bluewave
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https://www.nrcc.cornell.edu/services/blog/2023/11/15/index.html#:~:text=The Northeast is getting wetter.&text=The Northeast has seen a,is also expected to continue. Northeast is getting wetter. Precipitation has increased annually and in all seasons (see figure above). The Northeast is expected to see more precipitation under all global warming scenarios. The Northeast has seen a roughly 60% increase in the number of days with extreme precipitation, the largest increase of all the U.S. regions. The intensity of these events has also increased. This trend, along with an increased risk of flooding, is also expected to continue.
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The average July high temperature over the last 10 years at Harrison, NJ away from the sea breeze has been 89°. It has warmed up so much that a 90° day is pretty much the normal high temperature. As recently as the 2000s the average high was closer to 85°. So these days the more memorable heatwaves don’t really start until the warm spots reach 95°. Monthly Mean Max Temperature for HARRISON, NJ Click column heading to sort ascending, click again to sort descending. Mean 89.0 89.0 2024 90.4 90.4 2023 89.5 89.5 2022 91.0 91.0 2021 87.6 87.6 2020 90.3 90.3 2019 90.6 90.6 2018 88.6 88.6 2017 85.9 85.9 2016 88.9 88.9 2015 87.1 87.1 Monthly Mean Max Temperature for HARRISON, NJ Click column heading to sort ascending, click again to sort descending. Mean 85.6 85.6 2009 83.2 83.2 2008 87.5 87.5 2007 84.6 84.6 2006 88.5 88.5 2005 87.2 87.2 2004 83.0 83.0 2003 85.1 85.1 2002 89.7 89.7 2001 84.9 84.9 2000 81.9 81.9
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The strength is relative to the other years in the multiyear La Niña event. 10-11 was stronger than 11-12. 17-18 was stronger than 16-17. And 20-21 was stronger than 21-22 and 22-23. So the 3 strongest years within the multiyear La Ninas were the coldest and snowiest. And the 3 weakest years of those groups relative to the others were the warmest and least snowy winters.
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Interesting what happened yesterday with that afternoon coastal trough and the flash flooding on Long Island. For the last few days models had this feature more to the SW over NJ. But I mentioned how these features can often be fickle. This one followed the past pattern and wound up across Long Island instead of NJ. During the winter these IVTs or coastal local instability troughs often end up in areas other than forecast. The most extreme instance of one of these during the warm season was with Henri a few summers ago. The main system looped back into CT and the coastal trough wound up right through NYC with the flash floods. But the CAMS had the main axis further SW in NJ or Delaware. So these often become nowcast specials. At least the HFREF got the heavy rain potential correct both times. But the placement was way off.
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The first thing I do during a La Niña is see how amplified the MJO 5 is during October. For some reason the weaker La Ninas since 10-11 have all had weaker MJO 5s during October. This was followed by a stronger MJO 4-7 rebound in December. It’s why the weaker La Ninas since 10-11 have had warmer winters and the stronger La Ninas colder. Our best winters were 10-11, 17-18, and 20-21, which were stronger and colder ONIs and RONIs than the other grouped La Nias like 11-12, 16-17, and 22-23. But every La Niña since 11-12 has been warmer than average. The magnitude of the warmth was stronger during the weaker La Ninas. The stronger La Ninas had stronger MJO 5s in October and weaker MJO 4-7s in December. This relationship doesn’t work for stronger coupled El Niños or uncoupled El Niños since 15-16. The long range guidance always seems underestimate the MJO 4-7 forcing since 15-16 in any ENSO state coupled or uncoupled.The marine heatwaves in this area tend to focus the forcing here. Last winter also had a competing record marine heatwave in a MJO 2 leading to the colder pattern for a time out West in January. This increased to record MJO 4-7 forcing has resulted in an unprecedented 9 consecutive warm to record warm winters in a row for the Northeast.
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Yeah, just like the PNA.
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I like the Greenland Blocking Index which is like a combination of the AO and NAO. https://psl.noaa.gov/gcos_wgsp/Timeseries/Data/gbi.mon.data
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Very impressive departures there with the big drop in the AAO.
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I guess it can get a little confusing at times when people discuss blocking on the Atlantic side. Most blocks in recent years in this sector have been registering as -AOs rather than -NAOs. That’s why I like looking at the 500mb height anomalies to get a better read on the situation. In the past we would get the -NAO to fall in tandem with the -AO. But these days during the winters it has been more -AO dominant. Plus we have the more frequent south based blocks during the 2020s linking up with the Southeast ridge. While in the past this often wasn’t the case. Probably related to the record warming of the Gulf Stream and Atlantic.
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Yeah, it’s being driven by the continuing record marine heatwave near Japan.
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Maybe as soon as next spring?
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That’s pretty much to be expected from the NAM since it hasn’t been upgraded since March 2017. Over 3.00” now on Eastern LI. This is where the signal for the heaviest rains have been from most models since its closest to the subtropical low. NAM development was frozen after the March 2017 upgrade, and RAP/HRRR development with the WRF-ARW model will cease after the RAPv5/HRRRv4 upgrade in 2020. However, operational execution of these modeling and associated DA systems will continue until comparable FV3-based systems are able to give similar performance.
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The East End of Long Island is currently getting very heavy downpours with 1.50” estimated in the last hour.
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CT Shoreline the big winner again with over an inch the further east you do. Daily Precipitation Report Station Number: CT-NL-46 Station Name: Mystic 3.4 NW Observation Date 7/29/2024 7:00 AM Submitted 7/29/2024 7:08 AM Gauge Catch 1.23 in. Notes @19:00 =0”, OVC. <> @07:00.OBS: 1.23” overnight, 63°F, moderat
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The cooler pattern over the last 10 days allowed Newark to fall back away from the lead in 90° days. So Newark dropped from 3rd place down to 8th. A bit unusual to get a cooler pattern in what is typically one of the warmest 10 day periods of the year. Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. 1 2010-07-18 26 0 2 2021-07-18 24 0 - 1993-07-18 24 0 3 2024-07-18 23 0 - 1991-07-18 23 0 Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. 1 2010-07-28 36 0 2 1993-07-28 31 0 3 2022-07-28 29 0 - 1987-07-28 29 0 4 1994-07-28 28 0 5 2021-07-28 27 0 - 1991-07-28 27 0 6 2011-07-28 25 0 7 2024-07-28 24 0 - 2012-07-28 24 0 - 1999-07-28 24 0 - 1952-07-28 24 0 - 1949-07-28 24 0
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Depends on the MJO. Frequent MJO 4-7s will get you -EPO/- PNAs at times when the Aleutian ridge becomes more poleward. A -EPO/-PNA is a warm pattern with a La Niña in the Northeast. This is when we hit 80° back in February 2018. In order to get it cold in the Northeast we need a -EPO +PNA like we got from December 2017 into early January 2018. But that required a MJO 8 pattern.
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The latest HREF mean has one area of heavier rain further east closer to the low and a secondary area in NJ with the IVT-like feature similar to the GFS.
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It’s interesting how strong the 500mb La Niña pattern is across North America is despite the official ONI lagging behind. This -EPO +PNA and strong WAR east of New England were associated which much cooler Nino 3.4 ONIs during the summers of 2018, 2021, and 2022. Those 3 so far are the best 500 mb matches this summer. So my guess is that the strong -PDO and WPAC warm pool are driving this robust La Niña background state at the present time.
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Hopefully, that IVT like feature can deliver for you guys in CNJ and you don’t underperform again. But these features can be fickle. So not guarantees just yet.
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When the +PNA linked up with a south based block like in December 2020 the pattern was much warmer than if the the -NAO -AO block was further north. Probably a result of the much warmer SSTs off the East Coast boosting the ridge near New England. In the older days with colder SSTs this would have been a much colder December pattern in the Northeast. The greatest SST and 500 mb height variance between all the other strong +PNA -AO Decembers since 1950 is east of New England. The lower heights near Alaska were probably a function of the strong -PDO background state in the Pacific. So the very strong +PNA block was anchored a little further south than usual. It was the only such case of a greater than +1.20 +PNA combined with a lower than -1.500 -AO in December since 1950. So December 2020 was much warmer than past strongly +PNA and -AO Decembers. It’s one of the reasons that we have had a record 9 warmer winters in a row for the Northeast. Since it’s easier to get a warm winter when past teleconnections manifest differently in a warmer climate and don’t produce cold patterns like they did in a colder era. December 2020 compared to all previous Decembers with PNA greater than +1.20 and AO lower than -1.500 since 1950
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The +PNA NE PAC block in December 2020 was one for the record books. It was the highest December +PNA on record for a La Niña as strong as that one. There were some clues from the October MJO indicator. But that La Niña mismatch was quite impressive.
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That near record 500 mb block over the Arctic in June must have had a big effect since a favorable July pattern like this in the past would never have been accompanied by such a steep area decline.
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The 500 mb pattern generally leads the SST response. The +PDO and TNH SST pattern for the 13-14 winter had its origins with the very strong NE PAC block during the summer of 2013. The block just kept stronger right into 2015. Then we had the strong reversal during the winters which has lasted 9 years so far. The best NE PAC blocking since then has mostly been during the warm season leading to all the record heat, drought, and wild fires over Western North America. We did get a few decent intervals of NE PAC cold season blocking in December 2017, 2020, and Jan 2022. But the duration was too short to tilt the balance if the winter colder than average. The wall to wall blocking out there during the 13-14 and 14-15 winters were really memorable even if it was short lived during the winters which have followed.
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Looks like the heaviest rains and strongest winds will be further east with the subtropical low looping back into the Cape on Monday.
