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WeatherAlert-Forecast: An Automated Warning System for Southern Quebec

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Regions: Quebec | North America

Images created on Sat 25 Mar at 06:51Z

The approach of WeatherAlert-Forecast

WeatherAlert-Forecast is an automated warning system for Southern Quebec based on the North-American Ensemble Forecasting System (NAEFS). The approach follow the MOGREPS-Warning system develop at the UK Met Office to assist the forecasters in the issuance of weather warnings.

Warnings, ranging from 0 to 10 (where 10 is the highest level), are based on the likelihoods of weather events occurring and their impact on peoples' day-to-day activities if they do occur. Weather events and their impact degree (low, medium or high) are based on a priori defined threshold values for various weather parameters. The likelihood of each impact level for each parameters is calculated from the NAEFS forecasts. Likelihoods are transformed into a warning level according to the following matrix.


A warning level is found for each weather parameters. The highest level reach among all the parameters determined the final warning level. Warning levels 1 to 5 are colored in yellow, 6 to 9 in orange and 10 in red.

The following table show the 6 parameters currently taken into account as well as their threshold values. The threshold values follow, in part, the public weather warning criterion used by Environment Canada for continental Southern Quebec. Currently, the same threshold values are used over all the domain of WeatherAlert-Quebec. Maps of North America are shown only to allow the comparison of Southern Quebec's weather with the rest of the continent.

Impacts
Parameters Low Medium High
Rain over 24 hours >= 25 mm >= 50 mm >= 75 mm summer
>= 15 mm >= 25 mm >= 40 mm winter
Snow over 24 hours >= 5 cm >= 15 cm >= 30 cm winter only
Freezing rain over 24 hours >= 2 mm >= 5 mm >= 10 mm winter only
Wind (gusts) >= 60 km/h >= 80 km/h >= 100 km/h
Thunderstorm* CAPE >= 250 J/kg CAPE >= 1200 J/kg EHI >= 1.5 summer only
High temperature >= +30 C >= +33 C >= +36 C summer only
Humidex >= +34 C >= +40 C >= +46 C summer only
Low temperature <= -20 C <= -27 C <= -35 C winter only
Windchill <= -25 C <= -35 C <= -45 C winter only

* For thunderstorm risks, the probabilities to exceed CAPE (Convective Available Potential Energy) and EHI (Energy Helicity Index) thresholds are multiply by the precipitation probabilities to hide unstable areas where triggering mecanisms are lacking.

Warning: The information on WeatherAlert-Forecast is not guaranteed to be up-to-date and is prone to large errors. Never use for important decision making. Please always refer to Environment Canada's public forecasts and warnings. UQAM decline any responsibility for the usage of these data.

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