bluewave

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

A study out today expands on the rapid SST warming off the Northeast Coast that has been a big player for us. https://www.washingtonpost.com/climate-environment/2021/02/25/atlantic-ocean-currents-weakening-amoc-gulf-stream/

Looks like the EPS begins the first week of March with an omega and east based blocking pattern. Has near to below average temperatures in the Northeast. Sometimes these shorter wavelengths in early March can surprise. So it may take the models time to work out the storm details. March 1-8

Yeah, the strong blocking pattern this winter was the dominant factor for us. But you can see how the unfavorable MJO phases pretty much ran the table during the 18-19 and 19-20 winters.The pattern was more split between the unfavorable MJO and blocking during 15-16, 16-17, and 17-18 winters.

That’s a good question. The MJO data goes back to the 1970s. February 2010 had the MJO 7 going more quickly into phase 8. The MJO also went fairly quickly into a phase 8 in 1978. This year the MJO has been stuck in 6-7 for more than a month. But we have seen bigger AO swings in recent years. We also have the warmer WAPAC SSTs favoring longer and more amplified phases 4-7.

One of the more unusual weather records this month was how rapidly the AO rose from below -5 to over +2 today. I think this is why the models backed off their snowier forecasts that they had for mid to late February. The last 3 Februaries that went below -5 were 2010, 1978, and 1969. The AO didn’t reach +2 during 2010 until November. The AO made it to +2 in mid-March 1978. It also took longer in 1969 to get back to plus +2 in late October. https://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii

Yeah, temperatures look to drop back into the 30s this evening.

JFK is at 62 days so far. The record is 113 days with a low under 40 set during 00-01.

JFK snuck in a 53° back on January 2nd. So that is still the high for January and February. This is the first 60+ day streak with a low under 40 since the last one ended in March 2019.

Looks like we have a chance at our first January and February that could stay below 55° since 2003. Models have highs in the low 50s on Saturday. So warm ups remain tame by recent standards. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Jan 1 to Feb 28 Missing Count 2021-02-28 54 4 2020-02-29 69 0 2019-02-28 65 0 2018-02-28 78 0 2017-02-28 70 0 2016-02-29 61 0 2015-02-28 56 0 2014-02-28 58 0 2013-02-28 61 0 2012-02-29 62 0 2011-02-28 67 0 2010-02-28 57 0 2009-02-28 65 0 2008-02-29 68 0 2007-02-28 72 0 2006-02-28 64 0 2005-02-28 66 0 2004-02-29 59 0 2003-02-28 50 0 Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Ending Date Highest Max Temperature Jan 1 to Feb 28 Missing Count 2021-02-28 54 4 2020-02-29 70 0 2019-02-28 68 0 2018-02-28 80 0 2017-02-28 74 0 2016-02-29 65 0 2015-02-28 56 0 2014-02-28 61 0 2013-02-28 66 0 2012-02-29 64 0 2011-02-28 71 0 2010-02-28 59 0 2009-02-28 66 0 2008-02-29 69 0 2007-02-28 72 0 2006-02-28 63 0 2005-02-28 67 0 2004-02-29 62 0 2003-02-28 52 0

Impressive thaw pattern across the US.

It looks like NYC finally had a 40° low temperature today. This was the first time since December 24th. It’s also the first time going over 60 days since 2015. https://www.wrh.noaa.gov/mesowest/getobext.php?sid=KNYC&table=1&num=168&banner=off Number of Consecutive Days Min Temperature < 40 for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Run Length Ending Date Period of record: 2010-01-01 to 2021-02-23 1 63 2015-03-08 2 61 2021-02-23 3 56 2013-03-10 4 46 2011-02-16 5 41 2010-03-07 6 38 2014-02-21 7 29 2019-02-03 8 27 2018-03-28 9 26 2019-03-13 10 23 2017-02-18

Updated for February 2021.

Fairly tame warm up by recent late winter standards. Temperatures should rise to around 50° Wednesday. Maybe a few degrees warmer Saturday. So we are on track for our first January and February without any 60 degree days since 2014 and 2015. If both Newark and NYC remain below 55°, then it would be the first time since 2003. Newark may try to reach the top 10 for longest streak under 55° days. Newark is currently at 12th longest with 60 days. Number of Consecutive Days Max Temperature < 55 for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Rank Run Length Ending Date 1 111 1963-03-23 2 87 1941-03-22 3 84 2003-03-14 4 83 1956-02-24 5 78 1969-03-16 6 77 1977-02-22 7 76 1968-03-07 - 76 1948-02-17 8 69 1971-02-11 9 65 2015-03-10 10 63 2011-02-13 - 63 1940-02-11 11 60 2004-02-27 - 60 2021-02-23