Legend

The special cases.

• Best month, where none is ideal: the least rainy of the months with the right temperature; where the temperature is never right, the least hot or the least cold (in the plain colour if it keeps its reason). Months within 1 °C and 1 rain day of the best tie.
• Mountains: the rain days of "often rainy" rise in a straight line from 500 to 2000 m of the cells, since in the mountains it rains more often, in showers.
• Skiing: the cells' temperature leaves out the months when the snow is only on the peaks (or is a glacier all year, as at Cervinia) and polar cold. The face stays the visit's (frost and rain count), but a month ideal for skiing is not among the months to avoid.
• Aurora: the oval follows the magnetic pole, so it reaches lower over North America than over Europe; it counts only in months with at most 14 hours of daylight. The climate tells how cloudy the sky is on average, not whether the evening will be clear or the sun active. The face stays the visit's (frost and dark count), but a month ideal for the aurora is not among the months to avoid. A month can be ideal for the aurora, for skiing and to visit at once (skiing never in the polar night).

Hurricanes, typhoons and cyclones (the same storm, named by ocean): a month is a contraindication when one passes within 300 km in at least 20 % of the years, with winds of at least 64 knots (tropical storms do not count), only for places within 50 km of the sea. IBTrACS tracks, 1980–2025.

• Simple shows month tiles; advanced shows the charts on wide screens and month rows on narrow ones.
• The tabs: temperature, rain, daylight, the sea (places on the coast) and snow (where a month reaches 1 cm on the ground).
• Every page opens on simple and temperature; nothing is remembered. Switching moves nothing else on the page.

• The mean covers every cell of the territory, weighted by area, not by population.
• The warning appears when the annual mean temperature spans 8 °C or more across the territory (10th to 90th percentile of the cells), when the area reaches 1,500,000 km², or when it spans 20° of latitude or more; its tooltip gives the figures.
• Below the mean come the panels of the three main cities, under the same reading switch and tab bar.

• At the top the rain icon, then the temperature in a coloured pill.
• The colour is that of the month's mean temperature.
• The big number is the maximum, the small one the minimum (means of the daily maxima and minima).
• Under the pill a flag for extreme heat, extreme cold or snow likely.
• Under 640 px the tiles become one row per month.

• One bar per month from the minimum to the maximum, shaded with the colours of the scale it crosses. The dark tick is the mean.
• No numbers on the chart: hovering a month lights its column and a chip under the axis gives minimum and maximum.
• The name of an ideal month is boxed.

• The icon is the same as on the temperature tile.
• The flag marks a month of torrential rain.
• Under 640 px the tiles become one row per month.

• The height is the rain days (at least 1 mm), on a fixed axis from 0 to 30: the taller the bar, the more often it rains.
• The width is the water of a rain day, the month's mm divided by its rain days: full from 15 mm a day up, never thinner than about an eighth, so drizzle still shows.
• Height times width is the month's mm: bars with the same area bring the same water, in a few heavy days or in many light ones.
• The colour is the month's rain on the precipitation scale, as in the simple reading and on the compare page.
• On hover: the month's mm, rain days and mm a day.
• The margins are those of the temperature chart, so the months line up.

• The same bars turned: the length is the rain days (0–30), the thickness the mm on a rain day, the colour the month's rain.
• On the right the month's mm and, under them, the days.

• The month's mean cloud cover (ERA5) splits the bar from sunrise to sunset: the yellow band in the middle is the share of daylight under a clear sky, (100 − cloud) %, the grey the rest.
• The band sits in the middle by convention: it does not say at what time the sky is clear.
• Hover for the percentage; on a phone it is written at the right of each row.

• One column per month, from 0 to 32 °C: the mean sea surface temperature near the place.
• The dashed line is at 22 °C, from which the water is warm enough for a swim.
• The title carries the name of the sea.
• Hover to read the value. On a phone it is one bar per month.

• In the «When to go» block a sentence on the sea, under the one on the best months: «Ideal for the sea: June–September», in teal. They are the months when the water is at 22 °C or more and the mean cloud cover at most 75 %, which leaves out the monsoon months; where there are none the sentence is left out. Hot air is no reason to stay away from the sea, so it can sit next to an «Avoid» of the bar. The same months get the «swimming» mark on the sea tiles (values rounded as shown). It has no face of its own: the bar is for the weather, the sea is one more sentence.
• The «sea» badge under «What is the climate like?» (Advanced reading) says how much warmer the water is than in the baseline period, with the same colours and the same test as the temperature badge; its colour thresholds are lower because the sea warms less than the land.

• Snow on the ground (Advanced reading only, and only where a month has at least 1 cm).
• The mean depth of the snow cover, month by month.
• The axis tops at the first value of the series 10, 25, 50, 100, 150, 250, 400, 800 cm that holds the snowiest month, so a dusting is not squashed next to a mountain town. The colours are not: they are fixed.
• Hover to read the value.
• On a phone it is one bar per month, under the cloud cover.
• It is the same measure as the “good for skiing” rule of the “When to go?” bar.

• Cities, advanced reading: sunrise and sunset in local time, in the chart below (rows on narrow screens), with the sky.
• Countries and regions have no sunrise and sunset: the tiles in both readings, with the mean daylight over the territory.

• Wide screens: the hours of the day go up the axis; a grey bar runs from sunrise to sunset, with the yellow clear-sky band in the middle (see Cloud cover).
• Narrow screens: one row per month over the 24 hours (ticks at 6, 12 and 18), with the same bar; on the right the daylight hours and the cloud cover.
• Polar night: no bar. Midnight sun: a full bar.
• The values come on hover.

• Base: mean cloud cover (ERA5) picks clear, partly cloudy, mostly cloudy or overcast.
• Marks: rain days (ERA5-Land days with at least 1 mm, corrected with CRU TS) pick how many, 1, 2 or 3 drops.
• Intense rain: at least 15 mm per rain day (few days, lots of water). The marks are lightning, 1 to 3 by the month's mm, and they win over drops.
• Cold: with a mean temperature up to 0 °C the marks are snowflakes.
• The marks are added to the base, they do not replace it. A clear sky has no marks: a month with under 35 % cloud and rain takes the next base (partly cloudy), because a sun with rain or lightning makes no sense.

• Maps of countries and regions, «Climate zones» tab (the one they open on): every point falls in one of fifteen classes.
• Across: the mean temperature of the season (five bands, from freezing to torrid).
• Up: its mean monthly precipitation (three bands).
• The colour is bivariate: the hue tells the temperature (freezing indigo, cold blue, mild grey-green, hot ochre, torrid terracotta), the darkness the precipitation (dry pale, wet dark).
• The thresholds are fixed, so a colour means the same climate everywhere.
• The outer bands (under 0 °C and from 28 °C) tell the most extreme places apart: Sicily in summer is “Hot, arid”, Senegal in spring “Torrid, arid”; Siberia in winter is “Freezing, dry”, Oslo “Freezing” or “Cold” by season. The wet extreme zones are very rare and merge with their neighbours.

• Temperature: how much warmer the annual mean is than in 1961–1990. Pale ochre under 1 °C, orange between 1 and 2, red over 2, blue if cooler.
• Rain: how much the annual total changed, in %. Blue wetter, sand drier.
• Rain days: how much the days with at least 1 mm in a year changed, in %. Blue more days, sand fewer.
• Snow: how much the mean depth in winter changed (December–February north of the equator, June–August south of it), in %. Pale blue more snow, sand less. Shown only where the winter of the reference period had at least 2 cm of snow.
• Grey with ≈: the difference lies within the year-to-year variability (the test is in part 2).
• The full sentence is in the tooltip.

• Temperature of each year: one stripe per year since 1950, coloured by how much warmer (red) or colder (blue) the year was than the 1961–1990 mean. Sixteen colours, one every 0.3 °C, from −2.4 to +2.4 °C; beyond, a colour of its own, wine for warm and night blue for cold: the year is off the scale. The scale is the same for every city: the same red is the same warming everywhere.
• Rain of each year: how much more (blue) or less (sand) it rained than the 1961–1990 mean, in %, on a fixed axis of ±100 %.
• On narrow screens the years of the rain run from top to bottom, one row per year.

• Under the name of a country, a region or a city, when foreign ministries advise against going. The advice is for the whole country and holds for all its places. A click opens who gives it, the date of the check and the link to the UK Foreign Office advice for the country.
• No label does not mean the country is safe: only that the sources do not advise against the whole country. Many countries have areas advised against that do not show here.

• Sea: the page background, no marks. Land of the place: a light tone.
• Neighbouring countries (for a region, the other regions of its country too): grey, fading towards the edges. On wide screens they link to their pages, lit on hover.
• Regions: a thin border. Cities: dots with their name (on country maps the name of a city with no room appears on hover).
• Tabs above the map: the climate zones (on opening), or the maximum or minimum temperature or the precipitation of the chosen season, with a colour bar marking the season's range and the relief shaded over it. The maps do not depend on the simple or advanced reading.
• Continents show only the borders of their countries.

• To visit: the month is ideal on the place's own page (the green face).
• Sea: water at 22 °C or more and mean cloud cover up to 75 %.
• Snow: at least 40 cm of snow on the ground, a month ideal for skiing.
• Aurora: a month recommended for the aurora.

• The colour is that of the choice: green to visit, teal for the sea, lilac for snow, fuchsia for the aurora; the key here shows the green.
• Five classes, from the land's grey (none) to the full colour; a share and not a count, so a big country does not lead by its size.
• A click (a tap on narrow screens) on a country opens its page.

• Temperature: maximum over minimum, in the colour of the mean.
• Rain: the month's millimetres on the precipitation scale, the rain days under them.
• Daylight: the hours of daylight on the 15th, rounded (the exact time in the tooltip), on the daylight scale, the cloud cover under them.
• Wide screens: a row per place; narrow screens: a column per place and a row per month.