Today, NOAA implements enhancements to the hourly-updating High-Resolution Rapid Refresh model (HRRR) and its “parent” model, the Rapid Refresh model (RAP), which work hand-in-hand to provide the foundation for many vital forecasts issued by the National Weather Service each day.

The most notable improvement is the addition of the HRRR-Smoke model application, which allows the system to predict the height and potential direction of transport of wildfire smoke.

A HRRR-Smoke model forecast of vertically integrated smoke showing where wildfire smoke will travel across the U.S. This product displays the effect of fire smoke load that includes smoke in the boundary layer as well as aloft, illustrating the integral effect of fire smoke throughout the atmosphere.

Other enhancements to the RAP and HRRR models include improved methods of representing the water temperature of small lakes, more detailed information about the timing and intensity of thunderstorms and other severe weather threats, and the ability to more accurately predict amounts of cloud cover and precipitation in a timely manner.

Top: Observations of the actual severe weather event. This observed radar image shows that the HRRR Version 4 forecast did a much better job predicting that a derecho would be sweeping across eastern Iowa during the early afternoon of Aug. 10, 2020 than Version 3 did. Bottom from left to right: A comparison of NOAA High-Resolution Rapid Refresh model (HRRR) forecasts of the Midwest Derecho on Aug. 10, 2020. The left panel shows the forecast from HRRR Version 3, while the right panel shows the forecast from the upgraded HRRR Version 4 that was implemented today. â€‹

Additionally, the length of RAP and HRRR forecasts will be extended by 12 hours. This will allow meteorologists to issue detailed forecasts up to two days in advance using guidance from the high-resolution models. These improvements will not only make way for more accurate, timely and detailed forecasts — which provide better support to our partners — but will also provide the aviation industry with vital visibility and icing information that will help better alert the public to weather conditions that could result in flight delays or cancellations.

The updated models also will introduce new forecasting products for surface and upper-level smoke concentrations, a new hail size product, and several new parameters to help assess severe weather environments.

This will be the final upgrade to the RAP and HRRR models, as they will be subsumed by the Rapid Refresh Forecast System  — a rapidly-updating high-resolution ensemble forecasting system using the Unified Forecast System Short Range Weather Application in late 2023.

Additional Resources:

• RAPv5/HRRRv4 Evaluation Overview
• Service Change Notice