The Chui Valley is located in the extreme southern part of the temperate zone, farthest from the oceans and close to the deserts of Kazakhstan, which determines the high amount of heat, continentality, and dryness of its climate. In the central part of the Chui Valley (the capital Bishkek), the average annual sunshine duration is 2584 hours, which is more than in Almaty (by 6-13%) and less than in Cholpon-Ata (2613 hours) and Karakol (2657 hours).
The maximum duration of sunshine hours occurs in June-August (300-337 hours), while the minimum is in December-February (121-131 hours), which corresponds to 36% and 14% of the annual total sunshine hours, respectively. A large number of sunshine hours generally indicates a high amount of solar radiant energy. The maximum midday intensity in Bishkek is 1.53 cal/cm² min, observed in March when air transparency was high. In the other months of the spring-summer period, due to increased atmospheric dust, increased water vapor, and the appearance of haze, absorption and scattering of radiation increase, and the intensity of radiation decreases. The total solar radiation in the area of Bishkek is 92.8 kW/m², and it increases with altitude. In summer and autumn, direct radiation predominates in the Chui Valley, while in winter, diffuse radiation prevails; the share of absorbed radiation over the year is 70-80% of the total radiation.
On average, the radiation balance in Bishkek is 34.9 kW/m². Its maximum is noted in May-July. Tables 3 and 4 provide data on total solar radiation and the radiation balance of the active surface at the actinometric station in Bishkek over a long observation period.
The position of the Chui Valley in the northern part of the republic and its openness to the north and northwest facilitates the free penetration of cold air masses of Arctic origin. In winter, the valley is most often under the influence of the southwestern ridge of the Asian maximum and experiences cold frosty weather, which is occasionally interrupted by thaws. Due to the weakening of the influence of the Asian maximum in spring, Mediterranean cyclones gain access to the Chui Valley, bringing unstable weather with precipitation and returns of cold. In summer, a thermal depression establishes over the valley, as well as over all of Central Asia, under the influence of which cloudless, dry, hot, and hazy weather develops. Only over the mountain ridges do powerful convective movements develop, and cumulus cloudiness is observed.
In autumn, due to the decrease in insolation, the frontal zone shifts southward, and the thermal depression weakens and is replaced by frequent cold incursions from the west, northwest, and north, which are associated with slight cooling.
According to long-term average data, the highest pressure is noted in January around the Bishkek station, equal to 698 mb (928 mb). With altitude, pressure decreases significantly. Up to an absolute height of 1000 m, pressure drops by 11 mb for every 100 m, and above 3000 m - by 8 mb. In the annual course of pressure in the lower zone (up to 1000 m), the minimum is observed in July-August when a thermal depression is established throughout Central Asia, and the maximum is in October-December when the Asian maximum is actively influencing. Starting from January, the average monthly pressure decreases, and breakthroughs of southern cyclones intensify. The wind regime of the Chui Valley is formed by these two powerful centers of atmospheric action. Significant complications in the wind regime are also caused by the orographic structure of the territory. Due to the latitudinal extent, western and eastern winds prevail in the Chui Valley. Cold and moist air masses are associated with western winds. Their speed exceeds 5-8 m/s. They are most frequent in spring and autumn. Eastern winds are more common in summer and winter. Overall, the valley has weak winds, with an average annual speed ranging from 1 to 4.1 m/s. The average annual number of days with strong winds of 15 m/s is noted at the Bishkek station - 18, Belovodsk - 15, Chon-Aryk - 10.
Winds are not as frequent in the mountains (gorges). Usually, calm sunny weather prevails here, while in the foothill plains where Bishkek is located, winds are a rare phenomenon.
In the valley part, the average monthly wind speeds do not exceed 3 m/s, only at the Konstantinovskaya station do they reach 3.7 m/s; in the foothills and mountain valleys, they are even lower (Chon-Aryk - up to 2.3 m/s).
The number of days with strong winds in the Chui Valley can reach 18-20 per year.
According to long-term data, the average annual wind speed in Bishkek is 1.9 m/s within the city, while on its southern outskirts it is 2.6 m/s. For urban planning, the distribution of wind by altitude is of great importance. According to data from the aerological station, in the 1000-meter layer above Bishkek, western and northwestern winds prevail for most of the year (up to 40-50%), while eastern and southeastern winds account for up to 30-40%. The maximum wind speed in the 1000-meter layer can reach 30 m/s /Climate. Frunze, 1990, p.53/.
Along with this, local winds arise in the mountains of the Kyrgyz Ala-Too, which blow down from the mountains at night (mountain winds), especially along the gorges - valleys, and during the day, conversely, blow up into the mountains, forming valley winds. Sometimes they reach great strength, which all travelers in the mountains have had to observe repeatedly. Usually, the speeds of such winds range from 1.8 to 2.3 m/s.
The great variety of relief from foothill plains to high mountains and significant altitude fluctuations (from 500 to 4895 m) determine the pronounced altitudinal zonality and the sequential change of seasons in the region under consideration.
The continentality of the climate is reflected in the annual, monthly, and daily temperature trends. Thus, the average annual air temperature in the northern part of the valley is -8.5°C /Chui/, in the central part of the plain it is 10.1°C /Bishkek/. In the foothills, it is 6.3° - 7.3°C /Baitik, Arashan/, and in the high mountains, it is 1.0° - 1.4°C /Ala-Archa, Tyo-Ashuu/. The average temperature in January in the agricultural zone /Chui, Bishkek, Kant/ is -9.5° - -5.0°, -6.0°C; in the high mountains /Ala-Archa, Tyo-Ashuu/ - -12°C; the average temperature in July is 27.7°, 24.4° and 8.6°, 8.5°C /Tyo-Ashuu, Ala-Archa/.
Average monthly and annual air temperature (°C) for 1881-1980
The lowest (minimum) temperature in the northern low part of the valley is -41 °C /Chui/, in the central part -40° -38.0°С /Bishkek, Tokmok/. The highest temperature recorded in a hundred years was in Bishkek in July 1983 and reached 43°C.
The beginning of the warm period (above 0°C) in the foothill plain at an altitude of 2000-2500 m occurs in the second decade of March, and in the high mountains - at a later date.
The duration of the warm period in the agricultural zone is 240-250 days; the frost-free period is 174-186 days. The shortest frost-free period is 115 days (158), and the longest is 233 days (1947). The sum of temperatures above 10°C is 3400-3600 /Agroclimatic Handbook, 1972/.
Depending on the orography and altitude above sea level, the distribution of atmospheric precipitation in the Chui Basin is far from uniform. The minimum amount is noted in the northern and northwestern low part of the basin - 300-350 mm. In the east, the amount of precipitation slightly increases in Gokmoke to 384 mm, in Kemine (Bystrovka) to 400-425 mm, and in Kegeti to 427 mm. Additionally, there is an increase in the amount of precipitation from north to south as one ascends into the mountains. On the northern slopes of the Kyrgyz Ala-Too, in Chon-Aryk, it is 616 mm, in Baitik it is 538 mm, and in the area of the Tyo-Ashuu pass, it is 718 mm.
The increase in precipitation with height is more pronounced in the warm period of the year, while in the cold period, the difference in precipitation amounts at different altitudinal levels is small.
The maximum amount of precipitation in the Bishkek area occurs in the spring period (March-May), when about 53% of the annual total precipitation falls, while the minimum is from July to September, during which only 11% of the total precipitation occurs /Climate. Frunze, 1990/.
The distribution of precipitation on the northern slope of the Kyrgyz ridge is primarily determined by the orientation of the mountain slopes and exposure.
The highest precipitation is received by the ridge areas of the transverse spurs, their windward slopes, as well as the slopes of the foothills that extend the farthest north. With increasing altitude, the amount of precipitation slightly increases, but overall, on the northern slope of the ridge, the annual sums of precipitation vary insignificantly from 500 to 650 mm, and in the upper ridge areas, up to 650-700 mm.
Of great interest is the occurrence of the highest amount of precipitation in a single day, which is exclusively from downpours.
In the mountains of the Kyrgyz ridge, downpour precipitation is most often noted from May to June, with an average number of days with downpours in these months being 8-9.
It should be noted that the highest amounts, both daily and monthly, fall in the spring period and at the beginning of summer. It is during this time that downpours are most frequent. Therefore, the occurrence of mudflows and other undesirable phenomena should be expected precisely in the spring period and at the beginning of summer. At the same time, precipitation during this period is very favorable for sowing agricultural crops in the foothill zone and on the foothill plain when fields and gardens require a large amount of moisture. It should be noted that in rainy weather, the threat of rockfalls, avalanches, and flooding increases; in such cases, it is very difficult to walk in the mountains on grassy and clay slopes, as one can easily slip and fall.
In winter, there is little precipitation throughout the Chui Valley, which is associated with a thin snow cover. Its height increases from 10-15 cm in the northwest (Sary-Koo, Tashatkyl) to 15-20 cm in the south in the foothills. As one ascends along the slopes of the ridge, the thickness of the snow increases to 25-30 cm, and at an altitude of 3000 meters, it reaches 50-60 cm and lies for up to 140-150 days a year /Climate of the Kyrgyz SSR, 1965/.
As a rule, the first snow does not last long; it melts. The time for the formation of a stable snow cover at medium altitudes in the mountains occurs at the end of September, in the foothills - at the end of November. Melting begins on the plain in February, and in the mountains - at the end of March.
During the winter period, the snow cover in Bishkek is weakly stable. It most often forms in mid-December and is destroyed in mid-February. On average, there are 83 days with snow cover per year. Its stable lying lasts for 64 days /Climate. Frunze, 1990/. In cold winters, the duration of stable snow cover can increase to 91 days (1977-78), while in low-snow winters, snow may lie for less than 30 days (1964/65, 1965/66).
With the establishment of stable snow cover, its height gradually increases during the winter and reaches maximum values at the end of January. In January, the average decadal height in open areas is 8-9 cm. In field conditions, the highest average height of snow cover on the last day of the decade (10 cm) is also noted in January.
Typically, noticeable decreases in snow cover height due to melting and compaction begin in the second decade of February, and snow completely disappears in the second decade of March.
Atmospheric precipitation is associated with dangerous natural phenomena such as fog, thunderstorms, hail, and others. Fog or low clouds are often observed in the mountains of the Kyrgyz Ala-Too, especially in spring. Sometimes clouds are located below the mountain peaks, or fog can be present in the valleys at different altitudes. For example, in Chon-Aryk or Besh-Kunge, sunny weather prevails, while 3-4 km down the road, there is dense fog, or visibility is poor in Bishkek, while outside the city it is sunny, etc. Even in good weather, fog can envelop the mountains with a dense veil by midday. It sharply reduces visibility, making driving difficult, disorienting, and has a depressing effect on people. In fog, one cannot rely on senses; it is necessary to move along well-known landmarks. The number of foggy days per year in the plains and foothills is 17-25 /Bishkek, Belovodsk/, in the Kyrgyz ridge 30-40 /Baitik, Tyo-Ashuu/.
Another dangerous phenomenon associated with the climate is thunderstorms, which occur more frequently in the mountains than on the plain. During a thunderstorm, it is dangerous to be on mountain tops, under high solitary trees, to carry metal objects, or to set up tents on iron pipes. Thunderstorms can occur even on sunny days with little rain.
In the Chui Valley, in Bishkek, the average annual number of days with thunderstorms is more than 25. The highest number of thunderstorm days is observed in May-June at air temperatures from 16°C to 30°C. Most thunderstorms last for 1 hour. Thunderstorm activity predominantly develops in the afternoon and evening /Climate. Frunze, 1990/.
According to G.A. Apostolatov's data (1960 and 1962), thunderstorms (up to 80%) in the Chui Valley mainly occur on atmospheric fronts, most often on secondary ones.
Hail is a dangerous meteorological phenomenon. In the Chui Valley, hail falls from April to June. During the growing season, the average number of days with hail in the plain of the Chui Valley is 1-2, in the middle mountains 3-4 /Agroclimatic Handbook, 1972/.
Hail usually falls in a narrow strip ranging from hundreds of meters to 10-15 km wide and up to several hundred kilometers long. It causes mechanical damage to agricultural plants and fruit trees, knocking off flowers, leaves, and fruits, and breaking stems. Hail is especially dangerous when accompanied by strong winds and downpours. A downpour can cause crops to lodge, inflict mechanical damage to plants, and wash away the topsoil.
In Bishkek, hail can occur from April to June. In some years, there may be two instances of hail in these months. On average, there is one day with hail per year; the highest number of days with hail is 4 (Baitik). Hail is most often observed in the afternoon. The duration of hail is usually insignificant (less than 20 minutes). Strong hail in Bishkek is very rare.
Glaze ice is a layer of dense, glass-like ice that forms on the windward side of any objects during light frosts (0°-3°C) due to the freezing of supercooled raindrops or fog. Often, communication and power lines, tree branches, and roofs of houses are covered with a solid layer of glaze ice. In some cases, glaze ice can cause significant damage to property. Glaze ice phenomena occur throughout the winter period from 1 to 3 times a month and are observed annually /Climate. Frunze, 1990/.
Frosts are an unfavorable weather phenomenon. Spring and early spring frosts in the Chui Valley last on average 4-8 days. Spring frosts occur at the end of April, late frosts in May. Autumn frosts generally occur in September, with the latest in October. In Bishkek, the average duration of frosts at the soil surface is 3 days in April and 1 day in May. In the autumn period, starting from the third decade of September, the average duration of frosts of any intensity is 2-3 days. In some years, the duration of frosts can be significant - 5-7 days.
To identify the conditions for the occurrence of particularly dangerous frosts for each year from 1951 to 1977, the dates of the transition of the average daily air temperature through 10°C were determined. Over 27 years, 23 cases of particularly dangerous air frosts in spring and 12 cases in autumn were observed in the Chui Valley. Thus, particularly dangerous frosts in spring are noted almost annually in the Chui Valley, while in autumn, they occur once every two years.
The seasons are distinctly manifested in the Chui Valley. In climatology, the boundaries of seasons are determined by the dates of the transition of the average daily air temperature to certain limits and by some other criteria, not by astronomical signs.
Thus, the climate of the Chui Valley is diverse even over relatively short distances. The most significant feature is the clear differentiation of altitudinal climatic zones. In the plain zone and foothills, the climate is characterized by relatively dry hot summers and moderately warm, low-snow winters, with a sharply expressed continentality. The middle mountain zone is characterized by moderately hot summers, the maximum amount of precipitation, and mild warm winters. The high mountain belt is characterized by cool humid summers and harsh cold winters. This is the zone dominated by eternal frost, snow, and ice.
In conclusion, it is important to note that the upper limits of agricultural cultivation zones and the timing of sowing agricultural crops, as well as the duration of livestock grazing in mountain pastures, largely depend on the prevailing weather-climatic conditions and the altitude of the terrain. The long cold period of the year determines the insurance reserves of fodder and the types of agricultural and livestock premises.