Information Bulletin from Public Security (MSP) – Spring Flood Watch – May 1, 2023

Unofficial translation

Weather conditions

Meteorological Service of Canada’s Quebec Vigilance Map

Areas in the High Vigilance Zone

A quasi-stationary low pressure system over the south of the province will bring rain for several days until Wednesday. The heaviest rain event is currently underway.

This system has the potential to dump a total of 40 to 70 mm of water by this evening in an axis from

from the Outaouais to Charlevoix and even more locally.

Confidence level: High

Sectors located in the medium vigilance zone

A total of 30 to 50 mm of rain is expected by this evening.

High winds of 90 km/h will gust over the Saguenay and eastern Lac-Saint-Jean on Monday. In the National Capital Region and Trois-Rivières, gusts will reach 70 to 80 km/h overnight and Monday morning.

Confidence level: High

Sectors located in the low vigilance zone

Additional rainfall amounts could fall from Tuesday to Wednesday over southern and central Quebec. Expected amounts are in the range of 10 to 20 mm.

Confidence level: Low

Source: ECCC

Summary of rainfall since Sunday, and expected by Wednesday morning

The weather alert bulletins issued by ECCC can be found at the following link.

The multi-hazard vigilance map, compatible with mobile technologies, is available to the public on the Quebec Data website via the following link.

Vertical Inputs

For today, the rain from the low-pressure system will fade by the end of the day over most areas. For the rest of the week, precipitation will fall as showers from convective systems. Thunderstorms could lead to localized heavy rainfall.

24 hour vertical inputs – 1 May – 10:30

In the next 24 hours, vertical inputs will reach values above 50 mm for the southern Laurentians, Lanaudière and Mauricie. For the Capitale-Nationale, values could reach over 100 mm in Charlevoix.

Vertical inputs 48 hours – 1 May – 10:30

In the next 48 hours, vertical inputs will reach values above 70 mm for the north and south of the Laurentians, Lanaudière and Mauricie. In the north-western Outaouais, rainfall will reach 60 mm. For the Capitale-Nationale, values will remain above 100 mm in Charlevoix.

Vertical inputs 72 hours – 1 May – 10:30

Significant vertical inflows are expected over the next 72 hours, reaching more than 100 mm in places, on the north shore of the St. Lawrence, from Abitibi-Témiscamingue to the Capitale-Nationale, as well as on the eastern tip of the Gaspé Peninsula. The regions south of the St. Lawrence River, from the Eastern Townships to the central Gaspé Peninsula, as well as the Lac-Saint-Jean and Côte-Nord regions, will receive between 20 and 50 mm of water.

Water equivalent of snow on the ground

Water equivalent of snow on the ground – 1 May – 10:30

The amount of snow on the ground decreased considerably in all sectors, leaving partial snow covers of less than 50 mm water equivalent in general, with the exception of the mountainous regions of the Laurentian Wildlife Reserve and the Gaspé Peninsula, where snow amounts are still significant.

Impacts on watercourses

Rivers are reacting to the heavy rainfall with increases in flow and water levels. These increases will continue until Wednesday and will be more significant in the regions north of the St. Lawrence, from the Outaouais to Charlevoix. Monitoring and flooding thresholds could be reached again today. Maximum flood levels are expected to be reached between tonight and Wednesday for most small rivers.

The Ottawa River is currently rising and will continue to do so until the end of the week. Minor flood levels are expected in areas from Gatineau to Montreal and major flood levels may be reached in areas upstream of Gatineau. Nevertheless, levels are expected to remain below historical flood levels in all areas along the Ottawa River. The Mille-Îles, Des Prairies and Lake of Two Mountains rivers are rising and will continue to do so for the next few days.

The Saint-Maurice River is currently stable and could rise again over the next few days, but it is not expected to reach minor flood levels in the short term.

Lake Saint-Pierre is currently rising and this trend will continue until May 7 for the high tide period. Minor flooding is expected during this period.

Table of rivers that will reach thresholds over the next four days

Forecast – Montreal Archipelago

Updated on: 2023-05-01 at 10:03

Useful links

In addition to the flood monitoring bulletin, public information is available on various partner and Ministry of Public Safety (MSP) websites.

Information disseminated throughout the year :

New version of Vigilance – Flood Watch

Remember to change the site in your web browsers’ favourites! General public access:

• https://vigilance.geo.msp.gouv.qc.ca
• Carte vigilance multirisque
• Niveaux et débits du lac Ontario et du fleuve Saint-Laurent diffusés par le Conseil international du lac Ontario et du fleuve Saint-Laurent (CILO-FSL)
• Accumulation de précipitations – centre météo UQAM

Information disseminated during the spring flood:

• Niveaux et débits des rivières et des principaux réservoirs du bassin versant de la rivière des Outaouais de la Commission de planification de la régularisation de la rivière des Outaouais (CPRRO)
• Prévisions hydrologiques et hydraulique de l’Archipel de Montréal du ministère de l’Environnement et Lutte contre les changements climatiques, de la Faune et des Parcs (MELCCFP).
• Lien vers les données de températures et précipitations par région
• Lien des données vers Hydro-Québec.
• cruesgrandmontreal.ca/