Lamb weather types

The Lamb weather type is a method of classifying synoptic weather devised by H.H. Lamb (1972). It is based on the variation in surface pressure values around the British Isles. The Lamb system splits the prevailing synoptic conditions into one of ten categories: eight directional categories (the cardinal and ordinal compass points), and two vorticity categories (cyclonic or anti-cyclonic).
More recently, an objective system was devised by Jenkinson and Collinson (1977) and compared with the original Lamb data by Jones et al. (1993). It is the Jenkinson and Collinson system that is used for the data provided here.

About these data

This page continues the online record of weather types found at the Climatic Research Unit (CRU) at the University of East Anglia. The data on this site are derived from NCEP daily average surface-level pressures rather than source provided by the Hadley Centre and used in the CRU version. As a consequence, this version of the weather types are not exactly the same as those from the CRU. Nevertheless, there is considerable correlation between the datasets.

File format

The Jenkinson and Collinson system extended the original Lamb weather types to 26 by adding types that are hybrids of the pure direction and anti/cyclonic types e.g. anti-cylonic and north-westerly which is abbreviated to ANW. The data files provided here generally follow the conventions used in the CRU version and use a numerical coding of the types as shown in the table below. Each file contains leading comment lines preceded with a # character in the first column, this currently contains the name and checksum of the pressure data source file for traceability. Following the comment lines, the daily circulation values (coded according to the table) are given on a regular 31x12 grid i.e. one month per line with non-existent days included, and shown as no data (-9).

0 Anti-cyclonic 20 Cyclonic
1 ANE 11 NE 21 CNE
2 AE 12 E 22 CE
3 ASE 13 SE 23 CSE
4 AS 14 S 24 CS
5 ASW 15 SW 25 CSW
6 AW 16 W 26 CW
7 ANW 17 NW 27 CNW
8 AN 18 N 28 CN
-1 Unclassifiable-9 No data

The data are provided year-by-year in the grid below and as a single archive in this file(intermittently updated). These will be updated roughly once per month (around the 15th). The similar circulation types of Trigo and DaCamara (2000) for Portugal and Chen (2000) for Sweden will be added in the near future.

A word of caution: You are welcome to use the data, with the appropriate attribution, but you do so at your own risk. I have run a further series of tests on the processing which appears to be correctly implementing my interpretation of the formulae given by Jones et al. (1993). I do have some metrics for the correlation between these data and those that overlap in time with the CRU version. These show that 56% of the days are an exact match and 33% fall within one category (e.g. misses by one compass point (45°)). My conclusion is that the discrepancies between these data and the CRU version are caused by differences in the analysed surface level pressure fields.

You may need to right click and select 'Save linked content as' to download these files

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Produced in conjunction with the Lancaster Environment Centre, Lancaster University, UK. Scripts and web page © Andy Horseman 2012.