What is MOS?

Model Output Statistics (MOS) is a type of statisitical post-processing, a class of techniques used to improve numerical weather models' ability to forecast by relating model outputs to observational or additional model data. MOS was defined by Glahn and Lowry (pdf) in 1972 as the following:

Model Output Statistics is an objective weather forecasting technique which consisists of determining a statistical relationship between a predictand and variables forecast by a numerical model at some projection time(s). It is, in effect, the determination of the "weather related" statistics of a numerical model.

The predictors MDL currently uses are:

• NWP Model Forecasts
• Prior Observations
• Geoclimatic Data

Predictor points can come from either point observations or from data that has been calculated on / interpolated to points on a grid. The MOS products which are more heavily based on true observation points are referred to as station-based mos, while MOS generated based on gridded data is called gridded MOS (GMOS)

The models used for MOS data also can be changed. MDL is currently producing MOS based on the GFSEnsemble GFS, and NAM models.

The statistical method used by MDL is multiple linear regression (with forward selection). Other techniques are possible, such as: Polynomial or logistic regression; or neural networks. (For more information on these and other statistical techniques, see: Wilks, 2006: Statistical Methods in the Atmospheric Sciences).

MOS Products

MOS (Model Output Statistics)

Station-based MOS

MOS forecast guidance products are developed by relating NWP model data to observations using statistical methods. Station-based MOS provides general guidance based at meteorological observation stations.

There are currently MOS products available based on two NWP models:

Gridded MOS (GMOS)

GMOS forecast guidance products are developed by relating NWP model data to observations using statistical methods. GMOS provides guidance according to data on a geographic grid.

Ensemble Kernel Density MOS (EKDMOS)

Ensemble Kernel Density MOS (EKDMOS) uses output from the North American Ensemble Forecast System (NAEFS) to produce reliable and accurate probability distributions of sensible weather elements. Grids are generated twice daily, based on the 0000 and 1200 UTC runs of the NAEFS. To express the probability distribution, grids are produced for a number of percentiles as well as for the mean forecast.

LAMP (Localized Aviation MOS Program)

Station-based LAMP

LAMP produces forecast guidance products developed by relating Model Output Statistics (MOS) forecast guidance to observations using statistical methods. LAMP provides hourly aviation station-based forecast products that cover a 25-hour period.

Gridded LAMP (GLMP)

Gridded LAMP (GLMP) provides gridded analyses of observations and operational LAMP forecasts for aviation forecasting on the 2.5-km CONUS NDFD grid.  The GLMP grids are produced hourly and cover a 25-hour period.