bluewave

Blocking with closed lows this time of year usually means rainfall opportunities.

Maybe the blocking allowed for heavier rains around NYC instead of all the 2.00”+ amounts going NE. But the models like the Euro and RGEM did a good job indicating that there would be 2.00”+ amounts where the best convection set up.

That’s a pretty good method to use for determining the strongest the El Niño can get from the May reading especially during the strongest years. It’s probably why model forecasts issued after the spring are more reliable. I filled in some of the May to fall-winter monthly peaks in Nino 3.4 with El Niño years. The maximum range was in 2015 at +0.57C. But years that finish in the weak, moderate, and strong range usually need more than just the May Nino 3.4 reading to guess the final number. We saw the uncertainties in years like 14-15 and 09-10. So at least we can venture a guess at what the higher range might be rather than the lower. https://www.cpc.ncep.noaa.gov/data/indices/ersst5.nino.mth.91-20.ascii Super years bolded 2015-05….28.85…..+0.92…..2015-11….29.42…+2.72…super + 0.57 increase 2014-05….28.25……+0.32…..2014-11…27.46….+0.75…weak 2009-05…27.99…….+0.06….2009-12…28.34….+1.74…strong 2006-05…27.85……-0.09……2006-12...27.74…..+1.14… moderate 2004-05….28.00..+0.06……..2004-12…27.34…..+0.74…weak 2002-05…28.24….+0.31…….2002-11…..28.17……+1.47…. moderate 1997-05….28.58…..+0.64……1997-11…..29.12……+2.41…super 0.54 increase 1994-05….28.24…+0.31……..1994-12….27.85…….+1.25…moderate 1991-05….28.20….+0.26…….1992-02….28.53…….+1.78…strong 1987-05…28.56….+0.62…….1987-09…..28.36…….+1.65…strong 1986-05…27.40…..-0.53…….1987-02……27.88…..+1.13…..moderate 1982-05….28.39...+0.50…….1983-01…….28.89…+2.35….super +0.50 increase 1972-05….28.32….+0.38……1972-12…….28.69…..+2.09….super +0.37 increase

April has never averaged warmer than May before. But the monthly max has on a few occasions. Too difficult these days to get a May under 60° which would be necessary. Monthly Mean Avg Temperature for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Year Apr May Season 2023 59.0 M 59.0 2010 57.9 66.2 62.1 1994 57.4 63.7 60.6 2017 57.2 61.1 59.2 1985 57.0 67.1 62.1 1974 56.5 62.7 59.6 1941 56.2 63.1 59.7 2002 56.0 60.9 58.5 2006 55.7 63.8 59.8 2011 55.5 65.6 60.6 Monthly Highest Max Temperature for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Year Apr May Season 2002 97 90 97 1990 94 83 94 2023 93 M 93 2009 93 87 93 1976 93 83 93 2010 92 95 95 1994 92 95 95 1974 91 94 94 1960 91 83 91 1942 91 93 93 1941 91 95 95 1977 90 91 91 1962 90 98 98 Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Month of May Click column heading to sort ascending, click again to sort descending. Year Mean Avg Temperature Missing Count 2022 66.2 0 2021 64.3 0 2020 60.8 0 2019 63.5 0 2018 66.9 0 2017 61.1 0 2016 62.6 0 2015 68.2 0 2014 64.1 0 2013 63.3 0 2012 66.4 0 2011 65.6 0 2010 66.2 0 2009 63.3 0 2008 60.5 0 2007 65.1 0 2006 63.8 0 2005 59.1 0 2004 66.3 0 2003 58.9 0 2002 60.9 0 2001 64.0 0 2000 64.2 0 1999 63.2 0 1998 64.9 0 1997 59.2 0 1996 61.6 0 1995 62.7 0 1994 63.7 0 1993 67.0 0 1992 61.6 0 1991 68.9 0

It seems related to the MJO activity since early March. So it looks like Nino 1.2 has already peaked for the present time. So not sure how this will affect the overall development going forward. It will all come down to how the WWBs respond after the current pick up in the trades. The subsurface has also become less impressive in Nino 1.2 the last few weeks.

Lowest -AO since last December. https://www.cpc.ncep.noaa.gov/products/precip/CWlink/pna/norm.daily.ao.nao.pna.aao.gdas.120days.csv 21Apr2023-3.4547

Several more freezes possible for the higher elevations next week.

Less ice means more lake effect snow for the Great Lakes. https://glisa.umich.edu/resources-tools/climate-impacts/great-lakes-ice-coverage/ The number of days per winter with lake ice coverage has declined since the start of record in 1973. 1 In most areas, ice cover declines were a sudden shift as opposed to a gradual decline. For Lakes Michigan, Erie, and Ontario the shift occurred in the mid-1980s, but for Lakes Superior and Huron the shift occurred during the 1997/98 winter. 2 3 Ice cover has decreased the most in the north (i.e., Lake Superior, Northern Lake Michigan and Huron) and in coastal areas Ice cover on the Great Lakes will likely continue to decrease in the future, however, these decreases are expected to be interrupted by high-ice winters associated with cold air outbreaks. Reduced ice cover results in more winter lake-effect precipitation and increased winter wave activity. https://glisa.umich.edu/resources-tools/climate-impacts/lake-effect-snow-in-the-great-lakes-region/ Overall, snowfall has increased in northern lake-effect zones in the Great Lakes basin even as snowfall totals in Illinois, Indiana, and Ohio have declined with rising temperatures. Warmer Great Lakes surface water temperatures and declining Great Lakes ice cover have likely driven the observed increases in lake-effect snow.

Yeah, most of the rise has been since 1980 as emissions rapidly increased and aerosols declined. But you can see how it’s been an uneven rate of warming across the US. Places like BTV other locations around the Northeast have seen a faster rate of increase. Also a faster rate of increase around International Falls and slower to the SW over South Dakota. There has been a localized slowing of the rate across the corn belt especially with high temperatures. This is due to the rapid expansion of agriculture and associated irrigation. So it has prevented that region from experiencing the peak summer highs during the dust bowl. https://site.extension.uga.edu/climate/2021/01/how-temperature-and-precip-have-changed-over-the-past-60-years-by-county/ https://www.nature.com/articles/s41467-020-16676-w Model devegetation simulations, that represent the wide-spread exposure of bare soil in the 1930s, suggest human activity fueled stronger and more frequent heatwaves through greater evaporative drying in the warmer months. This study highlights the potential for the amplification of naturally occurring extreme events like droughts by vegetation feedbacks to create more extreme heatwaves in a warmer world.

Looks like only slow warming in 3.4 for the present time. These WWBs west of the Dateline have been much weaker so far than the years which had a trimonthly peak of +2.0 or greater. Notice how much stronger the trades have been than 72, 82,97, and 15. So the subsurface is much less impressive as GaWx posted a while back. Nino 1+2 is much warmer than the super years at this time but 3.4 and 4 is cooler. Need the WWBs west of the Dateline to increase to get to a Nino 3.4 +1.5 strong level. But we saw how years like 09 that got off to a later start in summer still made it to +1.6. The big question is how the WWBs will respond going forward as the models don’t really handle them well beyond 8-15 days. That’s one reason the model forecasts have been biased warm with the exception of 2016 with recent El Niño forecasts.

-PDO on steroids.

The warmer WPAC was more Niña-like. So the El Niño couldn’t couple. The same situation weakened the El Niño development in 14-15. But we still got the unusual MJO 4-6 activity in December 2015. https://www.climate.gov/news-features/blogs/enso/csi-enso-case-missing-central-pacific-rainfall However, among autumns since 1979 that had developed El Niño conditions by winter, 2018 was one of just two notable below-average-rainfall exceptions. The only other El Niño case with below-average central Pacific rainfall was 2014—a very similar atmospheric late bloomer for which an El Niño Advisory was not issued until March 2015. Perhaps the fall of 2018 was such an exception? The following figure shows how sea surface temperatures in the fall of 2018 differed from those of a typical El Niño of similar strength (1). Compared with a typical El Niño, the fall of 2018 featured a warmer sea surface in the western Pacific and a cooler sea surface in the eastern Pacific. This signifies an enhancement of the east-west sea surface temperature gradient relative to typical El Niño conditions. In other words, we failed to see the eastward movement of the warmest surface waters that we usually see with El Niño. It looks like this suspect fits the profile!

That is an important point since there is less UHI at the airports than at the Franklin Institute. The airports are further away from urban center. But the Franklin Institute is more downtown. So you can see it especially with the morning lows between the sites. The highs are nearly identical. Data for December 1, 2022 through February 28, 2023 Click column heading to sort ascending, click again to sort descending. State Name Station Type Mean Min Temperature PA PHILADELPHIA FRANKLIN INSTITUTE COOP 35.0 DE LEWES COOP 34.8 MD ROYAL OAK 2 SSW COOP 33.8 NJ CAPE MAY 2 NW COOP 33.7 DE GEORGETOWN-DELAWARE COASTAL AIRPORT WBAN 33.4 PA PHILADELPHIA INTL AP WBAN 33.2 MD STEVENSVILLE 2SW COOP 33.0 NJ SEABROOK FARMS COOP 33.0 DE DOVER COOP 32.8 NJ MARGATE COOP 32.8 NJ EB FORSYTHE NEW JERSEY RAWS 32.7 DE WILMINGTON PORTER RES COOP 32.0 NJ LONG BRANCH-OAKHURST COOP 31.1 DE WILMINGTON NEW CASTLE CO AP WBAN 30.9 PA NORTHEAST PHILADELPHIA AIRPORT WBAN 30.9 Data for December 1, 2022 through February 28, 2023 Click column heading to sort ascending, click again to sort descending. State Name Station Type Mean Max Temperature DE GEORGETOWN-DELAWARE COASTAL AIRPORT WBAN 53.6 MD ROYAL OAK 2 SSW COOP 51.7 NJ ESTELL MANOR COOP 51.3 DE DOVER COOP 50.9 DE LEWES COOP 50.7 NJ CAPE MAY 2 NW COOP 49.8 NJ ATLANTIC CITY INTL AP WBAN 49.8 NJ MOORESTOWN 4 E COOP 49.8 NJ EB FORSYTHE NEW JERSEY RAWS 49.7 NJ MILLVILLE MUNICIPAL AIRPORT WBAN 49.6 DE WILMINGTON NEW CASTLE CO AP WBAN 49.4 PA PHILADELPHIA INTL AP WBAN 49.2 NJ SOUTH JERSEY REGIONAL AIRPORT WBAN 49.1 NJ SEABROOK FARMS COOP 49.0 PA PHILADELPHIA FRANKLIN INSTITUTE COOP 48.9 PA PHOENIXVILLE 1 E COOP 48.9 MD STEVENSVILLE 2SW COOP 48.7 PA NORTHEAST PHILADELPHIA AIRPORT WBAN 48.7

Also a connection between the stronger trade winds and more Niña-like record WPAC warm pool in recent years. So 15-16 was the only El Niño since 2010 not to get resistance from both a -PDO and stronger trades. It was also the one El Niño over this period that was forecast relatively well. So it doesn’t seem like models handle resistance well but instead just try to increase or continue whichever state was present during initialization. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL098052

The local NWS office did a nice presentation on that event. http://weather.mynetgear.com/severe/1942/17Jul1942.pdf The rainfall analysis was literally based on a bucket survey with Short Run, PA having 11.9+ inches in a crock, 11.3+ in a wooden bucket, and 8.2+ inches in a milk pail. Pans, tubs, buckets, paint cans, coffee pots and similar devices rounded out the instrumentation set. Emporium, PA had 25.6 inches in a crock and Coudersport, PA had 25.5 inches of rainfall in a Milk Can. Official NWS COOP data analysis of this event indicates no 24 hour records and the official gage Coudersport recorded 8.48 inches. Far less than the Milk Can. The gage at Smethport “reported 6.68 inches before the gage was lost” (Gelber, 2002). Smethport reportedly set the 24 hour rainfall record of 30.60 inches on 17 July with an event total rainfall estimated to be 34.50 inches. There were no official rain gages within 40% of these values and as noted the Smethport gage was lost before the event ended. The official gage data indicated that when combining 17-18 July data rainfall, amounts over 8.48 inches were recorded and values much over 10 inches were difficult to find. Clearly, there was a large discrepancy between rain gage and bucket analysis. Gelber (2002) argues that the official 24 hour rainfall record for Pennsylvania is 19.81 inches set in Park Place, PA in July 1947. The impacts of the heavy rain were significant (Gelber, 2002) and similar to those one might associated with an intense widespread 6-10 inch rainfall event. The flooding claimed 16 lives, 6 of which occurred in Port Allegany. McKean County had damage to our lost 16 bridges.

Very strong blocking and closed low will slow down frontal passage. Need some training to get heaviest rains here. Slightly stronger block and heaviest rains would favor northern and western areas of the forum.

All we know at this point is that a warmer atmosphere holds more moisture and has been producing heavier precipitation events across the world and US. We will need an attribution study for this one to see how all the various factors came together. So what was considered a 1000yr recurrence interval in our older climate may have a shorter reoccurrence interval in our warmer climate. Plus land use changes can enhance flooding in extreme rainfall events. https://glisa.umich.edu/resources-tools/climate-impacts/extreme-precipitation/ Five weeks. Five instances of 1,000-year rain events. https://www.washingtonpost.com/climate-environment/2022/08/23/flood-united-states-climate-explainer/ Nowadays, however, our climate is evolving rapidly enough that previously defined recurrence intervals based on historic data might no longer apply. Event AEP map duration(s) Shapefile Fort Lauderdale, Florida, 12 April 2023 12-Hour link Hurricane Ian, Florida, 28-30 September 2022 6-Hour, 24-Hour Post-Tropical Depression Ida, Northeast, 31 August - 2 September 2021 3-Hour, 6-Hour, 12-Hour, 24-Hour link West Central Tennessee, 20-22 August 2021 12-Hour, 24-Hour link Imelda, 16-20 September 2019 12-Hour, 24-Hour, 48-Hour link Remnants of Barry, Arkansas, 15-16 July 2019 24-hour link South-Central Nebraska, 8 July 2019 6-hour link Arkansas River Basin, April - May 2019 30-day link Hurricane Florence, 13-18 September 2018 72-hour link Michigan and Wisconsin, 14-18 June 2018 6-hour, 24-hour, 72-hour link Ellicott City, Maryland, 27 May 2018 3-hour Hurricane Maria, 20 September 2017 12-hour link Hurricane Harvey, 25-31 August 2017 4-day Missouri, 28 April - 2 May 2017 48-hour link Hurricane Matthew, 6-10 October 2016 12-hour link Louisiana, 11-13 August 2016 48-hour Ellicott City, Maryland, 30 July 2016 3-hour Northern Wisconsin, 11-12 July 2016 6-hour West Virginia, 23-24 June 2016 24-hour Lower Mississippi River Valley, 8-12 March 2016 48-hour Corsicana, Texas, 24-25 October 2015 24-hour Austin, Texas, 30 October 2015 3-hour, 6-hour South Carolina, 2 - 4 October 2015 24-hour, 72-hour Central Texas, 23-24 May 2015 3-hour, 6-hour Oklahoma, April - June 2015 20-day,30-day, 60-day Phoenix, Arizona, 19 August 2014 12-hour Islip, New York, 13 August 2014 3-hour Pensacola, Florida, 29-30 April 2014 6-hour New Mexico, 9-16 September 2013 7-day Colorado, 9-16 September 2013 24-hour, 48-hour, 7-day Southern Missouri, 29 July - 8 August 2013 10-day San Antonio, Texas, 25 May 2013 6-hour Oklahoma City region, 31 May-1 June 2013 4-hour, 6-hour Tropical storm Debby, 24-27 June 2012 48-hour Duluth, Minnesota, 19-20 June 2012 24-hour Tennessee, 1-2 May 2010 48-hour Southeastern New England, March 2010 20-day

No problem. I believe it’s the daily version of the top PDO data set. -2 or lower daily readings are pretty strong. The NOAA version is probably lower the way they calculate that one. https://www.cpc.ncep.noaa.gov/products/GODAS/multiora/index/mnth.ersstv5.clim19912020.pdo_current.txt https://www.ncei.noaa.gov/access/monitoring/pdo/

It’s on the World Climate Service site. I like looking at the dailies so we can get an idea what the monthly will look like before it’s released. This current WWB is pretty moderate by April El Niño standards. So the subsurface warming and Nino 1+2 may have peaked for the current time. Would need a stronger and more sustained WWB later on for Nino 3.4 to go from neutral to weak El Niño above +0.5. A strong -PDO and very warm WPAC can keep the trades going and weaken WWB potential. We have seen this numerous times since 2012. The only spring the trades fully relaxed was back in 2015 which a very warm PDO and subsurface. Can’t really use -PDO analogs before recent years since the WPAC has warmed so much. Notice how much warmer the WPAC is now from 1972 along with the cooler tongue from California to the CPAC. So the WWBs are much weaker now. Need the -PDO to relax a bit in coming months to have a shot at a strong El Niño event. https://s2s.worldclimateservice.com/climatepanel/

https://www.weather.gov/owp/hdsc_aep https://www.weather.gov/media/owp/oh/hdsc/docs/202304_FtLauderdale.pdf

They are actually running a few degrees above 2010 for the warmest April so far. Time Series Summary for BRADFORD REGIONAL AIRPORT, PA Click column heading to sort ascending, click again to sort descending. Rank Ending Date Mean Avg Temperature Apr 1 to Apr 17 Missing Count 1 2023-04-17 52.2 0 2 2010-04-17 50.3 0 3 2017-04-17 47.8 0 4 1967-04-17 47.2 0 5 2021-04-17 46.9 0 6 1991-04-17 46.0 0 7 1988-04-17 45.3 0 - 1969-04-17 45.3 0 8 2002-04-17 44.9 0 - 1999-04-17 44.9 0 9 1968-04-17 44.8 0 10 2015-04-17 44.7 0

May be a struggle to get a really strong and sustained WWB while the daily PDO dropped again in the last few weeks.

Models just don’t have enough skill to forecast the El Niño details until after the spring predictability barrier. https://www.climate.gov/news-features/blogs/enso/spring-predictability-barrier-we’d-rather-be-spring-break Now let’s shift our attention to making an ENSO prediction for the coming winter season (for the November-January seasonal average). How useful are the models? Well, if you’re running a model using October data as input, then you’re in pretty good shape as you can expect close to 90% of the winter ENSO fluctuations to be predicted. In terms of lead time, that’s the same horizon as a forecast made in April for May-June-July (MJJ), and yet there is a huge difference in forecasting ability (5). The skill (or forecasting ability) of model runs based on February-October observations to predict the November-January (NDJ) average value in the Niño-3.4 SST region (ENSO). Results shown here are an average correlation coefficient from each of the 20 models between 2002-2011 (data used from Barnston et al, 2012). Percent Explained Variance (%) is calculated by squaring the correlation coefficient and multiplying by 100 (see footnote #1). Models that explain all ENSO variability would equal 100%, while explaining none of the ENSO variance would equal 0%. Graphic by Fiona Martin based on data from NOAA CPC and IRI. However, hope slowly grows as we emerge from the spring. In particular, models run based on May data are getting close to explaining half of the coming winter variability, which isn’t shabby. But, still, predictions are still far from assured. Using July and August data, about three-quarters of the winter ENSO fluctuations are predicted by the models. So while forecast “surprises” are becoming less frequent, they still lurk around. Overcoming the Spring Barrier? So, why is the accuracy of the models so bleak during the spring? Is there reason to believe that more model development will improve upon the low skill we see during the spring? While there are many ideas on why the spring barrier exists, there are no definitive culprits (Webster and Yang, 1992, Webster, 1995, Torrence and Webster, 1998, McPhaden, 2003, Duan and Wei, 2013). One of the reasons that the spring barrier is said to exist is because spring is a transitional time of year for ENSO (in our parlance, signals are low and noise is high). The spring is when ENSO is shifting around— often El Niño/La Niña events are decaying after their winter peak, sometimes passing through Neutral, before sometimes leading to El Niño/La Niña later on in the year. It is harder to predict the start or end of an event than to predict an event that is already occurring. There is also weaker coupling between the ocean-atmosphere in the spring due to a reduction in the average, or climatological, SST gradients in the tropical Pacific Ocean. However, for various reasons, these factors don’t fully explain why we see lower skill (6).

Looks like they made it to 96° on the update. RECORD EVENT REPORT NATIONAL WEATHER SERVICE BOSTON/NORTON MA 0519 PM EDT FRI APR 14 2023 ...RECORD HIGH TEMPERATURE SET AT HARTFORD CT... A RECORD HIGH TEMPERATURE OF 96 WAS SET AT HARTFORD CT TODAY. THIS BREAKS THE OLD RECORD OF 82 SET IN 1941.

Yeah, their earliest mid 90s by a few days. https://threadex.rcc-acis.org 4/7 93 in 2010 90 in 1991 90 in 1929 4/8 89 in 1991 87 in 1929 84 in 2010 4/9 85 in 1991 77 in 1945 75 in 2001+ 4/10 84 in 1922 79 in 2017 78 in 1955+ 4/11 88 in 2017 79 in 1955 78 in 2023+ 4/12 88 in 1977 81 in 2023 79 in 2008+ 4/13 92 in 2023 86 in 1977 85 in 1968 4/14 82 in 1941 81 in 1968 78 in 2022+ 4/15 88 in 1941 82 in 1994 82 in 1938 4/16 92 in 2012 90 in 2002 88 in 2017 4/17 95 in 2002 92 in 1976 78 in 2012+ 4/18 95 in 1976 92 in 2002 85 in 1964 4/19 96 in 1976 87 in 1972 86 in 2004