(°C) of the warmest month X5 = winter factor expressed in terms of (0 °C – X1)Rjan where Rjan represents the rainfall in January expressed in mm X6 = mean maximum snow depth in terms of S/(S+a) where a=25.4 if S is in millimeters and a=1 if S is in inches X7 = maximum wind gust in (km/hr) in 30 years. For practical purposes, Canada has adopted the American hardiness zone classification system. The 1990 version of the USDA Plant Hardiness Zone Map included Canada and Mexico, but they were removed with the 2012 update to focus on the United States and Puerto Rico. The Canadian government publishes both Canadian and USDA-style zone maps. European hardiness zones Selected European cities The table below provides USDA hardiness zone data for selected European cities: Britain and Ireland USDA zones do not work particularly well in the UK as they are designed for continental climates and subtropical climates. The high latitude, weaker solar intensity, and cooler UK summers must be considered when comparing to US equivalent. New growth may be insufficient or fail to harden off affecting winter survival in the shorter and much cooler UK summers. Owing to the moderating effect of the North Atlantic Current on the Irish and British temperate maritime climate, Britain, and Ireland even more so, have milder winters than their northerly position would otherwise afford. This means that the USDA hardiness zones relevant to Britain and Ireland are quite high, from 7 to 10, as shown below. In 2012 the United Kingdom's Royal Horticultural Society introduced new hardiness ratings for plants, not places. These run from H7, the hardiest (tolerant of temperatures below ) to H1a (needing temperatures above ). The RHS hardiness ratings are based on absolute minimum winter temperatures (in °C) rather than the long-term average annual extreme minimum temperatures that define USDA zones. Scandinavia and Baltic Sea Region Scandinavia lies at the same latitude as Alaska or Greenland, but the effect of the warm North Atlantic Current is even more pronounced here than it is in Britain and Ireland. Save for a very small spot near Karasjok, Norway, which is in zone 2, nowhere in the Arctic part of Scandinavia gets below zone 3. The Faroe Islands, at 62–63°N are in zone 8, as are the outer Lofoten Islands at 68°N. Tromsø(, a coastal city in Norway at 70°N, is in zone 7, and