A typical September weekend in Boulder runs 24°C by day and 9°C overnight with rain on about 23% of days — a baseline weekend score of 79/100. A January weekend drops to 41/100. 5 of 12 months keep weekend rain risk below one day in four. The live Saturday-versus-Sunday verdict for the coming weekend loads at the top of this page.
Typical September weekend score: 79/100
Climate baseline for Boulder, used to judge whether the coming weekend is typical. The head-to-head Saturday and Sunday comparison above is live Open-Meteo forecast data and updates hourly.
Conditions on this page are recalculated from the latest forecast every time it is opened, for the current date in the location's own time zone. Showing .
| Strongest weekend month | September — 79/100 |
| Weakest weekend month | January — 41/100 |
| Months with low rain risk | 5 of 12 |
| Typical best-month weekend | 24°C day / 9°C night |
| Daylight in the best month | 12.2 hours |
| Wettest weekend risk | August — rain on about 37% of days |
| Annual weekend spread | 38 points between the best and worst month |
| Forecast reliability | Weekend forecasts stabilise from Thursday onward |
Boulder swings 38 points between September and January, so booking a weekend far ahead is a real gamble outside the strong months.
Climate cannot tell Saturday from Sunday — only the live forecast can. What climatology does tell you is how much is at stake: in January the gap between a good and a bad day in Boulder is worth planning around, in September far less so.
September gives 12.2 hours of daylight per day against 9.2 hours at the low point of the year — that is how much usable weekend you actually get.
Across the year Boulder sees rain on roughly 103 days, so an average weekend carries about a 28% chance of a wet day.
Baseline expectations for a weekend in each month. Compare them against the live Saturday and Sunday forecast above to see whether this weekend is better or worse than normal.
| Month | Day / night | Rain risk | Sun | Daylight | Weekend baseline |
|---|---|---|---|---|---|
| January | 7°C / -7°C | 30% | 6h | 9.5h | 41/100 |
| February | 9°C / -6°C | 30% | 6h | 10.5h | 45/100 |
| March | 13°C / -2°C | 37% | 6h | 11.8h | 51/100 |
| April | 19°C / 4°C | 37% | 7h | 13.1h | 65/100 |
| May | 24°C / 9°C | 37% | 7h | 14.3h | 71/100 |
| June | 28°C / 13°C | 23% | 10h | 14.8h | 78/100 |
| July | 30°C / 14°C | 33% | 8h | 14.5h | 66/100 |
| August | 28°C / 13°C | 37% | 8h | 13.6h | 66/100 |
| September | 24°C / 9°C | 23% | 9h | 12.2h | 79/100 |
| October | 19°C / 4°C | 17% | 10h | 10.9h | 78/100 |
| November | 13°C / -2°C | 17% | 9h | 9.7h | 63/100 |
| December | 9°C / -6°C | 23% | 7h | 9.2h | 49/100 |
Each metric is scored for both days and the winner is marked per row in the live comparison for Boulder.
| Metric | Why it decides the day |
|---|---|
| Daily mean temperature | Full credit between 15°C and 25°C; sharp penalties below 0°C or above 35°C. |
| Rain probability | Under 20% is a clean go; 70% or higher removes the day from outdoor consideration. |
| Wind speed | Below 20 km/h is a bonus; gusts above 40 km/h cut the score sharply. |
| Cloud cover | Decides whether the day reads as bright or flat, and drives photography value. |
| UV index | Sets protection needs for a full day outside. |
| Daylight and sunset | Determines how late outdoor plans can run. |
Each day in Boulder starts at a neutral 50 and gains or loses points on four measured variables. The day with the higher score is the one we tell you to prioritize.
| Factor | Weight | What it measures |
|---|---|---|
| Temperature comfort | ±20 pts | Full credit when the daily mean sits between 15°C and 25°C; penalties below 0°C or above 35°C. |
| Rain probability | ±20 pts | Under 20% adds the full bonus; 70% or higher removes 20 points outright. |
| Wind speed | ±15 pts | Below 20 km/h is a bonus; gusts above 40 km/h cut the score sharply. |
| Baseline | 50 pts | Neutral starting point, so scores stay comparable between cities and weekends. |
Above 75 means go ahead with outdoor plans. Between 50 and 75 expect compromises. Below 50, plan indoors. Weekend forecasts are most reliable from Thursday onward.
The live comparison at the top of this page scores both days on temperature, rain probability, wind, cloud, UV and daylight, and names the winner. Climate alone cannot separate two consecutive days — only the current forecast can.
September, with a baseline weekend score of 79/100: 24°C days, 12.2 hours of daylight and rain on about 23% of days. January is the weakest at 41/100.
Checked on Monday, a weekend forecast is indicative only. From Thursday onward ensemble models converge and the Saturday-versus-Sunday call becomes dependable. We show forecast confidence alongside each day so you know which case you are in.
Above 75 means commit. Between 50 and 75 means go ahead with an indoor fallback. Below 50 means move weather-dependent plans to the other day or indoors.
With rain on roughly 103 days a year, an average day carries about a 28% chance of rain. In August that rises to about 37%.