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Documentation on the Probabilistic Products from NAEFS (North American Ensemble Forcasting System) Based on Ensemble and Deterministic Forecasts Site


The purpose of this site is to present the Probabilistic Products charts on Ensemble Forecasts issued every day for North America.

NAEFS (North American Ensemble Forecasting System):

NAEFS is an initiative involving Canada, the United States and Mexico. NAEFS establish meteorological forecasts combining American and Canadian ensemble systems

Introduction and Description of Ensemble Forecast

The Canadian Ensemble Prediction System

The Canadian Ensemble System is composed of 20 members and 1 control member. The 20 members are based on the Global Environmental Multi-Scale model (GEM). The 20 models don't have the same physical parameterization, assimilation cycle or perturbed observations. Fore more information on Ensemble Forecast system, click here.

The American Ensemble Prediction System

The American Ensemble System is composed of 20 members with 1 control. Each member represents a perturbed forecast. Perturbation come from independent breeding cycles. More details on this system are available at the following links:

Display of charts :

The screen displays for a meteorological variable, a large format chart of North America containing the probability of occurence of an event for periods varying from 1 to 15 days. Probabilities are computed for each point in the chart by counting the number of members which forecast the event during the period, divided by the total number of members.

Utilization :

The part of the display screen which allows the selection of charts is as follow :

Probabilistic Products by period for NAEFS

Probability of precipitation over 0.2 mm everyday


Before explaining the different parts of this screen, it is necessary to distinguish between forecast and issued dates. The issued date is the date when the forecast process was initiated. The forecast dates are the dates defining the period of the generated chart. Right now, every day (at 0 UTC and 12 UTC) forecasts based on ensembles are issued for the next 15 days.

At first when the page is open, the chart displayed represents the forecast probability for the current day issued that same day for precipitation amounts over 0.2 mm.

The selection options are divided in three lines :

The top line allows the selection of the charts issued date and time and gives access to the information screen.

The next line allows the user to change the period of the forecast by changing the beginning and ending forecast dates.

At the right and left of the dates, arrows pointing respectively left and right are shown. Clicking on the left arrow will make the chart of the preceding day appear. The same way, clicking the right arrow will make the chart of the following day appear. If one of the arrows is missing, it means that there is no chart available for the corresponding period.

While clicking on the issued date arrows, it is possible that no forecast corresponds to a new issued date. In that case, the system will automatically put back the forecast date 24 hours after the issued date.

The last line is used to select the product type. If the browser does not use JavaScript, a VIEW button will be present to activate the changes requested.

The next table gives a list of the probabilistic products available :

This table is a list of probabilistic products available
Meteorological variable Threshold Number encounter
Precipitation More than 0.2 mm Everyday
More than 2 mm At least one day
More than 5 mm At least one day
More than 10 mm At least one day
More than 25 mm At least one day
Accumulation of precipitation More than 0.2 mm Everyday
More than 2 mm Everyday
More than 5 mm Everyday
More than 10 mm Everyday
More than 25 mm Everyday
More than 50 mm Everyday
Surface Wind Speed Over 15 km/h At least one day
Over 50 km/h At least one day
Over 90 km/h At least one day
Minimum Surface Temperature Under 0°C At least one day
Under -5°C At least one day
Under -15°C At least one day
Under -30°C At least one day
Maximum Surface Temperature Over 0°C At least one day
Over 15°C At least one day
Over 30°C At least one day
Windchill Under -15 At least one day
Under -30 At least one day
Under -40 At least one day
Under -55 At least one day

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