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A new absolute minimum record for May in Iceland

On 2 May the automatic weather station at Brúarjökull registered a minimum temperature of -21.7°C. This is the lowest temperature ever measured in Iceland in May. However, it should be kept in mind, that this station has only been in place since 2005 and it is one of the coldest measuring sites in the country.

This cold spell is probably the most intensive one in May throughout the period of automatic observations in Iceland. The network was established in 1993 to 1998, becoming more dense since. New station minimum temperature records for May were registered at the majority of the automatic stations during the present cold spell.

The number of manned synoptic stations measuring temperature has decreased rapidly after 2004. A few of the remaining stations registered new minima for May during the present cold spell. These stations, except one, have only been in operation since 1988 or later. At the older synoptic stations the present minima did not exceed earlier records, except at one station. Most of these originate in a cold spell in early May 1982. One station which has been in operation since 1924 (not quite continuously, however) registered a new absolute record on 2 May this year.

The present cold spell seems to have been the most intensive in May in Iceland since at least 1982. Nobody knows how low the temperature at Brúarjökul was at that time.

On the measurements of minimum temperature in Iceland

At the “manual” stations the minima are measured with a traditional alcohol minimum thermometer. Readings are made two times per day, at 9 utc and at 18 utc The lower of the two readings becomes the minimum of the day. In the middle of winter the daily minimum is quite often recorded at 18 hrs, but during the other seasons most often at 9 in the morning.

At the automatic stations the minimum of the day is the lowest 2-minute average temperature during the 24 hour period from 00:01 to 24:00. At most of the automatic stations the temperature is registered every 10-minutes (a 2 minute mean) along with the highest and lowest 2-minute averages during the preceding 10 minutes. The automatic instruments have a somewhat faster response time compared to the traditional minimum thermometers placed in thermometer screens. In calm situations fluctuations of the minimum temperature are common as the temperature inversion nearest to the ground strengthens and mixes at irregular intervals.

This fluctuating behavior of the minimum temperature has not been examined systematically in Iceland.

The validity of the new record
The old record May minimum in Iceland was registered at the manned station Möđrudalur on 1 May 1977, -17.4°C. The new record is more than 3 degrees C lower than this and must be considered unquestionable even though the new record is made at an automatic station with different attributes than the traditional measurement.

The Brúarjökull station is located at 845 m above sea level at the snout of a very large and flat outlet glacier of the icecap Vatnajökull. This is well within the highlands of Iceland and almost 400 meters above the location of the earlier record station Möđrudalur.

The first all-year highland station in Iceland was established in 1965 and a few others were in drift for a few years or seasons until the advent of automatic stations. It has been customary to distinguish between the highland stations on one hand and the stations in the inhabited areas on the other in the listing of weather records. However, regarding the minima, the inhabited stations in the very flat northeastern highlands have been almost on par with the higher level highland stations proper during winter. The earlier May minimum record had thus persisted for 36 years even though many automatic stations have been in operation at higher levels for more than 15 years.

A new absolute minimum for the inhabited stations was also registered at the same hour as the new whole-country record. The minimum at the automatic station at Grímstađir (another northeastern inland station) plunged down to -17.6°C, 0.2°C lower than the old record.

The automatic station at Grímsstađir is new, however, established last autumn only. There still are ongoing measurements at the old manual station there. The in-screen minimum thermometer registered “only” -14.5°C on the morning of 2 May. The distance between the two stations is less than 100 meters.

The registrations at the new automatic station at Grímsstađir have not been compared to the manual registration in a systematic manner and a post-installation calibration has not been made. Until that is done the new record will not be formally confirmed.


August in Iceland

August was a very warm month in the northern, western and southwestern parts of Iceland. In Reykjavík it was the fourth warmest since the official beginning of observations in 1871. August of 2003, 2004 and 1880 were slightly warmer. The temperature was above average in the whole country but not much above in the southeast.

The highest temperature of the month was recorded at Eskifjörđur in the Eastern Fjords area on the 9th, 28.0 degrees C. This is the highest temperature measured in Iceland since 2008. The last week of the month was rather cold with overnight freezing temperatures at many inland locations. The lowest minimum of the month was -5.3°C registered at Brúsastađir in a valley in the north.

It is unusual that the maximum temperature of the country stays above 20 degrees C for more than a few days in a row. But this summer saw a new record in this respect, the period from 27 July to 19 August had an unbroken chain of country maxima above or equal to 20 degrees. During the warm period the overnight low temperatures were also unusually high and the minima close to being record high.

The precipitation was at average in Reykjavík but in most parts of the country it was drier than usual. In Akureyri the total of the month was only 8.4 mm, the driest August since 1960. The sunshine hours in Reykjavík were close to average but Akureyri has only once enjoyed more sunshine in August since the beginning of registration in 1928.

The first eight months of the year have been unusually warm in Iceland. This period of the year has only once been warmer in Stykkishólmur (in the west), that was in 2003. The record goes back to 1846.


July - a warm and sunny month in Iceland

July was both warm and sunny in most of Iceland. A small part of the East had temperatures just above average, in most other areas the month was one of the 10 warmest months of July.

In Vestmannaeyjar off the southern coast this July was the warmest since the station was moved to its present location in 1921. Temperature measurements, however, were done at another location at a lower elevation prior to that from 1877. And during 1869 to 1877 (unofficial) measurements were made at the third location. Older measurements exist for Vestmannaeyjar (during the 1840s) but they were clearly contaminated by the exposure of sunlight during summer. Since 2003, measurements have been made at two locations allowing the calculation of a site adjusted series back to 1877 (and unofficially back to 1869). This shows that July 1880 was probably about equally as warm as July now (2012).

The sun has been shining in the west and north as never before. The number of bright sunshine hours was well above average in Reykjavík and within 1 hour of the July record in Akureyri. But a look at the sum of the last three months reveals an exceptional situation at both stations. This period is the sunniest at both stations since the beginning of registration, in Reykjavík in 1911 and in 1928 in Akureyri. In Akureyri the old record (from 1939) was exceeded by 120 hours of sunshine and the total for the first seven months of the year is already close to the average annual total.

The precipitation in July was below average in all districts but not quite so as in May and June.

Even though the weather has been warm, days with maximum temperature above 20 deg C have been few and the Reykjavík absolute maximum of the summer is still below 19 deg C.

The month also brought the lowest July pressure ever recorded in Iceland (see a separate entry). Even so, the average monthly pressure was above the long-term mean.


A new low pressure record for July in Iceland

A remarkably deep low developed to the southwest of Iceland on 19 and 20 July 2012. According to the analysis of the ECMWF the central pressure in the low dropped to 966 hPa. This is amongst the lowest values ever observed in the North Atlantic in July.

After the low reached its maximum intensity it moved towards Iceland and filled gradually. In the evening of Sunday 22 July the pressure was at minimum near the south coast of Iceland. The lowest mercury barometer reading was 972.8 hPa, first at Vestmannaeyjar at 21 pm and then again at Kirkjubćjarklaustur 6 hours later. The lowest value at an automatic station was reached in Vestmannaeyjar during an extended period of one hour, 21:30 to 22:30, 972.4 hPa.

The pressure in Iceland has only on three occasions dropped down to 975 hPa or lower in the entire record extending back to the 1820s. These cases were 974.1 hPa in Stykkishólmur on 18 July 1901, 974.3 hPa in Stykkishólmur on 19 July 1923 and 975.0 hPa in Reykjavík 11 July 1912. It should be kept in mind that even the pressure was recorded at a few stations all over the country during the period from 1874 onwards, longer intervals passed between readings than now. Three readings per day were typical, but eight readings have been made at most of the barometric stations since the mid-1940s.

The low has brought rain to most of the country. Some parts have been experiencing an unusual drought since May. If the rain will alleviate the low water levels in the non-groundwater-fed rivers remains to be seen.

The country more or less escaped the high winds associated with the low as the centre passed just south of the country. The wind was strongest to the south of the low, as well as in the Greenland Strait (Denmark Strait) to the northwest of Iceland. The strongest gust associated with the low was measured 39.5 m/s at the station Steinar at the southern coast.


Temperatures in Iceland - as originally published

Due to the recent confusion regarding the Icelandic temperature series I have decided to post a list of monthly temperature averages as they were originally publised in the Icelandic and Danish yearbooks prior to 1960. Later original published data are available online at the website of the Icelandic Met. Office (IMO) (see the supplementary information attachment).

This post consists of three files, the data list (original_pub_temperature_values.txt), a station list (original_pub_temperature_stat_info.txt) and supplementary information (original_pub_temperature_values_suppl_info.txt) on the data format etc. Please feel free to download the attachments (viđhengi) at the end of this post.

The IMO has calculated series with some appropriate adjustments for each individual station. The IMO generally uses the version with adjustments made on pre-1961 data rather than the present dataset. These data are available on request (trausti@vedur.is) for individual stations but the whole dataset will be made available later.

It must, however, be emphasized that the adjustments will change in the future as more information on station history and inter-station comparison will be added. One should therefore expect changes in the adjusted dataset through time.  

The present dataset (original_pub_temperature_values.txt) will remain static, except for the addition of values from individual stations during the pre-1920 period which have not yet been digitized. Readers should note that these values are available in the Danish yearbooks (see a link in the supplementary information attachment).

Please feel free to comment and if you find any errors a note will be appreciated either by filling out the comment form (see below) or by sending your questions or notes to: trj@simnet.is

The comment form [The "athugasemdir" link near the bottom of the text] is in Icelandic, but most of it should be transparent to English readers. When you submit the comment you will be prompted for your name, e-mail (netfang - essential), vefslóđ (web link - not essential) and a question: What is the sum of two numbers? Just add the two numbers (within a short period of time) write the sum in the box and resubmit. This is for the spam-filter (ruslpóstsvörn).

[Dec. 4, 2012 The comment option has a timeout - please direct queries to trj@simnet.is}


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June 2012 in Iceland

June was very sunny in both western and northern Iceland. The total number of bright sunshine hours at Akureyri and Reykjavík were close to the all-time records. The total number of sunshine hours at these two stations in May and June as a whole is unprecedented.

It was a very dry month in most of the country. Parts of the west and northwest experienced the driest June (or even any month) ever. Stykkishólmur has the longest precipitation series in the country, the precipitation observations began in October 1856. June 2012 is the driest month on record, with the total being only 0.6 mm of rain. In some places in the northwest the earth is very dry and the vegetation suffers. A few farms are almost without clean running water and depend on tanking for water consumption. However, the main part of the winter had much precipitation in the area so there is some snow still surviving in the mountains feeding rivers and groundwater.

June was warm in the south and west, amongst the ten warmest on record in the Reykjavík area, but in the north and east it the temperature was slightly below average as northeasterly winds were prevalent.

The highest temperature in June was registered at the stations Hella and Árnes in the southern lowland on the 2nd, 22.8 degrees C. The lowest temperature of the month was registered at Gagnheiđi - a mountain in the east on the 5th, -5.7 deg C. The lowest temperature in inhabited areas was registered at Brú in the eastern inland, -4.4 deg C on the 13th. There were only ten nights entirely frost-free in the inhabited areas.

The full official report is available (in Icelandic) on the Icelandic Met. Office web.


May 2012 in Iceland

On the whole the temperature was close to the long-term average of the season. Actually the month was divided into two long spells, the first a very cold one lasting from the 6th to the 19th and a warm and sunny one for the rest of the month.

The weather was unusually sunny. In Reykjavík it was the 5th sunniest May since the beginning of observations in 1911 and in Akureyri (in the north) it was the second sunniest one, the observations starting there in 1928.

During the cold spell three new daily minimum records were set for the whole country. This was on the the 7th at Setur in the central highland, -13,7°C (older record, -13,4°C), on the 17th when the temperature at Brúarjökull in the eastern inland dropped down to -16,6°C (older one -11,0°C), and on the 18th also at Brúarjökull -13,1°C (older one -11,9°C). No new daily records for the country were exceeded in the inhabited areas where the observation series are much longer than in the highland. Many daily records where, however, exceeded at the individual stations during the cold spell, and also during the following warm spell.

The highest temperature measured in Iceland in May was 22,0°C at Kollaleira in the east on the 26th. The 20deg mark was exceeded somewhere in the country on six days in a row during the warm spell. This is unusual in May.

The full report for May (in Icelandic) is available at the web of the Icelandic Met. Office.


April colder than March in almost half of Iceland in 2012

April was colder than March in many parts of Scandinavia (met.no; smhi.se). This was also the case in the Eastern part of Iceland. On a whole this happened at 44% of the automatic stations. (Results are not in from all of the manned ones). 

That April happens to be colder in March is not that unusual, however. If all of the stations in all years are taken into the batch March is warmer than April about 17% of the time. On about 36% of the years at least one station is colder in April than in March.

One April out of 10 is colder than March at almost all (or all) of the stations. A majority of the stations had a colder April than March in 2010, but one has to go back to 1977 to find an all out April colder than March.

The likelyhood of a colder April after March is of course largest when March has been unusually warm. This was the case now.

But as a whole April was a rather warm month in Iceland, most of the stations had average temperatures above the 1961 to 1990 normal. Only a few stations in the East had below average temperatures.

The lowest temperature in the country was -25.7°C on the 2. (Brúarjökull, in the Eastern highland), but the highest 18.2°C on the 30. (Hallormsstađur, in a deep eastern valley).

April was rather dry in most areas.  

Official IMO April overview (in Icelandic only).


A new March maximum temperature record in Iceland

The last week has been warm in Iceland, especially in the north and east. Daily station records have been exceeded by the hundreds and also daily countrywide maxima on a few days. On Thursday 29 March the temperature at the farm Kvísker on the Southeast coast the maximum temperature reached 20.5 degrees C. This is a new March record for the whole of Iceland exceeding the old one by the large margin of 1.7 deg C.

The old record, 18.8 deg C, was set on 28 March 2000 in the town of Eskifjörđur in the Eastern Fjords.

The individual monthly temperature maxima in Iceland are:

MonYearMonthDaymaximum °CStation
January200011519,6Dalatangi East
February199821718,1Dalatangi  East
March201232920,5KvískerSoutheast
April200742923,0Ásbyrgi Northeast
May199252625,6VopnafjörđurNortheast
June193962230,5TeigarhornEast
July194671730,0HallormsstađurEast
August200481129,2EgilsstađaflugvöllurEast
September194991226,0DalatangiEast
October197310123,5DalatangiEast
November1999111123,2Dalatangi East
December2001121418,4SauđanesvitiNorth 

The official statement of the Icelandic Meteorological Office.

Dalatangi is a lighthouse on an peninsula at the East coast. It often experiences short „heat waves“ caused by decending warm air aloft along the very steep mountainside on the peninsula. The Dalatangi winter maxima have no diurnal preferences and often occur in the middle of the night. The station is however one of the most oceanic in Iceland the annual range of monthly temperatures is only 8.2 degrees C. At a few oceanic stations the heat waves of winter occasionally offer the highest maxima of the year. Later, I will give a list of these at this blog.

The station Sauđanesviti (Sauđanes lighthouse) is on the tip of a peninsula in the North, the topographical conditions are similar to the ones at Dalatangi.

The topography at Teigarhorn in the East is also similar to Dalatangi and Sauđanesviti. The warm descending winds are not as common as in the other locations, but the aspect to the noon sun in summer is more favourable.

Kvísker is located near the highest mountain in Iceland, Örćfajökull (a dormant volcano). The maxima at Kvísker typically occur in westerly winds blowing along the side and downwards the slope near the station.

The remaining stations are all located in the valleys of the northeast and east. Vopnafjörđur at the seaside in a broad fjord, Ásbyrgi in a very broad valley, but not far from the coast and Hallormsstađur and Egilsstađir airport well inland in the largest valley of the East.

 


Reykjavík - monthly means as originally published

Measurements in the modern style started in Reykjavík in May 1880. There are earlier observations available but made with unsheltered wall instruments. These can be added to the series back to 1866 and observations were also made in Reykjavík during 1820 to 1854. We will hopefully look at these early measurements later.

The history of the Reykjavík station is quite complicated. The Reykjavík station was operated by the Danish Met. Institute (DMI) from 1880 to 1910 and monthly mean temperatures were published in the yearbooks of the Institute (Meteorologisk Aarbog) which are available online (see an earlier post). During this period there were a few observers and the station was relocated within the town three or four times. A wall-mounted instrument screen was used during the first part of the early period but it was later replaced by a free standing one - the first one in Iceland.

The thermal characteristics of the early screens are better known than elsewhere in Iceland at this time as it was for a considerable period equipped with a thermograph which was read every hour. So we know the diurnal cycle quite well. It conforms well with later-time diurnal cycle observations. A few months of thermograph sheets are missing.

The main thermometer was read three times per day at fixed hours. The DMI always used the average of these + a separate fixed constant for each month (to account for the seasonal variation of the diurnal range). In comparison with modern methods these early calculations tend to have a daytime bias - resulting in slightly elevated temperatures. This is one of the main reasons for the adjustments that have been used later on the means. We will look at this problem later.

The climatic station in Reykjavík stopped making observations in December 1910, temperature measurements continued at a telegraph station in the town but data from this station were never published - and are not used in the attached dataset, except during 1920 and 1921 - which were published.

When the station in Reykjavík was discontinued in 1910 a new one was established just out of town at the newly built Vífilsstađir sanitarium. This location is slightly warmer in summer but colder in winter than the downtown stations. The published monthly means from this station are included in the attached dataset.

During the early period from 1880 to 1920 a few months are missing from the DMI publication. The Icelandic Meteorological Office (IMO) was established in 1920 and took over the DMI station net. Proper observations began again in Reykjavík (in a wall screen) in May 1920. Observations were made at fixed hours. In 1924 a thermograph was introduced again at the station and during 1924 to 1948 all the published temperature means in Reykjavík were calculated as the average of thermograph readings every two hours. There were daily comparisons of the thermograph and the fixed hour observations.

Since 1949 the Reykjavík monthly mean is calculated as the average of observations made every three hours.

The DMI also published the average monthly minimum temperature during the first few years. A minimum thermometer was, however, in use in Reykjavík during most of the early period, but the means were not published. The minimum thermometer was used for the calibration of the thermograph mentioned above during most of the 1884 to 1907 period.

The IMO has published monthly means of maximum and minimum thermometer readings since 1920. These means are included in the attached dataset.

wi-blog210312_s001t_original

The figure shows the annual mean temperature in Reykjavík 1881 to 2011 (as published). No external adjustments have been used.

Relocations are marked with vertical lines. In late 1931 the station was relocated to a rooftop in the town centre and remained there until the end of 1945. The data (above and in the attachment) have not been adjusted for this change nor others. Later versions of the dataset (e.g. the one available at the IMO website) do include adjustments for the relocations. All adjustments are subject to revisions at a later date.

Some internal adjustments are needed during the early part of the series due to later changes in calculation methods. The fixed-hour means that form the basis of both the DMI average method and recent adjustments by the IMO will be made available at this website later.

The data in the attachment are semicolon delimited with a period as decimal seperator.


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Iceland Weather blog

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Trausti Jónsson
Trausti Jónsson
Senior meteorologist at the Icelandic Met. Office. Speciality: Climatology
Okt. 2019
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