Season, עונה/עת

Israel’s climatological and seasonal characteristics are dependent upon its location: at 30˚N latitude, on the northern margin of the subtropical desert belt, it experiences the dominant effects of the Mediterranean Sea (winter cyclones) and topography.

The Hebrew Bible divides the year into two seasons—the wet and cool winter and the dry (no rainfall) and hot summer. The absence of rain in the summer is caused by the subsidence of the subtropical high pressure that prevents rain forming during the summer. The rainy winter is caused by the Mediterranean cyclones, known as Cyprus Lows in the region.[1] However, the Biblical division does not take into account variations in the climatic conditions within each season, i.e., inter- and intra-diurnal variations or the climatologic conditions at the transitional seasons, spring and autumn, as well as inter-annual variations, between rainy and drier winters.

Relating to divergent climatic variables, the four-season scheme was only introduced in modern times. Modern Hebrew refers to אביב (spring, following the winter) and סתיו (autumn, following the summer). These seasons exhibit specific climatologic characteristics, especially larger inter-diurnal variations in temperature and rainfall compared to summer and winter. During the transitional seasons, short events of high temperatures and low humidity—associated with strong, dry, hot easterly/southerly winds originating from the Sahara or the Arabian deserts that often appear with dust storms, known as שרב (“heat”)—occur. These are common during spring, less common during autumn, and rarely occur in summer, when the persistent westerly Etesian winds prevail, or winter (Porat 2005, 50) (see entry “Sharav”). These different climatic variables have prompted modern climatologists to suggest four-season divisions based on diverse variables: a) astronomical; b) temperature; c) precipitation; and d) synoptic systems, etc.

The astronomical system rests upon the angle of the sun and length of the day that determine the intensity of the sun radiation (Trewartha 1968, 14–15). For the northern hemisphere, this is as follows:

• Spring: 21 March (spring equinox) to 21 June (summer solstice);
• Summer: 21 June to 22 September (autumn equinox);
• Autumn: 22 September to 21 December (winter solstice);
• Winter: 21 December to 21 March.

21 March and 22 September are the spring and autumn equinoxes. Hereupon, the noontime sun is vertical to the earth at the equator, day and night being the same length across all latitudes. On 21 June, the earth’s orbit is midway between the spring and autumn equinoxes, the North Pole being inclined 23.5˚ towards the sun. The noontime angle of the sun is vertical at the Tropic of Cancer (23.5˚N), the effective solar radiation there and northward being at maximal strength. This is the longest day in the northern hemisphere—12 hours of light at the equator and up to 24 hours north of 66.5˚N latitude. On 21 December, the earth’s orbit is midway between the autumn and spring equinoxes, the South Pole being inclined 23.5˚ towards the sun. The noontime vertical sun angle lies at the Tropic of Capricorn (23.5˚S), the effective solar radiation there and southward being at maximal strength (minimal at Tropic of Cancer and northward). This is the longest day in the southern hemisphere, with 24 hours of light south of 66.5˚S latitude and the shortest day in the northern hemisphere, with 24 hours of darkness north of 66.5˚N latitude.

The temperature classification relates to the lag between the maximal solar radiation and maximal earth temperature, the warmest/coldest months trailing the maximum/minimum sun radiation by about a month. The sea warming at a slower pace than the land, the length of this lag depends on the specific location.

Three classifications of the seasons in Israel are presented below, each illustrating the annual climatic cycle:

a) Ovadia & Goldreich (1996) suggest the following classification based on temperature cycles. This corresponds most closely to the astronomical definition, each season being three months long:

• Spring: 14 March to ca. 13 June
• Summer: 13 June to 12 September
• Autumn: 12 September to ca. 12 December
• Winter: 12 December to 14 March

b) Jaffe (1977) suggests unequal periods based on rainfall, temperature, and humidity. The rainy winter season is the longest, the summer the shortest:

• Spring: April, May and June;
• Summer: July and August;
• Autumn: September and October;
• Winter: November, December, January, February, and March

c) Alpert et al. (2004a) adduce the prevailing synoptic systems that characterize each season, defining the entire period of each season and the high season (“peak”), at which the occurrence of the system is higher:

While סתיו (stav) probably signifies “rain” in Biblical Hebrew, in modern Hebrew (see above), it serves as the name of the intermediate season preceding winter (autumn).

The tables below present the seasonal average rain (Table 1) and average daily minimum/maximum temperatures in months representing the four seasons (Table 2) for three stations in Israel representing the coastal plain (Tel Aviv, 4m above sea level), the Judean mountains (Jerusalem, 810m above sea level), and the Dead Sea (Sodom, 388m below sea level), based on the climatic atlas of the Israel Meteorological Service (Alpert et al. 2004b).[2]

Table 1: Average rain amounts for 1980/1–2009/10

SON = September, October, November; DJF = December, January, February; MAM = March, April, May; JJA= June, July, August

Table 2: Average daily minimum/maximum temperatures for 1995–2009.

The rainfall amounts are negligible in Sodom in the southern Judean Desert, because the site is almost 400 meters below sea level. This fact is also responsible for the highest mean temperatures recorded there, in contrary to the coolest temperatures in the mountainous areas (Jerusalem) and temperate coastal temperatures (Tel Aviv).

The Bible only relates to temperature and rain, virtually ignoring the wind and dust that have climatological/agricultural impact. On occasion, rain is associated with wind (e.g., Prov 25:14).

The authors of the Bible were unfamiliar with the synoptic systems that cause the characteristics of the seasons, nor do they refer to intra-seasonal changes. The synoptic system that most affects the Israeli summer is the Persian Trough (PT)—the extension of a low pressure system from the Persian Gulf that reaches the Levant and Israel. Although low air pressure near the ground generally causes rain in Israel, in the summer the persistent upper-levels air descend (subsidence), causing warming and (in most cases) preventing rain clouds formation.[3] The low air pressure to the east, induced by the PT, and the fact that sea temperature is lower than land temperature causes a flow of cool air from the sea to the land (a west or north-west wind known as Daytime Breeze). During nighttime the land cools and easterly wind toward the sea develops, known as Night Breeze. The combination of the upper-level subsidence and the lower-level relatively cool and wet flow from the Mediterranean Sea results in humid conditions at the coastal plain and warmer and dryer conditions at the mountains and inland areas.

The weather in the summer is quite constant, small changes occurring from day to day due to the persistence of the PT system and the wind regime.

The synoptic system dominant in autumn is the Red Sea Trough (RST). A northward extension of the Sudan low along the Red Sea (Goldreich 2003, 204–205) is responsible for some of the rainfall in Israel, partially causing “Sharav” conditions and, occasionally, flooding in the Negev (southern Israel).[4] The synoptic systems responsible for most of the rainfall in Israel in winter are the Winter Lows (WLs)—centers of low air pressure near Cyprus, known as the Cyprus Lows, which appear in an average cycle of about once a week. In addition to rainy days, the winter can thus also produce relatively warm and bright days with stable cool nights or very cold days caused by strong easterly to northerly winds that penetrate extreme cold air from continental polar areas.

A synoptic system that has a dominant effect on the weather in the spring, though affecting the region only for few days a year, is the Sharav Lows (SL). Sharav Lows are centers of low air pressure that develop in the deserts of North Africa, moving eastward along the shore, and cause exceptional warmth, dry and hot, dusty winds (Goldreich 2003, 26). RST can also cause warm dry and dust flow from the Arabian deserts, more common in autumn, but can also cause rain and floods, as specified above.

In Deut 16:1, the Israelites are commanded to celebrate Passover in חדש האביב—i.e., when the barley is ripe. The lunar year being shorter than the solar year by about 11 days, the Jewish calendar adds a thirteenth month every seven years over a period (cycle) of 19 years. Gauss’ scheme (1802) allows us to compute the Common Era date of the first day of Passover (Rhodes 1977). To test this system, the years 1900–2100 were computed. Throughout this period, the first day of Passover never fell before 21 March—the beginning of the spring according to the astronomical classification. According to the Jewish calendar, the first month (30 days) of the spring ends on 19 April. Between 1900–2100, the date of the first day of Passover fell after 19 April in 26 years (e.g., years 2005, 2016, and 2024). The addition of a thirteenth month every seven years over a period of 19 years means that the first day of Passover always falls after the beginning of the spring month—and sometimes after the end of the spring month (Trewartha 1968, 15–16).

[1] See the respective entries.

[2] See https://ims.gov.il/en/ClimateAtlas.

[3] See https://ims.gov.il/en/ClimateAtlas.

[4] See the entry “Sharav.”

Alpert, Pinhas, et al. 2004a. “A New Seasons Definition Based on Classified Daily Synoptic Systems: An Example for the Eastern Mediterranean.” International Journal of Climatology 24(8): 1013–1021.

Alpert, Pinhas, et al. 2004b. “Semi-Objective Classification for Daily Synoptic Systems: Application to the Eastern Mediterranean Climate Change.” International Journal of Climatology 24(8): 1001–1011.

Goldreich, Yair. 2003. The Climate of Israel: Observation, Research and Application. New York: Kluwer Academic/Plenum.

Jaffe, Shemuel. 1977. “How Many Seasons are there in a Year?” Teva va’Arets 20(1): 8–10 (Hebrew).

Ovadia, Adi, and Yair Goldreich. 1996. “Year Division in Israel according to Temperature Data.” Judea and Samaria Research Studies 6: 293–297. (Hebrew).

Porat, Amos. 2005. “The Sharav in Israel.” PhD diss., Tel Aviv University (Hebrew).

Rhodes, Ida. 1977. “Computation of the Dates of the Hebrew New Year and Passover.” Journal of Computational and Applied Mathematics 3(3): 183–190.

Trewartha, Glenn T. 1968. An Introduction to Climate. New York: McGraw-Hill.