AbstractRecords of temperature over a 13‐year period in a Hertfordshire valley which has been described as possessing the most “continental” thermal climate yet investigated instrumentally in the British Isles are summarised, discussed, and compared with data from other stations. Among the facts brought to light are that only two of the 156 calendar months from 1930 to 1942 passed without ground frost on the valley floor; that screen frosts occur even in July and August; and that the mean night minimum temperature is at or below 32°F. for about three‐fifths of the year on the grass and for about two‐fifths of the year in the screen. Three examples of a diurnal range slightly exceeding 50°F. are examined in the light of Fourier analysis; statistical evidence is advanced to show that the probable limiting value for such ranges over a long series of years may be put at not less than 55–56°F. Thermograms are reproduced illustrating the greatest recorded daily variations, as well as the effects of katabatic winds and turbulence