donsutherland1

Record high temperatures were recorded in parts of the Great Lakes region today. Record highs included: Chicago: 61° (old record: 55°, 1971); Detroit: 58° (old record: 57°, 2016); Milwaukee: 58° (old record: 51°, 1936 and 2018); and, Toledo: 63° (old record: 62°, 1888). The closing days of December will generally be warmer to occasionally much warmer than normal. Based on the latest guidance, the warmth will likely be sufficient to ensure that much of the Middle Atlantic region will wind up somewhat warmer to warmer than normal for December. Through today, New York City's highest temperature this December is 58°, which occurred on December 10. The last December to have a monthly maximum temperature below 60° was December 2005 when the temperature peaked at 55° on December 24. However, the potential exists for the temperature to approach or reach 60° in New York City during the December 29-30 period. Through December 25, monthly anomalies for select cities were: Baltimore: +0.8°, Boston: +0.5°, Islip: -0.5°, New York City: -1.2°, Newark: -1.0°, Philadelphia: -0.5°, and Washington, DC: +0.1°. Colder air could return during the first week of January. The progression of the MJO in concert with the teleconnections could be crucial in determining whether most of North America's cold air stays bottled up north of the Canada-U.S. border beyond the first week of January or it comes southward into the region shortly after the start of 2020. Transient shots of cold would be possible under the former scenario, which currently appears to be somewhat more likely than not through the first week of January. Afterward, the predominant state of the EPO will likely be crucial to the persistence of the cold. Based on the forecast strongly positive AO to start January, the probability of a significant (6" or greater snowstorm) for the major cities of the Middle Atlantic region during the first week of January is low. Since 1950, the biggest snowfall for that region when the AO was +2.000 or above during the January 1-15 period occurred during January 14-15, 1954 when Philadephia received 3.0" snow and New York City picked up 2.0". Boston has had numerous 6" or greater snowstorms during such cases, including one 10" or greater snowstorm. Therefore, the risk of significant snow would likely be greatest over New England assuming this relationship holds (no significant offsetting variables). Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.8°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year. The ENSO Region 1+2 anomaly was +0.4°C and the Region 3.4 anomaly was +0.6°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged +0.56°C. The remainder of winter 2019-2020 will likely feature neutral-warm to weak El Niño conditions. The SOI was -28.39 today. That is the lowest SOI value since November 5 when the SOI was -34.49. Today, the preliminary Arctic Oscillation (AO) figure was -2.748. No significant stratospheric warming event appears likely through January 4, but some warming above 3 mb will likely commence in coming days. Wave 2 activity will remain relatively muted into the first week of January. Overall, most of the stratosphere is forecast to remain cold into the start of January on the EPS. On December 25, the MJO was in Phase 6 at an amplitude of 1.528 (RMM). The December 24-adjusted amplitude was 1.121. Based on sensitivity analysis applied to the latest guidance, there is an implied 87% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.5°.

We agree about the possible day 9-13 cold shot. I believe the modeled idea is legitimate. I am concerned how things might evolve should Atlantic and Pacific blocking fail to develop: namely the risk of a multi-week warm regime. I think we'll get some opportunities for snowfall, but am less certain about the monthly anomaly. I'm looking at a lot of data, but the forecast teleconnections argue that a mild January is not implausible.

Just before sunrise today:

Yes. That's the guidance right now. But it is somewhat disconnected with the forecast teleconnections. The MJO will certainly need to be watched closely. Hopefully, it will get into Phase 8 and stay there for some time, but a lot can change between now and 15 days. Overall, strong AO+/EPO+ patterns are warmer ones (not necessarily wall-to-wall warmth and not necessarily snowless). If the forecast teleconnections play out, one might begin to see more ridging in the Southeast, much as happened recently vs. ensemble forecasts from two weeks ago (a point Bluewave highlighted above). January 2000 was an exception to the rule concerning AO+/EPO+ January cases. The picture should become clearer in about a week or so. But right now there is consensus on the GEFS and EPS concerning the state of the EPO and AO, though not on the 500 mb pattern or 2m temperature anomalies.

Through at least January 10, a strong AO+/EPO+ pattern possibly coupled with a generally negative SOI for some of the period appears likely. Below is the latest GEFS 500 mb height anomalies at 360 hours: The answer to the question for the circled area depends on whether the AO+/EPO+ pattern persists. Here are the composite 500 mb height anomalies for January cases when the AO averaged +1.000 or above, the EPO was positive, and the SOI averaged < 0: Those are composite monthly figures. They do not preclude a pattern change to colder. Indeed, one such case (2006-07) saw a dramatic change to colder weather. Much of the eastern half of the CONUS was colder than normal during the closing 10 days of January. The January 22-31, 2007 average 500 mb height anomalies are below: In sum: - A persistent AO+/EPO+ (especially with an SOI-) pattern would favor a warm January overall in much or all of the East - Such a pattern would not preclude a dramatic pattern change later in the month

If the forecast teleconnections, especially the EPO and AO, on the 0z EPS and GEFS are reasonably in line with what will occur, a warmer than normal January would be favored in much or all of the East.

One shouldn't be surprised that Heller, who has no scientific background, would imply that the winter freeze suggests a healthy Arctic sea ice situation. The difference between the 12/23 extent and minimum extent is largely the result of a very low minimum figure. According to Heller's logic, 2012 would have been seen as a fantastic year, as sea ice extent increased by nearly 8.7 million square kilometers by December 23. Of course, 2012 saw a record low minimum extent figure of just under 3.2 million square kilometers. In fact, the 12/1-23 average of 11.144 million square kilometers is the 3rd lowest on record and is nearly 3% below the 2000-19 average. This is not a healthy Arctic sea ice situation. If multi-year "old" ice were increasing, that would be newsworthy. The annual refreeze in 2019 is not.

Thanks for the kind words and Holiday wishes. I hope your family and you have a great Holiday season.

After a frosty start, much of the region saw temperatures recover to the 40s. The closing days of December will generally be warmer to occasionally much warmer than normal. Based on the latest guidance, the warmth will likely be sufficient to ensure that much of the Middle Atlantic region will wind up somewhat warmer to warmer than normal for December. Through today, New York City's highest temperature this December is 58°, which occurred on December 10. The last December to have a monthly maximum temperature below 60° was December 2005 when the temperature peaked at 55° on December 24. However, the potential exists for the temperature to approach or reach 60° in New York City during the December 28-29 period. Through December 24, monthly anomalies for select cities were: Baltimore: +0.7°, Boston: +0.2°, Islip: -0.6°, New York City: -1.5°, Newark: -1.2°, Philadelphia: -0.6°, and Washington, DC: 0.0°. Colder air could return during the first week of January. The progression of the MJO in concert with the teleconnections could be crucial in determining whether most of North America's cold air stays bottled up north of the Canada-U.S. border beyond the first week of January or it comes southward into the region shortly after the start of 2020. Transient shots of cold would be possible under the former scenario, which currently appears to be somewhat more likely than not through the first week of January. Afterward, the predominant state of the EPO will likely be crucial to the persistence of the cold. Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.8°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year. The ENSO Region 1+2 anomaly was +0.4°C and the Region 3.4 anomaly was +0.6°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged +0.56°C. The remainder of winter 2019-2020 will likely feature neutral-warm to weak El Niño conditions. The SOI was -27.97 today. That is the lowest SOI value since November 5 when the SOI was -34.49. Today, the preliminary Arctic Oscillation (AO) figure was -2.097. No significant stratospheric warming event appears likely through January 3, but some warming above 3 mb is possible near the end of December. Wave 2 activity will be muted as December concludes and January begins. Overall, most of the stratosphere is forecast to remain cold into the start of January on the EPS. On December 24, the MJO was in Phase 6 at an amplitude of 1.124 (RMM). The December 23-adjusted amplitude was 0.923. Based on sensitivity analysis applied to the latest guidance, there is an implied 80% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.5°.

There's a fallacy that complexity of making weather forecasts at extended ranges means that climate forecasts years out are essentially not possible to make. A closer look is in order for purposes of a quick sketch. Take for example, New York City (Central Park). Let's say one is seeking to forecast the high temperature on January 1, 2020. The highest maximum temperature on record is 62°, which occurred in 1966. The lowest maximum temperature on record is 10° from 1918. The 0z GFS forecast a high of 36°. The historic range is 1.4 times the forecast high. Finally, let's say one is seeking to forecast the 2020 annual mean temperature. The warmest such reading was 57.4° in 2012. The coldest such reading was 49.5° in 1875 and 1888. Since 2000, the mean has averaged 55.7°. If one uses that estimate, the range of error is just under 0.15 times the estimate. That latter situation is the type of situation one is dealing with when it comes to making climate projections. Thus, the fallacy of synoptic complexity's precluding climate forecasts does not apply. When it comes to climate (and climate change) there are widely-established drivers of climate: solar and greenhouse gases are among the most important. Therefore, if one gets the forcings right, one should get a reasonable projection of the climate. Well, that's exactly what the research shows. Climate models have proved skillful. Retrospectively comparing future model projections to observations provides a robust and independent test of model skill. Here we analyse the performance of climate models published between 1970 and 2007 in projecting future global mean surface temperature (GMST) changes. Models are compared to observations based on both the change in GMST over time and the change in GMST over the change in external forcing. The latter approach accounts for mismatches in model forcings, a potential source of error in model projections independent of the accuracy of model physics. We find that climate models published over the past five decades were skillful in predicting subsequent GMST changes, with most models examined showing warming consistent with observations, particularly when mismatches between model-projected and observationally-estimated forcings were taken into account. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085378 Key takeaway: Climate should not be viewed through a synoptic lens. Finally, the physical properties of carbon dioxide are well-established. There's no serious scientific debate on that matter. Therefore, it should make little difference whether carbon dioxide is released through natural mechanisms or if human activities release carbon dioxide. The molecules should behave in the same fashion, not follow different rules depending on whether they were emitted into the atmosphere via volcanic eruptions or the burning of fossil fuels.

The rate of seasonal cooling from the third to the fourth week of December has slowed dramatically after 1990. This development is region-wide. In fact, the fourth week of December is only slightly cooler than the third week of December now. Mean Temperatures: December 15-21 vs. December 22-28, 1991-2018: Boston: 12/15-21: 35.1°; 12/22-28: 34.9° New York City: 12/15-21: 38.2°; 12/22-28: 37.9° Philadelphia: 12/15-21: 38.2°; 12/22-28: 37.7° At present, the fourth week of December is now warmer than the third week of December was during the 1961-1990 base period (prior to the period being measured above): Boston: 12/15-21/1961-1990: 31.1°; 12/22-28/1991-2018: 34.9° New York City: 12/15-21/1961-1990: 34.6°; 12/22-28/1991-2018: 37.9° Philadelphia: 12/15-21/1961-1990: 34.1°; 12/22-28/1991-2018: 37.7°

Some global climate data (though this really should be in the climate change forum): 10 Warmest Years (1880-Present) on GISS (ranked): 1. 2016 2. 2019 (all but certain) 3. 2017 4. 2015 5. 2018 6. 2014 7. 2010 8. 2013 9. 2005 10. 2007 5 Warmest Decades on GISS (ranked): 1. 2010-19 +0.8°C anomaly (December 2019 data is not yet in) 2. 2000-09 +0.6°C anomaly 3. 1990-99 4. 1980-89 5. 1940-49 This data clearly bears the marks of a warming climate. Absent warming, such outcomes would be all but improbable. Yet, natural forcings have not changed sufficiently to explain such warming. Total Solar Irradiance: https://www.ncdc.noaa.gov/cdr/atmospheric/total-solar-irradiance Global Temperature Trend (when solar, ENSO, and volcanic influence have been removed): Paper: https://iopscience.iop.org/article/10.1088/1748-9326/6/4/044022 Additional information from NASA: https://climate.nasa.gov/evidence/

Another day of abundant sunshine saw temperatures reach the upper 40s and even lower 50s across the region. Tomorrow will likely be a little cooler, but readings should still be above seasonal norms. The closing days of December will generally be warmer to occasionally much warmer than normal. Based on the latest guidance, the warmth will likely be sufficient to ensure that much of the Middle Atlantic region will wind up somewhat warmer to warmer than normal for December. Through today, New York City's highest temperature this December is 58°, which occurred on December 10. The last December to have a monthly maximum temperature below 60° was December 2005 when the temperature peaked at 55° on December 24. However, the potential exists for the temperature to approach or reach 60° in New York City during the December 28-29 period. Through December 23, monthly anomalies for select cities were: Baltimore: +0.5°, Boston: +0.1°, Islip: -0.8°, New York City: -1.8°, Newark: -1.5°, Philadelphia: -1.0°, and Washington, DC: -0.2°. Colder air could return during the first week of January. The progression of the MJO in concert with the teleconnections could be crucial in determining whether most of North America's cold air stays bottled up north of the Canada-U.S. border beyond the first week of January or it comes southward into the region shortly after the start of 2020. Transient shots of cold would be possible under the former scenario, which currently appears to be somewhat more likely than not through the first week of January. Afterward, the predominant state of the EPO will likely be crucial to the persistence of the cold. Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.8°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year. The ENSO Region 1+2 anomaly was +0.4°C and the Region 3.4 anomaly was +0.6°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged +0.56°C. The remainder of winter 2019-2020 will likely feature neutral-warm to weak El Niño conditions. The SOI was -21.64 today. That was the lowest figure since November 19 when the SOI was -27.36. Today, the preliminary Arctic Oscillation (AO) figure was -0.799. No significant stratospheric warming event appears likely through January 1, but some warming above 3 mb is possible near the end of December. Wave 2 activity will be muted as December nears an end. Overall, most of the stratosphere is forecast to remain cold into the start of January on the EPS. On December 23, the MJO was in Phase 6 at an amplitude of 0.928 (RMM). The December 22-adjusted amplitude was 0.568. Based on sensitivity analysis applied to the latest guidance, there is an implied 72% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.3°.

Under mainly sunny skies, temperatures across the region have reached the upper 40s and even lower 50s as of 1 pm. High temperatures through 1 pm include: Bridgeport: 50° Islip: 47° New York City: 47° Newark: 49° Philadelphia: 51°

At 8 am, it was 42° in New York City and 38° in Newark. Today will be another warmer than normal day, though not quite as warm as yesterday. High temperatures in both cities will likely top out in the upper 40s to around 50°. These readings will further reduce the now shrinking cold anomalies that had been accumulated during much of December. On December 21, New York City and Newark had monthly temperature anomalies of 2.7° below normal and 2.1° below normal respectively. After yesterday's warmth, those cold anomalies have been slashed to 1.8° and 1.5° below normal respectively.

Today, temperatures rose into the 50s in the Middle Atlantic and southern New England regions. High temperatures included: Atlantic City: 56°; Baltimore: 55°; Boston: 57°; Bridgeport: 50°; Islip: 55°; New York City: 57°; Newark: 57°; Philadelphia: 52°; and, Washington, DC: 53°. New York City's high temperature was the warmest reading since December 10 when the mercury topped out at 58°. On average, the final days of December will likely be warmer to occasionally much warmer than normal. Based on the latest guidance, the warmth could be sufficient to ensure that at least parts of the Middle Atlantic region could finish with at least a somewhat warmer than normal December. A scenario where much of the region winds up somewhat warmer than normal is not out of the question. The probability of more widespread warm anomalies has increased in recent days. Through December 22, monthly anomalies for select cities were: Baltimore: +0.3°, Boston: -0.8°, Islip: -1.3°, New York City: -2.5°, Newark: -2.0°, Philadelphia: -1.2°, and Washington, DC: -0.4°. Colder air could return during the first week of January. The progression of the MJO in concert with the teleconnections could be crucial in determining whether most of North America's cold air stays bottled up north of the Canada-U.S. border beyond the first week of January or it comes southward into the region shortly after the start of 2020. Transient shots of cold would be possible under the former scenario. Afterward, the predominant state of the EPO will likely be crucial to the persistence of the cold. Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.8°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year. The ENSO Region 1+2 anomaly was +0.4°C and the Region 3.4 anomaly was +0.6°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged +0.56°C. The remainder of winter 2019-2020 will likely feature neutral-warm to weak El Niño conditions. The SOI was -9.97 today. Today, the preliminary Arctic Oscillation (AO) figure was -0.212. No significant stratospheric warming event appears likely through January 1, but some warming above 2 mb is possible near the end of December. Wave 2 activity will be muted as December nears an end. Overall, most of the stratosphere is forecast to remain cold through the remainder of December on the EPS. On December 22, the MJO was in Phase 5 at an amplitude of 0.566 (RMM). The December 21-adjusted amplitude was 0.536. Through December 20, the AO had averaged +0.878 in December. Since 1950, there were 12 cases where the AO averaged +0.500 to +1.250. The January mean temperature for New York City was 33.0°. However, six cases (50%) had temperatures 1.5° or more above that average, while five cases (42%) had temperatures 1.5° or more below that average. Put another way, this data suggests that January has the potential to either be warmer/much warmer than normal or colder/much colder than normal rather than near normal. When the January EPO had a positive average 6/8 (75%) of those cases were warmer to much warmer than normal. When the January EPO had a negative EPO average, 3/4 (75%) of those cases were colder to much colder than normal. In sum, the predominant state of the January EPO will very likely determine the January temperature outcome. Based on sensitivity analysis applied to the latest guidance, there is an implied 65% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.0°.

Outside New York City, temperatures had fallen into the 30s with a number of locations reporting temperatures at or below freezing including Danbury (24°), Poughkeepsie (26°), and White Plains (32°). In Central Park, today was poised to be the first day with a low temperature at or above 40° since December 14 when the temperature bottomed out at 45°. Today will very likely see the first 50° or above reading since December 14 in New York City when the temperature hit 56°. The latest MOS guidance shows a high temperature of 52°. Further, since 1981, 92% of cases that saw Chicago record a high temperature of 52° or above (52° yesterday) saw the temperature reach or exceed 50° in New York City a day later in the December 20-30 timeframe.

Today, temperatures rose well into the 40s in the Middle Atlantic and southern New England regions. High temperatures included: Atlantic City: 51°; Baltimore: 52°; Boston: 45°; Bridgeport: 47°; Harrisburg: 46°; Islip: 47°; New York City: 46°; Newark: 48°; Philadelphia: 48°; and, Washington, DC: 47°. The first night of Hanukkah will feature above normal temperatures. Tomorrow, readings will likely surge into the lower and even middle 50s across the northern Mid-Atlantic and southern New England areas. Earlier today, Chicago had a high temperature of 52°. Following such a maximum temperature during the December 20-30, 1981-2018 period, the high temperature the following day in New York City reached 50° or above 91% of the time and 55° or above 70% of the time. The coldest maximum temperature in New York City the following day was 48°. On average, the final days of December will likely be warmer to occasionally much warmer than normal. Based on the latest guidance, the warmth could be sufficient to ensure that at least parts of the Middle Atlantic region could finish with at least a somewhat warmer than normal December. A scenario where much of the region winds up somewhat warmer than normal is not out of the question. The probability of more widespread warm anomalies has increased in recent days. Through December 21, monthly anomalies for select cities were: Baltimore: +0.3°, Boston: -0.8°, Islip: -1.4°, New York City: -2.7°, Newark: -2.1°, Philadelphia: -1.3°, and Washington, DC: -0.4°. Colder air could return during the first week of January. The progression of the MJO in concert with the teleconnections could be crucial in determining whether most North America's cold air stays bottled up north of the Canada-U.S. border beyond the first week of January or it comes southward into the region shortly after the start of 2020. Transient shots of cold would be possible under the former scenario. Afterward, the predominant state of the EPO will likely be crucial to the persistence of the cold. Record warmth covered parts of central and eastern Europe today. Records included: Bucharest-Imh, Romania: 63°; Bucharest-Otopeni, Romania: 63° (tied monthly record); Burgas, Bulgaria: 68°; Tirgu Mures, Romania: 59°; and, Tulcea, Romania: 66°. Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.8°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year. The ENSO Region 1+2 anomaly was +0.5°C and the Region 3.4 anomaly was +0.5°C for the week centered around December 4. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.05°C and the ENSO Region 3.4 anomaly has averaged +0.53°C. These recent conditions are consistent with a weak El Niño. Nevertheless, a neutral ENSO remains the base case for Winter 2019-20. The SOI was -11.57 today. Today, the preliminary Arctic Oscillation (AO) figure was +0.157. No significant stratospheric warming event appears likely through December 31, but some warming above 2 mb is possible late in the period. Wave 2 activity will be muted as December nears an end. Overall, most of the stratosphere is forecast to remain cold through the remainder of December on the EPS. On December 21, the MJO was in Phase 5 at an amplitude of 0.538 (RMM). The December 20-adjusted amplitude was 0.461. Through December 20, the AO had averaged +0.878 in December. Since 1950, there were 12 cases where the AO averaged +0.500 to +1.250. The January mean temperature for New York City was 33.0°. However, six cases (50%) had temperatures 1.5° or more above that average, while five cases (42%) had temperatures 1.5° or more below that average. Put another way, this data suggests that January has the potential to either be warmer/much warmer than normal or colder/much colder than normal rather than near normal. When the January EPO had a positive average 6/8 (75%) of those cases were warmer to much warmer than normal. When the January EPO had a negative EPO average, 3/4 (75%) of those cases were colder to much colder than normal. In sum, the predominant state of the January EPO will very likely determine the January temperature outcome. Based on sensitivity analysis applied to the latest guidance, there is an implied 60% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.0°. This shift in probabilities toward a warmer than normal December over the past week has been dramatic.

Sunset after a day on which the temperature rose to 46°:

Even 10-day forecasts have skill (coefficient of correlation around 0.7): Beyond 10-days such forecasts are not skillful (coefficient of correlation < 0.5)

Dreams of a white Christmas for the Middle Atlantic and southern New England regions will have to wait for at least another year. Milder air is now pushing into the region and will likely predominate through the much or all of the remaining days of December. Through December 21, snowfall amounts for select cities include: Allentown: 2.1" (1.6" below normal) Atlantic City: 0.5" (2.1" below normal) Boston: 11.5" (4.9" above normal) Bridgeport: 5.5" (1.9" above normal) Harrisburg: 0.2" (3.5" below normal) Hartford: 21.1" (14.8" above normal) Islip: 4.3" (1.7" above normal) New York City: 2.5" (0.5" below normal) Newark: 4.2" (0.7" above normal) Philadelphia: 0.1" (2.1" below normal) Providence: 8.0" (1.0" above normal) Worcester: 25.3" (13.5" above normal) Despite the warmth, which could take monthly departures toward and perhaps even above normal across many parts of the region, dreams of a snowy January persist. Perhaps a key to whether those dreams are realized will be the state of the Arctic Oscillation (AO) and Pacific North America (PNA) pattern. Since 1950, 52 snowstorms brought 6" or more snow to at least one of the following cities: Boston, New York City, or Philadelphia. 60% of those storms had an AO-, 64% had a PNA+, and 38% had an AO-/PNA+. From among the 18 storms that brought 6" or more snow to at least two of those cities, 83% occurred with an AO-, 83% occurred with a PNA+, and 67% had an AO-/PNA+. From among the 11 storms that brought 6" or more snow to all three of those cities, 91% occurred with an AO-, 91% occurred with a PNA+, and 82% had an AO-/PNA+.

It won't melt immediately and could take centuries to do so. Nevertheless, it appears that humanity is committing itself to a course that could lead to that outcome given little or no response to the need to reduce greenhouse gas emissions (projected to have increased another 0.6% this year). The latest Arctic Report Card provides a glimpse of what is currently happening in the Arctic. https://www.arctic.noaa.gov/Portals/7/ArcticReportCard/Documents/ArcticReportCard_full_report2019.pdf

Sea ice melt doesn't raise the sea level by itself. It does make an indirect contribution as a feedback mechanism that is accelerating Arctic warming. That warming affects the Greenland ice sheet. Greenland's melt, which has accelerated greatly over the past few decades, has been a key driver in rising sea levels.

A milder pattern began overspreading the region today after a cold start. Overall, the final days of December will likely be warmer than normal. Based on the latest guidance, the warmth could be sufficient to ensure that at least parts of the Middle Atlantic region could finish with at least a somewhat warmer than normal December. A scenario where much of the region winds up somewhat warmer than normal is not out of the question. Through December 20, monthly anomalies for select cities were: Baltimore: +0.5°, Boston: -0.6°, New York City: -2.5°, Newark: -1.8°, Philadelphia: -1.0°, and Washington, DC: -0.2°. Colder air could return during the first week of January. The progression of the MJO in concert with the teleconnections could be crucial in determining whether most North America's cold air stays bottled up north of the Canada-U.S. border beyond the first week of January or comes south and eastward into the region just after the start of 2020. Afterward, the predominant state of the EPO will likely be crucial to the persistence of the cold. In much of Europe, the long wait for winter goes on. Both the EPS and GEFS are in strong agreement that the first week of January will likely remain warmer to much warmer than normal in much of Europe. At present, it is likely that Europe will see a warmer than normal January with the greatest warmth in central Europe. Some parts of western Europe, particularly the United Kingdom, Spain and Portugal, have a greater chance of having near normal temperatures. Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.8°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year. The ENSO Region 1+2 anomaly was +0.5°C and the Region 3.4 anomaly was +0.5°C for the week centered around December 4. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.05°C and the ENSO Region 3.4 anomaly has averaged +0.53°C. These recent conditions are consistent with a weak El Niño. Nevertheless, a neutral ENSO remains the base case for Winter 2019-20. The SOI was -14.38 today. Today, the preliminary Arctic Oscillation (AO) figure was -0.248. No significant stratospheric warming event appears likely through December 30, but a brief period of some warming above 3 mb could develop toward the end of the forecast period before fading. Moderate Wave 2 activity will dissipate toward the end of December after leading to some temporary upper stratospheric warming. Overall, most of the stratosphere is forecast to remain cold through the remainder of December on the EPS. On December 20, the MJO was in Phase 5 at an amplitude of 0.452 (RMM). The December 19-adjusted amplitude was 0.545. Through December 20, the AO had averaged +0.878 in December. Since 1950, there were 12 cases where the AO averaged +0.500 to +1.250. The January mean temperature for New York City was 33.0°. However, six cases (50%) had temperatures 1.5° or more above that average, while five cases (42%) had temperatures 1.5° or more below that average. Put another way, this data suggests that January has the potential to either be warmer/much warmer than normal or colder/much colder than normal rather than near normal. When the January EPO had a positive average 6/8 (75%) of those cases were warmer to much warmer than normal. When the January EPO had a negative EPO average, 3/4 (75%) of those cases were colder to much colder than normal. In sum, the predominant state of the January EPO will very likely determine the January temperature outcome. Based on sensitivity analysis applied to the latest guidance, there is an implied 45% probability that December will wind up colder than normal in New York City with a monthly mean temperature just above 37.5°. This shift in probabilities toward a warmer than normal December over the past week has been dramatic.

Young ice melts fairly fast. It's the ice melt over the summer that has a large influence over how much of the incoming solar radiation is reflected and how much is not. Declining summer sea ice is playing a large role in Arctic amplification (as it is a feedback that amplifies the ongoing warming already underway). That's a major reason why Arctic warming has exceeded the rate of global warming, especially in recent decades.