Bloggfćrslur mánađarins, júlí 2012

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}


Skrár tengdar ţessari bloggfćrslu:

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.


Um bloggiđ

Iceland Weather blog

Höfundur

Trausti Jónsson
Trausti Jónsson
Senior meteorologist at the Icelandic Met. Office. Speciality: Climatology
Sept. 2017
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