sebastiaan1973

A nice read https://easternmassweather.blogspot.com/2023/06/what-growing-consensus-for-strong-el.html

EC46 by weer.nl [Netherlands, altough I think it is useful for the English weather lovers as well] Week 3: from Monday 10 to Sunday 16 July Summer warm again More sun, less showers Wind back to the east As the trough tilts and moves southward, a high-pressure area that had built up on the eastern flank of the trough over northwest Russia may move west toward Scandinavia. In the Netherlands we are in the border area between the two spheres of influence. Summer seems to be returning, according to the calculations, temperatures are well above normal again. The wind can also get an easterly component, especially in the north. In the south this is less certain. Showers and thunderstorms can also sometimes come in from the south here. Week 4: from Monday 17 to Sunday 23 July Northeast winds Warm and lots of sun A shower in the south According to the calculations for this week, the high pressure area will move further west, in the direction of Iceland and Greenland. If this happens, it would mean a recovery of the pattern from the first three weeks of June. The warm weather continues, the wind is probably blowing from the northeast and it remains quite sunny. Showers in the south seem to have a somewhat smaller chance, but that is not entirely certain. Week 5 and 6: from July 24 to August 6 Little change in summer weather Persistently warm A chance of showers, especially in the south Little will change in the pattern, with high pressure in the sea area in the far north and relatively low pressure over southwestern Europe and France. The strength of the high pressure in the north depends on whether it is a sunny weather image or a weather image in which a few showers can also penetrate our surroundings from the south. It also seems to remain warm and summery these weeks, with mainly northeasterly winds.

5. Conclusions The present work investigated the different ENSO impacts on the NAO during early and late winter and the possible roles of various mechanisms. Our observational analyses support the finding of the subseasonal variation in the ENSO-NAO linkage and identify the crucial physical processes responsible for the phase shift in NAO during ENSO early and late winters. During El Niño early winter, the North Atlantic experiences a positive NAO-like pattern of atmospheric pressure due to the weakening of the tropical Walker circulation and the associated alteration in the meridional circulation over the North Atlantic. However, the North Atlantic is dominated by a negative NAO-like atmospheric response over the North Atlantic during El Niño late winter. The phase shift in the NAO response to ENSO is closely related to the ENSO-induced NTA SST anomalies in late winter. During El Niño late winter, there appears obvious SST warming over the NTA, which can excite the local convection and thus, generate a negative NAO response. Moreover, the full establishment of the PNA teleconnection in late winter could also make some contribution to the simultaneous negative ENSO-NAO relationship. The strongly enhanced positive PNA teleconnection could partially account for the negative NAO response during El Niño late winter, but its effect is confined to the western edge of the NAO. Similar mechanisms work during La Niña. The understanding of different mechanisms for the subseasonal variation in the ENSO-NAO relationship from early to late winter provides useful information for seasonal prediction over the North Atlantic–European region. https://www.mdpi.com/2225-1154/11/2/47

According to Eric Webb it is East-based.

Still no rain in De Bilt (Netherlands). A new record. And never so much sunshine in a 30-day period.

12th of may the last rain in De Bilt, the Netherlands. A new record in a couple of days of the longest period without percipation.

Latest rainfall in De Bilt (Netherlands) 12th of may.

No rain since 12 of May here at De Bilt, Netherlands. No serious consequenses for the moment. Very wet spring.

https://www.sciencedirect.com/science/article/pii/S1674927822000144 Abstract Over the past decades, droughts and heatwaves frequently appeared in Western Europe (45°–65°N, 10°W–20°E) during boreal summer, causing huge impacts on human society and ecosystems. Although these extremes are projected to increase in both frequency and intensity under a warming climate, our knowledge of their interdecadal variations and causes is relatively limited. Here we show that the droughts and heatwaves in Western Europe have shifted in their trends in the last decade: for 1979–2012, wind speed and precipitation have both strengthened in Western Europe; for 2012–2020, however, Western Europe have experienced declined wind speed, decreased precipitation, and higher air temperature, leading to more frequent droughts and heatwaves there. Recent changes in the WE climate and extremes are related to the variations of the North Atlantic westerly jet stream. In 1979–2012 (2012–2020), the westerly jet stream shifted equatorward (poleward), which enhanced (reduced) transportation of water vapor fluxes from the North Atlantic Ocean to the European land areas, resulting in wetter (drier) surface in Western Europe. Further analysis suggests that phase changes in the Pacific Decadal Oscillation could have played a key role in regulating the position of the jet stream, providing important implications for decadal predictions of the Western Europe summertime climate and weather extremes.

El Nino and Ocean The start of El Niño, in the area along the equator between Peru on the one hand and Indonesia on the other, and the average high water temperatures in our part of the Atlantic Ocean appear to be important for the weather development in the coming summer. The start of El Niño is expected at any moment, because the deviation of the water temperatures in the central part of the aforementioned area is already at plus 0.5 degrees. That is the threshold for the start of an El Niño. Only in the west, in the vicinity of Indonesia, the warm water has yet to arrive in the near future. That area in the west, also known as ENSO Region 4, seems to be of great importance for the summer weather in Europe. There appears to be a fairly strong relationship between the average summer temperatures in the western half of Europe and the sea surface temperatures in that ENSO Region 4. The warmer the sea water there becomes (ie the stronger the El Niño), the greater the chance that the summer temperatures in the western half of Europe are clearly higher than normal. Funnily enough, there is hardly any connection with the central and eastern regions in the ENSO area. The faster El Niño expands westward in the coming weeks, the greater the chance that the summer will turn out to be warm in our country. https://www.weer.nl/nieuws/2023/zomerverwachting-2023-warm-zonnig-en-eerste-helft-vaak-droog Weer.nl Based on world climate service

Compared to late winter, the early winter response of the NAE region to ENSO is only starting to be understood (Abid et al., 2021; Ayarzaguena et al., 2018; King et al., 2018). The next section analyses the relationship between the EAP and wider climate drivers in early winter, to assess the physical processes involved. In early winter observations, a positive EAP is associated with warmer Pacific equatorial SSTs (El Niño, Figure 3a), increased rainfall over the tropical Pacific and western Indian Ocean (Figure 3b) and a weakened Walker circulation (Figure 3c). Such dynamics are known to generate Rossby waves which then propagate into the mid-latitudes (Abid et al., 2021; Ayarzaguena et al., 2018; Hoskins & Karoly, 1981; Scaife, Comer, Dunstone, Knight, et al., 2017). Two Rossby wave trains appear to be associated with the EAP, one originating in the tropical west Pacific and arching around the Pacific basin, the other originating in the Caribbean/Gulf of Mexico region, propagating north and east into the Atlantic basin (Figure 3d). The Rossby wave trajectories seen here agree with those observed in early winter El Niño events (Ayarzaguena et al., 2018, see their Figure 5 for example trajectories). The net effect of these Rossby wave trains is a low-pressure center to the west of the UK that projects onto the EAP. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL100712

In the Netherlands we still wait for the first official 25c tmax day 'zomerse dag'. Earlier forecast showed 25c at monday, the latest don't. It is quite uncommon to experience a spring without 25c [De Bilt].

El Nino 2023-2024 - Page 25 - Weather Forecasting and Discussion - American Weather WWW.AMERICANWX.COM "Thread discussing potential analog years based on moderate to strong east-weighted El Nino, -PDO, warm tropical Atlantic/Canary Current and Wet Sahel. The juxtaposition of relatively strong El Nino on the one hand and -PDO, very warm Atlantic and wet Sahel on the other hand (which generally don't go together with El Nino) is rather rare. Need to go pretty far back in time to find appropriate analogs IMHO:"

Strengthening tropical Pacific zonal sea surface temperature gradient consistent with rising greenhouse gases (nsf.gov) https://par.nsf.gov/servlets/purl/10137612 Sci-Hub | A spurious warming trend in the NMME equatorial Pacific SST hindcasts. Climate Dynamics | 10.1007/s00382-017-3777-8 https://sci-hub.ru/10.1007/s00382-017-3777-8 Frontiers | Prediction Challenges From Errors in Tropical Pacific Sea Surface Temperature Trends (frontiersin.org) https://www.frontiersin.org/articles/10.3389/fclim.2022.837483/full El Niño rapidly developing, could be "significant" event, NOAA warns (axios.com) https://www.axios.com/2023/05/11/el-nino-potentially-strong-noaa-warns

El Nino 2023-2024 - Page 23 - Weather Forecasting and Discussion - American Weather WWW.AMERICANWX.COM An interesting comparison.

Not them I'm aware of. So I searched for something else. See below. August till Oct. Looks to me, basin wide. https://charts.ecmwf.int/products/seasonal_system5_standard_ssto?area=GLOB&base_time=202304010000&stats=ensm&valid_time=202308020000

Latest EC. Seems to me a strong El Nino event in the autumn/ early winter.

https://iopscience.iop.org/article/10.1088/1748-9326/acbc37 Abstract A prolonged drought affected Western Europe and the Mediterranean region in 2022 producing large socio-ecological impacts. The role of anthropogenic climate change (ACC) in exacerbating this drought has been often invoked in the public debate, but the link between atmospheric circulation and ACC has not received much attention so far. Here we address this question by applying the method of circulation analogs, which allows us to identify atmospheric patterns in the period 1836–2021 very similar to those occurred in 2022. By comparing the circulation analogs when global warming was absent (1836–1915) with those occurred recently (1942–2021), and by excluding interannual and interdecadal variability as possible drivers, we identify the contribution of ACC. The 2022 drought was associated with a persistent anticyclonic anomaly over Western Europe. Circulation analogs of this atmospheric pattern in 1941–2021 feature 500 hPa geopotential height anomalies larger in both extent and magnitude, and higher temperatures at the surface, relative to those in 1836–1915. Both factors exacerbated the drought, by increasing the area affected and enhancing soil drying through evapotranspiration. While the occurrence of the atmospheric circulation associated with the 2022 drought has not become more frequent in recent decades, the influence of the Atlantic Multidecadal oscillation cannot be ruled-out.

In my opinion we see in EC46 the effects of the SSW. Please check Eur Blocking. Earlier I wrote about a relaxation around the middle of the month. After that an increased chance for northern blocking. This is what we see in EC46.

The role of North Atlantic–European weather regimes in the surface impact of sudden stratospheric warming events WCD.COPERNICUS.ORG Abstract. Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular in the North Atlantic–European (NAE) region. While the... For EuBL around the onset of the SSW event, a robust (10 % level) positive tropospheric anomaly can be observed at the time of the SSW (Fig. A4c). This anomaly is not significant (Fig. 3c), reflecting that it is not different from generic anomalies during EuBL. However, robust, significant, and strongly positive geopotential height anomalies are present in the troposphere at lags of 15–20 and 30–55 d after the SSW event. This is consistent with the classification of all of the here defined seven EuBL events as having a tropospheric impact in Karpechko et al. (2017). These positive anomalies are consistent with the finding that first AR and then GL are much more likely in the aftermath of an SSW with EuBL around lag 0 (compare to Fig. A2c). Furthermore, comparing to the panel for all SSW events (Fig. 3a) indicates that the EuBL cases dominate the perceived downward response in the canonical response for SSW events. During cyclonic regimes around the onset of the SSW, there is no substantial tropospheric anomaly in the NAE region at the time of the SSW, but a positive albeit weak anomaly can be observed around days 15–20 after the SSW event (Fig. 3d). This anomaly is not robust at the 25 % level, but it is significantly different from a random sample at the 25 % level (Fig. A4d). Several SSWs with a cyclonic regime around the onset are followed by GL at a longer lag (Fig. A2d), thus likely causing these anomalies. Still, the GL absolute frequencies remain below 30 % (Fig. A2). These findings and the small amplitude of the anomalies suggest that the variability in the tropospheric flow evolution after SSWs is large after a cyclonic regime at lag 0, which is also confirmed by the inspection of individual cases (not shown). ------------- So, I wasn't quite right. It can be that what see at the charts, can be a result of the first SSW (15th february) according to graphic. Or it is QTR by the second.

The first SSW didn't have a response, because of the cyclone setting at the moment. The second SSW has a anticyclone setting in NW-Europe. Which is a much better tropospheric setting for downwelling. So, we see in the charts for the coming days QTR.

"Consider 27th of february as the start date. When we take a look in the literature, we see this picture by Baldwin. The composite of weak vortex events. In 10-12 days after the start date [27th of february], we see less downwelling. Perhaps we see this too in the EC NAO forecast. First we have a negative NAO, around 11 of march it will become positive. When we fellow the picture of Baldwin, this will period will be short. After negative NAO, round the end of march again positive NAO, turning negative in april. Perhaps this is a guideline for things to come." First of all. Little akward to quote yourself EC46 is showing the pattern described above.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020RG000708 Right now we are experiencing the second SSW. [negative value 60N, 10 hPa.] Consider 27th of february as the start date. When we take a look in the literature, we see this picture by Baldwin. The composite of weak vortex events. In 10-12 days after the start date [27th of february], we see less downwelling. Perhaps we see this too in the EC NAO forecast. First we have a negative NAO, around 11 of march it will become positive. When we fellow the picture of Baldwin, this will period will be short. After negative NAO, round the end of march again positive NAO, turning negative in april. Perhaps this is a guideline for things to come.

This SSW is largely driven by Wave 1. This is a shame. This new study tells us: "Finally, we find that the mean NAO response in the first 10 d following wave-2-dominated SSWs is much more strongly negative than in wave-1 cases. However, the subsequent response in days 11–30 is very similar regardless of the dominant wavenumber." https://wcd.copernicus.org/articles/4/213/2023/

Northern Blocking (Greenland) most of the time.