This report describes the historical weather record at the Tromsø Airport (Tromsø, Norway) during the last 12 months. This station has records back to January 1973.

Tromsø has a humid subarctic continental climate with cool summers and no dry season. The area within 25 mi of this station is covered by tundra (47%), oceans and seas (36%), and forests (14%)

Daylight saving time (DST) was observed at Tromsø during the last 12 months. There were two time changes during the last 12 months:

2013 is not a leap year, so it has 365 days and no February 29th. The first leap year before 2013 was 2012 and the first after will be 2016.

The summer and winter solstices and the spring and fall equinoxes mark the passing of the seasons. They fall on nearly the same day each year, with differences of a day or two depending on the year. In 2013 they occurred on:

The hottest day of the last 12 months was July 13, with a high temperature of 70°F. For reference, on that day the average high temperature is 58°F and the high temperature exceeds 68°F only one day in ten. The hottest month of the last 12 months was July with an average daily high temperature of 56°F.

Relative to the average, the hottest day was May 17. The high temperature that day was 64°F, compared to the average of 46°F, a difference of 18°F. In relative terms the warmest month was May, with an average high temperature of 50°F, compared to an typical value of 46°F.

The longest warm spell was from November 14 to November 26, constituting 13 consecutive days with warmer than average high temperatures. The month of May had the largest fraction of warmer than average days with 68% days with higher than average high temperatures.

Temperature

The daily low (blue) and high (red) temperature during the last 12 months with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is red where both the daily high and low are above average, blue where they are both below average, and white otherwise.

The coldest day of the last 12 months was April 9, with a low temperature of 9°F. For reference, on that day the average low temperature is 27°F and the low temperature drops below 18°F only one day in ten. The coldest month of the last 12 months was March with an average daily low temperature of 20°F.

Relative to the average, the coldest day was April 9. The low temperature that day was 9°F, compared to the average of 27°F, a difference of 18°F. In relative terms the coldest month was March, with an average low temperature of 20°F, compared to an typical value of 24°F.

The longest cold spell was from March 1 to March 17, constituting 17 consecutive days with cooler than average low temperatures. The month of March had the largest fraction of cooler than average days with 74% days with lower than average low temperatures.

The longest freezing spell was from November 28 to December 18, constituting 21 consecutive days with temperatures strictly below freezing.

Hourly Temperature Bands

The full year of hourly temperature reports with the days of the year on the horizontal and the hours of the day on the vertical. The hourly temperature measurement is color coded into meaningful temperature bands: frigid is purple (below 15°F), freezing is blue (15°F to 32°F), cold is dark green (32°F to 50°F), cool is light green (50°F to 65°F), comfortable is yellow (65°F to 75°F), warm is light red (75°F to 85°F), hot is medium red (85°F to 100°F), sweltering is dark red (above 100°F), and missing data is pink.

The clearest month of the last 12 months was December, with 48% of days being more clear than cloudy. The longest spell of clear weather was from October 29 to November 4, constituting 7 consecutive days that were clearer than they were cloudy.

Cloud Coverage

The fraction of time spent in each of the five sky cover categories over the course of the last 12 months on a daily basis. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data. The bar at the top of the graph is gray if the sky was cloudy or mostly cloudy for more than half the day, blue if it is clear or mostly clear for more than half the day, and blue-gray otherwise.

The cloudiest month of the last 12 months was July, with 87% of days being more cloudy than clear. The longest spell of cloudy weather was from July 14 to August 1, constituting 19 consecutive days that were cloudier than they were clear.

Hourly Cloud Coverage

The full year of hourly cloud coverage reports with the days of the year on the horizontal and the hours of the day on the vertical. The sky cover is color coded: from most blue to most gray, the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

This station provides hourly reports of significant weather events at and around the station, but does not report the quantity of precipitation at the station itself. This is common for weather stations located outside of the United States, and for a small subset of stations in the United States that are located at lesser used and smaller airports.

Present Weather Reports

This station reports when significant weather events (including precipitation) are visually observed at or near the station. Such events do not always correspond to measured quantities of liquid equivalent precipitation, such as when the event is near by not at the station, or in the case of solid precipitation that does not melt in the collection basin.

The day in the last 12 months with the most precipitation observations was February 25. There were 24 hourly weather reports that day (out of a maximum of 24) in which some form of precipitation was observated at or near the station. The month with the most precipitation observations was March, with 274 hourly present weather reports involving some form of precipitation.

Precipitation Reports

The daily number of hourly observed precipitation reports during the last 12 months, color coded according to precipitation type, and stacked in order of severity. From the bottom up, the categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); and drizzle (lightest green). Not all categories are necessarily present in this particular graph. The faint shaded areas indicate climate normals. The bar at the top of the graph is green if any precipitation was observed that day and white otherwise.

As determined by the present weather reports, the longest dry spell was from August 12 to August 21, constituting 10 consecutive days with no observed precipitation. The month with the largest fraction of days without observed precipitation was August, with 55% of days reporting no observed precipitation at all.

The month with the largest fraction of days with at least some observed precipitation was March, with 84% of days reporting some observed precipitation.

Hourly Weather Reports

The full year of hourly present weather reports with the days of the year on the horizontal and the hours of the day on the vertical. The color-coded categories are thunderstorms (orange); heavy, moderate, and light snow (dark to light blue); heavy, moderate, and light rain (dark to light green); drizzle (lightest green); freezing rain and sleet (light and dark cyan); snow grains (lightest blue); hail (red); fog (gray); and haze (brownish gray).

Liquid Precipitation Reports

In this section we consider only those weather reports that indicate liquid precipitation. For the purposes of this analysis, we include thunderstorms even though some thunderstorms are not accompanied by liquid precipitation.

The month of the last 12 months with the largest number of those reports was July, with a total of 174 reports. The day with the largest number of those reports was February 25, with a total of 22 reports.

Liquid Precipitation Reports

The daily number of hourly observed liquid precipitation reports (including thunderstorms) during the last 12 months, with climate normals (faint shaded areas). The bar at the top of the graph is green if any liquid precipitation was observed that day and white otherwise.

This station reports both when snow is observed to be falling and the measured depth of the snow on the ground. Both are subject to erroneous reports, but the latter is significantly less reliable. Please bear this in mind when reading this section.

Reports

In this section we consider hourly weather reports that contain an observation of falling snow. These reports do not necessarily correspond to accumulation.

The first reported snow fall in the last 12 months was on May 28; the last was on May 8. The month of the last 12 months with the largest number of those reports was March, with a total of 268 reports. The day with the largest number of those reports was March 28, with a total of 21 reports.

Snow Reports

The daily number of hourly observed snow reports during the last 12 months, with climate normals (faint shaded areas). The bar at the top of the graph is blue if there was snow fall observed that day and white otherwise.

Depth

Snow depth on the ground is an optional and inconsistently reported part of standard weather reports. It is rarely reported more often than every six hours, it is often skipped, it is often reported erroneously, and a snow depth of zero is normally not distinguished from a missing report. These issues (particularly the last one) make it hard to collect statistics on snow depth with any confidence. To overcome this issue, we base our statistics on only those reports with present non-zero measurements of snow depth. Reports that fail to mention snow that is present, and reports that do not report snow depth because there is no snow on the ground are excluded because they cannot be distinguished from one another.

The first reported accumulation in the last 12 months was on October 26. The last day of the snow season with snow reported on the ground was December 29. The day with the deepest snow depth was October 26, with an average snow depth of 7.9" over the course of the day. The longest stretch of time during which there was always snow on the ground was from November 12 to November 17 (6 consecutive days).

Snow Depth

Snow depth on the ground (thick blue line) during the last 12 months with median value of non-zero reports from previous years (thick faint gray line), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile). The bar at the top of the graph is blue if there was snow on the ground that day and white otherwise.

Humidity is an important factor in determining how weather conditions feel to a person experiencing them. Hot and humid days feel even hotter than hot and dry days because the high level of water content in humid air discourages the evaporation of sweat from a person's skin.

When reading the graph below, keep in mind that the hottest part of the day tends to be the least humid, so the daily low (brown) traces are more relevant for understanding daytime comfort than the daily high (blue) traces, which typically occur during the night. Applying that observation, the least humid month of the last 12 months was May with an average daily low humidity of 50%, and the most humid month was January with an average daily low humidity of 73%.

But it is important to keep in mind that humidity does not tell the whole picture and the dew point is often a better measure of how comfortable a person will find a given set of weather conditions. Please see the next section for continued discussion of this point.

Humidity

The daily low (brown) and high (blue) relative humidity during the last 12 months with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Dew point is the temperature below which water vapor will condense into liquid water. It is therefore also related to the rate of evaporation of liquid water. Since the evaporation of sweat is an important cooling mechanism for the human body, the dew point is an important measurement for understanding how dry, comfortable, or humid a given set of weather conditions will feel.

Generally speaking, dew points below 50°F will feel a bit dry to some people, but comfortable to people accustomed to dry conditions; dew points from 50°F to 68°F are fairly comfortable to most people, and dew points above 68°F are increasingly uncomfortable, becoming oppressive around 77°F.

To take some examples, and basing our categorization on the daily high dew point in the last 12 months, June had 30 dry days, no comfortable days, and no humid days; September had 30 dry days, no comfortable days, and no humid days; December had 31 dry days, no comfortable days, and no humid days; and March had 31 dry days, no comfortable days, and no humid days.

Dew Point

The daily low (blue) and high (red) dew point during the last 12 months with the area between them shaded gray and superimposed over the corresponding averages (thick lines), and with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

The highest sustained wind speed was 48 mph, occurring on May 27; the highest daily mean wind speed was 26 mph (May 27); and the highest wind gust speed was 67 mph (May 27).

The windiest month was May, with an average wind speed of 13 mph. The least windy month was September, with an average wind speed of 7 mph.

Wind Speed

The daily low and high wind speed (light gray area) and the maximum daily wind gust speed (tiny blue dashes).

Visibility is the maximum distance at which a given reference object or light can be clearly discerned. In the United States, visibilities that are greater than or equal to 10 miles are typically reported as 10 miles.

The day of the last 12 months with the lowest average visibility was March 28, with an average visibility of 3.0 mi. The month with the lowest average visibility was March, with an average visibility of 5.3 mi. With an average visibility of 23.3 mi, the month of September had the highest average visibility.

Visibility

The daily average visibility, depicted as gray bars encroaching down from the top of the graph.

The cloud ceiling is the altitude of the lowest layer of clouds that are at categorized as broken (mostly cloudy) or overcast (cloudy). If no such cloud layer exists then the ceiling is unlimited and no value is reported.

The day of the last 12 months with the lowest average cloud ceiling was February 13, with an average cloud ceiling of 100'. The month with the lowest average cloud ceiling was January, with an average cloud ceiling of 3125'. The month of May has the highest average cloud ceiling, with an average cloud ceiling of 5281'.

Cloud Ceiling

The daily average cloud ceiling, depicted as gray bars encroaching down from the top of the graph. Missing data or days with insufficient clouds to define a cloud ceiling are shown as white columns.