तुषारदुर्दिनमगाधनिम्नप्रायं गहनतृणवृक्षं वा देशं ग्रीष्मे यायात् ॥ कZ_०९.१.३८ ॥
tuṣāra-durdinam agādha-nimna-prāyaṃ gahana-tṛṇa-vṛkṣaṃ vā deśaṃ grīṣme yāyāt
He should march in summer against a region characterized by frost and overcast days, or one full of deep depressions, or dense grass and trees.
Summer reduces cold and weather impediments and can improve passability and operational tempo in difficult terrain.