bluewave

This was the wettest first 3 weeks of July on record for many stations in the Northeast. So it’s no surprise that all the clouds and rain have kept the high temperatures down. It also resulted in warmer minimums across the board. So the the record heat at the end of June remains the strongest heat of the summer to date.

Currently getting the heaviest downpour of the day here in SW Suffolk.

Heavy thunderstorm in SW Suffolk continuing the wet July theme.

https://www.reuters.com/article/us-china-weather-henan/central-chinas-henan-province-swamped-after-heaviest-rain-in-1000-years-idUSKBN2EQ2CF From Saturday to Tuesday, 617.1 mm (24.3 inches) of rain fell in Zhengzhou, almost the equivalent of its annual average of 640.8 mm (25.2 inches). The three days of rain matched a level seen only “once in a thousand years”, meteorologists said. Like recent heatwaves in the United States and Canada and extreme flooding seen in western Europe, the rainfall in China was almost certainly linked to global warming, scientists told Reuters. “Such extreme weather events will likely become more frequent in the future,” said Johnny Chan, a professor of atmospheric science at City University of Hong Kong. “What is needed is for governments to develop strategies to adapt to such changes,” he added, referring to authorities at city, province and national levels.

Yeah, one of the stronger July MJO phase 5 patterns that we have seen.

That has been the story of this month so far. Clouds and rain have kept the maxes down and the mins up. HPN is similar to other stations in that regard. July HPN…max…-1.9…..min….+1.6 LGA…max…..-1.1…..min….-0.4 EWR…max...+1.0….min…..+1.9 ISP…..max…-0.9…..min…..+1.3

The magnitude of the warm up next week will probably come down to the strength of the Greenland block. The runs with stronger blocking have more of a 50/50 low near New England. The 0z runs kept the strongest heat to our south. But a weaker block in future runs would allow more warming into our area. New run strongest heat stays south Old run had less blocking and more heat into our area

Yeah, I can’t remember visibility down to only 2 miles at any of our airports in smoke before. LGA 20 Jul 2:51 pm 87 65 48 NW 8 2.00 Haze SCT050,SCT060,BKN250

Zones of record drought and flash flooding across the entire Northern Hemisphere. These stuck weather patterns are enhancing the dry and wet extremes across the globe.

Really extreme situation when 8 inches of rain falls in one hour. https://www.reuters.com/business/environment/dozen-central-chinese-cities-under-water-river-banks-burst-2021-07-20/ In Zhengzhou, the capital of Henan on the banks of the Yellow River, more than 200 mm of rain fell in one hour on Tuesday, forcing the city to stop all subway train services.

Yeah, devastating urban flash flood disaster there.

If you thought that the recent NYC subway flooding was bad…

Visibility steadily dropping with all the smoke. Some local stations are actually under 5 miles now. You can smell the smoke outside. 20 Jul 10:53 am 81 66 62 WNW 7 4.00 Haze CLR 29.46 29.95 20 Jul 9:53 am 79 66 65 N CALM 5.00 Haze CLR 29.46 29.95 20 Jul 8:53 am 75 66 74 6.00 Haze CLR 29.46 29.95 20 Jul 7:53 am 72 66 83 SW 5 7.00 CLR

Thickest smoke of the year so far looks like a milky thin overcast.

Scientists know that global warming is changing clouds, but they haven’t been sure whether those changes would heat or cool the planet overall. It’s an important question, because clouds have been the main source of uncertainty in projecting just how sensitive the climate is to increasing greenhouse gas concentrations, and because clouds have a huge effect on the climate system. Just a 20 percent change in their extent or reflectivity would have more of an impact than all the greenhouse gases released by human activities. A new study published today in the Proceedings of the National Academy of Sciences may help find an answer. The researchers analyzed 20 years of cloud data from satellites and found that it was 97.5 percent certain that changes in clouds brought about by climate change will amplify warming. Since the cloud effect has been uncertain, its accurate measurement also helps affirm other recent projections that a doubling of carbon dioxide in the atmosphere will warm the planet’s surface by about 5.8 degrees Fahrenheit, said said co-author Paulo Ceppi, a climate scientist with the Grantham Research Institute on Climate Change, London School of Economics and Political Science. “Most previous cloud studies focused only on certain regions or regimes, so say they look at places where there are low clouds and they look at low clouds only,” he said. “We did this analysis everywhere, at every point regardless of what type of cloud was there, and that allowed us to get a global picture.” The new research is an important update to the scientific understanding of clouds in the climate system, said Piers Forster, director of the Priestley Centre at Leeds University. “It is a really good step forward,” said Forster, who was not involved in the new study, but has worked on other recent research assessing the climate system’s response to building greenhouse gas levels. “It really tells us how clouds respond to changes in local surface temperature, especially the reflectance of low clouds,” he said. “This is then used to make an accurate estimate of the total cloud feedback: the amplifying effect that clouds have on global warming.” To get a sense of how important clouds are in the global warming equation, Ceppi said their effects can be compared to the warming effect of carbon dioxide. “We calculate that, on average globally, clouds reflect something like 50 watts per square meter of solar radiation,” he said. “You can compare that to the forcing from a doubling of CO2, which would be about 4 watts per square meter, much smaller than the average effect of clouds on sunlight. So even a very small change in how much sunlight is reflected by clouds would be comparable to the effect of a CO2 doubling.” In general, the new research confirms what some of those other studies have suggested, he said. “People have argued that clouds will amplify global warming because of solar impacts, so less reflected sunlight from low clouds, but also because of the greenhouse effect of clouds, where high clouds rise, which makes them have a larger warming effect,” he said. “Our study finds evidence of both. I’m not aware of any other studies that have been able to show that, especially the greenhouse part.” One recent study, led by University of Oslo researchers, shows global warming will reduce the amount of ice particles in widespread low clouds around Antarctica that currently reflect a huge amount of solar radiation back into space. That would make the clouds less reflective and amplify global warming, said cloud researcher Trude Storelvmo. Machine Learning Ceppi said using a machine learning approach is especially suited for complex problems like cloud changes. “It’s a complex situation because clouds depend on so many factors that all co-vary. For example, for a certain change in humidity, you get a certain response from clouds,” he said. “The machine learning method we use is smarter about learning these dependencies. It’s a complex statistical problem, and improved statistical methods can really help. There are so many relationships that it’s hard to calculate them manually. The statistical learning step gives us better predictive power.” Prior studies showed less strong relationships and thus came up with less reliable projections, he added. “One strength of our study is that we show, with 20 years of data from observations, we can really predict the feedback in model worlds where we know the answers,” he said. “Our results will mean we are more confident in climate projections and we can get a clearer picture of the severity of future climate change. This should help us know our limits and take action to stay within them.” While the research helps narrow the range of cloud responses and feedback to global warming, some uncertainties remain. “I would like to see a physical process understanding of how clouds respond,” Forster said. “This would add confidence that they are looking at the right statistics. It’s really about how much low clouds reflect sunlight in relation to both the local surface temperature and how quickly the temperature drops with altitude. Both of these temperatures are affected by global warming.” “Understanding how clouds respond locally to these temperatures,” he said, “builds up a complete picture of how clouds respond to global warming, and thereby how much global warming we expect from increasing levels of CO2.”

Too bad that the CPC doesn’t maintain a daily and monthly AD index like they do for the other teleconnections. The historic negative run from 2007 to 2012 set the stage for the big record sea ice declines in 2007 and 2012. But last year came close following impressive May preconditioning. This was followed by a strong July Dipole and historic Siberian Arctic heat. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2012GL053268 Table 1. Monthly AD Index for 2005–2012 May June July Aug. Sept. 2005 −0.42 −0.40 0.05 −0.23 −1.96 2006 −1.20 0.94 0.06 0.00 −1.89 2007 −0.52 −1.08 −1.65 −1.77 −1.23 2008 −1.06 −1.16 −0.58 −0.63 0.44 2009 2.40 −1.46 −1.95 −0.57 0.04 2010 −0.03 −1.86 0.36 −1.88 −0.72 2011 −0.36 −1.56 −1.20 −1.29 2.41 2012 −1.61 −0.84 Figure 2 Open in figure viewerPowerPoint Regression coefficients of the June-mean sea-level pressure anomalies from the NCEP/NCAR Reanalysis projected onto the first two EOF spatial patterns of the extended winter mean sea-level pressure north of 70–90°N [fromOverland and Wang, 2010]. The June AO is shown by gray bars, and the June AD is shown by blue solid lines. Both time series are normalized by their standard deviation for 1948–2012. [4] The only similar AD occurrence during the 63-year time series to recent years is a run of weak negative values from 1954–1960, when the NCEP/NCAR reanalysis fields had less supporting Arctic data. Thus we can say that a six year run of near one standard deviation negative excursions (2007–2012) is unique in the 63 year record. To further test the significance of the 2007–2012 AD patterns we randomly generated 10,000 time series, each with 63 points to match the observed time series and with a normal distribution without autocorrelation. For this simple calculation, the chance for having five consecutive values with a negative AD of magnitude greater than 1.0 standard deviation units in a sample size of 63 is rare, less than 1 in a 1000.

July has been much warmer in our area than Boston. Monthly Mean Avg Temperature for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Year Jun Jul Season Mean 73.5 79.9 76.7 2021 76.2 79.5 77.9 2020 74.4 80.8 77.6 2019 72.7 80.6 76.7 2018 72.1 78.2 75.2 2017 72.7 77.3 75.0 2016 72.9 79.9 76.4 2015 72.0 79.0 75.5 2014 72.8 77.0 74.9 2013 73.3 80.9 77.1 2012 72.4 80.8 76.6 2011 74.5 82.7 78.6 2010 76.2 82.3 79.3 Monthly Mean Avg Temperature for LAGUARDIA AIRPORT, NY Click column heading to sort ascending, click again to sort descending. Year Jun Jul Season Mean 73.6 80.2 76.9 2021 75.6 78.0 76.8 2020 75.9 82.9 79.4 2019 72.8 81.5 77.2 2018 72.9 79.8 76.4 2017 73.6 78.1 75.9 2016 73.6 81.1 77.4 2015 71.3 79.2 75.3 2014 72.5 77.0 74.8 2013 74.0 81.2 77.6 2012 72.9 80.4 76.7 2011 72.7 80.4 76.6 2010 76.0 82.8 79.4

The blocking was very strong over the Arctic this past winter. But really reversed in the spring. While there was some blocking in May, it wasn’t that strong. The low pressure has been at record levels in the Arctic since June.

The early season forecast based on the melt pond fraction came out with a 4.5 million sq km average extent for the whole month of September. The daily minimum extent would probably be just below that level. So a rebound off the lows of last year which was just above the 2012 minimum. But we would need an impressive slow down to bounce above 5.0 million sq km like 2013 did. These bounces after extremely low years are common as was discussed in the paper that I posted earlier in the thread. https://www.arcus.org/files/sio/32173/cpom_ucl_gregory_et_al.pdf Name of contributor or name of contributing organization: CPOM UCL (Gregory et al.) Is this contribution from a person or group not affiliated with a research organization? Name and organization for all contributors. Indicate primary contact and total number of people who may have contributed to your Outlook, even if not included on the author list. CPOM UCL (Gregory et al) Do you want your June contribution to automatically be included in subsequent reports? (If yes, you may still update your contribution via the submission form.) Include this submission in this month's report ONLY What is the type of your Outlook projection? Statistical Starting in 2017 we are accepting both pan-Arctic and pan-Antarctic sea ice extent (either one or both) of the September monthly mean. As in 2016, we are also collecting Alaskan regional sea ice extent. To be consistent with the validating sea ice extent index from NSIDC, if possible, please first compute the average sea ice concentration for the month and then compute the extent as the sum of cell areas > 15%. a) Pan-Arctic September extent prediction in million square kilometers. 4.5 b) same as in (a) but for pan-Antarctic. If your method differs substantially from that for the Arctic, please enter it as a separate submission.

The big weather swings pattern continues. After portions of New England had their warmest June on record, they will now be the center of the cooler pattern. Only the 3rd time that Boston had lower July average temperatures than June. Monthly Mean Avg Temperature for Boston Area, MA (ThreadEx) Click column heading to sort ascending, click again to sort descending. Year Jun Jul Season 2021 74.4 71.2 72.8 1976 73.4 72.9 73.2 1930 72.4 72.8 72.6 1994 71.9 77.5 74.7 1949 71.6 76.3 73.9 1957 71.3 74.1 72.7 2001 71.1 69.9 70.5

Though it’s not as extreme as we saw last year, models have the first dipole of the season in late July. So a reversal of the lower pressure pattern which has dominated the Arctic for the first half of summer. Several parts of the Arctic had near the lowest pressures on record for this time period. It’s a departure from recent years which had strong dipole patterns early and shifted to lower pressures later in the season.

It’s not surprising that we are tracking near the 2011-2020 mean in late July since it’s only 2021. The NSIDC site has the 10 year average September daily sea ice extent minimums. After big melt out years like 2012 and 2020, we have seen a bounce the following years. So it’s no surprise that we have recently fallen behind 2020. Just like 2013 had a nice rebound back above the 2012 lows. But the long term trend is downward which is probably the most significant feature which can get lost in the year to year noise. NSIDC September 10 year mean September daily minimum extents 2011-2020…..4.423 million sq km 2001-2010…..5.388 1991-2000…..6.499 1979-1990…...6.959

JFK is on track for the first 6 year stretch of 10 or more days reaching a 75° or higher dew point. https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=161&network=NY_ASOS&zstation=JFK&var=max_dwpf&dir=aoa&thres=75&month=all&year=2021&dpi=100&_fmt=js