In the current weather reports hears in connection with the current fine weather phase again and again from Indian summer. However, this is wrong, this is later, currently we are in late summer. More about the difference and in which season we are according to nature below.
Currently late summer weather phase
The current good weather phase is named differently in the different reports, sometimes one reads of a late summer phase, sometimes of Indian summer. Late summer is the phase until the beginning of autumn (this year on September 23 at 8:49 a.m.), which follows midsummer. The latter is characterized by hot phases, which usually end around the end of August. After that there are at most a few hot days, but the fair weather phases are often still summery warm, in this context it is called late summer. The current sunny phase can thus be classified as late summer. In contrast to Indian summer (see below), the larches in the mountains are typically not yet colored in late summer (see Fig. 1).
Fig. 1: Current picture from the Engadine (Celerina): In late summer the larches are not yet discolored; Source: roundshot
Indian summer later
Indian summer is later; it is a phase of stable, high-pressure, warm weather in the calendrical autumn, often between late September and mid-October. The dry weather allows for good distant visibility and thus great mountain weather, intensifies leaf fall and foliage coloration (cf. Fig. 2).
Fig. 2: Discolored larches in Indian summer in the Engadine (Morteratsch); Source: Roger Perret
Typical for this time are also fine spider threads on shrubs, trees and grasses, from which the name might be derived (cf. Fig. 3). These spider threads are formed during the often clear nights with dew formation, whereby the dew droplets settle on spider threads flying around. The weaving of spider webs was called "weiben" (today weave) in Old High German. In addition, the term "old" is to be understood as "late" in the context of Indian summer.
Fig. 3: Probable namesakes for Indian summer: spider webs with dew drops; Source: pixabay
Indian summer usually occurs from the end of September, which is about the beginning of our autumn calendar. This then very regularly: Statistically it holds in five of six years with us. As a grand finale of nature to be enjoyed, one says about it with a wink: It is the only summer that can really be relied upon! Once it has arrived, the autumnal period of good weather can last until the end of October, although October is also known as "golden October" or "Indian summer " (see Fig. 4).
Fig. 4: Indian summer with beautiful autumn colors; Source: pixabay
Nature already in early autumn
In addition to the astronomical calendar, there is also the calendar of nature, the so-called phenological calendar. In this calendar, the times of occurrence of characteristic phenomena, in the case of plants the characteristic stages of growth, are observed and recorded. The phenological calendar divides the year into a total of 10 seasons (see Fig. 5).
Fig. 5: Phenological calendar; Source: MeteoNews
Each season does not begin on a fixed day of the year, but at the start of the new development of a pointer plant. For the beginning of autumn, the flowering of the meadow saffron and the ripening of the black elder are used. The latter is current at low altitudes (cf. Fig. 6), so that by nature we are already in early autumn.
Fig. 6: Ripe black elderberry in Sarganserland; Source: Roger Perret