Billion-Dollar Disasters 'Harbinger' of Future Extreme Weather: NOAA (LiveScience.com)

SAN FRANCISCO — The 12 $1-billion-plus disasters that hit the United States this year are most likely not simply a matter of the stars aligning against us, according to the head of the National Oceanic and Atmospheric Administration (NOAA), who implicated climate change as a contributor. 

Climate change, caused by carbon dioxide and other greenhouse gases humans have emitted, is expected to increase certain types of extreme weather, leading to more disasters, according to a report being assembled by the Intergovernmental Panel on Climate Change (IPCC).

"The report that was released by the IPCC on extreme events suggests that what we are seeing this year is not just an anomalous year, but a harbinger of things to come for at least a subset of the extreme events we are tallying,"said Jane Lubchenco, NOAA's administrator, during a press conference held here this week at the annual American Geophysical Union meeting.

A summary of the report released in November predicts an increase in certain types of extreme weather, including daily high temperatures, heat waves, heavy precipitation and droughts, in some places. [Photos of Devastating Texas Drought]

Costly disasters

With this increase in extreme weather there will likely be an associated uptick in costs. Earlier Wednesday (Dec. 7) the agency announced that this year, so far, had broken the record for costly, weather-related disasters,including drought, wildfire, tornados, flooding, a blizzard and a hurricane. She noted that the agency is still tallying costs related to Tropical Storm Lee and the unseasonable snowstorm in the Northeast that occurred over Halloween weekend.

"I believe there are probably four reasons why we are seeing an increase," said Lubchenco, referring to the number of costly events. "One is there are more extreme events, period, but it is more complicated than that," Lubchenco said, adding that the country now has more people, who have more stuff to lose in disasters, and more people and their stuff now reside in harm's way, such as along the coasts. More people also have insurance that pays for their losses, magnifying the costs associated with a disaster.  

The previous record, for nine $1-billion-or-more weather-related disasters was set in 2008.

Climate-change connection

Of the types of extremes that battered the country this year, only certain large-scale phenomena among them —such as heat waves, droughts and heavy precipitation —have links to climate change.

"We are likely to see more and more of them down the road as climate continues to change," she said.

The connection between small-scale extreme events, such as a localized hailstorm or a tornado, and climate change is less understood, she said.

Since about 1970, NOAA's Climate Extreme Index —which tracks the percentage of the country affected by climate extremes over time —has shown an upward trend that is notably different than the activity in earlier decades, she told an audience of scientists at a talk earlier in the day.

This trend is driven by daily highs and lows, availability of water and heavy precipitation in a single day. Most notably, since 1970, more of the country is experiencing unusually warm nights, with less of the country experiencing unusually cool nights. This particular shift is significant, she said: "Warm overnight lows are related to heat stress in both people, and plants and animals; they never get a chance to cool off."

Likewise, while the country has had periods of severe drought, such as during the Dust Bowl of the 1930s, it has never become drier and wetter at the same time, as has happened in the last decade, she said.

You can follow LiveScience senior writer Wynne Parry on Twitter @Wynne_Parry. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

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The Science of the Fierce Santa Ana Winds (LiveScience.com)

Hurricane-force winds are whipping through much of the western United States today (Dec. 1), sparking wildfires, knocking out power and flipping semi-trucks — but there's no tropical storm driving the intense gusts.

In Southern California, these freakish winds are called Santa Ana winds, strong down-slope winds that blow through the Santa Ana Mountain passes at speeds of 40 mph (64 kph), according to the National Weather Service.

The current weather system is causing damage far outside of sunny SoCal, however, and the winds are among the worst in decades, meteorologists said. Widespread gusts as strong as those of Hurricane Irene at landfall are expected to continue into tomorrow (Dec. 2). Already, firefighters in California are responding to wildfires spread by the winds and a major stretch of interstate has been shut down because of toppled trucks.

The strong winds throughout the West Coast are caused by an extreme pressure change between the Northwest and Southwest regions. A sprawling high-pressure system following a cold front has created a difference in pressure that sends wind surging southward. In the Northwest, a strong high-pressure system built along with a clockwise flow of winds. In the Southwest, a low-pressure system developed along with a counter-clockwise flow. The tight so-called pressure gradient that formed between these systems is driving winds over mountains and through the California canyons.

The winds can be of tropical storm strength(winds less than 74 mph, or 119 kph) at lower elevations and hurricane-strength (74 mph or greater)above 1,000 feet (305 meters).

Winds this strong can topple trees onto power lines, knocking out power. Already today, 34,000 are without power in Northern California, 25,000 have lost power in Southern California and Los Angeles Airport lost power for an hour last night.

In Southern California, 80 mph (129 kph)wind gusts have been reported in higher mountain passes. Near Los Angeles, wind gusts of up to 40 mph have been reported and gusts of up to 80 mph have been seen in some canyons. Winds are so strong right now that Pasadena, Calif., firefighters are responding to calls of downed trees every 12 seconds, according to the Weather Channel.

Outside SoCal

The strong winds aren't just a Southern California thing. Near Sacramento, wind gusts of up to 40 mphhave been reported. At higher elevations, gusts have topped 100 mph (161 kph), said Bill Rasch, an NWS meteorologist in Sacramento. Rasch told OurAmazingPlanet that winds this strong aren't unusual for the area, but said "in general it's a pretty strong storm."

The winds aren't even confined to California. In Las Vegas, winds are gusting at 29 mph (47 kph). At Mammoth Mountain's summit, the winds topped 150 mph, equivalent to a Category 3 hurricane on the Saffir-Simpson Hurricane Scale.

The severe winds are even dangerous in Utah. Here, they are called simply "canyon winds," but the same phenomenon is at play. A high-pressure gradient east of the Rocky Mountains causes the winds to speed up going down the mountains. 

"By the time they hit the valley they're at an incredible speed," said Nanette Hosenfeld, a meteorologist with the NWS in Salt Lake City.

Wind gusts of up to 100 mph have been reported in Centerville, Utah. Interstate 15 has been completely shut down there because of flipped tractor-trailer trucks.

Wildfire hazard

The strong winds are a serious wildfire hazard in California. The NWS office in Los Angeles said there is "potential for high fire danger with rapid fire growth due to the strong offshore winds and low humidity values."

When the compressed winds are driven down mountain slopes they dry out and get hot.

"It can take a small fire and make it become a very large fire," said Julie Hutchinson, a battalion chief, with CalFire, the state's fire protection service. "If you get a fire started it can move very quickly."

In Southern California, the brush-covered hills are a big wildfire risk, Hutchinson said. Many areas of brush-covered hillsides have been sloughing off moisture in preparation for winter and are dangerously dry. Many areas are parched and battling a drought.

If a fire were to get out of hand, firefighters would not be able to use aircraft to fight the flames. Once the winds are above 35 mph (56 kph), firefighters must rely solely on boots on the ground, Hutchinson said.

Downed power lines are another big fire hazard. Los Angeles firefighters put out a 2-acre grass fire that burned overnight today at Occidental College sparked by downed power lines.

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

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Active 2011 Hurricane Season Comes to an End (LiveScience.com)

The 2011 Atlantic hurricane season was forecast to be a doozy and it delivered.

The season officially ends tomorrow (Nov. 30) and its legacy includes 19 tropical storms, seven hurricanes and three major hurricanes — including the devastating Hurricane Irene, the only hurricane to strike the United States this year. Irene was the first U.S.-land-falling hurricane in three years. Its billion-dollar damage brought the United States back to the reality of hurricanes after years of quiet.

"Irene reminded us that the Northeast can and does get hit byhurricanes," said Jeff Weber, an atmospheric scientist at the University Corporation for Atmospheric Research in Boulder, Colo.

Active trend

The 2011 season continued a trend of active hurricane seasons that began in 1995, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). Tropical storms came in with the third-highest total, at 19 (tied with 1887, 1995 and 2010), since records began, in 1851. An average season has 11 tropical storms. [See a video of the season's storms.]

The seven hurricanes and three major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Scale) that developed this year number only slightly above the averages of six and two, respectively.

The 2011 season affected the Mid-Atlantic more than the Gulf of Mexico. Hurricane Irene, the first hurricane to hit the United States since Ike hit Texas in 2008, socked the East Coast. The storm caused $7 billion in damage and became the worst tropical cyclone  to strike the Northeast since Hurricane Bob in 1991. Tropical cyclone is the generic term for tropical storms and hurricanes.

Irene inundated New York and Connecticut with water — up to 15 inches (38 centimeters) in some places. Irene was blamed for 46 deaths across 13 states.

As bad as the damage was, things could have been worse. Modern storm-tracking technology allowed NOAA forecasters to accurately map Irene's path for four days before its landfall Aug. 27, near Cape Lookout, N.C., allowing the population of the Outer Banks to evacuate. Irene was a major storm for a brief period, but it weakened to a Category 1 storm and so was not a major hurricane at landfall.

"We have now gone six years — since Wilma in 2005 — without a major hurricane making U.S. landfall," said Phil Klotzbach, an atmospheric scientist and hurricane forecaster at Colorado State University.

Few Gulf storms

Since 1878, when land-falling hurricane records begin, the 2006-2011 span is the longest stretch without a major hurricane hitting the United States, Klotzbach told OurAmazingPlanet.

While the East Coast was soaked by storms, the dearth of Gulf storms added tothe Texas drought.

One storm that did hit the Gulf was Tropical Storm Lee, which made landfall in central Louisiana. Lee spawned 38 tornadoes, the second most on record for a tropical storm.

Most storms were turned away from the United States by an anomalous trough of low pressure along the East Coast, "which helped steer storms moving towards the U.S. coast back out to sea before they could make U.S. landfall," Klotzbach said.

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

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Busy Storm Season Kept Hurricane Hunters in the Air (LiveScience.com)

The 2011 Atlantic hurricane season, which officially ends today (Nov. 30), has kept storm-chasing aircraft busy this year. The planes spend hours at a time flying through tropical storms and hurricanes to capture crucial data for forecasters on the ground.

Seven hurricanes and 12 tropical storms swirled across the Atlantic region this year, making 2011 one of the most active seasons on record. For the majority of those 19 storms, aircraft took to the skies to investigate.

The main arm of the United States' weather-scouting fleet is the Air Force Reserve 53rd Weather Reconnaissance Squadron, based at Keesler Air Force Base in Biloxi, Miss. — better known as the Hurricane Hunters.

"We had a lot of business this year, but it was a good year because not much of that [severe weather] impacted Americans in a negative way," said Lt. Col. Sean Pierce, pilot and director of operations for the 53rd.

Busy year

The Hurricane Hunters' workhorse is the massive WC-130J aircraft, a prop plane equipped with a bevy of weather-sensing instruments. There are only 10 of these aircraft on Earth, all owned by the 53rd. This year, one of the planes, all of which are close to 10 years old, was out for maintenance, so the squad was down to nine aircraft in what proved to be an active hurricane season. [Images: Hurricane Hunters in Action]

On a typical flight, which lasts more than 10 hours, the WC-130Js fly with a crew of five — two pilots, a navigator, a weather tech who deploys various instruments, and a meteorologist, who acts as flight director.

At least twice this year, aircraft were needed in up to three storms at once, "which is the most challenging environment for us operationally," Pierce told OurAmazingPlanet.

Hurricane Irene required some of the most flight time this season, and sent hurricane hunters farther north than usual.

During the final flight into the giant storm, a crew sent a dropsonde — a small, largely biodegradable weather sensor that travels aboard a tiny parachute — into the Hudson Bay, right near the Statue of Liberty, just as Hurricane Irene made landfall, Pierce said. Irene was the first hurricane to hit the United States in three years and caused more than $1 billion in damage.

Invaluable data

53rd Squadron hurricane hunters flew 868 hours on 88 missions this year, said John Pavone, chief of air reconnaissance coordination, all hurricanes, at the National Hurricane Center (NHC) in Miami.

"That's a little more than in an average year because this was a little more than an average year," Pavone said, adding that 2011 is tied with three other years — 1887, 1995 and 2010 — for third most active Atlantic hurricane season since record-keeping began in 1851.

The weather-sensing planes, at the behest of the NHC, take to the skies whenever tropical weather systems appear to threaten people or property. Hurricane-hunting crews fulfilled 127 of the 129 requests the NHC sent out this year for the Atlantic region, Pavone said, "which is a pretty high success rate, which is what we've come to expect from them over the years."

"Their data are critical to us," said Dennis Feltgen, meteorologist and spokesman for the NHC.

Feltgen said that over the ocean, where tropical weather systems originate, there's no infrastructure in place to monitor and record data for forecasters trying to predict what a storm will do.

"They are basically performing an MRI of the storm, and they give us an exact location; they're able to determine the structure of the storm and the strength of the storm," Feltgen told OurAmazingPlanet. "All that data is critical for going into the computer forecast models."

Dodging storms

Despite a busy year for pilots and crew, 2011 proved to be a fairly lucky year for the United States — aside from the devastation wrought by Hurricane Irene.

"This year we had a lot of storms, but the majority of them ended up turning out to sea," said Lt. Col. Jon Talbot, chief meteorologist for the hurricane hunters. "The big picture is it was very fortunate we had one major impact to the U.S.," Talbot said.

Although the official Atlantic hurricane season draws to a close on Nov. 30 every year, storms don't always stick to human schedules. It's extremely rare, but hurricanes can form in December.

In fact, the NHC is currently tracking a suspicious area of rough weather that developed on Tuesday (Nov. 29) that has a slight chance of developing into a tropical cyclone.

Talbot said the Hurricane Hunters, like storms themselves, are undeterred by the date on the calendar.

"If it forms, we're out there taking care of it," Talbot said. "It doesn't matter what month it's in — we're ready to go."

Reach OAP staff writer Andrea Mustain at Facebook.

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Dust Obscures Picture of Hurricanes in Warming World (LiveScience.com)

As a doozy of a hurricane season wraps up, scientists are eager to understand how these storms will change as the climate warms. They are finding several curious influences that can cause hurricanes to move in counterintuitive ways.

Scientists have a pretty good idea that hurricanes will become less frequent and more intense due to climate change, said oceanographer Chunzai Wang during a recent visit to the National Oceanic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratory (AOML) in Miami, where scientists study everything from ocean acoustics to hurricane forecasting.

But other curveballs that recently have come to light complicate the picture. One is dust.

Every year, storms over West Africa disturb millions of tons of dust, and strong winds carry those particles westward into the skies over the Atlantic Ocean, where many hurricanes form. [Infographic: Storm Season! How, When & Where Hurricanes Form]

During a dust spike triggered by heavy rainfall, there's a drop in hurricanes in the Atlantic basin, Wang said. As the dust spreads into the atmosphere, it increases what's called the vertical wind shear, the change in wind direction that comes with height, Wang said. That's bad news for hurricanes, because too much wind shear can break up tropical cyclones (the general term for hurricanes and tropical storms).

A few years ago, scientists at the University of Wisconsin, Madison, pored over satellite data from the past 25 years and found that during years when the dust storms rose up, fewer hurricanes swept across the Atlantic. Periods of low duststorm activity were followed by more-intense hurricane activity.

Another curveball is warm water. Earlier this year, Wang and colleagues also published a report finding that, counterintuitively, a large pool of warm ocean water in the Atlantic Ocean keeps hurricanes away from the United States.

Wang said a hurricane behaves like a leaf floating in a river, totally at the whim of the current. So goes the river, so goes the leaf. A large Atlantic warm pool causes the atmospheric "river" to steer toward the northeast, carrying a hurricane with it and away from the United States.

This scenario played out during the 2010 hurricane season, when a large warm pool kept an otherwise active hurricane season from having an impact on the United States.

This story was provided by OurAmazingPlanet, a sister site to LiveScience. You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

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Does October Snow Signal A Wild Winter Ahead? (LiveScience.com)

Between a second impending snowstorm in Denver and last weekend's 'Snowtober' storm in the Northeast, there's been a lot of early show across the United States. With so much snow so soon, it may seem like we're in for a long, snowy winter. But don't panic yet, weather forecasters say.

"There's no correlation or patterns that we're aware of that correlate October snow storms and how brutal a winter will be," said Carl Erickson, meteorologist with AccuWeather.

Erickson said this winter's forecast shows the main storm track focusing more to the west than last season. The big cities along the I-95 corridor should see a fairly typical winter, with a few big snow events, but nothing like two years ago where the East Coast had big snowstorms every few weeks. This year the Great Lakes region, including Chicago and much of Indiana will see the heavy snows.

Unfortunately, the Southwest and Southern Plains aren't likely to see any relief from the extreme drought conditions they have experienced this year, with warmer and drier than normal conditions expected to continue through the winter.

As a result of the Snowtober storm, more than 2 million people lost power and the storm has been blamed for at least 13 deaths. New York City set an October snow record with 2.9 inches (7.4 centimeters) accumulating, and towns in western Massachusetts piled up more than 30 inches (76 cm) of snow.

The historic nor'easter was the remnants of a storm that brought an October snow oddity to Denver earlier last week. The city went from a record daily high of 80 degrees Fahrenheit (27 degrees Celsius) to several inches of snow in 24 hours.

For the Frontal Range, the October snow, as wild of a weather swing as it was, isn't all that unusual, said Matthew Kelsch, a hydrometeorologist at the University Corp. of Atmospheric Research, in Boulder, Colo.

And that wild weather swing that is repeating today.

"Now we're seeing much of the east quieting down and more activity firing up across the Rockies," Erickson told OurAmazingPlanet.

The latest storm is already moving through the region today (Nov. 1). Snow is starting to accumulate in Wyoming and a blizzard warning has been issued for the south side of Denver tonight. The temperature was 74 F (23 C) yesterday and now the region is expecting 10 inches (25 cm)of snow. [The Snowiest Places on Earth]

"That's the continental climate for you," Kelsch said.

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

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Hurricane Season Is Past Its Peak (But Stay on Guard) (LiveScience.com)

This year's active hurricane season, already impressive in its activity, still has two months remaining. As Ophelia withers, the season seems to have hit another lull.

Are we past the peak of the season?

"From a climatological standpoint, about 75-80 percent of all hurricane activity has occurred," said Phil Klotzback, a hurricane forecaster at Colorado State University in Fort Collins. "So, yes, we are past the peak of the season."

Ophelia was the 15th named storm of the 2011 season, followed by number 16, Tropical Storm Phillipe, which is still swirling over the open Atlantic basin.

The 2011 season was predicted to be a doozy, with 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes (Category 3 or higher). So far, there have been 16 named storms, four hurricanes (Irene, Katia, Maria and Ophelia) and three major hurricanes (Irene, Katia and Ophelia).

But just because the season is past its peak is no reason to let down your guard. Hurricane season isn't officially over until Nov. 30, and deadly hurricanes can strike at any time through then, and even after. The tropics could heat up in these final months as storms shift their birthplace to the west in the Atlantic basin.

At the beginning of the season, tropical cyclones tend to form near Cape Verde, off the coast of western Africa. Cape Verde-typehurricanes are Atlantic basin tropical cyclones that strengthen into tropical storms within about 600 miles (1,000 kilometers) of the Cape Verde Islands and then become hurricanes before reaching the Caribbean, according to the National Hurricane Center. Cape Verde-type hurricanes are most common in August and September.  In rare years, such as 1995, a Cape Verde-type hurricane will form in late July or early October.

Toward the end of the season, storms begin closer to the United States.

"Typically, late-season [tropical cyclone] activity occurs in the Caribbean or the subtropical Atlantic," Klotzbach told OurAmazingPlanet.

This puts the southeastern United States in the crosshairs. October is typically an active month for that region.

And with the warm Atlantic waters and La Niña's return — which has been linked to active hurricane seasons — more big storms could be on the way.

You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

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Hurricane Irene Affirms 'Magic' Hurricane Date (LiveScience.com)

Hurricane watchers circle Aug. 20 on their calendars every year. This is the "magic" date when hurricane season seems to kicks into high gear.

Like clockwork, Hurricane Irene — the Atlantic's first hurricane of 2011 — was born on Aug. 22, later strengthening to a Category 2 hurricane. Last year was another good example of an active storm season ramping up after Aug. 20. All of the 2010's major hurricanes (those of Category 3 or higher) formed after Aug. 20, starting with Danielle on Aug. 21.

Aug. 20 seems to be special because around this time, the air and ocean are in just the right state to foster and feed the monster storms. In climate-speak, this time of year is when vertical shear (a change in wind directions with height) in the atmosphere is low enough and sea surface temperatures are warm enough to create big storms.

"Now, storms can get going before Aug. 20, but this is typically about when they start," said Phil Klotzbach, a hurricane forecaster at Colorado State University in Fort Collins.

This year was typical in saving its biggest storm so far for after Aug. 20, but it was unprecedented in the number of tropical storms that fizzled before reaching hurricane strength. The 2011 hurricane season began with eight tropical storms that all failed to become hurricanes before Irene broke the streak. One reason for the flurry of tropical storms is that scientists are naming more tropical storms than in past years, Klotzbach said.

The last time a hurricane season saw so many tropical storms before seeing a hurricane was 2002. That year, Tropical Storm Gustav eventually broke the string by strengthening to a Category 4 hurricane. Gustav struck Louisiana on Sept. 8, killing 112 people.

The hurricane forecast from the U.S. National Oceanic and Atmospheric Administration (NOAA) calls for 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes (Category 3 or higher).

Irene is currently a Category 2 storm, with winds of up to 100 mph (160 kph), and is the first serious threat to the U.S. coast in three years. If no hurricanes make landfall in 2011, this three-season lull will be the longest in recorded history.

Email OurAmazingPlanet staff writer Brett Israel at @btisrael.

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Japan Tsunami Is First Tracked by Radar (LiveScience.com)

Scientists in California got an early look at the tsunami generated by the massive earthquake in Japan as it rippled across the Pacific Ocean.

The March 11 Japan tsunami was picked up by high-frequency radar in California and Japan as it swept toward their coasts, according to U.S. and Japanese scientists. This is the first time a tsunami has been observed by radar, raising the possibility of new early warning systems.

"It could be really useful in areas such as southeast Asia where there are huge areas of shallow continental shelf," said John Largier, an oceanographer and study team member from the University of California, Davis. The continental shelf is the perimeter of a continent that is underwater and gradually descends to the ocean floor.

Largier and his colleagues have been using a high-frequency radar array at their lab to study ocean currents for the last 10 years. Together with collaborators from Hokkaido and Kyoto universities in Japan and San Francisco State University, the researchers used data from radar sites at Bodega Bay and Trinidad, Calif., and two sites in Hokkaido, Japan, to look for the tsunami offshore.

The radar detection is the latest in the string of new ways the Japan earthquake and tsunami were observed.Satellite images found that the tsunami was so powerful that it broke off huge icebergs thousands of miles away in the Antarctic. Scientists also found that the earthquake rattled the planet's upper atmosphere.

In the new study, scientists noticed that the radar picks up not the actual tsunami wave — which is small in height while out at sea — but changes in currents as the wave passes.

The researchers found they could see the Japan tsunamionce it entered shallower coastal waters over the continental shelf. As the waves enter the shallower water, they slow down, increase in height and decrease in wavelength until finally hitting the coast.

The continental shelf off California is quite narrow, and approaches to the coast are already well-monitored by pressure gauges, Largier said. But he said radar detection could be useful, for example, on the East Coast or in Southeast Asia, where there are wide expanses of shallow seas.

The study was published in the August edition of the journal Remote Sensing.

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2011's Billion-Dollar Weather Disasters Hit 9 Total (LiveScience.com)

From fires to floods to tornadoes, 2011 has already racked up a record-tying nine weather disasters that caused at least $1 billion in damage each.

The costliest weather disasters in the United States since 1980 were analyzed in a report by the National Climatic Data Center, which normalized the damage amounts to 2011 values. According to the report, 108 weather-related disasters produced overall damages that reached or exceeded $1 billion. All together, those weather events caused more than $750 billion in damages.

Already in 2011, the number of billion-dollar weather disastershas matched the total from 2008, and hurricane season has yet to hit full stride. Could 2011 surpass the 2008 record?

"Impossible to predict," said the NCDC's Scott Stephens. "An active Atlantic hurricane season does not necessarily equate to hurricane landfalls or hits along the U.S. coastline."

That was the case last year, which saw 19 named storms (including tropical storms and hurricanes) but no hurricanes hitting the United States. On the flip side, in 1992 there were only seven storms, but one of those was Hurricane Andrew, the Category 5 hurricane that hit South Florida and one of the costliest disasters in U.S. history.

All it takes is one big storm hitting the wrong place to create tremendous damage, active season or not, Stephens told OurAmazingPlanet.

Here are the nine U.S. billion-dollar disasters of 2011, which so far have combined to cause $35 billion in damages:

Upper Midwest flooding, summer: Melting of an above-average snowpack across the northern Rocky Mountains, combined with above-average precipitation, caused the Missouri and Souris rivers to swell beyond their banks across the Upper Midwest. An estimated 11,000 people were forced to evacuate Minot, N.D., due to the record high  level of the Souris River. Numerous levees were breached along the Missouri River, flooding thousands of acres of farmland. The flooding, which is ongoing, has caused more than $2 billion in damages.

Mississippi River flooding, spring-summer: Persistent rainfall (nearly triple the normal precipitation amounts in the Ohio Valley), combined with melting snowpack, caused historical flooding along the Mississippi River and its tributaries. The region suffered $2 billion to $4 billion in losses. At least two people died.

Southern Plains/Southwest drought, heat wave and wildfires, spring-summer: Drought, heat waves, and wildfires scorched through Texas, Oklahoma, New Mexico, Arizona, southern Kansas, western Arkansas and Louisiana this year. In Texas and Oklahoma, respectively, 75 percent and 63 percent of range and pasture conditions were classified as "very poor" as of mid-August. Wildfire fighting costs for the region are about $1 million per day. Well over $5 billion in damage has been done so far, with over 2,000 homes and structures lost.

Midwest/Southeast tornadoes, May 22-27: Central and southern states saw approximately 180 twisters and 177 deaths within a week . A tornado rated EF-5 on the tornado damage scale struck Joplin, Mo., resulting in at least 141 deaths, making it the deadliest single tornado to strike the United States since modern tornado record keeping began in 1950. The total losses were greater than $7 billion.

Southeast/Ohio Valley/Midwest tornadoes, April 25-30: This outbreak of tornadoes over central and southern states led to 327 deaths. Of those fatalities, 240 occurred in Alabama. The deadliest of the estimated 305 tornadoes in the outbreak was an EF-5 that hit northern Alabama, killing 78 people. Several major metropolitan areas were directly affected by strong tornadoes, including Tuscaloosa, Birmingham and Huntsville, Ala., and Chattanooga, Tenn. Total losses exceeded $9 billion.

Midwest/Southeast tornadoes, April 14-16: An outbreak over central and southern states produced an estimated 160 tornadoes. Despite the large overall number of tornadoes, few were classified as intense, with just 14 EF-3 --and no EF-4 or EF-5 -- tornadoes identified. Total losses were greater than $2 billion. Thirty-eight people died, 22 of them in North Carolina.

Southeast/Midwest tornadoes, April 8-11: An outbreak of tornadoes over central and southern states saw an estimated 59 tornadoes. Total losses were greater than $2.2 billion.

Midwest/Southeast tornadoes, April 4-5: An outbreak of tornadoes over central and southern states saw an estimated 46 tornadoes. Total losses were greater than $2.3 billion. Nine people died.

Groundhog Day blizzard, Jan 29-Feb 3: A large winter storm hit many central, eastern and northeastern states. Chicago was brought to a virtual standstill when 1 to 2 feet (0.3 to 0.6 meters) of snow fell across the city. Total losses were greater than $2 billion. The snowstorm killed 36 people.

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Rare, Severe 'Derecho' Windstorm Hits Midwest (LiveScience.com)

A severe storm is sweeping across the Midwest today with winds so strong that it has a special name: derecho.

A derecho (from the Spanish adverb for "straight") is a long-lived windstorm that forms in a straight line — unlike the swirling winds of a tornado — and is associated with what's known as a bow echo, a line of severe thunderstorms. The term "derecho" was first used over a century ago to describe a storm in Iowa. Across the United States, there are generally one to three derecho events each year.

The Midwest derecho has wind gusts between 60 and 80 mph (97 to 129 kph), according to the Weather Channel. Iowa, Wisconsin, Michigan and Illinois have all reported severe winds. These severe winds are the main cause of damage from the storm, said Rose Sengenberger, a meteorologist with the National Weather Service in Romeoville, Ill., but added that people should be on the lookout for other dangerous weather.

"With any long-lived storm, there is also the threat of lightning and heavy rain," Sengenberger told OurAmazingPlanet.

Tornadoes are not any more likely during a derecho, Sengenberger said. Still, the National Weather Service issued a tornado warning for parts of southwest Michigan. Dangerous rain-wrapped tornadoes could shoot down from the squall line, said the NWS. As their name suggests, rain-wrapped tornadoes are shrouded from view by pouring rains, making them even more potentially dangerous for their ability to surprise.

A derecho is not the worst of the windstorms, however. On May 8, 2009, a rare windstorm that swept across Kansas, Missouriand Illinois was in a league of its own. An intense vortex and eyelike structure similar to what forms at the center of tropical storms and hurricanes appeared in the bow echo. The storm was so severe that it earned a brand-new name: super derecho.

The super derecho gained strength as it moved across Kansas in the early morning, spinning off 18 tornadoes and packing wind speeds from 70 to 90 mph (115 to 145 kph) when it hit Springfield, Mo. The super derecho plowed a path of destruction through the state about 100 miles (62 kilometers) wide, crossed the Mississippi River with 90 to 100 mph (145 to 160 kph) wind gusts and blew through Illinois before dissipating at that state's eastern border.

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Is All the Wild Weather Connected? (LiveScience.com)

Natalie Wolchover, Life's Little Mysteries Staff Writer
LiveScience.com Natalie Wolchover, Life's Little Mysteries Staff Writer
livescience.com – Sat Jun 11, 8:00 pm ET

This has been a wild year, weather-wise.

In the winter, there was the record snowfall across the Northeast. Record rainfall and floods in Ohio Valley followed in April and May. The Southwest has been plagued by drought for months, while tornadoes have devastated the Midwest and South. Record heat is scorching most of the country this week — just days after snow fell in Hawaii. Meteorologists predict a harrowing hurricane season.

Is some underlying climactic condition driving these extreme weather events? There are two potential candidates: The first is La Niña, trade winds that blow through every five years, cooling the water of the equatorial Pacific Ocean and shifting the jet stream northwest. The second is global warming, the average worldwide temperature increase of 1 to 2 degrees Fahrenheit over the past century that has resulted from the dramatic rise of carbon dioxide levels in the atmosphere.

La Niña and global warming are both partly responsible for some of the episodes of wild weather, experts say. However, natural atmospheric variability has also come into play this year; to some extent, the pile-on of wild weather is random chance.

Drought here, floods there

According to Martin Hoerling, a research meteorologist and chairman of the climate variability research program at the National Oceanic and Atmospheric Administration (NOAA), "Some aspects of the recent U.S. climate anomalies, for example, the Texas, Arizona and New Mexico drought, are likely linked to a common factor: the cumulative effect of the prolonged La Niña event that has lasted from summer 2010 until this spring." [Read: La Niña Ends, So What's Next?]

"The impact of La Niña is also to generate wet Ohio Valley conditions in late winter," Hoerling told Life's Little Mysteries, a sister site to LiveScience. This year, however, the rains were heavier than in any prior year, La-Niña-year or otherwise. "The extreme nature of these rains is beyond what can be reconciled with La Niña alone."

Most NOAA researchers believe the extreme flooding is partially a result of climate change induced by global warming. "The flooding and the heavy rainfall are consistent with what we expect with global warming," said David Easterling, chief of the Global Climate Applications Division at NOAA's National Climatic Data Center. "Looking at some of the modern trends, we've seen increases in the amount of water vapor in the atmosphere, drawing a direct link between what's happening in the Midwest and global warming."

On top of global warming and La Niña, natural weather variability is undeniably playing a role, just as it does every year. "Natural atmospheric variability almost certainly contributed significantly to these extreme events," Hoerling wrote in an email. There have always been droughts and floods, and while global warming and La Niña may have helped them along this year, they may have hit hard regardless.

Heat everywhere

The nearly nationwide heat wave of the past week was caused by what meteorologists call a "high pressure ridge," a long strip of air that has high atmospheric pressure, making it warm and dry. While such ridges come about naturally, the record high temperatures this time around are linked to global warming, experts say.

The average temperature of the Earth has shifted higher in recent years, and that means the bell curve that represents the annual temperature variation has shifted over as well. Along with the higher average temperature, you therefore also get higher extremes. "An [average] warming of climate would indeed increase the probability of extreme hot periods," Hoerling wrote. [Read: What's Behind the Scorching Record Heat?]

Funnel storms

The link between global warming, La Niña and this year's violent tornadoes is unclear. Some scientists speculate that La Niña did have an impact by dying down earlier in the year than usual. "If La Niña had maintained its strength, perhaps we wouldn't have seen so many tornadoes," Bill Patzert, a climatologist at NASA's Jet Propulsion Laboratory in California, told OurAmazingPlanet, a sister site to LiveScience.

The jet stream, an "atmospheric fence" where cool, dry air meets warm, moist air, is usually pushed north by the La Niña trade winds in the spring, Patzert explained. This year, La Niña's early departure left the jet stream draped across the middle of the country, mixing cool, dry northern air with warm, moist southern air in tornado alley — a recipe for disaster.

Did global warming make the tornado season even worse? NOAA scientists have been trying to figure that out; so far, they say, the evidence is inconclusive.

Thermodynamic instability, the condition that causes thunderstorms by forming vertical clouds, combined with wind shear, which stabilizes the updraft and causes it to rotate, are the "perfect storm" that leads to a funnel. Trends associated with global warming do indeed amplify the first condition: Hotter air holds more moisture, so global warming increases the likelihood of vertical clouds forming. But you can't get tornadoes without wind shear, and "the expectation is that there will be less of that wind shear with global warming," Easterling said.

So with one tornado-conducive factor being increased and the other being decreased, it's really hard to say how global warming affects tornado activity. The scientists are still looking into it. "Inconclusive data does not lead you to conclude that there's no evidence of a connection," Hoerling said. [Read: Out of the Tornado Frying Pan and Into the Hurricane Fire?]

More extreme?

The scientists point out that there has always been extreme weather, and this year's events aren't entirely caused by La Niña and climate change. "I don't know whether climate has varied more extremely or not during recent decades," Hoerling wrote in an email.

Furthermore, "there is much more to extremes that just temperature and precipitation.  It's for example not clear how strong cyclones and their associated wind speeds will change [due to climate change]. There has been no evidence for a detected change in hurricanes or other violent wind storms.  Yet, there is an indication that heavy daily rain events have increased in some regions during some seasons.

"In sum, there are many measures of extremes, and it's unclear if any aggregate change in extremes has indeed occurred," Hoerling said.

This article was provided by Life's Little Mysteries, a sister site to LiveScience. Follow Natalie Wolchover on Twitter @nattyover. Additional reporting by Andrea Mustain, OurAmazingPlanet staff writer.

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