Live heat risk, updates hourly
Where It's Too Hot to Run Today
Air temperature is not what makes a run feel dangerous. Dew point is. When the dew point climbs above about 60°F (16°C), sweat stops evaporating efficiently, so the body cannot cool itself even when the thermometer looks reasonable. A muggy 75°F (24°C) morning in a humid city can slow a runner more than a dry 95°F (35°C) afternoon in a desert one, because the dry city's sweat still evaporates.
Every score below is RunWeather's Run Score, the same 0 to 100 verdict the app shows a runner before they head out. Heat stress uses wet-bulb globe temperature (WBGT), the heat-strain mechanism race directors use to call off events, so a city can carry high heat stress even on a day that does not look extreme on a normal weather app.
Last updated Sep 10, 2026, 8:25 PM UTC. Live data for 57 of 57 cities.
Hottest heat risk right now
The five cities carrying the worst heat stress today, ranked by estimated WBGT.
Every city, ranked worst first
All 57 cities, sorted by today's heat stress. Tap a city for its full hour-by-hour breakdown.
| City | Peak temp today | Dew point | Run Score | Heat stress | Best window today |
|---|---|---|---|---|---|
| Miami | 87°F (31°C) | 83°F (28°C) | 35 Poor | Extreme heat stress | No safe window today |
| Houston | 91°F (33°C) | 77°F (25°C) | 24 Poor | Extreme heat stress | 11 PM |
| Singapore | 83°F (28°C) | 75°F (24°C) | 36 Poor | Extreme heat stress | No safe window today |
| Bangkok | 87°F (31°C) | 75°F (24°C) | 40 Poor | Extreme heat stress | 7–8 AM |
| Austin | 94°F (34°C) | 74°F (24°C) | 18 Poor | Extreme heat stress | 12–1 AM |
| Atlanta | 89°F (32°C) | 73°F (23°C) | 34 Poor | Extreme heat stress | 2–8 AM |
| Nashville | 91°F (33°C) | 72°F (22°C) | 25 Poor | Extreme heat stress | 10–11 PM |
| Dallas | 96°F (36°C) | 71°F (22°C) | 15 Poor | Extreme heat stress | 4–8 AM |
| Dubai | 107°F (42°C) | 71°F (22°C) | 33 Poor | Extreme heat stress | 5–7 AM |
| Washington, D.C. | 88°F (31°C) | 71°F (22°C) | 39 Poor | Extreme heat stress | 4–9 AM |
| Hong Kong | 88°F (31°C) | 69°F (21°C) | 59 Fair | Extreme heat stress | 1–8 AM |
| Philadelphia | 86°F (30°C) | 69°F (21°C) | 39 Poor | Extreme heat stress | 5–8 AM |
| San Diego | 87°F (31°C) | 68°F (20°C) | 27 Poor | Extreme heat stress | 12–7 AM |
| Phoenix | 104°F (40°C) | 67°F (20°C) | 4 Poor | Extreme heat stress | 3–7 AM |
| Los Angeles | 99°F (37°C) | 67°F (20°C) | 23 Poor | Extreme heat stress | 12–7 AM |
| Las Vegas | 108°F (42°C) | 40°F (4°C) | 32 Poor | Extreme heat stress | 12–8 AM |
| Rome | 80°F (27°C) | 73°F (23°C) | 2 Poor | High heat stress | 1 AM–12 PM |
| New York City | 87°F (30°C) | 69°F (21°C) | 43 Poor | High heat stress | 5–9 AM |
| Boston | 84°F (29°C) | 66°F (19°C) | 46 Fair | High heat stress | 10–11 PM |
| Lisbon | 85°F (29°C) | 49°F (9°C) | 55 Fair | High heat stress | 6–9 AM |
| Montreal | 70°F (21°C) | 68°F (20°C) | 43 Poor | Moderate heat stress | 11 PM |
| Chicago | 71°F (22°C) | 67°F (19°C) | 71 Good | Moderate heat stress | 1–9 AM |
| São Paulo | 70°F (21°C) | 66°F (19°C) | 66 Good | Moderate heat stress | 3–4 AM |
| Tokyo | 69°F (20°C) | 66°F (19°C) | 61 Fair | Moderate heat stress | 12–2 AM |
| Lima | 74°F (24°C) | 64°F (18°C) | 50 Fair | Moderate heat stress | 4–11 AM |
| Portland | 76°F (25°C) | 58°F (15°C) | 68 Good | Moderate heat stress | 4–7 AM |
| San Francisco | 79°F (26°C) | 57°F (14°C) | 55 Fair | Moderate heat stress | 4–8 AM |
| Seattle | 69°F (21°C) | 57°F (14°C) | 79 Good | Moderate heat stress | 10–11 PM |
| Perth | 74°F (24°C) | 55°F (13°C) | 71 Good | Moderate heat stress | 9–11 PM |
| Toronto | 78°F (26°C) | 53°F (12°C) | 59 Fair | Moderate heat stress | 11 PM |
| Minneapolis | 76°F (24°C) | 53°F (12°C) | 59 Fair | Moderate heat stress | 5–7 AM |
| Mexico City | 74°F (23°C) | 53°F (12°C) | 66 Good | Moderate heat stress | 5–9 AM |
| Barcelona | 80°F (27°C) | 53°F (12°C) | 70 Good | Moderate heat stress | 4–10 AM |
| Nairobi | 75°F (24°C) | 51°F (11°C) | 84 Great | Moderate heat stress | 12–3 AM |
| Seoul | 76°F (25°C) | 51°F (10°C) | 92 Great | Moderate heat stress | 12–8 AM |
| Salt Lake City | 86°F (30°C) | 29°F (-1°C) | 53 Fair | Moderate heat stress | 4–5 AM |
| Madrid | 81°F (27°C) | 26°F (-4°C) | 73 Good | Moderate heat stress | 8–9 AM |
| Denver | 86°F (30°C) | 18°F (-8°C) | 53 Fair | Moderate heat stress | 8 AM |
| Dublin | 65°F (18°C) | 58°F (15°C) | 57 Fair | Low heat stress | 1–3 AM |
| Edinburgh | 61°F (16°C) | 58°F (15°C) | 68 Good | Low heat stress | 8 PM |
| Manchester | 60°F (16°C) | 57°F (14°C) | 66 Good | Low heat stress | 7–9 AM |
| Stockholm | 57°F (14°C) | 55°F (13°C) | 81 Great | Low heat stress | 2–3 AM |
| Brisbane | 69°F (21°C) | 53°F (12°C) | 90 Great | Low heat stress | 2–7 AM |
| Amsterdam | 63°F (17°C) | 52°F (11°C) | 84 Great | Low heat stress | 12–9 AM |
| Cape Town | 65°F (18°C) | 51°F (11°C) | 43 Poor | Low heat stress | 2 AM |
| Vienna | 65°F (18°C) | 50°F (10°C) | 85 Great | Low heat stress | 2–11 PM |
| Sydney | 65°F (18°C) | 50°F (10°C) | 79 Good | Low heat stress | 7–11 PM |
| Auckland | 57°F (14°C) | 49°F (9°C) | 76 Good | Low heat stress | 6–8 AM |
| Calgary | 59°F (15°C) | 47°F (8°C) | 70 Good | Low heat stress | 8–10 PM |
| Melbourne | 58°F (14°C) | 47°F (8°C) | 37 Poor | Low heat stress | 11 AM |
| London | 68°F (20°C) | 45°F (7°C) | 57 Fair | Low heat stress | 5–9 AM |
| Munich | 63°F (17°C) | 45°F (7°C) | 92 Great | Low heat stress | 3–9 AM |
| Paris | 70°F (21°C) | 44°F (7°C) | 82 Great | Low heat stress | 4–9 AM |
| Berlin | 65°F (19°C) | 44°F (7°C) | 88 Great | Low heat stress | 9–11 PM |
| Wellington | 55°F (13°C) | 44°F (7°C) | 47 Fair | Low heat stress | 8–11 PM |
| Buenos Aires | 65°F (19°C) | 43°F (6°C) | 73 Good | Low heat stress | 7–9 AM |
| Vancouver | 55°F (13°C) | 42°F (6°C) | 84 Great | Low heat stress | 6–9 PM |
A concrete example
Houston and Phoenix can both post a hot summer forecast, but they rarely carry the same risk. Houston's Gulf humidity keeps dew points in the 70s (Fahrenheit) for months, so sweat barely evaporates and the body keeps overheating, hour after hour. Phoenix runs hotter on the thermometer but far drier, so sweat still cools effectively and the heat stress reading is often lower, until the desert sun and low humidity push dehydration risk up instead. Same season, two different reasons to slow down. The dew point and WBGT columns above, not the raw temperature, are what to read first.
Heat risk for runners: FAQ
Why does dew point matter more than air temperature for heat risk?
Your body cools by evaporating sweat. When the dew point climbs above roughly 60°F (16°C), the air is already too saturated for sweat to evaporate efficiently, so heat builds up even on a day that does not look extreme on the thermometer. That is why a muggy 75°F morning can slow you more than a dry 95°F afternoon.
How is heat stress calculated on this page?
Heat stress uses an estimated wet-bulb globe temperature (WBGT), the heat-strain mechanism race directors use to decide whether to delay or cancel an event. It folds in temperature, dew point, sun, and wind, so it can flag risk even when air temperature alone looks moderate.
What is the Run Score shown for each city?
A 0-100 verdict for how running conditions feel right now, the same score the RunWeather app shows before a run. It blends heat, dew point, wind, sun, and precipitation into one number: 80+ is Great, 65-79 is Good, 55-64 is Fair, 45-54 is Tough, and below 45 is Poor.
How often does this page update?
Every hour, from each city's live hourly forecast. The ranking, temperatures, and best windows all refresh on that cycle.
What happens if live data is not available for a city?
That city falls back to its typical conditions for the current month, computed from three years of hourly ERA5 history (2022 to 2024), and is marked as an estimate in the table. The page is built to keep showing a genuine number instead of an error, which matters most on the exact days (a heat wave) when live data is most valuable.
Get this on every run, automatically
RunWeather syncs with Strava, plans your week, and learns your heat tolerance, so the right time to run finds you. Free on iPhone and Android.
Running weather guides
How each kind of weather changes your run, and the cities where it matters most.