I was wondering if the pro mets on this board believe that extreme precipitation events ae the result of climate change. Stories keep appearing in the media of how many scientists and climatologists believe that severe precip events (such as Montreal receiving 33mm of rain in a 15 minute period last week) are the result of climate change. They seem to be implying that what was once considered a "once in a century event" is now happening more often and that insurance companies will have to prepare for more calls like this in future.

I'm not a meteorologist or a climatologist but to me that seems strange. There have always been extreme preip events.

http://www.canada.com/montrealgazette/news...45-3b533e55d4b3

The definition of Climate Change was hijacked....so it depends on which definition you use.....
....the old definition?? Well, yes....over a period of time, if you have a decided period of time where the climate has "changed" (ie more extreme events in a given area) then you have witnessed the "climate changing"....
....if you mean the previously named anthrolopological global warming......then NO!!!!!!!!

Any change in climate will affect the weather, anthropogenic or not. By most accounts, extreme precipitation events are more likely in a warmer climate (not that they didn't happen before). Therefore, if you believe that humans have had a hand in warming the climate, then a natural extension of that would be to affect extreme precipitation events. However, the overall effect is likely small, and very difficult to quantify. Stating that an individual precipitation event is due to AGW would be silly, but stating that there is a greater chance of those types of events due to a warmer climate is not nearly as much of a leap.

In the northern temperate climates then, why are the colder months wetter?

I think it is all backwards. Climate change results from individual events, not the other way around.
TW

Precipitation generally depends on large-scale factors. California gets more precipitation in the winter months because of the storm track. But most of the US is wetter in the summer. I'm not quite sure what you are going for here.

Climate is the sum total of all the weather events but in the big picture extreme events are merely a small part of that total. The way to put this in perspective is to remember the old saying "Climate is what you expcet, weather is what you get". What MN says is probably the best way to say it. Eventually, climate change may lead to more frequent extreme events but to blame a single event on climate change is not justifiable since randomness is a major player in atmospheric processes as well. Personally, I don't think we are at the level yet where GW could have a major effect on the frequency of extreme events-also, it's important to note that whatever is happening to the climate is NOT due to one factor alone but a combination.

Steve

Umm, they aren't.

January

Click to view attachment

July

Click to view attachment

Temperate being the key word there "Y"

So, in your estimate then, the west coast temperate zones precip is dependent upon what?

Total annual precipitation in the west is generally highly dependent on the average position of the jet stream during the winter.

Extreme events are not related to the average position of the jet stream, but instead to the position at a given time. The amount of precipitation an extreme event produces is dependent upon many factors, some of which are related to temperature (i.e. strength of an extratropical storm, amount of precipitable water, etc).

So precipitable water quotient is a factor governed only by heat?

I'm not so sure about that. According to historical records, there were some severe floods in Europe during the onset of the LIA. And there are some theories about atmospheric cooling leading to more precipitation, at least initially. Hardly a definite answer one way or the other, I think.

And I have always thought that labeling an event a "100 year" or "500 year" is taken to literally sometimes. It's just a general approximation, usually based on a climate record that is far too short to really know anyway.

Who said that?

Depends upon the station. Close to home, PWM has a late fall maximum and late summer minimum, consistent with coastal storms and seabreeze-undercut convection. CAR (and most fully continental temperate areas) has a summer maximum and a midwinter minimum.

Also, the attachments, though accurate in principle, illustrate the problems with cherrypicking, in this case choosing a single month to demonstrate a climatological truth.
Precip last winter IMBY (and most of New England was parallel):

DEC: 5.12" (+1.21")
JAN: 2.81" (-0.11")
FEB: 5.75" (+2.86") Many NNE stations had a lot more precip in 2/08.

So again, where does abundant and anamolous heat figure into the precipitation
maximum on the west coast?

Posting to an article that suggests increasing heat will increase rainfall tables, then by proxy
you are in agreement.

I am stating that the obvious course of action is to look at our northern temperate climates to
see if indeed there is rudimentary proof in so much that a logical hypothesis could be based
on such a premise.

There are NO signatures that increased heat in our temperate zones have that marker, there
by extrapolation then one could conclude that though all weather is a result of opposing forces
heat and cold being one of them, it is not suggestive that more heat causes more rain.

I would think, both of you, who know a hell of lot more about weather than I, hang on to each
AGW claim and try to find merit in it, interesting indeed.

Minnie, and Mallow, tell me something, what do you find comes first(in deciding weather prominence):

Barometric Pressure, Wind, or Temperature?