bluewave

These days any months that don’t make the top 10 warmest feel cooler against the higher baseline we have gotten used to.

This is due to spring arriving earlier and the last freeze of the season holding more steady over time. We notice this around the NYC Metro area. The first 70° of the year is a month earlier than it was in 1950. So the plants are blooming a month earlier than they used to. But the last freeze of the season has been holding steady.

Strong onshore flow pattern this month with the only positive departures west of NYC. EWR….+1.0 NYC…..-0.3 LGA…….-1.2 ISP……..-0.7

The last week of May since 2009 has given us some clues how many 90° days a warm spot like Newark usually gets. The last two Mays were a good example of this. Newark gets more 90° days when it reaches 90° than the years it stayed in the 80s. All the years with higher totals over 40 days at least reached 94° during the last week of May. 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 May 25 to May 31 Annual 90° days 2023-05-31 80 29 2022-05-31 98 49 2021-05-31 94 41 2020-05-31 86 31 2019-05-31 90 27 2018-05-31 92 36 2017-05-31 80 22 2016-05-31 96 40 2015-05-31 91 35 2014-05-31 88 15 2013-05-31 94 25 2012-05-31 92 33 2011-05-31 92 31 2010-05-31 95 54 2009-05-31 84 14

Bradford, PA continues to be one if the fastest warming parts of the state. The minimums have risen +3.5° since 1994 and the maximums at +3.2°.

The amount of blocking showing up on the ensembles for the rest of the month could prevent the warm spots like Newark from reaching 90°. It looks like the warmer days should generally make it into the low 80s. This will be different than the pattern since 2010. The last two times Newark reached 90° during the first week of May like this year were in 2018 and 2010. Both those years had follow up 90s during the last week of May. We have to go back to 2000 and 2001 for 90° during the first week of May without 90s during the last week of May. May 1-7 max Newark 2024…90° May 1-7 max Newark 2018…94°…May 25-31 max 92° May 1-7 max Newark 2010…90°…May 25-31 max 95°

Yeah, nice cold pool developed to our east with all the blocking since March 20th.

Absolutely. This would have been a nice pattern over the winter.

Yeah, the EPS forecast 500 mb pattern through day 15 doesn’t look like it will produce any 90°heat around NYC the area. The warmest days with these teleconnections would probably be upper 70s to low 80s with numerous days cooler than that. So it looks like the strongest warmth this month will turn out to have been frontloaded unless we start seeing warmer changes near the end of the month in later runs. The higher latitude ridging and blocking appears to keep the Southeast ridge on hiatus for a while.

Yeah, the rise in minimum temperatures at the airport is nearly identical to the one in Mt Holly at the NWS forecast office over the last 30 years. The population at Mt. Holly has remained nearly steady at 10k as the population in Philadelphia has held steady around 1.5 million. So it doesn’t appear that the Philadelphia UHI intensity has changed much in 30 years. So all the warming over the last 30 years is the result of a steadily warming climate and not a local increase in UHI intensity. Philadelphia International Airport 30yr minimum temperature rise +2.6°F. Mt.Holly NWS WFO 30 year minimum temperature rise +2.8°F

Very well defined backdoor pattern this month in the Northeast.

It could be a combination of the record warm Atlantic SSTs along with the record warmth over the Western Pacific causing these further south Greenland blocks during the 2020s to link up with the Southeast ridge. In the 1950-1970 era of strong -PNA patterns, this wasn’t the case when there was a strong Greenland block. There was usually an upper low over the East at the same time there was a deeper -PNA trough out West.

Plenty of low pressure around on the ensembles over the next 10 days. So a continuation of rain chances every several days. The warmest days that are drier look like 70s to perhaps around 80°for the usual warm spots. But no 90° heat showing up yet like we got through the first 10 days of May. It’s same the back and forth pattern that began around March 20th.

We have actually seen a shift in the way the -PDO has been manifesting in recent years. It’s now defined by the 2nd EOF which is being driven by the extreme marine heatwave east of Japan. So this is the first El Niño around +2.0 or higher with a -2.09 PDO in April. https://www.ncei.noaa.gov/pub/data/cmb/ersst/v5/index/ersst.v5.pdo.dat https://www.nature.com/articles/s43247-023-00839-wIn this study, we evaluate the ocean warming pattern derived from four decades of satellite measurements. We find widespread strong subtropical ocean warming, concentrating mostly on the western ocean basins. In contrast to these observations, studies of paleoclimate suggest that the greatest ocean warming occurs at higher latitudes. By pairing the observed warming pattern with SST evolution in long-term climate simulations, we propose that the observed warming pattern is constrained by ocean dynamics of surface convergence (downwelling, subtropical gyres) and divergence (upwelling, subpolar gyres) rather than being dominated by internal variabilities, such as the https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL101078 The fundamental result of this study is that the first EOF of SST in the North Pacific has changed starting in 2014. For more than 20 years, the PDO has been used to describe the state of the North Pacific. However, since the marine heatwave of 2014, there have been remarkable changes to the dominant mode of SST in the North Pacific. The spatial pattern of the first EOF of SST from 1950 to 2021 is notably different from the PDO, suggesting that though the PDO served as a useful metric of SST variations until 2014 (Johnstone & Mantua, 2014), it may no longer be as effective a climate index for the North Pacific. From 1950 until the 2014 MHW, the first EOF remained consistent in its proportion of positive and negative regions with both taking up roughly half the area of the North Pacific (and with the positive region taken to be the eastern Pacific). When EOFs are calculated from 1950 to endpoints after 2014, the first EOF has a maximum positive region covering 77% of the North Pacific, with a PC indicating the largest anomalies on record. These changes to the first EOF/PC of North Pacific SST are nothing short of remarkable. In concert with these changes, the second EOF/PC of SST has also undergone profound evolution since 2014. This second EOF now accounts for approximately 18% of the variability, growing from 13% during the 1950–2013 period. The spatial structure of the second EOF now is positive over almost the entire basin, with a PC that has grown strongly positive in the last several years. Thus, the second EOF/PC describes warming over much of the Pacific not in the positive lobe of the first

Too bad we couldn’t get southward corrections like this during the winter. New run Old run

PHL has had a similar amount of 90° days since 2010 as more rural to suburban COOP sites in NJ. Monthly Number of Days Max Temperature >= 90 for PHILADELPHIA INTL AP, PA Click column heading to sort ascending, click again to sort descending. Year Apr May Jun Jul Aug Sep Oct Season Mean 0 2 6 15 9 3 0 35 2023 0 0 1 13 3 7 0 24 2022 0 3 5 19 19 2 0 48 2021 0 3 9 10 15 0 0 37 2020 0 0 5 21 10 0 0 36 2019 0 1 4 18 8 3 1 35 2018 0 1 4 11 10 4 0 30 2017 0 3 6 11 4 2 0 26 2016 0 3 5 16 17 5 0 46 2015 0 1 7 10 12 7 0 37 2014 0 0 3 11 3 2 0 19 2013 0 3 4 12 0 1 0 20 2012 0 2 7 21 8 1 0 39 2011 0 3 5 21 4 0 0 33 2010 0 2 15 19 12 7 0 55 Monthly Number of Days Max Temperature >= 90 for HIGHTSTOWN 2 W, NJ Click column heading to sort ascending, click again to sort descending. Year Apr May Jun Jul Aug Sep Oct Season Mean 0 2 6 15 9 3 0 35 2023 0 0 2 18 5 6 0 31 2022 0 3 3 22 19 2 0 49 2021 0 3 10 14 13 1 0 41 2020 0 0 5 23 13 1 0 42 2019 0 0 4 16 10 4 1 35 2018 0 3 4 12 13 4 0 36 2017 0 3 6 11 4 2 0 26 2016 0 4 4 17 16 5 0 46 2015 0 3 7 9 10 7 0 36 2014 0 0 7 12 2 6 0 27 2013 0 1 7 11 0 2 0 21 2012 1 2 6 16 5 1 0 31 2011 0 2 4 16 5 0 0 27 2010 1 3 10 17 11 6 0 48 Monthly Number of Days Max Temperature >= 90 for FREEHOLD-MARLBORO, NJ Click column heading to sort ascending, click again to sort descending. Year Apr May Jun Jul Aug Sep Oct Season Mean 0 2 6 15 8 3 0 34 2023 0 0 1 13 0 4 0 18 2022 0 2 4 22 11 3 0 42 2021 0 3 14 13 12 1 0 43 2020 0 0 6 18 14 2 0 40 2019 0 0 4 16 8 4 1 33 2018 0 5 7 15 17 4 0 48 2017 0 3 5 10 4 2 0 24 2016 0 4 2 16 14 6 0 42 2015 0 0 4 10 13 7 0 34 2014 0 0 4 10 0 5 0 19 2013 0 1 7 12 0 2 0 22 2012 1 1 5 17 5 1 0 30 2011 0 0 3 16 5 0 0 24 2010 1 3 12 19 12 5 0 52

Article Highlights Satellite observations reveal that global mean net flux (NET) at the top-of-atmosphere (or equivalently, Earth’s energy imbalance) has doubled during the first twenty years of this century. The increase is associated with a marked increase in absorbed solar radiation (ASR) that is partially offset by an increase in outgoing longwave radiation (OLR) While ASR and OLR changes within sub-periods corresponding to the hiatus (03/2000–05/2010), transition-to-El Niño (06/2010–05/2016), and post-El Niño (06/2016–12/2022) vary substantially, NET flux changes are remarkably stable (within 0.1 Wm−2 per decade), implying a steady acceleration of climate warming The increase in ASR is associated with decreases in stratocumulus and middle cloud fraction and reflection in the Northern Hemisphere, and decreases in middle cloud reflection in the Southern Hemisphere. The cloud changes are especially large in areas with marked increases in sea-surface temperature, such as over the eastern and northern Pacific Ocean Continued monitoring of Earth’s radiation budget and new and updated climate model simulations are critically needed to understand how and why Earth’s climate is changing at such an accelerated pace

For 90° days they were much warmer than even 2010. There was a very +AO +NAO pattern during springs like 1986, 1991, and 2002. So if we ever got a pattern like that in our much warmer 2020s climate Newark would have its first spring with 10+ 90° days. The only thing that has been preventing this has been all the blocking during recent springs. Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Mar through May Click column heading to sort ascending, click again to sort descending. Rank Year Number of Days Max Temperature >= 90 Missing Count 1 1991 8 0 2 1986 6 0 3 2002 5 0 - 1959 5 0 4 2022 4 0 - 2021 4 0 - 2018 4 0 - 2000 4 0 - 1987 4 0 - 1977 4 0 - 1965 4 0 - 1939 4 0 - 1936 4 0 5 2023 3 0 - 2017 3 0 - 2016 3 0 - 2010 3 0 - 2009 3 0 - 2001 3 0 - 1999 3 0 - 1996 3 0 - 1993 3 0 - 1992 3 0 - 1985 3 0 - 1974 3 0 - 1964 3 0 - 1962 3 0 - 1934 3 0 - 1931 3 0

Blocking is always warm when it links up with the Southeast ridge and becomes more south based. But it results in frequent backdoor cold fronts in the spring. So we get a back and forth between warm ups and cool downs with the warm departures ultimately winning out. We had very strong blocking in the spring during 2010 also. But it build down SW to the Great Lakes which made it the warmest spring blocking pattern on record. The ridge axis wound up to our west so we had less onshore flow than this spring.Since with more more S to SW flow. This spring the ridge axis is more into Eastern New England allowing more frequent onshore flow and backdoor cold frontal passages.

Newark is still +3.6 on the month for max temperature departures. But it’s very rare in May to get repeating +15 to +21 days so close to -15 days. So plenty of back and forth. Data for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Date Max Temperature Max Temperature Departure 2024-05-01 79 10.6 2024-05-02 90 21.3 2024-05-03 66 -3.0 2024-05-04 62 -7.3 2024-05-05 54 -15.6 2024-05-06 76 6.1 2024-05-07 83 12.8

Yeah, these morning warm fronts usually overperform this time of year.

It’s easy to lose track of all the 20”+ flood events they have been getting in recent years.

The general pattern of 2-3 days making it to 80s in the warm spots before clouds,showers, and onshore flow along with cooler temperatures looks to continue. Ensembles keep a trough near by. So chances for showers and thunderstorms every few days with generally above normal rainfall.

Could be some locally heavy downpours with the elevated convection tomorrow morning due to the very high PWATS for this time of year.

The cooling effect was very small so not much of a factor in regard to the big global temperatures. One point to emphasize: the net effect is cooling, but it’s a small effect. Without it, globe would not be much warmer.