Trends in weather type frequencies across North America

Abstract

While 20th century changes in many individual meteorological variables are well documented, the trends in multivariate synopticscale air masses-or weather types-largely remain unexplored. Utilizing a recently developed gridded weather typing classification system, this research investigates the changes in the frequency of weather types (WTs) across North America, 1979America, -2017. Averaged across the study domain as a whole, Humid Warm WTs are occurring 22 more days per year, while Dry Warm WTs have increased by 10 days/year. These increases are offset mostly by decreased frequency of Dry Cool (−17 days/year) and Cool WTs (−21 days/year). The largest absolute changes are in the Canadian Archipelago, where the Warm WT is occurring 42 more days/year and the Cool WT is occurring 48 fewer times per year. In western Canada all humid types are occurring more frequently, including a Humid Cool type that is occurring 16 more days/year. The Desert Southwest US and northern Mexico show significant increases in Dry Warm WTs (+33 to +40 days/year). Cold front and warm front passages show increases in most of the US and decreases in most of Canada. Describing these secular changes to the frequency of intuitive weather types may be an effective means of communicating these climate trends to policymakers and the general public, especially considering their large magnitude.

Examining trends in multiple parameters of seasonally‐relative extreme temperature and dew point events across North America

“…Though little research explicitly examines trends in extreme humidity events, these general changes in the various aspects of extreme dew point events are largely in agreement with previous research that suggests a warming atmosphere will accommodate additional absolute water vapour (Wentz et al, 2007) – implying a general increase in XHEs and decreased XDEs. This research also supports the spatial patterns of the trends in various humidity variables that are noted elsewhere, such as the trend towards drying (and increased XDEs) conditions in the desert regions of southwestern North America along with increased humidity (and XHEs) generally found elsewhere (Lee and Sheridan, 2018; Willet et al, 2008).…”

“…Interestingly, a large portion of the western United States is seeing increases in XCEs in autumn. While this result contradicts the overarching direction of trends, similar trends in cold weather have been noted in previous research (e.g., Lee and Sheridan, 2018), are projected to happen into the future (Vavrus et al, 2006), and have even been projected to occur slightly more frequently in the coming decades for some areas of the western United States (Kodra et al, 2011). Nonetheless, this result warrants further examination.…”

“…Of particular note is the summer in the western United States, where both XDEs (dry) and XWEs (hot) are increasing in frequency in areas already prone to large wildfires, with both types of events also showing significantly increasing durations. Previous research (Lee and Sheridan, 2018;Knight et al, 2008;Kalkstein et al, 1998) has noted the relative increase of concurrently hot and dry weather in these areas already stressed by growing populations and a limited water supply. Further, both hot (XWEs) and humid (XHEs) events in autumn are also occurring substantially more frequently across much of the eastern half of the continent (especially eastern Canada), as well as becoming significantly longer.…”

The gridded weather typing classification version 2: A global‐scale expansion

“…While the usefulness of a dataset is largely unpredictable upon its initial development, there are many potential future applications of the GWTC‐2. The GWTC‐1 has been used in three previous applications: looking at connections to cardiovascular‐related mortality in various US cities (Lee, ), relationships with teleconnection and oscillation phases (Lee, ), and examining multi‐decadal trends in the climate system (Lee and Sheridan, ); and it is currently being used to examine water clarity in the Great Lakes (Great Lakes KDI, ). Each of these applications could be undertaken with the GWTC‐2 as well.…”

Environmental Hazards: A Coverage Response Approach

“…Thus additional questions arise as to the functionalities of Smart Systems in the advance education, preparation, and warning process. When facing increasing environmental hazards in large population areas [31], the combination of public responses to perceived harm [32]-regardless of the frequency, recurrence, or intensity of a particular hazard [33,34]-creates uncertainty when applied to locations with specific yet variable characteristics.…”