Norwesters are violent pre-monsoon thunderstorms that are especially prominent in which pair of countries in South Asia?

Introduction / Context:
Norwesters are a well known seasonal weather phenomenon in South Asia. They are violent thunderstorms that occur mainly in the hot pre-monsoon months and are locally called by various names. In India, they are often known as “Kalbaishakhi” in parts of eastern India. General knowledge and geography questions frequently ask where these storms are most prominent, as this helps test understanding of regional climatology.

Given Data / Assumptions:

• The term used is “Norwesters”, referring to a specific pattern of thunderstorms.
• Four pairs of neighbouring countries are listed as options.
• We assume basic knowledge of where such storms are commonly reported in weather and climate discussions.

Concept / Approach:
Norwesters typically affect eastern and north-eastern parts of India and large areas of Bangladesh during the hot weather season. They are associated with strong winds, lightning, heavy rain and sometimes hail. The name arises because the storms often move in from north-westerly directions relative to affected localities. Among the options, the pair that correctly captures the primary region of occurrence is India and Bangladesh. The other pairs include countries where Norwesters are not normally described as a prominent seasonal phenomenon.

Step-by-Step Solution:
Step 1: Recall that Norwesters, also called Kalbaishakhi in local Bengali terminology, occur mainly over eastern India, especially West Bengal, Assam and neighbouring states, and across much of Bangladesh. Step 2: These storms usually develop during late afternoons and evenings in the pre-monsoon months due to intense surface heating, moisture influx and atmospheric instability. Step 3: Because they affect both eastern India and Bangladesh extensively, these two countries together form the core area associated with Norwesters. Step 4: Examine the options: India and Bhutan, Bhutan and Nepal and Bangladesh and Myanmar all include at least one country where Norwesters are not commonly highlighted as a major named phenomenon in exam-level climatology. Step 5: India and Bangladesh is the only pair that matches the widely taught geographic distribution of Norwesters. Step 6: Therefore, the correct answer is the pair India and Bangladesh.

Verification / Alternative check:
School and competitive exam geography books often describe Norwesters with a map showing their maximum intensity over Bengal and Assam in India and over Bangladesh. The storms are particularly feared by farmers and urban residents in these regions because they can damage crops, trees and weak structures. Weather reports in the pre-monsoon season from Kolkata and Dhaka also frequently use related terms. In contrast, Bhutan, Nepal and Myanmar are not usually mentioned as the primary region for Norwesters in exam-oriented climatology, confirming that India and Bangladesh is the correct pair.

Why Other Options Are Wrong:

• India and Bhutan: While eastern India is correct, Bhutan is not typically cited as a principal region for Norwesters in standard textbooks.
• Bhutan and Nepal: Both are Himalayan countries where local thunderstorms occur, but they are not the classic Norwester belt.
• Bangladesh and Myanmar: Bangladesh is part of the Norwester zone, but Myanmar is again not commonly included in exam-level discussions of Norwesters.

Common Pitfalls:
A typical mistake is to focus only on the fact that these countries are in or near the Himalayas and to guess randomly among neighbouring pairs. Another pitfall is to over generalise any pre-monsoon thunderstorm as Norwester, regardless of region. Remember that in exam context, Norwesters are particularly associated with eastern India and Bangladesh, and knowing this association helps quickly eliminate the distractor options.

Final Answer:
India and Bangladesh