Weather and climate forecasts

Weather and climate forecasts

   Overview
   Weather forecasts
   Subseasonal climate forecasts
   Seasonal climate forecasts
   Decadal climate forecasts

Overview

Weather and climate forecasts address the ubiquitous desire to know how the weather (temperature, precipitation, winds, cloud cover, etc.) will evolve over the coming hours, days, weeks, and months. Weather forecasts refer to forecast periods of 14 days or less, a time frame over which the evolution of the current atmospheric pattern can be more directly predicted, and very specific and high-resolution (in time and space) predictions of weather variables can be made. The skill of weather forecasts over mid-latitude continental areas like the Colorado River Basin is very high for the first 1-2 days, lower for the next 3-4 days, and then drops off dramatically.

Climate forecasts or outlooks are for longer periods (14 days to several months or more), and over these time frames, what is typically forecasted is tendencies towards weather anomalies (warmer/cooler temperatures; higher/lower precipitation) rather than specific quantities. Both the spatial and temporal resolution of the climate forecasts tend to be lower. The sources of predictability for climate forecasts are more diverse than for weather forecasts, which require only the initial conditions and patterns of the atmosphere. The skill of climate forecasts is much lower than for weather forecasts in all parts of the world, and this is true also in the Colorado River Basin.

Incomplete knowledge about future weather conditions is a major uncertainty in streamflow forecasts; most of the forecast error in April 1st seasonal streamflow forecasts is due to weather over the April-July period being different from that assumed in the most-probable forecast (the average of past April-July temperature and precipitation).

Figure 1. CBRFC forecast evolution plot showing the multiple probabilistic forecasts of April-July Lake Powell inflows that were made at each stage of the 2020 forecast season as the snowpack evolved. Image: CBRFC; Annotations: Jeff Lukas.

Relevance

Weather forecasts (out to 10 days) are routinely used by stakeholders across the basin for guiding short-term operational decision-making, such as in agriculture, recreation, and transportation, and water resource management. NOAA Colorado Basin River Forecast Center (CBRFC) incorporates weather forecasts (out to 10 days) into their short-term streamflow forecasts and peak runoff forecasts, and also into their Seasonal streamflow forecasts.

Climate forecasts and outlooks are consulted by stakeholders, including agricultural producers and water managers, but because of their relatively low forecasts accuracy/skill it is challenging to use them to support planning and decision-making like how weather forecasts and seasonal streamflow forecasts are used. Reclamation and CBRFC are exploring ways to incorporate climate forecasts into basin runoff and reservoir outlooks.

Additional Resources

State of the Science Report

Chapter 8 of the State of the Science report covers many aspects of Streamflow Forecasting in greater detail; Section 8.4 is specific to mid-range forecasts (seasonal and longer). Chapter 6, on Hydrologic Modeling, has a detailed description of the CBRFC forecast model framework in Section 6.3, under National Weather Service Models.

New and Notable Research (2020-present)

Summary