1/n Really interesting Post on The Climate Brink from Dr. Kevin Trenberth.
TIL: "Weather systems reach out and gather in moisture typically from over a distance about four times (3 to 5) the diameter of the precipitating area.”
Handy guide!
But there is a paragraph in particular that intrigues me and I want to parse it out in the next couple replies/toots in this thread.
#BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
2/n part1 "Because land temperatures are rising faster than ocean temperatures [figure attached] as air moves from the ocean to the land as part of the hydrological cycle (ocean evaporation, wind moisture transport to land, rain on land, runoff and flow of water in rivers back to the ocean), the relative humidity of air drops. This is now clearly observed on land even as the total moisture has increased.”
#BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
3/n “Because onset of rainfall depends on relative humidity, rain events on land become less frequent. But when rain events are triggered by weather systems, they become larger, more intense and more likely to cause flooding, as is also observed to be happening”
We have most definitely seen this change in behaviour on Vancouver Island!
#BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
4/n Thinking about it... Port Alberni in the summer is a very dry place. As the sun rises higher in the sky in Spring, there is more opportunity to dry out the air and land... combine that with rising average temperatures, especially on the low end (at night/early morning) and that means the air is drier making it less likely to rain when we would normally receive rain from even small frontal systems.
#BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
5/n We have also noticed far fewer foggy days in Port Alberni in Spring and Fall and this year there were almost none in Summer, when in previous decades we could expect to see fog on more than few days.
These are all indications (anecdotal) that would go along with the notion that as the temperature is rising, the air is drying, making precipitation in general much less frequent.
#BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
6/n What I don't believe we have yet experienced in Port Alberni — as a matter of luck — is the full force of a extra-water-vapor-laden Atmospheric River event.
Whereas before #PortAlberni could rely on our geography to 'squeeze' moisture out of almost any frontal system as it rammed into the inland Vancouver Island mountain ridges, today with generally warmer/drier air, that's not enough.
#BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
7/n We have seen a number of times in the past 10 years, most dramatically in 2021, where small and large Atmospheric River events have seemed to "go around" Port Alberni... often impacting the Lake Cowichan area most.
Our strongest events have always been when winds lined up best with the opening of the Alberni Inlet, roughly South to Southeast. So we will have our moment.
#PortAlberni #BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
8/end The question is.. what will those totals look like?
Could we see a 150mm-200mm in-a-day rainfall event? 1000mm over a few days? More?
Or perhaps even if it happened just right in January or February, could we see a massive snowfall event reminiscent of last century?
We won't know until it happens, but we can see the signs that our time is coming.
#PortAlberni #BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
P.S. Important and much appreciated input from Ed Wiebe M.Sc. at UVic Earth & Ocean Science
https://mstdn.ca/@edwiebe/115265785432541292
#PortAlberni #BCWx #Weather #BCStorm #AtmosphericRiver #ClimateChange #ClimateExtremes #Flooding
@[email protected] Much of what you write is reasonable but be careful about using recollections to think about what was. Anecdotal evidence is absolutely unreliable. Our summers are dry because of large scale circulation effects. The jet stream moves north in the summer (and weakens) and we tend to live under a large high pressure pattern. That drives sinking air (decreasing relative humidity). That's not going to go away in a warming climate. However, the strength of the jet stream relies on the temperature gradient from south to north (weaker in summer, thus weaker summer jet stream). That gradient is changing. High latitudes are warming more than mid-latitudes. Winter storms move along under the jet stream (simply speaking) and they bring the moisture inland. Atmospheric rivers are different again. There's more moisture for them to bring as we warm. I don't know how climate change will affect their frequency and range.
Alberniweather ☔️ ☀️ ❄️ 🌬️