Book by Mark L. Morrissey

Chance of Rain

What Probability Really Means in Everyday Life

Probability is not a way to eliminate uncertainty. It is a way to behave intelligently in its presence.

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Chance of Rain book cover
Chance of Rain book cover

The central idea

Better questions before reality arrives

A forecast is not a promise, a rare event is not impossible, and a confident number is not automatically a trustworthy one.

This general-reader book begins with weather because nearly everyone has misunderstood a rain forecast. It then carries the same reasoning into medical tests, hurricanes, insurance, climate projections, artificial intelligence, markets, and daily decisions.

“Probability is a long-run language forced to speak to people who live one Tuesday at a time.”
  • Understand what a 30 percent forecast actually means.
  • Combine probability with consequences instead of demanding false certainty.
  • Judge forecasts by calibration and repeated evidence, not one memorable outcome.
  • Recognize base-rate mistakes, tail risk, model limits, and overconfident AI answers.
  • Use a practical framework for making decisions when uncertainty cannot be removed.

Inside the book

Twelve chapters from forecasts to decisions

  1. The Forecast Is Not a Promise
  2. What Does 30 Percent Mean?
  3. The Umbrella Problem
  4. Wrong Once, Useful Many Times
  5. Rare Does Not Mean Impossible
  6. The Cone of Uncertainty
  7. Base Rates: The Boring Thing That Matters
  8. Models Are Maps
  9. Climate Is Not Tomorrow's Weather
  10. AI and the Confidence Problem
  11. Markets, Models, and Mirage
  12. How to Think in Probabilities

Who it is for

Readers who want useful uncertainty, not vague hedging

Weather users

Anyone who has wondered whether a forecast was “wrong” because one afternoon turned out differently.

Decision-makers

Readers weighing medical, insurance, financial, emergency, or everyday choices where consequences matter as much as likelihood.

Critical thinkers

People who want to evaluate models, AI systems, market claims, and confident predictions without either blind trust or blanket cynicism.

General-information disclaimer: This book and page are for educational purposes. They are not medical, legal, financial, trading, or emergency-management advice. Consult qualified professionals and official sources for specific decisions.