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Then, afternoon cumulus clouds form which rarely cause rain in the vicinity of Chabua, although they may be intense west of Jorhat. An average afternoon in the valley is marked by a few scattered cumulus clouds with thunder showers west of Jorhat. These clouds clear during the evening. Then, during the early morning hours, the stratocumulus decks form again along with occasional thunderstorm clouds.

[[underlined]] c. [[/underlined]] A variation in the summer pattern in the valley is caused by local cold fronts moving up the valley fifteen to twenty miles per hour. Such disturbances may occur at any time during the day and last for brief periods of time sometimes as long as two hours. The clouds roll in from the southwest, cause rain showers and clear away, perhaps within a half hour. Surface winds increase to fifteen and twenty miles per hour and light to moderate rain falls. These storms offer little difficulty if the pilot can afford to circle for an hour or so while the rainy weather passes by.

[[underlined]] d. [[/underlined]] Another infrequent variation in the summer pattern in the valley is caused by strong incursions of air from the Bay of Bengal. At these times rain may last all during the morning and afternoon, dropping off during the evening and increasing again during the early morning hours.

3. [[underlined]] CHINA TERMINALS [[/underlined]]

[[underlined]] a. [[/underlined]] The summer season et Yunnanyi and Kunming lasts from May through September. May brings an increase of 600% in the rainfall over the amounts for preceding months. There is a continued monthly increase through July and then a gradual decrease through September, the last monsoon month. Summer weather is the result of a series of frontal waves which form south and east of Kunming and suck in the moist air from the South China Sea. Weather outbreaks may last for a week at a time with ceilings varying between 300 and 1,000 feet, accompanied by intermittent rainfall all during the period. Only occasionally does visibility drop as low as one mile in rain. Surface winds at Kunming shift into the southeast, east or northeast and increase to ten to fifteen miles per hour. During the worst of these disturbances, there are usually breaks in the clouds at least by mid-afternoon. On days not affected by strong frontal activity the low clouds in the mornings are usually 1,000 feet or more above the ground and are replaced by broken to scattered cumulus clouds during the afternoons. Afternoon and early morning thunderstorms occur infrequently at China Terminals, but storms at Kunming have kept the field closed for one to two hours and caused crack-ups of ships attempting to land while the storms were in progress. Such storms can readily be avoided, either by waiting or by flying to an alternate field.

[[underlined]] b. [[/underlined]] Yunnanyi is often open when Kunming is closed during the monsoon season and when both these fields are closed, there is an emergency landing field at Chaotung, 220 miles east-north-east of Likiang. It is at Chaotung that the monsoon effect stops and there is very little summer rain.

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(Page 5, ICW-ATC Cir #18, 26 March, 1944)

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