmer the US average temperature was than the 09-10 winter which was the last time we had a -1 or lower AO for all 3 winter months. So that resulted in the more tucked in storm track with the ridging and record warm SSTs east of New England.

Yeah, this is our first snowy winter in a while when the heaviest snowstorms only had 990s mb pressures. Our last snowy winter in 17-18 featured the 950mb benchmark blizzard and other deep lows in March. Even 16-17 which was so warm , had the deeper MLSP blizzards mixed in.

Probably not since the easterly flow was so strong with that event.

Very unusual to get a snowy winter with such a tucked in storm track. This is only the 3rd time since 1996 that EWR had near 10” or more of snow than ISP or BNL. I use BNL before 2010 due to missing ISP snowfall data. This winter featured the record south based blocking and record warm SSTs east of New England. So this allowed the ridge to build east of New England with storm tracks very close to Southern NJ. Most other years we had more of a benchmark storm track further east favoring Suffolk over Newark. Time Series Summary for ISLIP-LI MACARTHUR AP, NY Click column heading to sort ascending, click again to sort descending. Ending Date Islip Snowfall Newark Snowfall 2021-04-30 33.5 45.7 2020-04-30 6.8 6.9 2019-04-30 12.8 22.0 2018-04-30 65.9 39.4 2017-04-30 39.3 30.0 2016-04-30 41.4 32.8 2015-04-30 63.7 46.4 2014-04-30 63.7 61.1 2013-04-30 46.9 29.5 2012-04-30 4.7 8.8 2011-04-30 55.3 68.2 2010-04-30 53.8 47.9 Click column heading to sort ascending, click again to sort descending. Ending Date Newark Snowfall Oct 1 to Apr 30 BNL LI Snowfall 2009-04-30 27.1 43 2008-04-30 14.6 11.5 2007-04-30 16.5 9.5 2006-04-30 37.9 30.5 2005-04-30 43.4 78.5 2004-04-30 47.8 60.2 2003-04-30 53.1 62.1 2002-04-30 3.6 5.5 2001-04-30 39.3 51.2 2000-04-30 18.4 14.0 1999-04-30 12.8 23.0 1998-04-30 6.9 4.5 1997-04-30 16.3 18.0 1996-04-30 78.4 90.7

Yeah, looks like the TPV that gives us the brief Arctic outbreak Monday night into Tuesday acts to suppress the southern stream for a while.

Warmest day of the month so far here on the South Shore at 52° and sunny.

Getting the first sun of the day now here in SW Suffolk as the fog clears out. Late day high temperatures with 51° now in Wantagh.

Newark actually made the top 10 for snowiest DJF. Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Dec through Feb Click column heading to sort ascending, click again to sort descending. Rank Season Total Snowfall Missing Count 1 1960-1961 69.5 0 2 2010-2011 66.0 0 3 1995-1996 62.8 0 4 2013-2014 60.5 0 5 1993-1994 55.8 0 6 1977-1978 52.9 0 7 2009-2010 47.9 0 8 1947-1948 47.0 2 9 2020-2021 45.7 2 10 2002-2003 44.8 0

It took an AO drop under -5 to get only the 4th colder winter month since December 2015. NYC Dec 15....+13.3 Jan 16....+1.9 Feb 16....+2.4 Dec 16....+0.8 Jan 17....+5.4 Feb 17....+6.3 Dec 17....-2.5 Jan 18.....-0.8 Feb 18....+6.7 Dec 18....+2.6 Jan 19....-0.1 Feb 19....+0.9 Dec 19....+0.8 Jan 20....+6.5 Feb 20....+4.8 Dec 20.....+1.7 Jan 21.....+2.2 Feb 21.....-1.6

The cool high temperatures drove the departures this month across the region. So a continuation of the warmer minimums theme. Narrow 54/17 temperature range this month in NYC. POU...max...-4.3....min...+0.9 HPN...max...-3.0....min...+0.9 NYC...max....-3.3....min....-0.3

This month was pretty even around the area. More variance between NYC and other stations in 2014. But 2015 was close among the stations. Not sure why so much NYC the snow cover data is missing between 1996 and 2000 on the XMACIS2 site. Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Month of Feb Click column heading to sort ascending, click again to sort descending. Year Number of Days Snow Depth >= 1 Missing Count 2021 23 3 Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Feb Click column heading to sort ascending, click again to sort descending. Year Number of Days Snow Depth >= 1 Missing Count 2021 24 3 Time Series Summary for LAGUARDIA AIRPORT, NY - Month of Feb Click column heading to sort ascending, click again to sort descending. Year Number of Days Snow Depth >= 1 Missing Count 2021 23 3 Time Series Summary for JFK INTERNATIONAL AIRPORT, NY - Month of Feb Click column heading to sort ascending, click again to sort descending. Year Number of Days Snow Depth >= 1 Missing Count 2021 24 3 Time Series Summary for ISLIP-LI MACARTHUR AP, NY - Month of Feb Click column heading to sort ascending, click again to sort descending. Year Number of Days Snow Depth >= 1 Missing Count 2021 23 3

This matches the theme since the 18-19 winter of an opposite response to the expected ENSO pattern. All the competing influences have made winter forecasts extremely challenging last three years. So it’s not easy doing extended winter forecasts in a changing climate. https://www.climate.gov/news-features/blogs/enso/did-northern-hemisphere-get-memo-years-la-niña Did the Northern Hemisphere get the memo on this year's La Niña? Author: Nat Johnson February 25, 2021 We are rapidly approaching the end of the meteorological winter, and it has been quite a finish for much of the United States, especially for those who have suffered the devastating effects of recent extreme cold. As discussed on this blog, we have been in the grips of a healthy La Niña, but the weather outside of the tropics often hasn’t behaved as we would expect for La Niña, even before this period of extreme cold and winter storms. In this post, we’ll investigate what was going on for the first two-thirds of this winter. Feeling the pressure As Emily mentioned back in January, the early winter temperature pattern over North America looked more like a typical El Niño than what we would expect from a moderate-to-strong La Niña. This unexpected temperature pattern resulted from shifts in the jet stream that we usually don’t see during La Niña. Forecasters and scientists often evaluate the large-scale atmospheric circulation using pressure about three miles above the earth’s surface, the so-called 500 hectopascal (hPa) or, equivalently, the 500 millibar (mb) level (1). When we view the average pattern that occurred across the Northern hemisphere in December – January, we see a broad area of lower pressure extending from northeast Asia across the North Pacific into southwest Alaska as well as a strong area of higher pressure over northeast Canada and Greenland. (Top) Geopotential height anomalies (m) at the 500 hectopascal (hPa) pressure level during December 2020 through January 2021. Cold colors indicate below-average atmospheric pressure and warm colors indicate above-average atmospheric pressure at a level about three miles above the Earth’s surface. (Bottom) The average 500 hPa geopotential height anomalies from December – January for the 13 strongest La Niña episodes since 1950, including December 2020 through January 2021. Note the different scaling between the top and bottom figures. The top figure has a wider range of values because the top figure includes contributions from both predictable signals, like La Niña, and random weather variability, whereas the bottom figure has filtered out most of the random weather variability. Anomalies are calculated with respect to the 1991-2020 base period for the top figure and with 30-year base periods updated every 5 years (see here for a description). NOAA Climate.gov figure with NCEP/NCAR Reanalysis data obtained from the NOAA Physical Sciences Laboratory. The map in the bottom panel shows the average December – January pressure pattern for the 13 strongest La Niña episodes since 1950 (2), including the current episode. Typically, La Niña brings anomalous high pressure over the North Pacific, low pressure over northwestern North America, and high pressure to the southeast U.S., a pattern referred to as the negative phase of the Pacific-North American (PNA) pattern. This pattern generally brings cooler-than-average conditions over much of Canada and the northern US and warmer-than-average conditions across much of the southern U.S., but clearly the atmosphere had different ideas this past December and January. Par for the course? Was the mismatch that we saw in December-January really that unusual? We know from previous blog posts (like this one) that the atmosphere varies quite a bit from one La Niña to the next, and the atmosphere never fully resembles the average of all events. To address this question, I evaluated the similarity between the individual December-January 500 hPa maps and the average La Niña pattern (for the 13 moderate-to-strong La Niña episodes). For this calculation, I use the pattern correlation, a metric that summarizes the similarity in a single number: a value of 1 means perfect match, 0 means complete mismatch, and -1 means mirror opposites (3). Pattern correlations between the individual La Niña and average La Niña December – January 500 hPa geopotential height anomalies north of 15°N for the 13 strongest La Niña episodes since 1950. Positive values indicate at least some degree of pattern matching, with 1 indicating a perfect match, and negative values indicate a mismatch between the two patterns. NOAA Climate.gov figure with NCEP/NCAR Reanalysis dataobtained from the NOAA Physical Sciences Laboratory. The pattern correlations are usually substantially positive for moderate-to-strong La Niñas, which indicates that most events share some basic similarity with the average La Niña pattern. This confirms that La Niña is a reliable source of predictability outside of the tropics (and a big reason that we have an ENSO Blog!). However, the pattern correlation for the December 2020 – January of 2021 is the lowest of the 13 events and is actually slightly negative. That means you can argue that the Northern Hemisphere atmosphere looked a little more like El Niño than La Niña! Early clues or whimsical butterflies? So far, our calculations confirm that there was an unusual mismatch between the actual and typical La Niña atmospheric circulation pattern. Was this mismatch due to some competing influence that we should have been able to anticipate? Did the forecasters miss something? Or was the mismatch due to chaotic weather variability that we cannot predict well in advance? This is the question that forecasters and research scientists grapple with and often agonize over time and time again. Our dynamical prediction models might provide some clues to address whether there may have been a competing influence (4). These models provide seasonal forecasts that, in principle, incorporate all sources of predictability, not just ENSO (but all models have errors!). For this analysis, I use a new prediction model from the NOAA lab in which I work, the Geophysical Fluid Dynamics Laboratory (GFDL), called SPEAR (5). SPEAR is the newest member of the North American Multi-Model Ensemble (NMME), making its real-time debut in early February. Here, I analyze one of the SPEAR test predictions from early November of 2020 (6). The predicted 500 hPa geopotential height anomalies (m) for December 2020 through January 2021 from the ensemble average of 30 SPEAR dynamical model forecasts issued in early November of 2020. NOAA Climate.gov figure with SPEAR data obtained from the NOAA Geophysical Fluid Dynamics Laboratory. As is always the case for seasonal predictions, and as Emily eloquently described in this post, SPEAR is run many times (30 to be exact) with slightly different initial conditions (think different flaps of a butterfly’s wings). Individual forecasts (ensemble members) diverge rapidly due to the inherently chaotic nature of the climate system, but the average of those 30 ensemble members filters out that chaotic variability and provides an estimate of the predictable signal. The ensemble average December – January pressure pattern predicted by SPEAR in early November looks a lot like the average La Niña pattern. This indicates that according to SPEAR, the typical Northern Hemisphere response to La Niña was the best prediction forecasters could have made at least a month in advance, even though it did not occur. So, then what about the role of chaotic weather variability? This would include influences of phenomena like the Madden-Julian Oscillation and sudden stratospheric warmings that clearly influence our weather but that are difficult or impossible to predict more than a few weeks in advance. It’s very difficult to come up with a definitive answer, but we can get more clues from the diversity within the 30 SPEAR ensemble members. Remember, all 30 members are run under nearly identical conditions except for tiny perturbations in the initial conditions that reflect our imperfect knowledge of the climate state. We can examine the distribution of pattern correlations between the actual and individual forecast December – January 500 hPa maps. Pattern correlations between the individual SPEAR ensemble member forecasts and the observed December 2020 – January 2021 500 hPa geopotential height anomalies north of 15°N for SPEAR forecasts issued in early November 2020. Higher pattern correlations indicate better forecast performance. The dashed red line indicates the pattern correlation between the ensemble average and the observed geopotential height field. NOAA Climate.gov figure. We see quite a wide range of pattern correlations, both negative and positive, indicating that some ensemble members do a very poor job and others do reasonably well. If we look at the ensemble member with the highest pattern correlation, we see a lot of similar features to what actually occurred, including a broad area of low pressure in the North Pacific that is opposite to what we expect during La Niña. Remember, this reasonably accurate ensemble member outlier comes from the exact same model that said the best bet was for a typical La Niña pattern! Again, the only things that distinguish this high-performing ensemble member from the low-performing ensemble members are tiny perturbations in the initial conditions roughly equivalent to flaps of butterfly wings. Did I mention that seasonal prediction is tough? The predicted December 2020 through January 2021 500 hPa geopotential height anomalies (m) for the SPEAR ensemble member with the highest pattern correlation with the observed pattern. NOAA Climate.gov figure with SPEAR data obtained from the NOAA Geophysical Fluid Dynamics Laboratory. Please note that this does not prove that chaotic weather variability is a primary culprit for the mismatch. It’s certainly possible that other factors were at play, and our forecast models may not be capturing all important sources of seasonal predictability, such as stratospheric-tropospheric interactions (7). The main point of this analysis is that it’s very challenging to rule out the influence of chaotic weather variability, and underscores why our seasonal forecasts are always issued in terms of probabilities. So, you may be wondering what this means for NOAA’s Winter Outlook that was first issued last October. Keep in mind that this outlook covers the full three months of meteorological winter, and I don’t have to tell our U.S. readers that February brought some big weather changes that I haven’t covered here. Stay tuned for next month’s post when Tom returns to give us a complete breakdown of NOAA’s 2020-2021 Winter Outlook!

Yeah, new all-time winter high temperatures and temperature swings. https://earther.gizmodo.com/unseasonable-european-warmth-smashes-all-time-february-1846357348 Germany has seen its its biggest temperature swing since records began - with an increase of 41.9 degrees in one week. Climate researchers at the German Weather Service (DWD) on Tuesday said the country had never before experienced a swing like the one that occurred at the weather station in the central German city of Goettingen. A low of minus 23.8 degrees Celsius was recorded there on February 14. Seven days later, on February 21, the high was 18.1 degrees Celsius, The previous record had been set in May 1880, in the early days of weather record-keeping. At that time, a temperature rise of 41 degrees had been measured within seven days, said a DWD spokesperson. In northern Germany, two regional winter heat records had also been broken on Monday. In the town of Quickborn, the high was 18.9 degrees Celsius, passing the record of 17.8 degrees measured two years earlier. In the Hamburg area, the Neuwiedenthal weather station hit 21.1 degrees on Monday. The previous record of 18.1 degrees at the same station just more than a year earlier was thus "pulverized," a DWD spokesperson said. "For the first time since temperature records began, the temperature in Hamburg has thus risen above 20 degrees in winter," he said.

The record AO rise makes more headlines.

Not bad for an average temperature above freezing. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Feb Click column heading to sort ascending, click again to sort descending. Year Number of Days Snow Depth >= 1 AVG Temperature 2021 24 33.2 2020 0 40.2 2019 2 36.2 2018 1 42.0 2017 6 41.6 2016 2 37.7 2015 28 23.9 2014 28 31.6

Looks like we have a chance for the 5th year since 2014 that NYC drops below 20° during the first week of March. The real feel may be closer to 0° early Tuesday. Winds are forecast to gust in the 40-50 mph range with temperatures dropping under 20°. So it may feel colder than many days this winter. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Lowest Min Temperature Mar 1 to Mar 7 Missing Count 2020-03-07 25 0 2019-03-07 18 0 2018-03-07 32 0 2017-03-07 14 0 2016-03-07 26 0 2015-03-07 12 0 2014-03-07 13 0 2013-03-07 27 0 2012-03-07 25 0 2011-03-07 20 0 2010-03-07 32 0