Running Weather Glossary: Complete Guide to Weather Terms Every Runner Should Know

Weather affects every run. Understanding weather terminology helps you interpret forecasts, make better decisions, and communicate more effectively about conditions. This glossary covers all the weather terms runners encounter, organized by category with explanations of why each matters for running.

Temperature Terms

Ambient Temperature

Definition: The actual air temperature measured by a thermometer, typically in shade at standard height (about 5 feet above ground).

Why it matters for running: Ambient temperature is your starting point for dressing decisions, but it's not the complete picture. The same ambient temperature can feel very different depending on humidity and wind.

Running application: Use as baseline, but always check feels-like temperature for more accurate planning.

Feels-Like Temperature (Apparent Temperature)

Definition: A calculated temperature that represents how conditions actually feel to the human body, accounting for wind and humidity effects.

Why it matters for running: This is often more useful than ambient temperature because it reflects your actual experience. A 50°F day with 20 mph wind feels much colder than a calm 50°F day.

Running application: Dress for feels-like temperature, not just the thermometer reading. This prevents both overdressing and underdressing.

Heat Index

Definition: A measure that combines air temperature and relative humidity to determine how hot it actually feels. Also called "humiture" or "humid heat."

Why it matters for running: When humidity is high, sweat doesn't evaporate efficiently, impairing your body's cooling system. The heat index quantifies this effect.

Heat index scale for runners:

Below 80°F: Comfortable for most
80-90°F: Caution needed; reduce intensity
90-105°F: High caution; significantly reduce pace
Above 105°F: Dangerous; consider indoor alternatives

Running application: In summer, heat index matters more than temperature alone. Check before hot-weather runs and adjust expectations accordingly.

Wind Chill

Definition: A measure that combines air temperature and wind speed to determine how cold it feels on exposed skin. Based on heat loss rate from the body.

Why it matters for running: Wind strips heat from your body much faster than still air. A moderate temperature with significant wind can feel extremely cold.

Wind chill reference points:

Above 30°F: Standard cold-weather precautions
15-30°F: Serious cold; protect all exposed skin
0-15°F: Frostbite risk on exposed skin within 30 minutes
Below 0°F: Frostbite risk within 10-15 minutes

Running application: In cold weather, wind chill determines your gear needs. Dress for wind chill, not thermometer temperature, especially for extremities and exposed skin.

Dew Point

Definition: The temperature at which water vapor in the air would condense into liquid water. Measures the absolute amount of moisture in the air.

Why it matters for running: Dew point is a better indicator of running comfort than relative humidity because it's an absolute measure. The same dew point means the same moisture regardless of temperature.

Dew point guide for runners:

Below 55°F: Comfortable; sweat evaporates easily
55-60°F: Comfortable for most runners
60-65°F: Getting uncomfortable; performance impact begins
65-70°F: Uncomfortable; significant performance impact
Above 70°F: Oppressive; dangerous for hard efforts

Running application: Check dew point before summer runs. High dew point requires pace adjustment regardless of temperature.

Wet Bulb Temperature

Definition: The lowest temperature achievable through evaporative cooling. Measured by wrapping a wet cloth around a thermometer bulb.

Why it matters for running: Wet bulb temperature indicates how well your body can cool through sweating. If wet bulb temperature exceeds skin temperature, evaporative cooling fails.

Running application: Rarely checked by recreational runners but valuable in extreme heat. Wet bulb temperatures above 80°F are dangerous for exercise.

Wet Bulb Globe Temperature (WBGT)

Definition: A composite temperature used to estimate heat stress that accounts for temperature, humidity, wind speed, sun angle, and cloud cover (solar radiation).

Why it matters for running: WBGT is the most comprehensive heat stress indicator, used by military and sports organizations for activity guidelines.

WBGT guidelines:

Below 65°F: Generally safe for all activities
65-73°F: Monitor high-risk individuals
73-82°F: Increase rest, reduce intensity
82-87°F: Limit intense activity
Above 87°F: Cancel strenuous activity

Running application: WBGT is often reported at races; understand what the number means for your pacing decisions.

Moisture and Precipitation Terms

Relative Humidity

Definition: The percentage of water vapor currently in the air relative to the maximum the air could hold at that temperature.

Why it matters for running: High humidity impairs sweat evaporation. But the same relative humidity feels different at different temperatures (80% humidity at 60°F vs. 80°F are very different experiences).

Limitations: Relative humidity changes with temperature even when actual moisture stays constant. Morning humidity is often high, but that doesn't mean midday will feel humid if temperature rises.

Running application: Consider relative humidity alongside temperature. High humidity is most problematic when combined with high temperature.

Precipitation

Definition: Any form of water—liquid or solid—falling from the atmosphere. Includes rain, snow, sleet, freezing rain, hail, and drizzle.

Why it matters for running: Precipitation affects visibility, footing, comfort, and safety. Different types have different implications for running.

Precipitation Probability (Chance of Rain)

Definition: The likelihood that precipitation will occur somewhere in the forecast area during the specified time period.

What it actually means: If a forecast says 40% chance of rain, it means that given similar conditions 100 times, rain would occur 40 times. It does NOT mean 40% of the area will get rain or that it will rain for 40% of the time.

Running application: Check hourly precipitation probability. A 40% chance for the day might be concentrated in one period, leaving other hours clear.

Drizzle

Definition: Light precipitation consisting of very small water droplets (smaller than rain droplets).

Why it matters for running: Drizzle is usually comfortable to run in. It doesn't typically soak you quickly and can actually feel cooling.

Running application: Drizzle alone rarely requires gear changes. Light drizzle on a mild day is pleasant running.

Rain Intensity

Definition: How much rainfall occurs per unit time, typically measured in inches per hour.

Light rain: Less than 0.10 inches/hour
Moderate rain: 0.10-0.30 inches/hour
Heavy rain: Greater than 0.30 inches/hour

Why it matters for running: Light rain is usually fine; heavy rain affects visibility, footing, and comfort significantly.

Running application: Light rain is no reason to skip a run. Heavy rain may warrant adjustment or postponement.

Thunderstorm

Definition: A storm producing lightning and thunder, typically associated with heavy rain, strong winds, and sometimes hail.

Why it matters for running: Thunderstorms are dangerous for runners. Lightning can strike miles from the storm center, and winds can blow debris.

Running application: Do NOT run during thunderstorms. If you hear thunder, lightning is close enough to be dangerous. Seek shelter immediately.

Freezing Rain

Definition: Rain that falls as liquid but freezes on contact with cold surfaces, creating ice coating.

Why it matters for running: Freezing rain creates extremely dangerous running surfaces. Ice forms invisibly on roads and paths.

Running application: Do not run outdoors during or immediately after freezing rain. Even with traction devices, conditions are hazardous.

Sleet

Definition: Ice pellets that form when snow melts then refreezes before reaching the ground.

Why it matters for running: Sleet creates slippery conditions and can be uncomfortable to run in (ice pellets hitting face/skin).

Running application: Sleet signals challenging and worsening conditions. May want to head inside.

Snow

Definition: Ice crystals that form in clouds and fall to the ground, maintaining solid form.

Why it matters for running: Light snow can be beautiful to run in. Heavy snow affects visibility and footing. Accumulated snow changes running dynamics significantly.

Running application: Fresh light snow is often pleasant. Heavy snow or icy conditions require appropriate footwear and caution.

Accumulation

Definition: The amount of snow, sleet, or ice that collects on surfaces, measured in inches or centimeters.

Why it matters for running: Accumulation affects footing and route selection. A few inches of snow is manageable; significant accumulation changes running plans.

Running application: Check accumulation forecasts and actual conditions. Your route may need modification.

Wind Terms

Wind Speed

Definition: The rate of air movement, typically measured in miles per hour (mph) or kilometers per hour (kph).

Why it matters for running: Wind affects perceived temperature (wind chill), running effort (headwind/tailwind), and balance at high speeds.

Wind speed categories for running:

Calm (0-5 mph): Negligible effect
Light (5-10 mph): Minimal effect
Moderate (10-15 mph): Noticeable; may affect pace
Fresh (15-20 mph): Significant; affects effort and dressing
Strong (20-30 mph): Challenging; affects safety
Very strong (30+ mph): Consider postponing

Wind Direction

Definition: The compass direction from which wind is blowing. A "north wind" blows FROM the north (toward the south).

Why it matters for running: Wind direction determines whether you face headwind or tailwind on different sections of your route.

Running application: Start runs into the wind to finish with wind assistance. Plan route direction based on wind direction.

Headwind

Definition: Wind blowing directly against your direction of travel.

Why it matters for running: Headwinds significantly increase energy expenditure. Running 8 mph into a 10 mph wind means you're pushing through 18 mph of air resistance.

Impact estimates:

10 mph headwind: ~12-20 seconds/mile slower at same effort
15 mph headwind: ~20-30 seconds/mile slower
20 mph headwind: ~35-50 seconds/mile slower

Running application: Expect slower paces in headwind. Don't try to maintain normal pace; run by effort.

Tailwind

Definition: Wind blowing in the same direction as your travel.

Why it matters for running: Tailwinds reduce air resistance and provide assistance, though less than the equivalent headwind costs.

Running application: Enjoy the assistance but recognize tailwind helps less than headwind hurts. Net effect on out-and-back routes is always negative.

Crosswind

Definition: Wind blowing perpendicular to your direction of travel.

Why it matters for running: Crosswinds don't affect pace as much as headwinds but can be annoying and affect balance at high speeds.

Running application: Crosswind is generally manageable. May cause slight lateral movement.

Sustained Wind

Definition: The average wind speed over a period (usually 2 minutes in weather reporting).

Why it matters for running: Sustained wind indicates the consistent wind you'll face.

Running application: Sustained wind is your baseline expectation for conditions.

Wind Gusts

Definition: Brief increases in wind speed above the sustained level.

Why it matters for running: Gusts can catch you off guard, affect balance, and are more disruptive than the same average speed as sustained wind.

Forecast format: "Winds 15 mph with gusts to 25 mph" means expect mostly 15 mph wind with bursts to 25 mph.

Running application: Note the gust speed. Large differences between sustained and gust indicate variable, potentially difficult conditions.

Calm

Definition: Wind speed below 2-3 mph; essentially no perceptible wind.

Why it matters for running: Calm conditions eliminate wind chill and wind resistance, creating optimal conditions for many runners.

Running application: Calm conditions are generally ideal, except in heat (when breeze would help cooling).

Air Quality and Atmospheric Terms

Air Quality Index (AQI)

Definition: A standardized measure of air pollution levels, reported as a number from 0 to 500.

AQI categories:

0-50 (Green): Good; no limitations
51-100 (Yellow): Moderate; sensitive individuals may notice
101-150 (Orange): Unhealthy for sensitive groups
151-200 (Red): Unhealthy for all
201-300 (Purple): Very unhealthy
301-500 (Maroon): Hazardous

Why it matters for running: Exercise increases breathing rate, meaning more pollutant intake. Runners are especially vulnerable to poor air quality.

Running application: Check AQI before running. Above 150, consider indoor alternatives. Above 100, reduce intensity.

UV Index

Definition: A measure of solar ultraviolet radiation intensity at the Earth's surface, scaled 1-11+.

UV Index scale:

1-2: Low; minimal protection needed
3-5: Moderate; seek shade midday
6-7: High; protection essential
8-10: Very high; avoid midday sun
11+: Extreme; avoid outdoor exposure

Why it matters for running: High UV exposure causes sunburn, increases skin cancer risk, and can cause eye damage.

Running application: Apply sunscreen before running, wear protective clothing and sunglasses. Consider timing runs to avoid peak UV (midday).

Barometric Pressure (Atmospheric Pressure)

Definition: The weight of the atmosphere pressing down on a point, measured in inches of mercury (inHg) or millibars (mb).

Why it matters for running: Some runners are weather-sensitive and feel different with pressure changes. Falling pressure often precedes storms.

Running application: Generally not critical for run planning unless you're weather-sensitive. Falling pressure may signal incoming precipitation.

Visibility

Definition: The distance at which objects can be clearly seen, affected by fog, haze, precipitation, and atmospheric conditions.

Why it matters for running: Reduced visibility affects safety (cars can't see you) and navigation.

Running application: In poor visibility (fog, heavy rain), wear reflective/bright clothing and exercise extra caution near traffic.

Ozone

Definition: A gas that at ground level is a pollutant harmful to respiratory systems.

Why it matters for running: Ground-level ozone irritates airways and can cause breathing difficulty, especially during exercise.

Running application: Ozone levels typically peak in afternoon on hot, sunny days. Morning runs may have lower ozone exposure.

Forecast and Observation Terms

Forecast

Definition: Prediction of future weather conditions based on atmospheric models and meteorological analysis.

Reliability windows:

0-24 hours: Very reliable
2-3 days: Quite reliable
4-5 days: Moderate reliability
6-10 days: Low reliability
Beyond 10 days: Trends only

Running application: Trust short-term forecasts for specific planning. Use longer-range forecasts for general preparation only.

Radar

Definition: Technology that detects precipitation by bouncing radio waves off water droplets, showing precipitation location and intensity.

Why it matters for running: Radar shows where rain/snow is actually falling right now, not just forecasted.

Running application: Check radar before running if precipitation is possible. Great for timing runs around weather.

Current Conditions (Observations)

Definition: Actual weather conditions as currently measured, not forecasted.

Running application: Always check current conditions before heading out. Forecast may have changed.

Advisory/Watch/Warning

Definition: Official weather notices indicating potential or actual hazardous conditions.

Advisory: Conditions may cause inconvenience; not expected to be life-threatening
Watch: Conditions are possible; be prepared
Warning: Conditions are occurring or imminent; take action

Running application: Watches warrant attention to conditions. Warnings may require postponing outdoor running.

Key Takeaways

Feels-like matters more than actual. Dress and plan for apparent temperature, not thermometer reading.
Dew point beats humidity. For summer running, dew point is the better moisture indicator.
Wind chill is real. In cold weather, wind chill determines frostbite risk and gear needs.
Probability isn't duration. 40% chance of rain doesn't mean 40% of the day will be wet.
Lightning means shelter. Thunder = danger. Don't hesitate; get inside.
AQI affects runners especially. Check air quality before running; our elevated breathing makes us vulnerable.
Short-term forecasts are reliable. Trust tomorrow's forecast; be skeptical of next week's.
Radar shows reality. For timing around precipitation, radar shows what's actually happening.

Understanding weather terminology helps you make better running decisions. Run Window interprets this data for you, turning weather complexity into simple recommendations for when to run.