New upgrade to weather forecast model the latest in ‘ongoing revolution’ of advanced predictions

Weather Blog

Photo Courtesy: NOAA

One of the National Oceanic and Atmospheric Administration’s (NOAA) highly-used computer forecast models known as the Global Ensemble Forecast System, or GEFS, is undergoing significant upgrades. This latest update is part of an “ongoing revolution of numerical modeling that began with the introduction of ensemble modeling into operations over 25 years ago”, said Louis W. Uccellini, Ph.D., director of NOAA’s National Weather Service.

GEFS – what is it?

Think of a weather forecast model in two parts — the input (weather observations) and the output (the computer-generated forecast). A computer model uses current weather observations as a starting point, analyzes that data, and spits out a forecast based on the known physics of how our atmosphere functions.

Some forecast models are run a few times using slightly different inputs to create different outputs in an effort to capture all possible outcomes. The congregate of these forecasts are then plotted together to address the uncertainty of an event/pattern (wider spread = greater uncertainty). We call these models – ensemble models.

The GEFS model is an ensemble model made up of 21 members, each producing a different possible outcome (forecast).

New features/updates to GEFS:

The latest upgrade to the GEFS centered around the addition of the Finite-Volume Cubed-Sphere (FV3) dynamical core, a tool used to predict long-range weather patterns at time frames ranging from multiple decades to interannual, seasonal and subseasonal. It was first introduced to the original Global Forecast System (GFS) last year but is now being implemented in the GEFS. The improvements include:

  • first-ever numerical weather predictions 3-4 weeks in advance, providing more lead time for decision making than ever before
  • increased resolution from approximately 33km to 25km (lower the number = less space between grid points in the model = greater resolution = finer detail)
  • the number of members increases from 21 to 31
  • increase forecast period from 16 to 35 days
  • improved prediction of week-two tropical cyclone activity
  • first-ever coupling of wave and aerosol components with an atmospheric model
GEFS output for Friday, Sept. 25th 2020 – 31 members of GEFS

The goal of the upgrade

The goal of the GEFS upgrade is to improve forecast skill, reduce uncertainty in medium/long-range predictions and provide better lead-time on high-impact weather events.

As described by Ivanka Stajner, Ph.D., acting director of NOAA’s Environmental Modeling Center, “… [the upgrade to] GEFS is like replacing the engines in a fleet of cars. Each car takes advantage of the power of this new engine, and with slightly different features, they represent the forecast uncertainties more accurately, aiding the forecasters and decision makers with information on a range of possibilities to be considered when issuing the forecasts.”

Fore more information, visit NOAA’s website here.

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