Canada is “sandwiched” between two atmospheric rivers
The Weather Network says British Columbia should prepare for a series of storms
The Weather Network is advising British Columbians to prepare for wetter weather as a series of storms move through the area.
After weeks of unprecedented flooding, forecasts call for heavy rainfall from Wednesday, November 24 through Friday as two storm systems move through the province. The first system will move to the north and central coasts, then move to southern British Columbia by Wednesday evening.
Flood-affected areas could receive 100 to 200mm of rain by Friday evening, which could further delay the recovery, notes a Press release. However, the Lower Mainland, including places like Abbotsford and Hope, will likely experience less precipitation (40-80mm) by the end of the week. Still, it could likely make recovery efforts worse.
Rain and wind warnings, as well as special weather reports, are in place for the coastal sections and the Lower Mainland. Non-essential travel restrictions also remain in place for several highways affected by the flooding.
Thursday & Friday: a fairly ordinary atmospheric river (always impacts). The Saturday / Sunday system is more sinister; the tropical humidity of Southeast Asia merges with the humid flow of Hawaii. Touch and go, B.C. #BCStorm pic.twitter.com/0ou0qWzTQB
– Tyler Hamilton (@ 50ShadesofVan) November 24, 2021
Canada sandwiched between atmospheric rivers
The Weather Network strong points how atmospheric rivers form in the Atlantic and Pacific Oceans and can occur simultaneously. Today, Canada is sandwiched between atmospheric rivers on the east and west coasts.
Powerful atmospheric rivers can deliver catastrophic amounts of precipitation on the order of hundreds of millimeters, causing devastating flooding and damage to infrastructure, like the recent event in British Columbia.
Although they are still part of our atmosphere, the report’s authors note that they reach their highest intensity in autumn and winter, “when the temperature contrast between the mild tropics and the freezing arctic is strongest. “.
The difference in intensity “comes down to time and altitude.”
Atmospheric rivers: the west coast versus the east coast
In British Columbia, atmospheric rivers generally last longer because âwarm, humid water is found to the west and south of the land mass. In general, we know that the atmosphere likes to flow from west to east, so these atmospheric rivers can be particularly stable and long. sustainable. “
On the east coast, atmospheric rivers last less and “tend to sweep the coast faster since warm, humid water is found south of the land mass.”
British Columbia also has more intense atmospheric rivers due to its very mountainous terrain. For heavy precipitation there must be a “lifting mechanism – moisture combined with equal rising precipitation”.
The west coast has much larger mountain ranges, so “the mountain pulse is stronger”, and more moisture is drawn from the atmospheric river to fall as precipitation.
Environment Canada is in the process of creating its own impact-based rating scale for atmospheric rivers based on the Atmospheric River Matrix. It will include the current scale of the air: intensity and duration of humidity; prerequisites: total runoff, maximum hourly precipitation, area size and more; and also consequences based on the assessment of the scale.
The Weather Network notes that the prerequisites are “of vital importance when predicting flooding.”