Reply on RC1

The manuscript by Lisa-Ann Kautz and co-authors presents an extensive review of the state of research on atmospheric blocking with a strong focus on their impacts. It starts with an overview of blocking types including the most important mechanisms during a blocking live-cycle. Then the impacts of blocking on several types of extreme events are addressed: temperature, hydrological, wind, and compound. For each extreme an overview is given, the involved dynamics are explored and some case studies are given. In the final part of the manuscript the predictability of blocking induced extremes events as well as their relationship in a changing climate is investigated. The manuscript ends with a summary of the most important open research questions in relation with blocking.

This review manuscript presents a timely and extensive overview of the manifold blocking impacts, that can sometimes seem contradictory at first glance (hot/cold and wet/dry extremes can both be caused by blocking). The topic it addresses is well motivated, it is well-written and -structured. Mostly, the authors manage to generalize and combine results from different studies to clear top-level messages (one exception is mentioned in my comments below). My only real point of critique are the first two figures: they are never mentioned in the text and the information I could extract from them was limited. I think both of them aim to address important topics (blocking locations and their naming as well as impacts depending on their relative position to the block) but fail to fully do so.

Apart from that I only have a few minor comments outlined below. Given that the authors address them my evaluation is that this manuscript should be published in Weather and Climate Dynamics.

Reply: We thank the reviewer for his/her generally positive feedback and are grateful that he/she supports a publication in WCD.

We understand the main criticism addressing the figures, especially Figure 1 and 2, and we agree they could be better explored and interlinked with the text. Regarding Figure 1, we agree that it could be replaced by a figure that includes even more aspects on the occurrence of atmospheric blocking over the Euro-Atlantic sector – for examples considering seasonal differences. Therefore, we will follow the suggestions of the reviewer and change the figure accordingly, and perform the according changes in the main text.

Regarding Figure 2, we aimed to provide a summary of the many influences blockings can have for different types of natural hazards. Therefore, we have opted to add everything into one figure as a synthesis instead of splitting the surface influences into several figures. As some of the processes shown in Figure 2 can occur simultaneously, we think this is the more adequate representation. Specifically, we rather want to show here where the extremes can occur relative to the blocking - using an omega block as the example. Nevertheless, we will enhance the text to provide a better connection between the figure and the text and make the statements clearer.

Minor Comments

Figure 1: I personally find this figure to be too schematic. What is the authors aim with it? If it is only in the paper to indicate the names of the different areas in use it should be stated so. Otherwise, it might be better to use some figure which gives more realistic representation of blocking regions, potentially also distinguishing between winter and summer (such as figure 1a/e in Davini et al. 2020) In any case, if the authors show the figure is should be discussed and referenced in the text.

Reply: We agree with the reviewer that Figure 1 could be improved and better connected with the text. Please refer to our reply to the main comment above.

Figure 2: Basically the same comment as for figure 1: It is not discussed at all and I am unsure what to take away from it. What are the different impact areas based on? Does a single block have all these effects or are these merely all the potential effects that have been observed/reported at some point? Are they only valid for an omega block in the exact region as indicated or is this to be understood more generally?

Reply: Figure 2 is about "phasing", i.e. where relative to the blocking certain surface extremes occur. This is exemplified by an omega block. So when an omega block is present, these extremes can occur at the marked locations. A good example of this is the case in the summer 2010. There was a heat wave below the blocking ridge (i.e. over Russia/Eastern Europe) and flooding in Pakistan, i.e. associated with the eastern trough (eastern flank of the block). There were also some extreme rainfall events below the western trough (western flank of the block). However, as pointed out by the reviewer, these explanations are missing in the text and need to be added. Please see also our reply to the main comment above.

Some of the shaded areas are quite small (e.g., high IVT and heavy precip to the north), how can they be interpreted? Are there physical mechanisms that can lead to heavy precip only in that area or is it rather that it has just been reported in this area for a specific case?

Reply: We thank the reviewer for the specific questions regarding Figure 2. We will address these questions in the revision and enhance both the figure and the text.

I think it could even be helpful to have several figures with blocks at different locations and their impacts in a more general sense. These could then be referenced in the relevant sections in the text.

Reply: In the previous replies, we have already tried to clarify what our intention was with this figure. We have chosen the omega block as it can be used to explain the different influences very well. In general, dividing the figure into different panels is a good idea. However, we estimate that it is hardly possible to clearly distinguish the impacts of different blocking types based on the existing literature. This is related to the variety of different indices and definitions. Therefore, we think it is not feasible to provide this distinction in the figure. However, we will split the figure in terms of seasonal differences, which was suggested by Anonymous Referee #2. Therefore, please also look at the responses to Anonymous Referee #2.

section 2.3: Could the authors try to better distinguish the different datasets used to investigate blocking here and in section 2 in general? (or explicitly state whenever statements are valid for simulating blocking in general)

E.g., it is mentioned that blocking representation is a concern in numerical models (line 147) is this referring to global climate models (as discussed in the rest of the paragraph) or also to NWP models? It is further stated that blocking is underestimated but relative to what?

Conversely, are the considerations discussed from line 154 for weather forecast systems also valid for climate models?

Reply: We agree that we should clearly state which statements are based on reanalysis data and which references analyzed NWP or GCM model data. We will improve the text in the manuscript.

216 “separately form each”

Reply: We will implement the suggested change in the manuscript.

Figure 3: Please make clear that temperature is indicated as shading and gp as lines. Please make clear that dots refer to significance of the temperature anomalies (as I assume).

Reply: We will enhance the figure as suggested.

323: Not sure if the * should be removed from Kautz*?

Reply: Thanks for pointing this out. It will be removed.

421: “surface negative temperature anomalies” should be “negative surface temperature anomalies”?

Reply: This will be changed.

435: I acknowledge that the dynamics of precipitation are more complex but I find this paragraph a bit convoluted (in particular compared to, e.g., the one about temperature extremes). Could the authors try to extract clearer high-level impacts here? E.g., it seems a bit strange to me to separately explain the effect of blocking between 0-40E and 0-30E or to switch between clearly defined areas (0-40E) to more general geographical terms (‘Central Europe’, ‘several regions in Europe’)

Reply: Thanks for the suggestion, we will enhance the text as suggested to enhance clarity and consistency.

508: “We next move to blocking related flood cases in Europe” This first example was also about flood in Europe?

Reply: We chose this formulation because a thunderstorm case was introduced in the previous paragraph and because we wanted to say that we are now continuing with flooding cases. However, flash floods also occurred in the thunderstorm case, thus, we will remove this sentence.

525: “In October 2000 a feedback between heavy precipitation events could be identified.” between heavy precip and blocking?

Reply: Yes, this will be changed in the manuscript.

Figure 4a: The last category is a precipitation anomaly exceeding -100% of the climatology and it seems to exist on the map. This should not be possible, right?

Reply: We agree with the reviewer that there cannot be less than -100% here. The very dark red color is -100%. We will adjust the color bar so that it no longer looks as if -100% is exceeded somewhere.

572: “low wind conditions” weak wind? or low wind speed conditions?

Reply:  We mean “low wind speed conditions”, this will be changed in the revised manuscript.

702 “changes blocking occurrence”

Reply: This will be changed.

Reply on CC1

Please see our reply on RC3.

Reply on RC2

The manuscript describes the relationship between atmospheric blocking over the Euro-Atlantic sector and a plethora of extreme events, starting from the more classical heat waves and cold spells up to droughts, extremes of precipitation and compound events.

The discussion is detailed, facing different aspects of both blocking and extreme dynamics, providing a comprehensive state-of-the-art of the scientific knowledge on the topic. Predictability and impacts of climate change are also analyzed.

My main concern is Figures 1 and 2 – the latter is not even referenced in the text! – as they appear as completely disconnected from the main body of the paper. Moreover, they provide much less information that what can be easily achievable with a short climatological/composite analysis.

However, the manuscript provides a useful reference for future studies on the topic, and highlights in which direction the scientific community is showing a lack of knowledge. Therefore, I believe that the manuscript can be easily published in Weather and Climate Dynamics after the suggested revisions are included in the new revision.

Reply: We thank Anonymous Referee #2 for his/her assessment and understand the criticism regarding the embedding of the Figures 1 and 2.

Major points

• As mentioned above, there is no discussion and refencing of Figure 2 in the text: furthermore, Figure 1 is barely described, and the different sectors highlighted in the panel are not analyzed in the text.

Reply: We agree. This point was also criticized by Anonymous Referee #1. We will replace Figure 1 and describe the new figure appropriately in the text. We will enhance the text to provide a better connection between the figure and the text and make the statements clearer. Please refer also to our reply to Anonymous Referee #1.

• In this direction I believe that Figure 1 will be much more informative if it shows a climatology of atmospheric blocking according to both one reversal and one anomaly index, in a similar fashion to what done by Woollings et al. 2018. This can go hand in hand with a defining, as currently done in Figure 1, a set of “blocking regions”, which should be always used in the rest of the manuscript. There is no need of lon-lat definition, but at least something more detailed of “North Atlantic blocking” should be used. Indeed, several times in the text I spotted references to “Atlantic blocking”: this is a rather vague entity since it depends on which index is used, and such blurry definition may confound the reader. This is particularly true for this manuscript since we are discussing extremes, where the location of the blocking is fundamental.

Reply: Thanks for this comment. Anonymous Referee #1 has also stated that the informative content of Figure 1 should be increased and has already referred to potential expansion possibilities. We will compare the reviewers' suggestions, check which figure actually has an added value for the article and then fundamentally revise Figure 1 accordingly. We will also add clearer definitions of blocks depending on their region of occurrence at the beginning of the paper.

• Similarly, Figure 2 would be much more informative if instead of the current simplified sketch – that is completely disconnected from the current discussion – the authors can provide a composite analysis – based on one or more regions of blocking defined in Figure 1 - bringing together all the dynamical fields they mention. It would be extremely useful if such figure can be divided in both summer and winter, and perhaps if it includes two blocking indices, so that the reader can assess by himself the different nuances of summer and winter blocking and the limitation induced by the blocking index definition (which has been mentioned by the authors in Section 8 has a key issue).

Reply: We agree that Figure 2 is not sufficiently explained in the text. This point was also highlighted by Anonymous Referee #1. Thus, please also see the responses to Anonymous Referee #1, where we also explain our intention with this figure. We would like to keep the figure as simple as possible to provide a good synthesis / overview, but recognize that the distinction between the seasons is an important point. Therefore, we will split the figure into two panels so that the extremes for the warm and cold seasons are shown separately.   

• Although the manuscript is in general well written, I found some imprecise discussion in the abstract and the introduction. I highlighted some of them in the minor points below, but I recommend the authors to double-check the text and the associated statements.

Reply: We thank Anonymous Referee #2 for highlighting some of these points. We will check our text again carefully.

Minor points

• L1: “regarding associated impacts”. These last words seem not connected to the rest of the sentence, please rephrase.

Reply: We will rephrase this sentence.

• L9: I might have misunderstood, but why do you mention “longwave radiation warming” under clear sky condition? Perhaps you mean “shortwave” here?

Reply: This is a mistake – “shortwave radiation” is correct here.

• L11: I would say “meridional advection from higher latitudes” or “horizontal advection from continental landmasses”. Horizontal advection from high latitude is by definition meridional.

Reply: We will rephrase this.

• L12: The connection between snowfall, blocking and storm track is a bit confusing, I am not sure the three things are robustly related, so that I wonder if it is fundamental to highlight this in the abstract. Extreme snowfall events over Europe are usually associated with easterly or northerly winds of Arctic origin, it is unclear to me what is the role of extratropical cyclones here. Please clarify.

Reply: We will explain these connections better in the abstract.

• L28: The reference to derailed train, although fascinating, does not seem like a relevant information here (no reference is added).

Reply: We will remove this sentence.

• L30: please remove “layer up to 10-12 km”, the troposphere height is season and latitude dependent.

Reply: We will remove this.

• L31: Why blocking is defined as a “self-sustaining tropospheric flow”? Blocking is not a flow – it blocks the flow - but rather an atmospheric pattern or structure.

Reply: In line 33, we have defined blocking systems as “self-sustaining tropospheric flow features”. We will change this to “self-sustaining tropospheric flow patterns”.

• L37: The plural of blockings is not commonly used in English, while “blocks” is a generally used definition in this case.

Reply: We will correct this at this point and also at other points in the text.

• L88: I would say meridional gradients instead of horizontal gradients, since both the referenced indices uses a meridional gradient.

Reply: We will replace “horizontal” by “meridional”.

• L99: Northern Hemisphere

Reply: We will correct this at this point and also at other points in the text.

• L165: given that orography has been shown in the last years for being responsible of shaping the mid-latitude flow and having a relevant role in weather and climate model biases, I think this should be mentioned here (e.g., Jung et al 2012, Berckmans et al 2013, Pithan et al. 2016)

Reply: Thanks for the suggestion! We will take the references into account and make appropriate additions to the text.

• L167: A recent work by Davini et al (2021) on seasonal blocking might be of interest here.

Reply: Thanks for this reference. We will take a look at it and see how it can be included.

• L194: this sentence is a bit strange: a barotropic pressure positive anomaly will lead in the Northern Hemisphere to an anticyclonic circulation: colocation is not a requirement, is a definition. Please rephrase.

Reply: We will rephrase this sentence.

• L246: Why there should be adiabatic compression induced by horizontal advection? Please explain.

Reply: We agree with the reviewer that the sentence can be somewhat misleading. The second part of the sentence refers specifically to the temperature increase. We wanted to say that the advected air becomes warmer and that this warming is caused, among other things, by adiabatic compression. However, this does not mean that horizontal advection automatically leads to adiabatic compression. We will reformulate the sentence in order to enhance clarity and avoid possible misunderstandings.

• L248: here – and in other instances, as far as I understand – the authors follow the perspective of an anomaly-based index. This a good choice, but it should be pointed out somewhere in the text that the authors follow this “view” (for this reason I suggest – see main points - showing a blocking climatology in Figure 1 and define a few clear geographical sectors). I would suggest the authors to pay attention to the geographical definition used in the different part of the manuscript, since for example reversal-based blocking indices will show the blocking discussed at these lines over Greenland. Indeed, when using a reversal index blocking in the “North Atlantic” might lead also to a poleward displacement of the jet.

Reply: Since we have not done own new analyses specifically for this paper, we have not limited ourselves to one particular approach. However, we understand that it is necessary to make it clearer in the text which approach was used in the referenced studies. Please also consider our reply to the first major comment on this matter.

• L249: Please remove “in the regions north of these cyclones”.

Reply: We will rephrase this sentence as suggested.

• L261-270: this section makes a bit of confusion among seasons. As an example, a warm extreme can be driven by blocking in winter due to advection of warm air from the ocean for a prolonged time. I would encourage the authors to reorganize this part taking the different seasons into consideration.

Reply: Thanks for this suggestion. Our focus is on cold anomalies in winter and warm anomalies in summer. We will emphasize this more clearly in the text.

• L305: a brief discussion of marine heat waves and their relationship with blocking might have been interesting here.

Reply: We will add a short paragraph on marine heat waves.

• L324: Why Kautz reference has a *?

Reply: The asterisk was automatically taken from the Bib-file, as the first author L. Kautz and the second author I. Polichtchouk are equally contributing authors in the study. We will remove the asterisk in the text.

• L329: I guess that here we are talking about Greenland blocking (Hanna et al. 2016).

Reply: Thanks for this comment. We will compare the exact definition of North Atlantic blocking by Cattiaux et al. 2021 with that of Greenland blocking by Hanna et al. 2016 and revise the text accordingly.

L343: what drives the wet anomaly on the eastern flank of the blocking? I can see it coming on the western flank due to the moister low latitude air, but it is a bit unclear to me how this can occur on the downstream side. Is this depending on the geographical placement, i.e., if a blocking is on land or on ocean?

Reply: We would like to formulate our reply using the occurrence of wet anomalies on the eastern flank of the blocking based on the floods in Pakistan in summer 2010 (cf. Martius et al. 2012) as an example. In this case, one crucial factor was the wave-breaking downstream of the blocking anticyclone (which itself was associated with the Russian heat wave). The breaking waves had an impact on the surface wind field so that moist air was transported towards the mountains downstream of an upper-level trough where the forced ascent lead to precipitation. In addition to wave breaking, monsoonal forcing also played an important role. This example shows that the occurrence of precipitation anomalies on the eastern flank of blocks also depends on the location and that other factors must also be included. We will clarify this point in the paper.

• L480-492: this is another example where a clear geographical region or sector definition may help. It is unclear which kind of blocking episode leads to such dry spell. An “Atlantic blocking” as referred at L487 might have moved the storm track and leads to increase rainfall over Iberia.

Reply: As noted above, the blocking regions will be better defined. We will then use these definitions consistently in the text.

• L545: again, it is not very clear here: a high latitude blocking event over the Euro-Atlantic sector might be over Scandinavia so that it can potentially have a limited effect on the storm track.

Reply: Santos et al. (2013) provides a comparison between two exceptional winters – 2010 and 2021. They have compared the location of blocking occurrence and the jet position and found that in 2010, there were an equatorward shifted jet and frequent high-latitude blocking while in 2012, a poleward shifted jet and frequent low-latitude blocking were observed. In both cases, the shifted jet has influenced cyclone activity and thus, the occurrence of precipitation anomalies. This study, which we have also cited, suggests that high-latitude blocks have an influence on the storm track.

• L555: does orography – as the Alps - play a role in such configuration?

Reply: For example, the paper of Hofherr and Kunz (2010) provides an extreme wind climatology of winter storms in Germany. They pointed out that over complex terrain, the near-surface wind field is dominated by orography.  Since we focus on the influence of atmospheric blocking in this paper, we have not explained this aspect in detail in the manuscript.

• L567: I wonder if this configuration reflects the double wave breaking structure discussed by Messori et al. (2019)

Reply: We thank the reviewer for pointing this out. We will check the reference and enhance the text accordingly.

• L624: power plants?

Reply: We will replace “power plants” by “losses in power plant operation”.

• L703: a comprehensive analysis of blocking duration in future scenarios has been done also by Dunn Sigouin et al. (2013)

Reply: Thanks for this reference. We will take a look at it and see how it can be included.

• L706: there are more recent references which analyze and discuss blocking trends, and I think some of the are also referenced in this manuscript (Masato et al 2013, Davini and D’Andrea 2020, etc…)

Reply: Thanks for the additional references. We will check and add them to the manuscript.

• L730: Screen (2014) might be referenced here.

Reply: Thanks for this reference. We will take a look at it and consider it to inclusion in the paper.

• Figure3/Figure 4: is this geopotential or geopotential height? Those numbers seem a little too small to me for being m2/s2.

Reply: We thank the reviewer for this question, there is indeed a mistake in the description. We do not show the geopotential in Figure 3 and Figure 4, but the geopotential height. We will correct the captions accordingly. 

Some of the above references:

Berckmans, J., Woollings, T., Demory, M.-E., Vidale, P.-L. and Roberts, M. (2013), Atmospheric blocking in a high resolution climate model: influences of mean state, orography and eddy forcing. Atmos. Sci. Lett., 14: 34-40. https://doi.org/10.1002/asl2.412

Davini, P, Weisheimer, A, Balmaseda, M, et al. The representation of winter Northern Hemisphere atmospheric blocking in ECMWF seasonal prediction systems. Q J R Meteorol Soc. 2021; 147: 1344– 1363. https://doi.org/10.1002/qj.3974

Dunn-Sigouin, E., and Son, S.-W. (2013), Northern Hemisphere blocking frequency and duration in the CMIP5 models, J. Geophys. Res. Atmos., 118, 1179– 1188, doi:10.1002/jgrd.50143.

Hanna, E., Cropper, T.E., Hall, R.J. and Cappelen, J. (2016), Greenland Blocking Index 1851–2015: a regional climate change signal. Int. J. Climatol., 36: 4847-4861. https://doi.org/10.1002/joc.4673

Messori, G., et al. On the low-frequency variability of wintertime Euro-Atlantic planetary wave-breaking. Clim Dyn 52, 2431–2450 (2019). https://doi.org/10.1007/s00382-018-4373-2

Pithan, F., Shepherd, T. G., Zappa, G., and Sandu, I. (2016), Climate model biases in jet streams, blocking and storm tracks resulting from missing orographic drag, Geophys. Res. Lett., 43, 7231– 7240, doi:10.1002/2016GL069551.

Screen, J. Arctic amplification decreases temperature variance in northern mid- to highlatitudes. Nature Clim Change 4, 577–582 (2014). https://doi.org/10.1038/nclimate2268

Reply on RC3

Recommendation: suggested revision

Comments: This paper surveys current and recent literature describing the weather and climate implications of atmospheric blocking over the Euro-Atlantic sector. Temperature, hydrological, winds and compound anomalies are discussed, together with predictability and future climate projections.

It is widely recognized that blocking patterns drive surface weather anomalies but there are few papers that catalog many specific events that demonstrate their associations and this review paper is unique in that regard. On the other hand, the discussion of hazard types and case studies is sprawled over many disparate events and pertinent publications yet it is hard to grasp key points other than that each event is different (it was a laborious read). Certainly section 8 nicely summarizes the current state of the field and main challenges (I agree with all the points raised in that section), but instead of just laying them out in the conclusion, the authors can proactively structure the text to address some of these challenges.

Reply: We thank Noboru Nakamura for his positive and insightful review. We have tried to outline the difficulties and challenges of this area of research in the main text. In section 8, we summarize these challenges, but also address specific points that should be investigated in future research. Following the reviewers’ suggestions, these will be implemented during the revision. In addition, we will better motivate the individual sections and add some explanations and concluding statements.

For example:

• I think it is important to stress the importance of case studies at the beginning because (i) the sporadic nature of events hinders statistical analysis of data and (ii) there is a wide variety of weather extremes associated with the types and position of blocks

Reply: Thank you very much for this pertinent suggestion! We agree that the importance of case studies has not yet been sufficiently emphasized in the manuscript. Thus, we will take the reviewer’s suggestion and point it out already in the introduction.

• How one generally determines whether a surface event is related to blocking is probably worth discussion before diving into the list of case studies, even though this may reveal the main challenge of the field (metric dependence, etc).

Reply: We agree with this point and that this could be better captured in the text. We will therefore add a paragraph on how studies conclude that a blocking has had an impact on the development/formation of a surface weather extreme event.

• It would be useful to have a table (possibly in the supplementary material) that lists the notable events mentioned in this paper, with the dates, affected regions, the types of hazards, the association with the block according to the region specified in Figs.1 and 2, the phase of NAO, and the estimated damage/fatalities. (It is not easy to find an authoritative estimate of economic losses even remotely associated with blocking. The list will be an easy reference for scientists who search for past relevant events.)

Reply: That is a great idea. We will add such a table in the revised manuscript as an overview.

• If we have a list of events in the table mentioned above, perhaps Sections 3-5 may be shortened, highlighting only quintessential examples.

Reply: After the table has been compiled, we will carefully re-evaluated sections 3-5 and check where we can shorten the text.

Other points:

LL17-20 (also Section 3.1): I’m not sure about Europe, but in the US, heat waves on average kill more people annually than any other form of natural hazards: https://www.nrdc.org/sites/default/files/tracking-silent-killer-heat-health-fs.pdf (and many are demonstrably related to blocking). Since heat affects the population in otherwise cool climate the most, its potential danger may be stressed more.

Reply: Thanks for the comment. Also in Europe, heat waves are among the deadliest natural hazards, while storms and floods are among the costliest. We will add further information to the introduction and re-phrase the text to enhance clarity and details.

LL122-124: This reads like low PV air generated near the surface is advected upward. Is it what it implies? — I suspect latent heating can occur over a column of the troposphere; in that case it is the upward diabatic mass flux that ‘dilutes’ PV in the upper troposphere that leads to a negative PV anomaly (what gets advected from the boundary is mass, not PV)? (Hayne s and McIntyre 1987, JAS p.828 Fig.2)

Reply: Exactly, we do not want to imply that low PV air is just passively advected upward from the surface. We will reformulate the sentence accordingly. Methven (2013) investigated PV in WCB outflow in general and could show that the PV distribution within a WCB depends primarily on the net diabatic transport of mass.

LL128-133: Meridional displacement of PV is generally related to Rossby wave transience, but it can operate in different ways — feeding of transient Rossby waves from upstream is an important ingredient but the modulation of quasi-stationary Rossby waves by the remote (sub)tropical sources can be also important.

Reply: Thanks for this suggestion! We will add this statement to the text.

LL235-240: Does orography play any role at all (e.g. adiabatic heating associated with a foehn wind)?

Reply: Some studies have provided evidence that warming associated with foehn winds can play a role during heat waves (e.g. Ma et al. 2014). However, since our aim was not to describe the dynamic processes of heat waves in general, but rather to focus on the impact of blocking, we have excluded the information of the orographic effects in the manuscript.

LL254-259: Does the balance between radiative cooling and adiabatic warming (subsidence) play more prominent role in summer (in association with heat waves) when advection is weaker?

Reply: Yes, these mechanisms are more important during summer than in winter. In summer, heat waves can develop well underneath (blocking) anticyclones, as the short-wave radiation reaches the ground in an unhindered manner during daytime. In addition, there is adiabatic heating due to subsidence. The radiation-induced cooling then plays a role, especially at night, counteracting the warming through subsidence. As a result, there is a temperature drop during nighttime. However, this temperature drop can be very small - for example during tropical nights when the temperature nevertheless remains above 20 degrees.

LL349-359: I think droughts here largely refer to meteorological droughts, but there are other types of droughts (hydrological, agricultural, socioeconomic, and ecological) that could spawn from persistent blocking events and making that distinction may be useful.

Reply: Thank you for pointing this out. We will address the definition of droughts in the revision.

L482: One of the most exceptional drought —> One of the most exceptional droughts

Reply: We will correct this.

LL534-535: Record-breaking snowfall happened the northern part of the Alps —> Record-breaking snowfall happened in the northern part of the Alps

Reply: We will correct this.

L584: Costal storm surges —> Coastal storm surges

Reply: We will correct this.

L600: the presence of and a blocking system —> the the presence of a blocking system

Reply: We will correct this.

L624: power plants —> power outages (?)

Reply: We will replace “power plants” by “losses in power plant operation” as suggested.

LL630-637: The discussion in Section 6 focuses on short-term predictability. But climate models tend to underestimate blocking occurrences in the Euro-Atlantic sector. Does that mean that climate models also underpredict the frequency of extreme weather?

Reply: The representation of blocking systems in climate models was discussed in detail in the review by Woollings et al. (2018) and is therefore not dealt with in section 6. However, we do consider this topic in section 7, where we point out that it is not possible to transfer the possible trends in blocking frequency to the occurrence of weather extremes. This is partly because weather extremes can also develop without the influence of blocking. In addition, there are complex interactions on different space and time scales, which make it difficult to make statements about causal relationships under future climate conditions. Thus, one can expect that a change in the frequency of blockings will also have some impact on the occurrence of weather extremes – but there is not enough evidence now to quantify this effect.