Monday, August 31, 2015

Cyclones Aplenty

If you're a tropical weather enthusiast the last week to ten days has been an interesting period. In the Atlantic Danny was briefly a hurricane, but fizzled out pretty quickly and fell apart last Monday in the eastern Caribbean producing heavy rain but not much else. In the wings was Tropical Storm Erika, which in the early stages appeared to be a threat to Florida. However, Erika never did make hurricane strength. It quickly fell apart as strong wind shear and the mountains of Hispaniola combined to weaken it, and the storm dissipated off the northeast coat of Cuba. Erika did bring heavy rain to the Caribbean last week and the remnant trough of low pressure continued to produce heavy rain across Florida and the southeast coast this weekend.


7-day accumulated rainfall for Puerto Rico ending the morning of 8/31/2015

24-hour precipitation for the southeastern U.S. ending the morning of 8/31/2015

A low pressure system that move off the west coast of Africa became Tropical Storm Fred Sunday,  Hurricane Fred early this morning, and was downgraded to Tropical Storm this evening. Fred is a small cyclone and likely will be moving into unfavorable upper air conditions in the next few days. Current forecasts call for it to be only a tropical depression by the end of the week.


Forecast track for Fred.

Conditions are even more interesting in the central Pacific, where three hurricanes are spinning.

NOAA GOES-West image of three hurricanes in the Pacific: Kilo (left), Ignacio (middle), and Jimena (right).


Hurricane Kilo is a Category 4 hurricane located several hundred miles east of Wake Island. Hurricane Ignacio is a Category 2 storm (it was a Category 4 storm on Sunday) located about 350 miles east of Honolulu. Hurricane Jimena is another Category 4 storm with peak sustained winds of 145 mph. Ignacio is not expected to directly threaten Hawaii, but it is producing dangerous surf conditions. This is the first time three major hurricanes (category 3 or higher) have been observed over the central Pacific at the same time.

The eye of Hurricane Jimena taken by astronaut Kimiya Yui on the International Space Station

The tropical cyclone activity in the Pacific is being supported by some very warm water. Below is an image of the Pacific sea surface temperature anomaly as of today.

Sea surface temperature anomaly on August 31. The water over which the hurricanes are located is 1.5°C to more than 2.5°C (2.7°F to 4.5°F) above normal.

Finally Tropical Depression 14-E developed in the eastern Pacific and late today was located about 700 miles south of the southern tip of Baja California. It is expected to strengthen to a tropical storm in the next 24 hours and turn to the north.

Wednesday, August 26, 2015

An Index of "Perfect Pleasant" Weather

I was reading through a recent post of Minnesota Weathertalk Blog by Mark Seeley, an Extension climatologist and meteorologist at the University of Minnesota when his mention of a "Camelot Climate Index" caught my attention.  There are a laundry list of indices used in meteorology and climatology of various types and purposes (Heat Index, Wind Chill Index, Southern Oscillation Index, lifted index, etc. etc.) but the "Camelot Climate Index" was a new one to me. Intrigued, I looked into it further.

The Camelot Climate Index attempts to identify locations with the "perfect pleasant climate", according to Jan Null, a Certified Consulting Meteorologist who developed the index. True to its name, the index was inspired by the lyrics to "Camelot" written by Alan Jay Lerner for the the 1960 musical. (Click image to see a larger version).


Null started thinking about such an index in the early 1990s, inspired by articles and rankings of the "best places to live". Most of these used the annual number of sunny days, which he felt fell short of truly defining a pleasant place to live. His idea of the ideal climate is sunny and relatively mild with few extremes in temperature, humidity or precipitation, and no snow. An interest in musical theater led to the connection with Camelot, and so he went on to develop the Camelot Climate Index using these variables.

The index is calculated using the 1981-2010 monthly average values of maximum and minimum temperature, average afternoon relative humidity, the number of days above 90 and below 32, precipitation, and sunshine data. He calculated weighting factors for the variables, and then subtracted the weighting values from 100 (100 represents "perfect" weather).

The resulting map of values indicates that the weather best meeting the criteria Null established extends from the Desert Southwest to and up the west coast. The highest index values (and thus the "perfect pleasant climate", as Null puts it) is along the California coast.




A complete description of the values and calculations used can be found on his Camelot Climate Index web page.

Null is the first to admit that the Camelot Climate Index is completely subjective because it's based on his perception of what makes the perfect climate - yours and mine may be different. Some time in the future he would like to construct a "variable" index that might be compiled for different perceptions of an "ideal climate".

We have been enjoying some beautiful (dare I say perfect?) late summer weather here in much of the Midwest this week. Skies have been mostly sunny, daytime highs in the 70s, overnight lows in the 50s, and no rain. While that's great weather for a week or three, to me at least, I don't think I could deal with it year round. I enjoy the four distinct seasons and the weather they produce. So while San Diego might be a great place to visit, I wouldn't want to live there. I have to have my snow and thunderstorms. Heck, even the song "Camelot" mentions snow.

Tuesday, August 18, 2015

Stirrings in the Subtropical Atlantic

It has been a quiet tropical storm season so far this year. As of today there have been only three named storms: T.S. Ana from May 8-11, T.S. Bill from June 16-20, and T.S. Claudette from July 13-14.  This morning Tropical Depression #4 was identified by the National Hurricane Center, and this afternoon it was upgraded to Tropical Storm Danny.

The first three named storms of 2015.

While this season may seem quiet, it is actually running close to normal this year so far. Normally by this date in August there are only three to perhaps four named storms, with one of those hurricane. None of the three storm this year attained hurricane strength.

Climatology of tropical cyclones in the Atlantic Basin. The green lines intersect at about today's date.

NOAA's outlook for the 2015 hurricane season, updated on August 6, maintained its earlier outlook for a below average tropical season. The outlook estimates a 90 percent probability for the following:

    6-10 named storms, which includes the three named storms to date
    1-4 hurricanes
    0-1 major hurricanes
   
The climatological average for a season is 12 named storms, 6 hurricanes, and 3 major hurricanes.

The outlook for a below-average season is the state of the current oceanic and atmospheric conditions and predicted conditions through the fall. These include the strengthening El NiƱo, which tends to produce strong vertical wind shear and enhanced sinking motion across the tropical Atlantic and Caribbean Sea, both kryptonite to tropical storm development, and cooler than average sea-surface temperatures in the tropical Atlantic.

There were only eight named storms in 2014, and then you have to back to 1997 to find a season with that few storms. The period from 1991 through 1994 were seasons with 8, 7, 8, and 7 storms respectively.  Residents of the Atlantic and Gulf coasts should not get complacent and drawn in to a false sense of security, however. It only takes one storm to cause devastation. Hurricane Andrew in August of 1992 was only one of seven storms that year, and was, at the time of its occurrence, the costliest hurricane in U.S. history. It is now second only to Katrina in 2005 (adjusted to 2010 dollars).

So what is the normal character of the season at this time? The season rapidly spins up to a peak about September 10, with a small secondary peak in mid October.



The typical origins and paths of tropical cyclones in August and September are shown below.

The origins and prevailing tracks of tropical cylones in the Atlantic Basin in August (top) and September (bottom).


Tropical cyclones can originate just about anywhere in the basin from August 21-31, with a band from the west coast of Africa through the subtropical Atlantic to the Caribbean most favored.

Locations of tropical cyclone formation for the period from August 21-31. Data for the Atlantic is from 1851-2009.
Source: National Hurricane Center
 

These maps and much more information can be found on the National Hurricane Center's Tropical Cyclone Climatology web page.

Tropical Storm Danny is currently expected to attain hurricane strength Thursday afternoon. It will several days before any threat to land can be determined. In the meantime you can follow the National Hurricane Center's outlooks and advisories on the NHC website.

Advisory on Tropical Storm Danny issued at 5:00 p.m. EDT August 18.

Tuesday, August 4, 2015

Tampa and West Central Florida Slosh Through Two Weeks of Heavy Rain

It has been a very quiet tropical season in the Atlantic Basin. There have been only three named systems in the Atlantic so far this season (Ana, Bill, Claudette), and none of these tropical storms have directly affected Florida. Typically the west-central coast of Florida gets about 60 percent of its annual average rainfall in the months of June through September, coinciding with the first half of the tropical storm season.

Tampa flooding on August 2.
Credit: John Kassel via Facebook
In the past two weeks west-central Florida has received from 10 to 24 inches of rain resulting in persistent flooding and a general mess for residents. The Tampa Bay areas has been been the bulls-eye for the heavy rain, with Pasco, Pinellas, and Hillsborough Counties recording the highest rainfall totals.



14-day accumulated precipitation for Florida.
Source: NWS Advanced Hydrologic Prediction Service

The rain has resulted in persistent and widespread flooding. The flooding has closed numerous streets and roads, overloaded wastewater pumping stations, and forced the suspension of trash collection. In Pasco County the Anclote River threatened 5,700 homes with flooding, with more than 320 homes evacuated.

Flooding on August 4 in the Seven Springs area of Pasco County.
Credit: Pasco County Sheriff

The river crested at 25.25 feet at 11:45 a.m. EDT this morning and is expected to steadily fall to below flood stage on Friday. The record crest for the Anclote is 27.7 feet set on August 8, 1945. The last time the river was this high was in June 2012 when it reached a crest of 26.81 feet.



The reason for the rain was a frontal system which stalled over central Florida and a series of low pressure waves along that front. The cold front pushed into northern Florida on July 24. It stalled over central Florida on July 25, and that's when the skies opened up. Two to seven inches of rain fell on the Tampa Bay area in the 24 hour period ending on July 25, and it has rained every day since.

Surface map for 8:00 p.m. EDT July 25, 2015

The chart below plots the last 14 days of rainfall for CoCoRaHS Stations FL-HB-55 (Tampa 5.0 NNE),FL-PS-4 (Port Richey 2.0 NNE), and FL-PN-41 (Tarpon Springs 5.6 E), the highest totals for the period in Hillborough, Pasco, and Pinellas Counties respectively. Though the rainfall totals for the stations for the two-week period are similar, the three stations generally had wide day-to-day differences in rainfall. Note that there is no observation available for FL-PN-41 for August 4 as of this post, but other CoCoRaHS observers in the vicinity had another two to three inches of rain this morning.



Although July 25 marked the start of the very heavy rain, rain has fallen in this area every day since the middle of July. As of today FL-HB-55 has had 21 consecutive days of measurable rain, FL-PN-41 21 days, and FL-PS-4 23 days. The average July precipitation for this area is about 7.90" and the average August precipitation 8.80".  Average annual precipitation for this area is about 52 inches.

The 11.84 inches measured in July at the Tampa International Airport was the 8th highest July total since records began in 1939. The record is 20.59 inches in 1960.   However, it was on the low end of totals reported by CoCoRaHS observers in the areas. A few Hillsborough County stations reported more than 15 inches for July. However in Pasco County FL-PS-4 tallied 20.90 inches for July, and in Pinellas County FL-PN-41 measured 26.90 inches.

The Tampa Bay area got a break today, as most rain was north and east of the area as the low pressure system lifted northeast. It was located on the South Carolina coast today. More than four inches of rain was reported  along the South Carolina and North Carolina coasts this morning.

24-hour precipitation ending the morning of August 4.
  The low is expected to continue into the Atlantic before merging with another weather system, but not before more rain and winds affect the coastal areas.

Wednesday, July 29, 2015

A Wild Two Days in the North

It was an interesting and exciting start to the week in the northern Rockies, northern Plains, and southern Manitoba. Snow, a long-lived tornado-producing storm, and hurricane force wind gusts were the result of an unusually strong low pressure system that developed over the northern Rockies on Monday and then rapidly intensified as it moved northeast into Manitoba. This system was fed by very warm, humid air to the southeast of the low and cold, dry air to the northwest, and was associated with a strong closed upper level low.

500 millibar map Tuesday, July 28, at 7:00 a.m. showing closed low over northern Montana and southern Manitoba.
Surface map for July 27 at 10:00 p.m. CDT

On Monday there was snow in Wyoming, Montana, and Idaho. There were several inches of snow above 8,000 feet elevation, including snow at ski areas in Jackson Hole, WY and in Glacier National Park in northwestern Montana. Flurries were even reported in Missoula. Temperatures on Sunday in western Montana and northwestern Wyoming were in the mid 80s, but on Monday daytime high temperatures were only in the low to mid 50s.

Surface temperatures at 5:00 p.m. MDT on July 27.


Strong thunderstorms developed northeast of the low pressure system late Monday, and one particularly strong storm developed over southwestern Manitoba during the early evening. This thunderstorm put down a tornado southwest of Melita, Manitoba around 8:30 p.m. CDT.

Radar image showing strong thunderstorm over southwestern Manitoba at 9:41 p.m. July 27. A hook echo is evident on the south end of the storm.


Radar base velocity image for 9:56 p.m. CDT on July 27. The white oval marks where rotation is indicated. Green colors are movement toward the radar. Red colors are movement away from the radar.

The tornado moved north-northeast over the next two and a half to three hours. At 10:55 p.m. CDT the storm was observed near Virden, and it's possible it lasted for a time after that but was not observed because of darkness.


Map showing approximate locations and times of the observed tornado.

It's possible that the thunderstorm produced multiple tornadoes rather than one very long-track tornado, but there was no doubt this was a monster storm. At one time the storm was estimated to be one kilometer (.62 mile) wide. Fortunately the tornado missed populated areas and there were no known serious injuries. The tornado did damage farm buildings, trees, power lines, and actually ripped pieces of asphalt from a highway. Meteorologists from Environment Canada have been investigating the damage and preliminarily assigned it a high EF-2 rating on the Enhanced Fujita scale. The damage survey has been hampered by the fact that the tornado did not hit many structures and spent much of its time over open fields. Of course, for the residents of the area that's a good thing.

On Tuesday the strong low was moving through Manitoba, and the intensifying low generated strong winds across southern Manitoba and North Dakota. Winds gusted to 70 mph and more at several locations in North Dakota, with the highest wind gusts of 76 mph reported at Garrison in central North Dakota and Alkabo in the northwestern corner of the state. Wind gusts in excess of 55 mph were common in western and central parts of the state. In eastern North Dakota winds gusted from 40 to 50 mph with the highest gust 59 at Devil's Lake and McHenry.


Surface map for Tuesday, July 28, 4:00 p.m CDT
Large-scale strong low pressure systems such as this are rare during the summer. This type of system typically occurs in the late fall to early spring, and often is associated with snow and blizzard conditions in the winter.

Thursday, July 23, 2015

Record Rain in Southern California Just a Drop in the Bucket

At the start of this week there was some unusual weather in southern California - heavy rain. A low pressure system off the coast that used to be Hurricane Dolores and the southwestern monsoon flow combined to produce showers and thunderstorms from western Arizona west through southern California.

Visible satellite image of the southwestern U.S. at 4:00 p.m. PDT July 19. Green arrows show direction of winds.

Dolores attained hurricane status on July 13 off the central Mexican coast, then moved north northeast parallel to Baja California. It was downgraded to a tropical storm on Friday, July 17. By Sunday, July 19 it had weakened even further and was a post-tropical cyclone.  The circulation was well-defined, and the low pumped moisture from the Pacific into northern Mexico and southern California. This augmented the moist flow of air associated with the southwestern monsoon, and the result was record-breaking July rainfall for many locations in southern California. San Diego has received 1.71 inches of rain in July so far which breaks the old 150 year-old record of 1.29 inches set in 1865.

Some rainfall records in southern California. From NWS San Diego.

One of our CoCoRaHS observers in San Bernadino County received 3.75 inches of rain over two days (by far the highest amount reported so far that I've seen), with a total for the month of 3.83 inches. Seven observers have measured more than 3.00 inches this month, and another several dozen observers have measured an inch of more. Not bad for an area where the normal July rainfall is just a few hundredths of an inch.  Downtown Los Angeles has received 0.38 inches of rain this month. The normal is 0.01 inch.

24-hour CoCoRaHS totals the morning of July 20.

Total rainfall for the period from ~7:00 a.m. PDT on July 18 to &:00 a.m. PDT on July 20 in southern California.

As you might expect, that amount of rain caused problems. Many roads were flooded and washed out. Power was knocked out in some communities. A bridge on Interstate 10 between Coachella, CA and the Arizona state line washed out on the eastbound side and was compromised on the westbound side by flash flooding. The I-10 eastbound lanes are closed indefinitely until the bridge is repaired. The westbound lanes were opened again on Tuesday (July 21). About 27,000 vehicles normal travel this section of I-10 every day.

Firefighters stabilize a pickup truck that drove into washed out I-10 bridge. The driver was rescued.
Photo credit: CalFire Riverside


Map showing location of damaged bridge on I-10 and section closed (yellow).

On Sunday (July 19) the baseball game between the San Diego Padres and the Colorado Rockies in San Diego was first in a rain delay (6th time in history) and then eventually called off. It was only the second time in Petco Park history (since 2004) that a game has been rained out. The last rain-out occurred in 2006.

The rain did little to relieve drought conditions. The rain, while significant, is just a very small drop in a very large bucket. With evaporation rates on the order of 0.20 to 0.25 inch per day what didn't run off will soon be back in the atmosphere. The water balance chart from CoCoRaHS station CA-RV-21 in Riverside, CA shows just how little dent the recent rain made in the water deficit since May 1.
 


Drought conditions over the western U.S. and particularly California remain unchanged. They are likely to remain unchanged until the wet season begins in the winter, and then only if precipitation occurs regularly and is well above normal.

Wednesday, July 8, 2015

Improving Communication of the NWS Forecast

If you have frequented your local National Weather Service office's web site for your local point forecast through the "point and click" map interface you are familiar with the "forecast-at-a-glance" across the top of the page accompanied by icons depicting the type of weather expected. Effective July 7 the NWS instituted changes to these icons to make them even more representative of the weather expected. Changes include new graphic images for a variety of expected weather conditions. the ability to depict forecast for six-hour intervals, and colored "hazard boxes" to highlight watches, warnings, and advisories in the forecast period.

The icons weren't changed just for the sake of changing them. The changes were made based on research conducted by the National Center for Atmospheric Research (NCAR) in Boulder, CO, and by comments collected from users last year. Researchers surveyed people from across the country and found that most had been frequent and long-time users of the map interface. Researchers tested the former icons and the newly designed icons and presentation format. They found that the colored boxes drew attention to watches and warnings, and users were more aware of hazardous weather threats with the addition of start and end times to the hazard information. If you would like to read more about this research and evaluation see "Improving effectiveness of weather risk communication on the NWS point-and-click web page".

This is the sample forecast presentation that the NWS has on its page explaining the change in format. Note that in periods where the probability of precipitation is increasing or decreasing that change is shown on the icon. A yellow hazard box highlights the period of a severe thunderstorm watch, and also includes the icon for the first period of the forecast. The severe thunderstorm watch is also highlighted in the 12-hour forecasts in the background.  The icon for Saturday depicts the expected weather for both the early and later part of the day.



If there are multiple watches and or warnings, these can be displayed as well. In the example below the forecast for Muskogee, OK for Wednesday depicts a Flash Flood Watch (yellow) into the evening (7:00 p.m. in this case) and a Flash Flood Warning (red) until 1:30 p.m. This information can be seen by clicking the "i" button at the top or on the multiple hazards box.


In the example below, a Red Flag Warning (favorable conditions for wildfire) is in effect for Jordan Valley, OR.


The point and click forecast pages on the NWS web sites receive on average 2 million hits per day, and during major severe weather events that number is substantially higher. If only, say, five percent of those viewing the page have a better understanding of the forecast and weather risk, that's tens of thousands of people who are more aware.

The NWS has a web page that lists all the weather conditions/forecasts and their associated icons (more than three dozen of them). They will continue to accept feedback about the new forecast-at-a-glance presentation and icons, and an email address to do so is provided on the page.

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.