Climatological basis for prediction of temperature regime on ground

Data on air and road surface temperatures not being available, climatological data from the site of the meteorological station have been used to determine the temperature relations needed for predicting road slipperiness. The analysis has been made for the cold period of the year (September to May) for the 10-year period 1971-1980 at the Zagreb-Maksimir station, located in the Sava River valley at the foot of Mount Medvednica. The analysis involves the relations between minimum air temperatures at two levels, 2 m and 5 cm as well as between minimum air temperatures at 2 m height and soil temperatures at 5 cm depth at 7 a.m. during various weather situations, defined according to average cloudiness, wind conditions, fog and frozen ground during the night preceding the occurrence of minimum temperatures. In weather situations with prevailing radiation processes (clear/calm and partly cloudy/calm), the minimum surface air temperatures are always lower than at 2 m height. On the other hand, after cloudy nights, regardless of wind velocity, the minimum surface temperatures are lower than those at 2 m only above determined temperature levels. The minimum air temperatures at 5 cm height are lower than 0 degree C when the minimum temperatures at 2 m height are lower than 3 degree C during clear/calm, clear/windy and partly cloudy/calm situations. During partly cloudy/windy, cloudy/calm and cloudy/windy situations, the differences between minimum temperatures at these two levels are smaller, and consequently, negative minimum surface temperatures appear if the minimum temperatures at 2 m are about 0 degree C. The relations between minimum air temperatures and soil temperatures do not differ significantly for different weather types. However, they differ considerably from month to month. According to these conclusions, soil temperatures should be predicted particularly by means of regression equations obtained for each month.Original Abstract: U nedostatku podataka o temperaturi na povrsini ceste, za prognozu klizavosti kolnika koriste se temperaturne veze prema klimatoloskim podacima s meteoroloskih postaja. Analiza je provedena za hladni dio godine (od rujna do svibnja) prema podacima za 10-godisnje razdoblje 1971-1980. s meteoroloske postaje Zagreb-Maksimir, smjestene u dolini rijeke Save u podnozju Medvednice. Proucavani su odnosi izmedu minimalnih temperatura zraka na dvije visine, na 2 m i na 5 cm iznad tla, te veze izmedu minimalnih temperatura na 2 m i tempe