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Abstract Wind chill temperature (WCT) is a widely recognized biometeorological variable that quantifies atmospheric conditions that have consequential impacts on many aspects of society, especially human health through exposure to winter conditions that can result in hypothermia, frostbite, and cardiorespiratory mortality. The spatial and temporal variations in WCT and extreme WCT (E WCT) (coldest 1%) were examined using hourly surface measurements collected at 133 stations across Canada and the United States during 40 winters (1979/80–2018/19). Most locations experienced an overall warming in both mean and extreme WCTs. The most substantial and statistically significant warming of mean WCT occurred across Alaska and the Canadian Northwest Territories with values of +3.2° to +6.4°C during the 40-winter time period. Statistically significant warming of mean WCT also occurred along the East Coast of Canada and the United States, as well as across the southeastern United States. Extreme WCT was found to be 10°–30°C colder than the mean WCT, and generally, the extreme WCT warmed at a greater rate than the mean WCT at locations. For example, extreme WCT warmed as much as +10.4°C during the 40-winter time period across portions of Alaska and the Canadian Northwest Territories. Warming air temperatures were found to have a large relative contribution to warming of mean and extreme WCTs with a smaller contribution coming from decreasing wind speeds (WS). 

Abstract An investigation of lake effect (LE) and the associated synoptic environment is presented for days when all five lakes in the Great Lakes (GL) region had LE bands [five-lake days (5LDs)]. The study utilized an expanded database of observed LE clouds over the GL during 25 cold seasons (October–March) from 1997/98 to 2021/22. LE bands occurred on 2870 days (64% of all cold-season days). Nearly a third of all LE bands occurred during 5LDs, although 5LDs consisted of just 17.1% of LE days. A majority of 5LDs (56.5%) had lake-to-lake (L2L) bands, and these days comprised 43.5% of all L2L occurrences. 5LDs occurred with a mean of 26.1 (SD = 6.2) days per cold season until 2008/09 and then decreased to a mean of 13.8 (SD = 5.5) days during subsequent cold seasons. January and February had the largest number of consecutive LE days in the GL with a mean of 5.7 and 5.4 days, respectively. As the number of consecutive LE days increases, both the number of 5LDs and the occurrence of consecutive 5LD increase. This translates to an increased potential of heavy snowfall impacts in multiple, localized areas of the GL for extended time periods. The mean composite synoptic pattern of 5LDs exhibited characteristics consistent with lake-aggregate disturbances and showed similarity to synoptic patterns favorable for LE over one or two of the GL found by previous studies. The results demonstrate that several additional areas of the GL are often experiencing LE bands when a localized area has active LE bands occurring. 

Abstract Adverse weather has been shown to be spatially and temporally variable across high‐latitude locations. The current study provides a unique investigation of limited surface visibility time periods at five coastal Greenland locations from 1979 to 2018 and identifies the coincident adverse weather, as well as the local and large‐scale atmospheric conditions during limited surface visibility time periods. Locations on the east coast of Greenland have the largest percentage of hours with limited visibility each month with maxima during February. Western and southern coastal locations have fewer occurrences of limited visibility. Warm‐season maxima are present in the northern locations, while warm‐season minima occur at all other locations. Fog is reported during each month at all five stations, however, a substantial increase of hours occurs at the northern and eastern stations during the typical melt season on Greenland. There is a seasonal difference in the percent of limited visibility hours linked to precipitation with a minimum in the warm season and maximum across the cold season. Limited visibility attributed to precipitation generally has the largest percentage of hours each month except for the northern and eastern locations during the melt season. The location and number of cyclonic circulations, as well as the spatial scale of troughs, across northeastern Canada and the North Atlantic Ocean greatly influence the adverse weather linked to prolonged limited surface visibility events. Limited visibility events at Thule, Greenland during both the warm and cold seasons are largely influenced by the presence and intensity of a cyclone over northeastern Canada. At Danmarkshavn, Greenland limited visibility events in both seasons generally have a cyclone positioned to the east, an area of higher pressure over Greenland and a cyclone positioned to the west of Greenland. 

Abstract Lake-effect precipitation is convective precipitation produced by relatively cold air passing over large and relatively warm bodies of water. This phenomenon most often occurs in North America over the southern and eastern shores of the Great Lakes, where high annual snowfalls and high-impact snowstorms frequently occur under prevailing west and northwest flow. Locally higher snow or rainfall amounts also occur due to lake-enhanced synoptic precipitation when conditionally unstable or neutrally stratified air is present in the lower troposphere. While likely less common, lake-effect and lake-enhanced precipitation can also occur with easterly winds, impacting the western shores of the Great Lakes. This study describes a 15-year climatology of easterly lake-effect (ELEfP) and lake-enhanced (ELEnP) precipitation (conjointly Easterly Lake Collective Precipitation: ELCP) events that developed in east-to-east-northeasterly flow over western Lake Superior from 2003 to 2018. ELCP occurs infrequently but often enough to have a notable climatological impact over western Lake Superior with an average of 14.6 events per year. The morphology favors both single shore-parallel ELEfP bands due to the convex western shoreline of Lake Superior and mixed-type banding due to ELEnP events occurring in association with “overrunning” synoptic-scale precipitation. ELEfP often occurs in association with a surface anticyclone to the north of Lake Superior. ELEnP typically features a similar northerly-displaced anticyclone and a surface cyclone located over the U.S. Upper Midwest that favor easterly boundary-layer winds over western Lake Superior. 

Abstract Atmospheric rivers (ARs) are a frequently studied phenomenon along the West Coast of the United States, where they are typically associated with the heaviest local flooding events and almost one-half of the annual precipitation totals. By contrast, ARs in the northeastern United States have received considerably less attention. The purpose of this study is to utilize a unique visual inspection methodology to create a 30-yr (1988–2017) climatology of ARs in the northeastern United States. Consistent with its formal definition, ARs are defined as corridors with integrated vapor transport (IVT) values greater than 250 kg m −1 s −1 over an area at least 2000 km long but less than 1000 km wide in association with an extratropical cyclone. Using MERRA2 reanalysis data, this AR definition is used to determine the frequency, duration, and spatial distribution of ARs across the northeastern United States. Approximately 100 ARs occur in the northeastern United States per year, with these ARs being quasi-uniformly distributed throughout the year. On average, northeastern U.S. ARs have a peak IVT magnitude between 750 and 999 kg m −1 s −1 , last less than 48 h, and arrive in the region from the west to southwest. Average AR durations are longer in summer and shorter in winter. Further, ARs are typically associated with lower IVT in winter and higher IVT in summer. Spatially, ARs more frequently occur over the Atlantic Ocean coastline and adjacent Gulf Stream waters; however, the frequency with which large IVT values are associated with ARs is highest over interior New England.