Summery forecast; extreme weather climate link grows

What you see is what you get these days across Minnesota. Our summery weather forecast looks locked in place. Mixed sun, highs near 80 and the occasional rain chance?

Sounds like summer in Minnesota to me.

Weak high pressure means little change in our weather forecast the next few days. The storm track pushes another low pressure cell through the Ohio Valley with more concentrated rain and thunder. Minnesota rides the relatively dry and sunny northern fringes of that system.

Rain chances include a slight chance of a pop up thundershower this afternoon. A better chance of rain rolls in by Sunday. Here's a look ta the rainfall forecast over the next seven days. The Ohio Valley soaks up several inches of rain.

Here's a more detailed breakdown of the forecast. Today through Saturday look like splendid summer days.

Rain chances increase Sunday. Humidity levels rise next week as dew points slog into the sweaty mid to upper 60s. You'll be tempted to reach for the air conditioning switch more often next week.

Climate change and extreme weather events

Scientists and the public often ask if any given extreme weather event was caused by climate change. Maybe we've been asking the wrong question.

A new study by the National Center for Atmospheric Research's Kevin Trenberth suggests a more refined way to question how extreme weather events are tied to climate change.

By looking at how the thermodynamics of climate change played a role in any given extreme weather event, we may be better able to attribute the climate change component of extreme weather. How much does a warmer ocean or atmosphere capable of delivering more water vapor into a storm "juice" the system?

The study finds credible ties to climate change form storms like Hurricane Sandy.

Here's more from the study in the journal Nature Climate Change.

There is a tremendous desire to attribute causes to weather and climate events that is often challenging from a physical standpoint. Headlines attributing an event solely to either human-induced climate change or natural variability can be misleading when both are invariably in play.

The conventional attribution framework struggles with dynamically driven extremes because of the small signal-to-noise ratios and often uncertain nature of the forced changes. Here, we suggest that a different framing is desirable, which asks why such extremes unfold the way they do.

Specifically, we suggest that it is more useful to regard the extreme circulation regime or weather event as being largely unaffected by climate change, and question whether known changes in the climate system's thermodynamic state affected the impact of the particular event.

Some examples briefly illustrated include 'snowmaggedon' in February 2010, superstorm Sandy in October 2012 and supertyphoon Haiyan in November 2013, and, in more detail, the Boulder floods of September 2013, all of which were influenced by high sea surface temperatures that had a discernible human component.

University of St. Thomas professor John Abraham has this perspective in the Guardian.

In short, the atmosphere can become either warmer and wetter or warmer and dryer, depending on where you are. The general rule of thumb is that areas which are currently dry will become drier; areas that are currently wet will become wetter; and rains will occur in heavier downbursts.

The scientists list the following questions as a guide to their study.

1. Given a particular weather pattern, how were the temperatures, precipitation, and associated impacts influenced by climate change?

2. Given a drought, how was the drying enhanced by climate change and how did that influence the moisture deficits and dryness of the soils, leading to a more intense and long-lasting drought?

3. Given a flood, where did the moisture come from? Was it increased by warmer ocean waters?

4. Given a heat wave, how was that influenced by drought, changes in precipitation, and extra heat from global warming?

5. Given extreme snow, where did the moisture come from? Was it related to oceans that are warmer?

6. Given an extreme storm, how was it influenced by sea temperatures, ocean heat content, unusual moisture transports?

7. Was a storm surge worse because of higher sea levels?

Lake Mead reaches new record low

What do hotter temperatures and prolonged drought mean to water supplies in the west? Lake Mead water levels reached a new low this week.

Las Vegas digs a new deeper $1.5 billion straw to draw water from the shrinking lake. Yet another hidden climate change adaptation tax?

USA today has more.

The bureau reported Lake Mead's elevation at 1,074.98 Tuesday night. But the elevation climbed slightly above 1,075 since 2 a.m. MST. Elevation measures are updated every hour.

But Tuesday's record low signals that Colorado River water users consume more than the river provides, said water-policy manager Drew Beckwith of the Western Resource Advocates, a nonprofit environmental law and policy organization.

"This is the check-engine light," Beckwith said. "It really does (make critical) the fact that we have to start changing."

For Las Vegas, the record reinforces the need for a nearly $1.5 billion project to tap deeper into Lake Mead. The Southern Nevada Water Authority soon will complete a 3-mile tunnel that will suck water from an 860-foot elevation level. The plan also includes a pumping station.