Thundersnow
A rare phenomenon where thunder and lightning occur during a snowstorm. Thundersnow typically happens in intense winter storms and is often associated with heavy snowfall rates of 2-4 inches per hour.
More Precipitation Terms
Freezing Rain
Rain that falls as liquid but freezes on contact with surfaces at or below 32°F (0°C), creating a coating of ice called glaze. Freezing rain is extremely dangerous as it can make roads impassable and cause widespread power outages from ice-coated power lines.
Sleet
Frozen raindrops that bounce when hitting the ground. Sleet forms when snowflakes partially melt falling through a warm layer, then refreeze in a cold layer near the surface. Unlike freezing rain, sleet is frozen before it hits the ground.
Hail
Balls or irregular lumps of ice produced in severe thunderstorms. Hailstones form when updrafts carry raindrops into extremely cold areas of the atmosphere where they freeze. Repeated cycles through the updraft can create hailstones larger than softballs.
Graupel
Soft, small pellets of ice formed when supercooled water droplets freeze onto falling snowflakes. Also called snow pellets, graupel is crumbly and opaque, unlike the hard, clear ice of hail. It often occurs in spring and fall storms.
Virga
Precipitation that falls from clouds but evaporates before reaching the ground. Virga appears as wispy streaks extending from the base of clouds and is common in dry or desert climates where the air below clouds has low humidity.
Snow Squall
An intense, short-lived burst of heavy snow accompanied by strong winds and often causing a sudden drop in visibility to near zero. Snow squalls can create extremely dangerous driving conditions despite lasting only 30-60 minutes.
Drizzle
Very light precipitation consisting of tiny water droplets less than 0.5mm in diameter that appear to float in the air. Drizzle typically falls from stratus clouds and reduces visibility more than light rain of the same intensity.
Atmospheric River
An atmospheric river is a long, narrow corridor of concentrated water vapor moving through the lower atmosphere, typically 250 to 375 miles wide and often more than 1,000 miles long. When one comes ashore and is lifted over mountains, it produces prolonged heavy rain and snow. Atmospheric rivers are rated from AR 1 (weak) to AR 5 (exceptional) by strength and duration.
Pineapple Express
A strong atmospheric river that carries moisture from the tropical Pacific near Hawaii to the West Coast of North America. Because the air is warm, a Pineapple Express raises mountain snow levels, so more precipitation falls as rain and can melt existing snowpack, increasing the flood risk.
Thundersnow: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
Weather Education
Weather Fronts Explained: Cold Front vs Warm Front, Occluded Fronts, and Map Symbols
What cold, warm, stationary, and occluded fronts are, how each is drawn on a weather map, and the clouds, rain, wind shift, temperature, and pressure changes to expect before, during, and after one passes.
Weather Education
What Does a 30% Chance of Rain Mean? Probability of Precipitation Explained
A 30% chance of rain means a 3 in 10 chance that at least 0.01 inch falls at your location during the forecast period. Learn how forecasters build the number, why hourly and daily chances differ, and what it says nothing about.
Weather Education
What an El Niño Winter Usually Brings, Region by Region
Seventy-five years of NOAA records show what strong El Niño winters actually did across the U.S.: a mild northern tier, a wet southern one, and why weak events barely shift the odds.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Tool
Snow-to-Liquid Ratio Calculator
Estimate snowfall from liquid equivalent and snow-to-liquid ratio.
Guide
Understanding Snow Totals
Why snow forecasts give ranges instead of exact numbers: snow ratios, banding, and elevation effects.
Guide
What Causes Thunder and Lightning?
How lightning forms through charge separation, what causes thunder, and how to stay safe.
Guide
Lightning Safety Guide
Know when lightning becomes dangerous, how far away it can strike, and when to move indoors.
Explore Other Terms
Kp Index
The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
Epicenter
The point on Earth's surface directly above where a fault rupture begins. It is a single map location, not the whole earthquake: a large event can break hundreds of kilometers of fault, so severe shaking often extends far beyond the epicenter.
Tornado
A tornado is a violently rotating column of air in contact with the ground, extending from a thunderstorm. Tornadoes are rated from EF0 to EF5 on the Enhanced Fujita scale by the damage they cause. Most last less than 10 minutes, but the strongest can stay on the ground for more than an hour.
Wind Chill
Wind chill is how cold the air feels on exposed skin once wind is taken into account. Wind strips heat from the body faster than still air does, so the wind chill temperature is lower than the air temperature. At 0°F with a 15 mph wind, the wind chill is -19°F, and exposed skin can freeze in 30 minutes.
Reflectivity
A measure of how much radar energy is reflected back by precipitation, measured in dBZ (decibels of Z). Higher values indicate heavier precipitation or larger particles. Values above 50 dBZ typically indicate heavy rain or hail.
ECMWF
ECMWF is the European Centre for Medium-Range Weather Forecasts, an intergovernmental organization supported by 35 states, and the name commonly given to its global weather model, often called the European model or the Euro. Its physics-based Integrated Forecasting System (IFS) runs on a global grid of about 9 km and forecasts up to 15 days ahead.
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