ABSTRACT Severe damage was caused by a flooding event across eastern Canada during the first week of May 2017. Thousands of residences were affected, and many people were evacuated from their homes in southern Quebec and eastern Ontario. This event was mainly caused by persistent heavy rainfall during that week. In this study, the ability to make a useful prediction of this flooding event about two weeks in advance is assessed for 11 subseasonal-to-seasonal prediction models. It is found that the above-normal precipitation in eastern Canada during the week of 1–7 May was predicted by most of the models a few weeks in advance although the forecast anomaly was, in general, weaker than observed. These models also predicted a high probability of extreme precipitation. Analysis of the atmospheric circulation pattern associated with the flooding event revealed a wave train of 500 hPa geopotential height anomaly along mid-latitudes from the North Pacific across North America to the North Atlantic, which sets up a favourable environment for strong water vapour transport from the Gulf of Mexico and the western Atlantic to eastern Canada. Most models were able to predict this wave train. We found that this flooding event is likely connected to the tropical Madden–Julian Oscillation (MJO) through atmospheric teleconnections. During the week of 24–30 April the MJO was observed to be in phase 7 with enhanced convection in the western-central Pacific. A numerical experiment was conducted using a linear model with specified tropical diabatic heating similar to MJO phase 7. The resulting 500 hPa geopotential height response has many similarities to the observed wave train that was responsible for the flooding event.

中文翻译：

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2017 年加拿大东部洪水及其次季节预测

摘要 2017 年 5 月的第一周，加拿大东部发生了洪水事件，造成严重破坏。数以千计的住宅受到影响，许多人从魁北克南部和安大略省东部的家中撤离。该事件主要是由于当周持续的强降雨造成的。在这项研究中，评估了 11 个亚季节到季节预测模型能够提前大约两周对这次洪水事件做出有用预测的能力。发现5月1-7日这一周加拿大东部的降水高于正常水平是大多数模型提前几周预测的，尽管预测的异常通常比观察到的要弱。这些模型还预测了极端降水的高概率。对与洪水事件相关的大气环流模式的分析表明，从北太平洋穿过北美到北大西洋，沿中纬度存在 500 hPa 位势高度异常的波列，这为来自北太平洋的强水汽输送创造了有利环境。墨西哥湾和西大西洋至加拿大东部。大多数模型都能够预测这个波列。我们发现这次洪水事件很可能通过大气遥相关与热带马登-朱利安振荡 (MJO) 相关联。在 4 月 24 日至 30 日这一周，观测到 MJO 处于第 7 阶段，中西太平洋对流增强。使用类似于 MJO 阶段 7 的具有指定热带非绝热加热的线性模型进行了数值实验。