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

Abstract

s previous all-time maximum temperature record dating back to 1937 was exceeded on 29 June by 5 K (Abraham, 2021;Philip et al., 2021). Although heat waves are expected to become hotter in a changing climate (Seneviratne et al., 2021) and the probability of record-breaking extremes with temperatures well above previous records will increase (Fischer et al., 2021), early attribution studies suggest that even under consideration of the current state of climate change, the temperatures of this event were extraordinarily unusual (Philip et al., 2021): the 2-m temperature anomaly with respect to the June to July climatological mean from 1979 to 2019 reached up to 20 K (Figure 1a). It is well-known that such extratropical heat waves are typically linked to persistent, quasi-stationary, strongly amplified, upper-level ridges that are embedded in extratropical Rossby waves (

Amplification of Chinook Heatwaves in a Warming Climate

“…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.…”

“…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 .…”

“…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.…”

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

“…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).…”

Warm conveyor belts as amplifiers of forecast uncertainty

“…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).…”