Weather and Forecasting
Introduction[edit]
The weather is the single most important factor in determining whether it’s safe to enter a canyon. For canyoneers, the ability to accurately interpret a forecast is therefore extremely important.
Public forecasts are designed to be simple and quickly understood. Some rely on visuals—icons, graphs, or hourly timelines that provide an instant snapshot of expected conditions. Others are text-based, with short descriptions like “Slight chance of rain this afternoon near Hanksville, UT.” Many combine both. The style may differ, but the purpose is the same: to deliver fast, intuitive information without requiring the user to dig deeper. For most everyday choices—commuting, picking clothes, planning errands—that approach works perfectly. People don’t need to know exactly which hours “afternoon” covers, what intensity qualifies as “rain,” or the precise geographic boundaries of the forecast zone. A general impression is usually enough.
As canyoneers, however, a simple understanding of the forecast is not enough. We must arm ourselves with a greater ability to interpret the forecast.
Note: This page is somewhat U.S.-centric, as it refers to forecast information from the National Weather Service and National Oceanic and Atmospheric Administration. However, the general principles discussed here apply universally, even if forecast sources differ in other parts of the world.
Forecast Area[edit]
Whether stated as a vague region or with clearly defined boundaries, every forecast is tied to a geographic area. Without knowing where a forecast applies, it is impossible to use it meaningfully. In everyday life, a reference to a town like “Hanksville” or “Escalante” might feel intuitive—you just assume it means somewhere around that place. For canyoneering, though, that kind of assumption is not good enough. Terrain, elevation, and watershed boundaries do not line up neatly with civic names, and relying on them can give a false sense of accuracy. We need more precision.
The National Weather Service uses two main types of areas:
- Point forecast: A 5 km × 5 km grid cell. Clicking on a location in the NWS map highlights the cell and provides the forecast specific to that point.
- Forecast zones: Larger areas defined by the NWS, often aligning with counties or groups of smaller zones. For example, Salt Lake County is its own forecast zone, while the “Wasatch Back” combines multiple zones. Zone forecasts may be derived from the collection of grid cells that make up the area.
These zones are not vague labels—they are official, mapped boundaries:
Time Period[edit]
Every forecast specifies not only what may happen but also when it may happen. Terms like “afternoon,” “overnight,” or “morning” may sound intuitive and casual, but they are more precise than most people realize. The National Weather Service (and many other providers) uses these terms within a standardized system, each tied to specific time windows.
Forecasts are stated in local time unless otherwise noted. Some specialized forecast products may instead be issued in Zulu time (UTC), but general forecasts for the public are almost always given in local time.
- 12-hour periods:
- "Today" – 6:00 a.m. to 6:00 p.m.
- "Tonight" – 6:00 p.m. to 6:00 a.m.
- 6-hour periods:
- "Morning" – 6:00 a.m. to 12:00 p.m.
- "Afternoon" – 12:00 p.m. to 6:00 p.m.
- "Evening" – 6:00 p.m. to 12:00 a.m.
- "Overnight" – 12:00 a.m. to 6:00 a.m.
- Hourly forecasts: Refer to the hour beginning at the stated time (e.g., “3:00 p.m.” means from 3:00–4:00 p.m.).
Forecast Metrics[edit]
The metrics included in a forecast vary depending on the source, and not all of the ones listed below will appear in every forecast. The following are some of the most common. Click the links to learn more about each metric and how to interpret them effectively.
- Probability of Precipitation (POP): The chance of measurable precipitation, typically expressed as a percentage.
- Temperature: Expected highs and lows for the time period.
- Sky Condition: How cloudy or clear the sky is expected to be, using terms like “partly cloudy,” “overcast,” or “sunny.”
- Wind: Direction and speed, sometimes with qualifiers like “breezy” or “gusty.”
- Relative Humidity: Expressed as a percentage.
- Dew Point: Expressed in relation to temperature.
- Thunder/Lightning Probability: How likely thunder or lightning will accompany a storm.
- Precipitation Type: Specifies the form of precipitation—rain, snow, hail, or a mix—when relevant.
- Quantitative Precipitation Forecast (QPF): The estimated amount of precipitation. This is not always shown in everyday forecasts but is available through NWS and similar sources.