The July isotherm of 80° crosses the state a little N.
The January isotherm of 15° F.
And S.; thus Odessa and Konigsberg are situated on the same winter isotherm of 28°; St Petersburg, Orel and the mouth of the Ural river on about 20°; and Mezen and Ufa on 9°.
The summer isotherm of 68° F., which in Europe passes through Cracow and Kaluga, traverses Omsk, Krasnoyarsk and Irkutsk, whence it turns north to Yakutsk, and then south again to Vladivostok.
Both the midwinter isotherm of Montreal and the midsummer one of Washington, D.C., pass through the state.
Of the 80° isotherm the average temperature for July is between 80° and 85°.
The same effect is well shown by the linguiform isotherms. In January, for example, the isotherm of 14°, after skirting the north coast of the Scandinavian peninsula, turns southward along the Keel, crossing the upper part of the district of the great northern lakes.
The south-eastern corner is crossed by an annual isotherm of 60°, the north-western by one of 50°; and although in the former region sometimes not a day in the year may show an average temperature below freezing-point, at Jefferson City there are occasionally two months of freezing weather, and at Rockport three.
Odessa experiences the influence of the continental climate of the neighbouring steppes; its winters are cold (the average temperature for January being 23.2° F., and the isotherm for the entire season that of Konigsberg), its summers are hot (72.8° in July), and the yearly average temperature is 48.5°.
Russia; thus the isotherm of 39° runs from St Petersburg to Orenburg, and that of 35° from Tornea in Finland to Uralsk.
The isotherm of - 22° F., which touches the north point of Novaya Zemlya, passes in Siberia through Turukhansk (at the confluence of the Lena and the Lower Tunguzka) and descends as low as 55° N.
As a result, the isotherms of July are strongly convex poleward as they cross the United States, the isotherm of 70 Sweeping up to the northern boundary in the north-west, and the heat equator leaping to the overheated deserts of the south-west, where the July mean is over 90.
Again, the July isotherm of 75° crosses the middle section of the Caspian, nearly coinciding with the January isotherm of 25°, while that of 80° skirts the southern shore of the sea, nearly coinciding with the January curve of 40°, so that the mean annual range over the northern section of the sea is 60° and over the southern section 40°.