Rainfall Routing Walkthrough

A weather desk receives daily rainfall readings. Trace a loop plus a branch: every reading is visited once, but only days at or above the warning threshold add to the alert count.

const rainMm = [4, 18, 0, 23, 12];
let alertDays = 0;

for (const mm of rainMm) {
  if (mm >= 15) {
    alertDays += 1;
    console.log(`Alert: ${mm} mm`);
  } else {
    console.log(`Normal: ${mm} mm`);
  }
}
console.log(`Alert days: ${alertDays}`);

Run it, then change the threshold from 15 to 20. Predict which day changes category before you run again. alertDays starts outside the loop so its value survives each iteration; the if chooses which message to log. In the next lesson, use this pattern on a different batch of values.