Sea level pressure: Unusually low in Iceland this winter

The sea level pressure has been persistently low in Iceland since early December. Pressure has been recorded in Iceland during 200 winters (Dec to Feb) now. The present average is tied for the lowest of the whole series along with the values for the winter of 2013 to 2015 and 1989 to 1990. Due to some measurement uncertainties there are three earlier record contenders as well (see figure below).

The figure shows the December to February averages from 1820-1821 to 2019-2020 (columns) and a 10-year running mean as well (red trace). There is a very large year-to-year variability - much larger than the measurement uncertainty - this variability seems to be more or less random, although some clustering of high or low values is evident - as seen in the considerable variability of the 10-year mean. The overall trend (-1.0 hPa/century) is insignificant (smaller than the possible measurement bias in the series).

The sea level pressure in Iceland is a very good indicator of the state of both the NAO and AO indices. The positive excursions of the pressure are concurrent with the negative values of the indices. There is a very good correlation between the pressure and temperature anomalies in large parts of Europe - also during the early part of the series. This relationship is not fixed in time, however, there are other factors in play as well - as e.g. global warming.

Although the AO index is usually not calculated further back than 1950 there is no ground for supposing that the good relationship between it and the winter pressure in Iceland as only existed throughout this post 1950-period - but not earlier. Some long-term discrepancies are, however, likely.

[For a discussion of the series and reference see: 

Jones, P.D., T. Jónsson, and D. Wheeler, (1997) Extension to the North Atlantic Oscillation using early instrumental pressure observations from Gibraltar and South-West Iceland, International J. of Climatology Vol.17, 1433-1450]