Tuesday, June 30, 2015

Lightning Data - Where to Find It

No doubt you have seen lightning strike displayed by your local TV station and other weather outlets. Where does that data come from, and how can you access it?

The lightning data you see shown along with radar displays likely comes from the National Lightning Detection Network (NLDN). The NLDN began operation as a regional network run by the State University of New York at Albany in 1983. The NLDN was eventually acquired by Global Atmospherics, Inc., and then in 2002 by Vaisala, Inc., a company that develops, manufactures and markets products and services for environmental and industrial measurement, especially meteorology and hydrology. The NLDN became national in coverage in 1989. It consists of over 100 remote, ground-based sensing stations located across the United States that instantaneously detect the electromagnetic signals given off when lightning strikes the earth's surface. These remote sensors send the raw data via a satellite-based communications network to the Network Control Center (NCC) in Tucson, Arizona. Within seconds of a lightning strike, the NCC's central analyzers process information on the location, time, polarity of the strike, and communicate this information to users across the country.

This lightning data is used by the utility industry, NASA, the National Weather Service, aviation, forestry, and many others. More information on the NLDN can be found here.

A map from Vaisala's "Lightning Explorer". Data on the map is 20 minutes delayed and updated every 20 minutes.

Blitzortung
Blitzortung.org is sort of a CoCoRaHS for lightning. It is a world-wide lightning detection network for the location of electromagnetic discharges in the atmosphere (lightning discharges) based on the time of arrival (TOA) and time of group arrival (TOGA) method. It was developed by a few people in Germany several years ago, and since has expanded world-wide. This lightning detection network consists of volunteers with lightning detectors constructed from a kit developed by the Blitzortung group. The detectors transmit data to a central processing server over the Internet, which then processes the data to determine the location of lightning strikes. Other volunteers include programmers who develop and/or implement algorithms for the location or visualization of sferic positions (sferics are a type of radio signal produced by lightning), and people who assist to keep the system running. There are about 110 detection stations in the U.S. Lightning data is also available for Europe and eastern Australia.

The web site includes a world-wide live map of current lightning strikes, an archive of lightning data, and information on how to obtain a kit to build your own lightning detector. The construction of the detector requires some knowledge of and skills in electronics.

LightningMaps.org
LightningMaps.org is a community project with free lightning maps and applications. Real-time lightning data is available on a map-based interface utilizing the data from Blitzortung. New lightning strikes are depicted by yellow dots with red circle.The red circle disappears after 30 seconds, and the dots become darker as the time from the strike increases. There is an option to view the "thunder ring", a white circle that expands out from the strike at the speed of sound. There is also an option that allows you to turn on a layer showing the radar reflectivity.

Lightning strikes as displayed by lightningmps.org.

There are a number of apps available for your smart phone and tablet to alert you of nearby lightning strikes. One I like is free and uses the Blitzortung data feed.It's called "Blitzortung Lightning Monitor" and has some really nice features, including the ability to notify you of nearby lightning strikes. This is an Android version. I don't know if it is available for iOS.

The Blitzortung Lighting Monitor app. Click the image to enlarge and read the annotations.


More Information on Lightning

Severe Weather 101: Lightning Basics (National Severe Storms Laboratory)


Lightning in Super Slow Motion – video clip from Discovery Channel's "Raging Planet" on the subject of lightning.


Lightning:  JetStream – Online School for Weather (NOAA)


Sunday, June 28, 2015

Lightning Safety - Rules to Live By

I certainly had an appreciation for lightning throughout my career as a meteorologist, but probably not enough as I should have. I've been outside when I should not have been, or stood on my porch watching thunderstorms as many of us probably have done. As I was gathering information for a web page on lightning and these blog posts, it was clear to me that I haven't been careful enough. The last two blog posts hopefully have made it clear - you don't mess with lightning - ever. Ben Franklin was one lucky guy, to say the least.

Take the threat of lightning seriously. Since most deaths and injuries occur outdoors, we'll look at these safety rules first.

“When Thunder Roars, Go Indoors!”

Credit: NOAA/NWS
This slogan was adopted by the National Weather Service several years ago, and while on the surface it might seem a little corny it gets right to the point .

If you are outdoors, find shelter in a nearby safe building or metal-topped vehicle with the windows closed. If you can hear thunder then you are at risk from lightning. The furthest distance from a lightning strike you can typically hear thunder is about five miles and seldom more than 10 miles, depending on atmospheric conditions. That "distant" rumble of thunder could only be several miles away, and just because you can’t hear thunder doesn’t necessarily mean you are safe. Lightning bolts are known to arc out tens of miles from the parent thunderstorm and may seemingly "come out of the blue". Stay inside at least 30 minutes after you last hear thunder.

Many injuries and fatalities from lighting were people who were headed to shelter but started to seek shelter too late. Pay attention to the weather and at the first sound of thunder or flash of lightning head to shelter. Fully enclosed buildings with plumbing and wiring provide the best protection. A hard-topped metal vehicle also provides protection. If you cannot find safe shelter there are some steps you can take to lessen your risk. However, it bears repeating that no place is safe outdoors in a thunderstorm.
  • Avoid open fields, the top of a hill or a ridge top.
  • Stay away from tall, isolated trees or other tall objects. If you are in a forest stay near a lower stand of trees.
  • If you are in a group, spread out to avoid the current traveling between group members.
  • If you are camping in an open area, set up camp in a valley, ravine or other low area. However, be aware of flash flooding potential in low-lying areas. Remember, a tent offers NO protection from lightning.
  • Stay away from water and wet items such as ropes, as well as metal objects such as fences and poles. Water and metal do not attract lightning but they are excellent conductors of electricity. The current from a lightning flash easily travels long distances.
    Crouching doesn't make you any safer outdoors. Run to a substantial building or hard topped vehicle. If you are too far to run to one of these options, you have no good alternative. You are NOT safe anywhere outdoors.

    However, the National Outdoor Leadership School along with NOAA recommends the lightning position when getting to safety is impractical or not possible. This may help minimize injuries if you are struck. You can download the complete brochure on backcountry lightning risk management here.





     Lightning Safety Indoors

    • Stay off corded phones. You can use cellular or cordless phones.
    • Don't touch electrical equipment such as computers, TVs, or cords. You can use remote controls safety.
    • Avoid plumbing. Do not wash your hands, take a shower or wash dishes.
    • Stay away from windows and doors that might have small leaks around the sides to let in lightning, and stay off porches.
    • Do not lie on concrete floors or lean against concrete walls.
    • Protect your pets. Dog houses are not safe shelters. Dogs that are chained to trees or on metal runners are particularly vulnerable to lightning strikes.
    • Protect your property. Lightning generates electric surges that can damage electronic equipment some distance from the actual strike. Typical surge protectors will not protect equipment from a lightning strike. The National Lightning Safety Institute has information on protecting your home and electronics from lightning. Do not unplug equipment during a thunderstorm as there is a risk you could be struck.

    You can find more information at the Lightning Safety page from the National Weather Service.
       
    If all of this is not enough to convince you to be careful, there are plenty of videos on YouTube showing the incredible power of lightning. Here's one of them: Lightning video

    Next: Lightning data and more information

Friday, June 26, 2015

Lightning Strike - A Life-Changing Experience

Being struck by lightning is a life-changing experience for most people, and not in a good way. If you are fortunate to not be killed (only about 10 percent of people struck by lightning are killed), the injuries you suffer with may be with you the rest of your life.

There are five ways you can be struck by lightning.

A direct strike occurs when the person, usually in an open area, becomes part of the main lightning discharge channel. A portion of the current moves along and over the skin, and a portion moves through the body.

A side flash occurs when the lightning strikes a taller object near the person (like a tree) and part of the current jumps from that object to the person.

A person may also be affected by a ground current. When lightning strikes a tall tree, for example, the charge travels down the object to the ground and then along the ground surface. Ground current can cover a large area and is the cause of most lightning casualties. The current enters the body at the point closest to the lightning strike (for example, your foot) and exits the body at a point farthest away from the strike (your other foot). The greater the distance between these two points the greater voltage difference. The voltage difference is what drives the electrical current through your body and causes injury or death. Ground current is often fatal to livestock because of their large size, i.e. there is a large voltage difference between their front legs and rear legs and current travels trough the entire body.

Turf damage caused by ground current from a lightning strike.
Photo credit:  AlGamaty on Reddit

Conduction of lightning through wires or other metal surfaces allows lightning to travel long distances. Fences, electrical lines, pipes, or other metal surfaces can provide a pathway for lightning. Most indoor lightning casualties are related to conduction. That is why it is important to stay off of a corded phone, and stay away from anything plugged into an electrical outlet, water faucets and showers, or windows and doors.

Streamers develop as the downward-moving leader approaches the ground. These are upward streamers, and usually only one of the upward streamers makes contact with the leader to provide the main channel for the return stroke. However, when the main channel discharges, so do all the other streamers in the area. If a person is part of one of these streamers, they could be killed or injured during the streamer discharge even though they are not part of the main discharge.

A more detailed description can be found on the NWS Lightning Safety web page.

While some lightning strikes result in death, the majority do not. However, disabilities from a lightning strike can be severe and long-term.

Most people can survive a lightning strike because much of the current dissipates over the skin (what is known as flashover)instead of entering the body. The electrical current is taking the path of least resistance, and can travel easier along the skin than it can within the body. When you hear about people who have had their shoes or clothes blown off it is because the flashover causes rapid heating of any moisture in the shoes or under the clothes (e.g. from sweat). The water vapor (steam) rapidly expands producing enough force to tear shoes or clothing from a person's body. This tends to occur with side flashes.

When lightning strikes your home it may damage your computer, television, and other electronics. When lightning strikes a person the primary injuries are to the body’s “electronics” – the nervous system and the brain. The most readily apparent effect may be cardiac arrest. Serious burns seldom occur. Most burns are caused by other objects (rainwater, sweat, metal coins and necklaces, etc.) being heated by the current passing through them and causing the burn rather than being caused by the lightning itself. The  90 percent of victims who are not killed by lightning exhibit various degrees of short and long-term disability.

Damage to the nervous system and the brain may not be readily apparent. Symptoms may include fatigue, intense headaches, inability to concentrate, inability to process information, personality changes, and others. Some symptoms may not manifest themselves until sometime after the incident.  Often conventional medical testing (imaging, lab tests, etc.) will not show any physical changes that can be attributed to the lightning strike. Neurocognitive or neuropsychological testing may be used to identify functional and cognitive deficiencies.

There is research being done on the injuries resulting from lightning. Dr. Mary Ann Cooper, M.D. at the University of Illinois at Chicago heads the Lightning Injury Research Program. Her article “Disability, not Death, is the Main Problem with Lightning Injury” contains more information on the effects of lightning injuries.

The behavioral and personality changes that may be experienced by lightning-strike survivors are often hard for family and friends to understand.  Lightning Strike & Electrical Shock Survivors International, Inc. is a non-profit support group formed by a lightning strike survivor in 1989. Its mission is to provide support for survivors, spouses, and other interested parties as well as to provide education on the prevention of lightning and electrical injuries.

"The Body Electric"  is an excellent article on the experiences of and injuries suffered by lightning strike survivors.

For more information on the medical aspects of lightning injuries, see Lightning Injuries.
 
John Jensenius, Jr., a Lightning Safety Specialist for the National Weather Service performed an analysis of 261 fatalities from lightning in the U.S. from 2006 through 2013. While many of us associate golfing with most lightning fatalities, that is in fact not the case. He found that fishermen account for the majority of deaths (30, vs. 8 for golf). Men accounted for 81 percent of all fatalities. Jensensius broke down the data into a number of categories, including age, sex, general type of activity (work, leisure), and specific activities within those categories. He found the two-thirds of those killed were involved in leisure activities.

From "A Detailed Analysis of Lightning Deaths in the United States from 2006 through 2013" by John Jensenius, Jr.

You can read the entire report (12 pages) here.


Next: Lightning Safety

Wednesday, June 24, 2015

Where There is Thunder, There is Lightning

This week is Lightning Safety Awareness week in many parts of the country. If your local National Weather Service office is participating then you may have seen their links to some lightning information on their web page. I'll be sharing some information about this topic in my posts over the next several days.

Lightning is one of the oldest recorded natural phenomena. Despite our long study of lightning (remember Ben Franklin?) it remains on the frontier of atmospheric science.

Lightning occurs throughout the country and in all seasons. The area of highest incidence extends from the central and southern Plains through the Midwest and in the Southeast. Florida is the lightning capital of the U.S. with an average of 27 to more than 33 flashes per square mile per year.



We credit Ben Franklin with discovering that lightning was electrical in nature and was in fact static electricity. Ben was one incredibly lucky man with that experiment.

As Ben discovered, lightning is a sudden electrostatic discharge from a thunderstorm. These giant sparks can extend from the cloud to the ground or objects on the ground, between clouds, within the cloud, or even between the cloud and air.

In many respects lightning is similar to the static electricity spark you may see or feel during the winter when the air is very dry and you touch a metallic object. When you walk across a carpet, for example, electrons move from the atoms in the carpet to you.  You are, in effect, negatively charged. When you touch a metallic object like a door knob, the electrons move from you to the knob. The zap you feel and may hear are the electrons moving from you to the door knob through an electric spark.

Similar processes occur in a thunderstorm. As the thunderstorm develops the updrafts and downdrafts within the storm result in collisions between the precipitation particles within the cloud. Near the top of the storm these are usually small ice crystals. The ice crystals become positively charged and are carried higher into the storm because they are lighter. As a result the top of the storm becomes positively charged, while the middle and lower layers become negatively charged. Small ice crystals and small hail occur in the middle of the storm, while in the lower layer raindrops and melting hail occur. The collisions between these particles cause some to lose electrons and become negatively charged. The negative charge in the middle and lower layers of the thunderstorm cloud induces a positive charge in the ground underneath the storm, and the positively charged anvil induces the ground under the anvil to become negatively charged.

How electrical charges are distributed in a thunderstorm. Credit: NOAA

In the early stages of thunderstorm development the air acts as an insulating layer between the cloud and its surroundings. As the electrical charges build up within the thunderstorm, the difference between, for example, the negatively charged middle portion of the cloud and the ground become large enough to overcome the insulating effects of the air, and a lightning discharge occurs. When this discharge occurs between the middle of the cloud and upper portion of the storm, “in-cloud” lightning occurs.

In-cloud lightning. 
Credit: jpdavey.deviantart.com

When the discharge occurs between the negatively charged region of one storm and the positively charged region of another, it is called cloud-to-cloud lightning.


Cloud-to-cloud lightning over Washington D.C.
Credit: Kevin Ambrose, Capital Weather Gang

 Lightning can also occur between the cloud and the surrounding air.

Cloud-to-air lightning.
Source: YouTube


Cloud-to-ground lightning occurs when the discharge happens between the cloud and the ground.

Cloud-to-ground lightning.
Credit: UK Met Office

Cloud-to-ground lightning strikes account for about 25 percent of the lightning flashes worldwide. They are some of the most spectacular and also the most dangerous because they hit the ground or objects on the ground. The lightning discharge lasts only a few microseconds, but the process of its formation is complex.

Credit: NOAA
A lightning strike begins when an ionized channel of air, called a step leader, develops from the thunderstorm to the ground. As the step leader zigzags toward the ground, the electrical field increases as the quantity of positive charge residing on the Earth's surface becomes even greater. The electric field is strongest on grounded objects whose tops are closest to the base of the storm such as trees and tall buildings (that’s why you stay away from tall objects during a thunderstorm). This charge begins to migrate upward through buildings, trees and people into the air. When this upward rising positive charge – an upward leader or streamer – meets with the leader in the air above the surface, a conductive path is completed. Electrons surge along this path creating the visible lightning bolt. The rapid flow of electrons heats the surrounding air causing it to explosively expand, sending out a shock wave we hear as thunder.


Lightning is the third highest cause of weather-related deaths after flooding and extreme heat, causing an average of 51 fatalities a year with hundreds more injured. The National Lightning Safety Institute estimates that costs and losses due to lightning in the U.S. could be as high as $8 - $10 billion per year.

In my next post we'll look at how people are struck by lightning, the effects of being struck, and some statistics  on lightning fatalities that may surprise you.

Wednesday, June 17, 2015

Bill Leaving Soggy Footprints

Radar image from Houston, TX at 3:21 p.m. CDT June 16.
Tropical Storm Bill came ashore along the Texas Gulf Coast yesterday and since then has made his way well inland.

Although Bill was downgraded to a tropical depression this morning, there were still tropical storm force winds being recorded in Oklahoma this evening. The big impact from Bill is not the winds but the copious amounts of rain he's laying down along his path.

 
24-hour precipitation ending the morning of June 17, 2015.
Source: NWS Advanced Hydrologic Prediction Service

Rainfall was heaviest yesterday and last night  in Jackson and Wharton Counties between Port O'Connor and Houston, TX.  The CoCoRaHS observer at TX-JK-5 (Ganado 1.5 W) recorded a whopping 11.77 inches of rain for the 24-hour period ending this morning, and a total of 15.06 inches from June 14-17. There were a number of 24-hour amounts in excess of 7.00 inches in this same area. Fortunately there was almost two weeks of dry weather before Bill waded ashore.

24-hour precipitation ending the morning of June 17 in Jackson County, TX

4-day CoCoRaHS precipitation totals for coastal Texas near T.S. Bill landfall as of June 17.

As of noon today T.D. Bill was located north of Dallas and moving NNE. This evening the center of circulation was just south of Ardmore, OK.

Surface map for 7:00 p.m. CDT June 17, 2015

That's another part of the country that really doesn't need any more heavy rain. Expected rainfall in eastern Oklahoma is from 3 to 7 inches, with locally higher amounts. By Thursday and Friday the moisture associated with Bill will be moving into Missouri and the mid-Mississippi Valley, with three to four inches of rain expected there. This will be on top of already soggy ground resulting from the showers and thunderstorms associated with the frontal boundary that has been oscillating north and south this week in a very moist air mass.

There is some good news in all of this. Showers and thunderstorms are likely to drop some healthy amounts of rain from Indiana east through Ohio, Kentucky and through the mid-Atlantic coast. This area has been rather dry the past six weeks, with precipitation from 75 percent to less than 50 percent of normal.
Quantitative Precipitation Forecast (QPF) for the period from 6:00 p.m. CDT June 17 to 6:00 p.m. CDT June 20, 2015


It appears that rain gauges throughout the central and eastern U.S., including the Upper Great Lakes and the Northeast, will be getting a good workout in the next three to seven days.


Quantitative Precipitation Forecast (QPF) for the period from 6:00 p.m. CDT June 17 to 6:00 p.m. CDT June 24, 2015

Friday, June 12, 2015

It's Official - May 2015 was the Wettest Month on Record in the U.S.

The NOAA National Centers for Environmental Information has crunched the numbers, and 4.36 inches of precipitation for the 48 contiguous states during May 2015 made it not only the wettest May on record in 121 years, but the wettest month ever.


The previous wettest May was in 1957 with 4.24 inches of precipitation, and the previous wettest month was October 2009 with 4.29 inches of precipitation.That one number representing the average precipitation across the lower 48 states is calculated using climate division data in each state. An average for each climate division is determined from the precipitation observations mapped to a 5 kilometer grid.

It's interesting to note that the May 1957 precipitation departures were also highest in the southern and central Plains, but also extended west to California. In all three cases the percent of the U.S. that was classified as very wet (in the top ten percent of the historical distribution) was 43 to almost 45 percent.

Percent of mean precipitation for May 1957 which is now the second wettest May on record.

Percent of mean precipitation for October 2009, now the second wettest month on record.

The fact this was a record wet May is not surprising news for those living in the southern and central Plains. It was the heavy precipitation over a rather large area that contributed to the record total. It was the wettest month ever in Texas and Oklahoma, and Colorado recorded its wettest May on record. It was the second wettest May in Arkansas, Kansas, and Utah.

Wednesday, June 3, 2015

A Weird, Wet May Across Much of the U.S.

The first tropical storm of the season, Ana, developed off of the southeastern U.S. nearly four weeks before the official start of the season. As Ana weakened and moved away, a late spring storm dropped from one to feet of snow on Colorado, Wyoming, and western Nebraska, with lighter but significant amounts in South Dakota and North Dakota.



California continued to suffer through another month of extreme drought, and the eastern U.S. along and east of the Appalachians was dry with less than 50 percent of average precipitation for most of the area. The notable exception was coastal North Carolina which benefited from the rains from the close approach of T.S. Ana. It was very warm across Alaska and many locations experienced a "top five" warmest May. In the eastern Interior and northern Southeast Alaska this was the warmest May of record. A high temperature of 91°F recorded in Eagle, AK on May 23 was the earliest in the season for 90°F or greater to be reached in Alaska.



In much of the U.S. between California and the Appalachians precipitation was much above normal, well more than twice normal from the Gulf Coast northward through the central Rockies.


The heaviest precipitation, however, was concentrated in Texas and Oklahoma, particularly in northeastern Texas through central Oklahoma.


May precipitation was very heavy from the Gulf Coast northward into eastern Kansas with amounts raining from 10 to almost 30 inches.

It was hard not to know what was going on during the three weeks from May 5 to May 26 if you paid any attention to the news. Oklahoma experienced its wettest month ever since 1895 with average statewide precipitation of 14.40 inches, 9.58 inches above normal and almost four inches higher than the previous record of 10.75 inches in October 1941. In addition, many locations in Oklahoma had their wettest month on record. Oklahoma City had 19.48 inches of rain during the month, beating the precious record of 14.66 inches set in  June 1989. Normal may precipitation for Oklahoma City is 4.65 inches.

CoCoRaHS observers were there to document the historic rainfall. Of 204 Oklahoma CoCoRaHS stations reporting in May,  an astounding 59 of them had 20 or more inches of rain during the month. There were 92 stations reporting on at least 28 days (90 percent) during the month, and of these the largest amount was 26.58 inches at OK-PG-7 (Krebs 0.3 WNW), with the lowest 4.48 inches at OK-CM-2 (Keyes 10.5 ESE)

A large portion of Texas experienced heavy rain during May, but the heaviest rain was concentrated in north-central Texas. Of the 1775 CoCoRaHS stations with reports in Texas during May, 672 reported a foot or more of rain during the month. The highest CoCoRaHS amount was 27.32 inches at TX-GA-9, Pottsboro 7.1 WNW in Grayson County along the Oklahoma-Texas border. A U.S. Cooperative observer in Gainesville, TX, (west of Pottsboro in Cooke County) reported a total of 28.90 inches for the month.

The heavy rain brought a dramatic end to the drought that plagued Oklahoma and Texas since 2010. As of the May 26 U.S. Drought Monitor only 5.4 percent of the state of Texas was in Moderate Drought or greater. The last time that number was this low was on May 11, 2010 when it was 3.51 percent. Five years ago this month there was no drought in Oklahoma, but the drought ramped up there in October 2010.  It peaked in the fall of 2011. The drought disappeared briefly except in the Oklahoma Panhandle and the western half of Texas by the spring of 2012, but then reestablished and intensified, persisting at various intensities until this spring.


The drought in Texas in September 2011 (left), when it was at its peak, and on May 26, 2015.

The drought in Oklahoma on September 2011 (left) and on May 26, 2015.

This particular form of drought relief had other consequences as well. Significant flooding continues to occur along many rivers in Texas, particularly the Trinity River and the Red River. A number of locations along these rivers are expected to remain at major flood stage into next week.


Wednesday, May 6, 2015

Alaska Breakup - the Transition Between Winter and Non-Winter

While attention in the lower 48 states has been on warmer spring weather and severe storms, it's ice breakup season in Alaska.

Heavy rain, snow melt, and sometimes ice jams sometimes result in spring flooding in the lower 48 states. The primary threat for flooding in the spring along Alaskan rivers is ice jams caused by the breakup of ice. Snowpack and precipitation also contribute, but ice breakup on the rivers in Alaska is when residents along the rivers collectively hold their breath.

River-ice break is a major annual event, and the primary ice breakup window is April and May. Thick ice that formed during the long cold winter begins to soften and melt as the weather warms and the sun climbs higher in the sky during the spring.  Breakup tends to occur earlier when temperatures and river flow are above normal.

Ice jams form when ice accumulates at bends in the rivers, causing more ice to pile up at that spot. Water backs up behind these jams, and the river can leave its banks, flooding communities along the river. Flooding might also be caused by the rapid release of water from the breakup of an ice dam, causing more of a flash flooding situation. As you might expect, flooding risks increase when river levels are higher than normal. Even in years where water levels may be low, ice jams can quickly turn a low flood potential into a high flood potential.

Map showing locations of Eagle and Nenana, AK.
Communities along the Upper Yukon River suffered major flooding in 2013 and in 2009. The flood of 2009 marked the highest peak flood stage on the river. During the first week of May an ice jam formed about 10 miles downstream of Eagle, AK, near the Alaska/Yukon border. Homes and other buildings in the Alaskan Native village of Eagle Village were scoured from their foundations by the massive chunks of ice, and the village of Eagle suffered serious flooding. The river rose up to eight feet on buildings, and businesses were damaged by the floating ice. Flooding also occurred on other rivers, but flooding along the Upper Yukon was the worst. The flooding was preceded by a winter with above normal snowfall across most of Alaska. The early arrival of much above normal to record warm temperatures in the spring caused rapid melting of the snow and increased flow into the rivers.

A huge slab of ice sits across a road near Eagle, AK in May 2009.
Credit: www.lightshineministies.org

Ice and damaged homes in Eagle, AK in 2009.
Credit: National Park Service

There are two main processes for ice breakup on the Alaskan rivers, thermal and dynamic. Dynamic breakups tend to produce the worst flooding. These occur when the river levels rise due to runoff from rapid snowmelt or heavy precipitation. The changing water level helps break up the ice, usually into large sheets. These large pieces of ice can easily be jammed up at bends or narrow portions in the river, causing an ice jam. During a thermal breakup the ice melts in place because there is not enough flow to move the ice downstream. It becomes thinner and thinner, and when it does break up it usually is in smaller pieces rather than massive sheets of ice. However, ice jams and flooding are still possible.

After a warm and snow-starved winter, Alaska experienced its 9th warmest and 11th wettest April on record. The heavier April precipitation was offset by the lack of snow and warm weather during the winter and early spring, reducing the flood threat. This year the flood potential is on the low side for most Alaskan rivers as a thermal breakup is likely on most rivers.

It has been much warmer than normal the past 60 days across central and eastern Alaska.

A number of communities have contests to predict when ice breakup will occur. The best know of these is the Nenana Ice Classic. This began in 1917 when railroad engineers bet $800 guessing when ice on the Tanana River would break up,  and it has been conducted each year since. People from all over the world participate. A tripod is set two feet into the river ice 300 feet from shore. It is connected to a clock on shore that stops once the ice breaks up and the tripod tips over. This year the ice breakup occurred on April 24th, and the winner walked away with over $300,000.

The tripod being installed in the river ice for the 2015 Nenana Ice Classic.
Credit: Nenana Ice Classic

The National Weather Service River Forecast center in Alaska and the Alaska Department of Homeland Security and Emergency Management have begun a Riverwatch program to monitor the breakup of river ice and keep communities informed about river conditions and flood potential.

You can read about ice breakup conditions on the NWS Alaska River Forecast Center web site.

Thursday, April 23, 2015

Not Where You Would Expect a Tornado

With much cooler air over much of the country this week has been rather quiet with respect to severe weather. Wednesday has been the most active day with a number of severe storms in northeastern Texas, including several weak tornadoes and hail to three inches.

On Tuesday there was a somewhat rare occurrence in the desert of southern California. A landspout tornado developed out of an isolated thunderstorm and caused some damage to a solar panel array near Desert Center, CA, near the California-Arizona border. If you're wondering what a "landspout tornado" is, it's a tornado that is not associated with a mesocyclone or rotating thunderstorm. They are typically weaker and smaller than tornadoes associated with a supercell and tend to have a smooth appearance, similar to a waterspout (hence the name "landspout"). It is a tornado because the rotating column of air is in contact with the ground and with the parent cumulonimbus cloud - the definition of a tornado.

Landspout tornado near Desert Center, Ca on April 21.
Photo via NWS Phoenix Facebook

The tornado was first reported by a pilot flying in the area. The circulation associated with the tornado was not evident on radar since it was at low levels. The nearest radar was in Yuma, AZ, and at the distance the radar beam at the location of the storm is at about 10,000 feet above the ground. A news crew and a number of other people were able to capture photographs of the tornado.

Another photograph of the Desert Center landspout.
Photo by Russell Fischer via Facebook.


This is the radar image of the storm at 4:00 PDT, about 13 minutes after the tornado was first reported by the pilot. This was at the storm's peak strength. Fifteen minutes later the storm had weakened considerably. The tornado icon indicates where the tornado was reported.
Based on early reports of damage, mostly to the solar array, the National Weather Service has preliminarily given this a rating of EF0. A number of panels were bent and twisted and others were damaged by rocks and other debris flung about by the tornado.

Solar panels damaged by the landspout

The NWS will be sending out a team to survey the damage in a few days. A description of this tornado, photos, and maps can be found at the NWS Phoenix web site.

Thursday, April 16, 2015

April 9th Tornadoes in Northern Illinois

This year's severe weather season got off to a slow start for much of the country. In fact, the first severe weather watches in March weren't issued until March 24, which was the latest first March watch in 45 years. In the three weeks following another 53 watches have been issued, a rate more typical of this time of year. Last year there were 1045 severe weather reports through April 15, and this year the count was at 923.

2015 severe weather reports (wind (blue), hail (green), and tornadoes (red)) through April 15.
One of the more spectacular, impressive, and certainly damaging events of the year to date occurred on April 9 in the Midwest.

By now you have probably seen some of the photos and video taken of the tornado in northern Illinois. Now that the dust has settled on this event it's a good time to look at some of the summaries and descriptions of the event that are available. It's not too unusual for there to be numerous videos and countless photographs of tornadoes these days, but this event caught my attention because it was, for lack of a better description, so photogenic and several people captured incredible images. Wide open spaces and clear views of storms are usually the calling card of the southern, central, and northern Plains, not northern Illinois.

Last Thursday's severe weather was anticipated and well-forecast by the NWS. The bulls-eye location for this severe weather event extended from eastern Iowa through northern Illinois, an area located southwest of an intensifying surface low. A warm, humid highly unstable air mass was in place over this area, strong winds aloft, converging winds at the surface, and a 30°F temperature difference from north to south of the warm front.

Annotated surface map for 6:00 p.m. April 9.
Source: National Weather Service Chicago

Most of Illinois and eastern Iowa was in an area of Enhanced Risk for severe weather in the 11:30 CDT convective outlook from the Storm Prediction Center.

The convective outlook issued at 11:30 a.m. CDT on April 9 showing and area of Enhanced Risk from Texas to Illinois and Indiana. On the left is a graphic showing the highest tornado probability from eastern Iowa across northern Illinois.


Storms began to develop during the late afternoon in eastern Iowa and northwestern Illinois. By 6:00 p.m. a strong thunderstorm was developing in northern Ogle County. At 6:09 p.m. the National Weather Service issued a tornado warning for this storm.

Radar image at 6:10 p.m.


At 6:29 p.m. a funnel cloud was reported south of the Rockford Airport, and eight minutes later a tornado was on the ground just south of Cherry Valley, IL. This was a short-lived EF0 tornado. The storm that produced the EF4 was was rapidly developing to the southwest of the first storm.


At 6:35 p.m. a tornado warning was issued on the big supercell. A tornado was reported on the ground near Franklin, IL, between Dixon and Rochell just north of Interstate 88.


Radar image at 6:35 p.m.showing warned storm that produced the Fairdale tornado.
The Fairdale tornado just after formation as it intensifies and strikes Crest Foods in Ashton, IL. Debris is clearly seen in the lower half of the funnel.  Photo by Walker Ashley, used with permission.

Over the next 40 minutes this tornado traveled 30 miles, destroying much of the village of Fairdale, IL and producing EF4 damage at several points along its path.this one thunderstorm eventually produced six tornadoes.

When the day was over there were a total of 11 tornadoes confirmed in Illinois, seven of those in northern Illinois, and one in Iowa. There were also three tornadoes reported in eastern Missouri and three in Texas that day.

The path of this tornado was through a lightly populated area of northern Illinois, well west of the Chicago metropolitan area. However, it passed just three miles north of Rochelle, a city of 9,500 people. Had the path of this tornado been located 13 miles to the northwest it would have plowed through the city of Rockford (pop. 150,250). If the track of this tornado were 15 miles to the southeast of the actual path the tornado would have passed through De Kalb (pop. 43,850), the home of Northern Illinois University, and Sycamore (pop. 17,500).

Here is a map of all severe reports received on April 9 superimposed on the outlook issued by the Storm Prediction Center at 11:30 CDT.



There are number of descriptions of the analysis and events of that day that are worth reading. The NWS Chicago office has an updated page, "April 9, 2015 Tornado Event, Including Rochelle/Fairdale EF-4 Tornado". At the bottom of that page are links to event descriptions from NWS Quad Cities, NWS Central Illinois, and NWS Paducah, KY where the other tornadoes occurred. The page has photos, detailed tornado  tracks, radar images, and an analysis of the weather of that day.

Walker Ashley, a professor of meteorology at Northern Illinois University, Certified Consulting Meteorologist,  and well-known storm chaser has written a blog post about his experiences that day chasing the Fairdale tornado, including remarkable photographs and videos he recorded.

The NWS Chicago has a Facebook photo album of storm photos submitted by the public of the storms that day. You do not need a Facebook account to view these.

Dennis Mersereau at The Vane also has a nice blog post with an in-depth look of the tornado.
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