Everything Hits at Once: How Remote Rainfall Matters for the Prediction of the 2021 North American Heat Wave

Oertel, Annika; Pickl, Moritz; Quinting, Julian; Hauser, Seraphine; Wandel, Jan; Magnusson, Linus; Balmaseda, Magdalena; Grams, Christian M.

doi:10.1029/2022gl100958

Cited by 14 publications

(20 citation statements)

References 66 publications

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“…For other times, trajectory analysis produced similar results with the majority of trajectories originating below the 800 hPa level. features 13,16,19 . Here I emphasize the pattern of ascent followed by descent, consistent with Chinook flow, as a mechanism for the extreme heat of the lower-tropospheric air mass.…”

Section: Resultsmentioning

confidence: 99%

“…The June 2021 Western North American heatwave was responsible for hundreds, perhaps thousands, of fatalities in the province of British Columbia and the states of Washington and Oregon 8 . Numerous studies have described the meteorological and climatological aspects of this event [9][10][11][12][13][14][15][16][17][18][19][20][21] . These studies analyze large-scale circulation patterns preceding the heatwave event 9,15 and the mechanisms leading to amplification of the associated blocking ridge, with an emphasis on upstream diabatic processes 13,19 .…”

Section: Introductionmentioning

confidence: 99%

“…Numerous studies have described the meteorological and climatological aspects of this event [9][10][11][12][13][14][15][16][17][18][19][20][21] . These studies analyze large-scale circulation patterns preceding the heatwave event 9,15 and the mechanisms leading to amplification of the associated blocking ridge, with an emphasis on upstream diabatic processes 13,19 . Mo et al (2022) 16 clarify the role of an unusual late-season atmospheric river in building the upper-level ridge but stop short of emphasizing a Chinook-or Foehn-type mechanism for extreme lower-tropospheric heat.…”

Section: Introductionmentioning

confidence: 99%

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Amplification of Chinook Heatwaves in a Warming Climate

Lackmann¹

2023

Preprint

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A category of dynamically forced warm-season heat events are associated with Chinook (or foehn) flows in the vicinity of substantial topography. Latent warming of such flows exhibits exponential dependence on temperature, which for warm-season events, can result in extreme heat. The June 2021 Western North American heatwave event featured air trajectories that experienced latent warming over the Gulf of Alaska and during orographic ascent in coastal regions of Southeast Alaska. Thermodynamic analysis of air trajectories demonstrates that a Chinook-type mechanism can explain the extreme lower-tropospheric warmth in coastal regions of the Pacific Northwest and British Columbia. Using projected end-of-century warming values for the trajectory source region, thermodynamic analysis and model simulations indicate that Chinook warming amplification of up to 75% would occur. This additional warming is driven by exponential growth of latent warming, a formidable amplifier of climate warming for this class of topographically forced heat events.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Amplification of Chinook Heatwaves in a Warming Climate

Lackmann¹

2023

Preprint

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“…This heatwave shattered the long‐standing Canadian temperature record by a margin of 4.6°C, and local temperature measurements exceeded previous long‐term records by several degrees centigrade even 1 month before temperatures usually peak in this area (Philip et al., 2022). Both the unprecedented event intensity (Thompson et al., 2022) and the severe impacts with several hundred reported excess deaths (Henderson et al., 2022) stimulated exceptional scientific interest in the meteorological drivers (Bartusek et al., 2022; Mo et al., 2022; Neal et al., 2022; Qian et al., 2022; Schumacher et al., 2022; Wang et al., 2023) and the predictability (Emerton et al., 2022; Lin et al., 2022; Oertel et al., 2023).…”

Section: Introductionmentioning

confidence: 99%

The Effect of a Short Observational Record on the Statistics of Temperature Extremes

Zeder,

Sippel,

Pasche

et al. 2023

Geophysical Research Letters

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In June 2021, the Pacific Northwest experienced a heatwave that broke all previous records. Estimated return levels based on observations up to the year before the event suggested that reaching such high temperatures is not possible in today's climate. We here assess the suitability of the prevalent statistical approach by analyzing extreme temperature events in climate model large ensemble and synthetic extreme value data. We demonstrate that the method is subject to biases, as high return levels are generally underestimated and, correspondingly, the return period of low‐likelihood heatwave events is overestimated, if the underlying extreme value distribution is derived from a short historical record. These biases have even increased in recent decades due to the emergence of a pronounced climate change signal. Furthermore, if the analysis is triggered by an extreme event, the implicit selection bias affects the likelihood assessment depending on whether the event is included in the modeling.

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“…Therefore, systematic evaluations of WCBs in forecast data sets and their role for forecast uncertainty are very rare, and most studies either choose a case study approach (e.g. Joos and Forbes, 2016; Grams et al ., 2018; Berman and Torn, 2019; Oertel et al ., 2023) and/or use Eulerian metrics to quantify the impact of WCBs on the upper‐level flow indirectly (e.g. Baumgart and Riemer, 2019; Sánchez et al ., 2020).…”

Section: Introductionmentioning

confidence: 99%

Warm conveyor belts as amplifiers of forecast uncertainty

Pickl

Quinting

Grams

2023

Quart J Royal Meteoro Soc

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Warm conveyor belts (WCBs) are rapidly ascending air streams associated with extratropical cyclones. WCBs exert a substantial influence on the evolution of the large‐scale midlatitude flow and have previously been related to increased forecast uncertainty in case studies. This study provides a first systematic investigation of the role of WCBs for errors in medium‐range ensemble forecasts in the Atlantic‐European region. The study is enabled through a unique data set allowing for a Lagrangian detection of WCBs in three years of operational ensemble forecasts from the European Centre for Medium‐Range Weather Forecasts. By analysing the relationship between commonly used error metrics of variables that characterise the large‐scale flow and WCBs, the study aims to shed light on the question to what extent WCBs act as a source of forecast errors and as an amplifier of pre‐existing errors in a state‐of‐the‐art global operational numerical weather prediction model.We show that forecasts with high WCB activity are on average characterised by an amplified Rossby wave pattern and anticyclonic flow anomalies downstream. We find that the forecast skill is generally reduced when the WCB activity is high, and that WCB activity is particularly increased when the error growth is largest. To establish a causal relationship, we employ two composite approaches. The first focuses on the time of largest error growth and the second calculates normalised forecast error fields centered on WCB objects. Both approaches yield a consistent picture: anomalously high errors are initially associated with mis‐representations of an upstream trough. In regions of WCB ascent and outflow the errors grow rapidly in terms of magnitude and scale and are projected to the upper‐level large‐scale circulation. We also find indications that WCBs can cause errors even when the upstream flow is well represented. Notwithstanding, evidence is robust for WCBs acting as amplifier of forecast uncertainty.This article is protected by copyright. All rights reserved.

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Everything Hits at Once: How Remote Rainfall Matters for the Prediction of the 2021 North American Heat Wave

Cited by 14 publications

References 66 publications

Amplification of Chinook Heatwaves in a Warming Climate

Amplification of Chinook Heatwaves in a Warming Climate

The Effect of a Short Observational Record on the Statistics of Temperature Extremes

Warm conveyor belts as amplifiers of forecast uncertainty

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