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Expert Corner

Jul 12
Typhoon Nepartak shows Unique Lightning Signature

​Supertyphoon Nepartak traveled for several days in the Northwest Pacific until it struck Taiwan on July 8, 2016. Wind gusts over the open ocean on July 8th were forecast to exceed 200 mph, although no measurements could be made at the surface at that time. Along its track in Figure 1, Vaisala’s Global Lightning Dataset GLD360 network detected a unique signature consisting of lightning in the eyewall that is located directly along and near the track of the center. While this signature has been observed in a few storms for up to 24 hours since GLD360 data became available in 2011, none of the storms had this feature that lasted nearly as long as the 72-hour period in Nepartak (Figure 1). It shows lightning enveloped along the track, a phenomenon which is being observed only to occur in very strong tropical cyclones that lack outer rainbands. Further studies are planned of the few other storms since 2011 that had a least a few hours of this signature. The ability of GLD360 to track lightning continuously far from land makes this type of observation possible. Satellite imagery in Figure 2 shows an intense tropical cyclone with a sharply defined eye within a uniform circular annulus, but no outer rainbands.

FIGURE 1. Map of track and GLD360 strokes for supertyphoon Nepartak in North Pacific Ocean from 03 through 08 July 2016. Strokes are color coded by day, and daily totals are in parentheses. Taiwan is in the upper left portion of the map, and the Philippines are to the southwest.

FIGURE 2. Satellite image of supertyphoon Nepartak at 1200 UTC on 06 July 2016.​

Jul 12
​Nowhere is Safe Outdoors When Lightning is Near
Our friends at KGUN9 in Arizona interviewed Vaisala lightning expert, ​Ron Holle, recently to discuss how to stay safe when lightning is near, and some myths about protecting yourself. Holle reminds us that nowhere is safe outdoors when lightning is near, and that lightning can strike from storms that are then or fifteen miles away. View the entire story at KGUN9's web site:​

When you hear thunder, head for your vehicle or the nearest building.
Apr 05
Very Frequent March 2016 Lightning in the United States and Globally
March is the beginning of meteorological spring in the Northern Hemisphere. Frequent spring storms in the United States combined with improvements to Vaisala’s NLDN and GLD360 networks resulted in very large counts of lightning during March 2016. This was true in both the United States and around the globe.
Storms occur in the southeast half of the United States every spring, but this year the March lightning activity was more similar to mid to late April (comparing to past years). The NLDN underwent a substantial upgrade in cloud pulse detection through the summer of 2013, and more than twice as many cloud pulses are now detected since the upgrade than before the summer of 2013.

A particularly intense period of lightning occurrence began on 8 March and lasted several days. A nearly stationary frontal boundary from Texas to the northeast resulted in strong low-level flow from the south bringing copious amounts of moisture northward. There were hundreds of thousands of strokes and rain up to 15 inches in Louisiana and Arkansas during this period. Several additional but less intense multi-day scenarios were established later in the month across the southeast United States that produced very large lightning frequencies.

Globally, the GLD30 network doubled the number of detections beginning on 18 August 2015. This major change in network performance took place somewhat after the summer lightning maximum in the Northern Hemisphere activity. The increased detection is becoming especially apparent as Northern Hemisphere lightning increases again, and such record counts compared with the same months last year can be expected to continue through 2016.

Since both the NLDN and GLD360 network have been substantially upgraded, the global and United States lightning frequencies reached levels for the month of March not seen in the past as spring storms erupted over the southeast United States.
Nov 06
Eyewall Lightning in Hurricane Patricia

Hurricane Patricia began as a tropical cyclone, forming in the eastern Pacific. It rapidly intensified into a Category 5 hurricane, making landfall on Oct. 23 at 6:15 p.m. CDT near Cuixmala in Jalisco state of southwest Mexico. As the storm approached Mexico it was interesting to watch the continuous lightning pattern.

As you can see from the images, lightning was present in a tight circle in the eyewall.​ This is somewhat uncommon because about 90% of named tropical systems do not have lightning in the eyewall region. Lightning is typially in the outer bands.

The important lesson about this type of continuous lightning pattern is that when it does appear, the storms are almost always very strong. This was the case for Hurricane Patricia, with some of the highest winds recorded and lowest pressure readings. On Oct. 23, wind speeds reached an intensity estimate of 184 mph (160 kt), which is tied with eastern north Pacific Hurricane Linda of 1997 for the strongest on record. A Vaisala dropsonde released into the eye measured a sea-level pressure of 892 mb (adjusted for surface winds), which breaks the record for the lowest pressure of an east Pacific hurricane.

More about the images:
The first Patricia map shows activity during the hours of the hurricane hunter reconnaissance on October 22, 2015. The eyewall lightning consolidated around the track during the hours of that recon flight.

The second map shows 17 hours on October 23, 2015, where the tight circle of lightning is continuing. Impressive
Jul 15
Investigating the Increase in Lightning Fatalities through July 2015

​For the first few months of 2015, the cumulative total of lightning fatalities was somewhat above normal compared with the previous ten years (Fig. 1). After a period of several days this month, the cumulative total has now returned to normal compared with recent years. This graph was developed by Mr. William Roeder and distributed to members of the National Weather Service Lightning Safety Awareness team. This team provides the lightning safety information found at

FIGURE 1. Cumulative number of U.S. lightning fatalities by day of the year for 2015 compared with the most recent ten years.

This early start to the lightning fatality totals for the year kept the 2015 curve in Fig. 1 above normal until yesterday. As a result, several ideas were proposed regarding the cause. Among them were a very much higher number of 2015 cloud-to-ground (CG) flashes and/or more positive CG flashes.

In order to examine this possibility, data from Vaisala’s National Lightning Detection Network (NLDN) were examined. Figure 2 shows the results for all CG flashes over the continental United States land area, and Figure 3 shows positive counts. The 2015 CG flash counts are currently 13% ahead of the ten–year average, while the positive CG flash count for 2015 is 1% larger than the average of recent years, as of early July.

Note that both 2015 NLDN curves are below normal earlier in the year when the fatality curve in Fig.1 was above normal. It can be concluded that no apparent relationship exists between the number of fatalities and number of CG flashes, or positive CGs.

FIGURE 2. Cumulative number of U.S. cloud-to-ground lightning flashes by day of the year for 2015 compared with the most recent ten years. Data from National Lightning Detection Network (NLDN).

FIGURE 3. Same as Figure 2 for positive cloud-to-ground flashes.

Apr 24
Vaisala’s GLD360 Records Spectacular Volcanic Lightning from Chile

Around 21:00 UTC on 22 April 2015, the Chilean volcano, Calbuco, began its first eruption in over 40 years, sending up a massive ash cloud that generated spectacular displays of lightning. Vaisala’s GLD360, the world’s most accurate and truly global lightning detection system, located a large number of discharges during the event. Starting at 22:28 UTC on 22 April, shortly after the initial eruption was reported, and extending over a period of about 10 hours, GLD360 recorded a significant number of flashes within 50 km of the volcano. Most of the discharge positions were clustered close to the volcano, but some were spread out to the northeast, in exact agreement with the propagation of the ash cloud as seen by satellite images recorded throughout the night and with the 12:00 UTC (22 April) sounding taken at nearby Puerto Montt. The map shows that while there was a lot of lightning activity across the north of the continent and into the Atlantic ocean,  there was little to no lightning elsewhere within 2,500 km of the volcano.

Vaisala Radiosonde Verifies Observations
At 12:00 UTC (22 April), the Dirección Meteorológica de Chile released a weather balloon with a Vaisala Radiosonde from a nearby sounding station at Puerto Montt. The radiosonde data confirmed southerly to southwesterly winds near and above the tropopause, where the highest part of the ash cloud was reported by the Volcanic Ash Advisory Center, Buenos Aires, as the plume crossed the Chilean-Argentine border.

Vaisala Radiosondes, combined with Vaisala DigiCORA Sounding System MW41 are used to conduct reliable and accurate upper-air weather observations.
According to Martin Murphy, Senior Scientist at Vaisala, “Information about the polarity and estimated peak currents of lightning generated by volcanic ash clouds could provide additional insights into the mechanism that produces these discharges. Detailed studies of volcanic lightning have revealed two phases of activity, one of which produces large, discrete discharges such as those shown here. These discharges emit radio-frequency energy that can be observed remotely by the Vaisala GLD360.

Apr 03
Lightning in Super Typhoon Maysak

​Typhoon Maysak developed and grew last week in the southwestern Pacific Ocean. It became strong enough to be classified as a super typhoon; gusts were forecast to reach 190 mph/352 km per hour. This is one of the earliest storms of this intensity in the North Pacific Basin. It caused five fatalities and major devastation on the islands of Chuuk and Yap. It is forecast to weaken significantly before reaching the Philippines.

Figure 1 shows the location of the eye during its strong tropical phase from formation to rapid intensification from 27 March through 01 April. Due to the uniformly high detection of GLD360 over these regions, lightning can be plotted over this entire oceanic region. The 29,575 lightning events detected in this region by GLD360 are shown during these six days with a 250-km buffer around the track.

Figure 1. Map of track and GLD360 strokes for supertyphoon Maysak in North Pacific Ocean from 27 March through 01 April 2015. Strokes are color coded by day, and daily totals are in parentheses. The islands of Yap and Chuuk are indicated.

Three features of well-organized tropical cyclones have been observed and documented in publications by Demetriades and Holle of Vaisala, and others. First, the eye in the center has a small amount of intermittent lightning. Second, there is an annulus of minimal lightning outward from the eye. Third, there is usually an outer rainband area farther out, often to the south through east in the Northern Hemisphere. These rainbands are areas of heavy convective rainfall that are often a significant threat for widespread flooding.

During the first few days, Figure 1 shows widespread lightning activity to the south and east of the storm center during its development phase. Once it was organized, however, there is a near complete absence of lightning except in occasional bursts in the eyewall next to the track, and in a few large outer bands.

Figure 2 shows a satellite view early on 01 April when Maysak was at its peak in terms of organization. Note the clearly-defined eye surrounded by very smooth clouds. The storm is not especially large in area but tightly organized. At this time, that uniform circular annulus indicates the region which is often an area without much lightning, as indicated well by GLD360. There are no large outer rain bands in the satellite image, indicating that no widespread heavy rain was likely outside of the main circulation. Such information is very helpful in diagnosing the potential for heavy rains over a large area away from the center, which is not the case in Maysak.

Figure 2. Satellite image of supertyphoon Maysak at 0423 UTC on 01 April 2015.

Mar 27
NLDN Detects Very Frequent Lightning in First U.S. Spring Storms

​The month of March 2015 set a U.S. record for the longest period to start March without any tornado reports, through the 24th of the month. However, that streak came to an abrupt end when a major severe thunderstorm event began on the 25th.

Figure 1 shows the severe weather reports to be concentrated in Oklahoma and surrounding states. Unfortunately, one person was killed by a tornado that struck a mobile home park in NE Oklahoma. This storm began in the Oklahoma area and extended to the ENE and WSW along a cold front. Strong straight-line winds and large hail were more common than tornadoes in this event.

Figure 1. Map of 177 severe storm reports collected by the Storm Prediction Center during the 24 hours ending at 1159 UTC on 26 March 2015.

Vaisala’s National Lightning Detection Network (NLDN) provides Advanced Total Lightning data, and shows very extensive lightning activity for a 24-hour period during this storm. Figure 2 shows more than one-third million detected cloud-to-ground (CG) strokes and cloud pulses. This high-resolution map shows long streaks that represent individual thunderstorms better than any single radar or satellite depiction can indicate. Storms begin east of a north-south line though western Oklahoma, due to the location of the dry line where storm initiation is common. Roughly 70% of the detected lightning events were cloud lightning pulses. The NLDN underwent a major upgrade in summer 2013 that resulted in excellent cloud pulse detection, as is shown in this example. The time series of CG and cloud events is shown in Figure 3 for these 24 hours. A more rapid ramp-up in the number of lightning events occurred at the start of the storm, than the slower decline. Typically, thunderstorms have quicker increases in lightning toward the beginning than at the end.

Although severe weather in the event was not as extreme as it tends to be later in the spring, the lightning threat itself is significant. Such a large number of lightning events caused power outages at homes and manufacturing sites, set fire to several structures, affected emergency communications, and downed power lines that contributed to widespread disruption to more people than those affected by the reported severe weather events.

Figure 2. Map of more than one-third million lightning events detected by the NLDN from 1200 UTC on 25 March to 1200 UTC on 26 March 2015.

Figure 3. Hourly time series of more than one-third million events detected by the NLDN in the area of Figure 2 from 1200 UTC on 25 March to 1200 UTC on 26 March 2015.

Feb 06
Federal Aviation Administration Chooses Vaisala to Supply Real-Time Lightning Data

Vaisala, a global leader in environmental and industrial measurement, has won a five-year contract to supply real-time lightning data to the Federal Aviation Administration (FAA). The data will be used to generate more accurate short-term weather forecasting for use in aviation and aerospace operations in order to improve the safety of en-route flights and terminal areas. 

The FAA relies on real-time lightning maps and individual lightning strike characteristics to closely monitor thunderstorm development, occurrence, location and paths in order to generate more accurate short-term weather forecasting for use in aviation and aerospace operations. The FAA uses lightning data to increase aviation safety both en-route and in the terminal areas to aid in the efficient movement of aircraft and to determine if thunderstorms are occurring at, or in the vicinity of Automated Weather Observation System (AWOS), Automated Surface Observing System (ASOS) and Automated Weather Sensor System (AWSS) observation sites. In addition, the FAA uses lightning data to support research and development efforts. 

Under this contact, Vaisala will supply the FAA streaming, real-time cloud-to-ground lightning data covering the contiguous United States, the Caribbean, Alaska and Hawaii. The FAA will receive data from the Vaisala National Lightning Detection Network (NLDN) and Global Lightning Data Set GLD360.  The NLDN is a precision lightning network, owned and operated by Vaisala.  Using a network of over 100 sensors in strategically placed locations around the U.S., the NLDN detects both cloud-to-ground and cloud lightning, delivering significant lightning accuracy with 70% fewer sensors. GLD360 utilizes long-range lightning detection technology, and adds value to the FAA by providing additional data for the lower 48 states, as well as Alaska, Hawaii and the Caribbean. The U.S. National Weather Service has also been using both NLDN and GLD360 data, stating that their Ocean Prediction Center and National Hurricane Center have benefited from using the lightning information to better forecast and research storm behavior. 

The NLDN and GLD360 have been scientifically validated against rocket-triggered lightning, and detect both cloud-to-ground and in-cloud lightning data.  The FAA receives trusted information for weather forecasts and warnings, resulting in a safer national airspace system, as well as improved safety and efficiency for aviation operations and the traveling public.

"The FAA will be using thunderstorm and lightning warning systems with the most accurate, validated and reliable lightning data available in the market," comments Dan Donahue Key Account Manager for the FAA at Vaisala. "We are committed to helping the FAA enhance their weather safety and research programs, including the addition of cloud lightning data and classification, and supporting new weather programs, such as oceanic weather radar proxy and airport lightning warning systems."

Vaisala has been providing lightning data to the FAA for over 10 years, winning a competitive bid last year to extend service through September 24, 2019.

Dec 31
Vaisala Releases Top 10 Lightning Flash Days in 2014 from its NLDN and GLD360 Network

Vaisala monitors lightning activity around the world, and today has released the Top 10 lightning flash days in 2014 as detected by its National Lightning Detection Network (NLDN) and Global Lightning Dataset GLD360 network. The NLDN is a precision lightning network owned and operated by Vaisala and detects in-cloud and cloud-to-ground lightning throughout the United States. Both the GLD360 and NLDN provide information to agencies such as the National Weather Service and the Federal Aviation Administration, for forecasting, safety and to support operational decision-making. GLD360 detects lightning around the world with very long-range sensors that allow continuous coverage over land and oceans.

U.S. Top 10 Lightning Flash Days

The following lightning data are the Top 10 days in 2014 with respect to cloud-to-ground only lightning in the contiguous U.S.:

1. June 19 - 361,927 cloud-to-ground flashes   Top State: South Dakota

2. June 18 - 357,318 cloud-to-ground flashes   Top State: South Dakota

3. June 05 - 297,052 cloud-to-ground flashes   Top State: Tennessee

4. July 27 - 291,615 cloud-to-ground flashes   Top State: Kentucky

5. April 28 - 284,409 cloud-to-ground flashes   Top State: Mississippi

6. July 23 - 277,924 cloud-to-ground flashes   Top State: Arkansas

7. Sept. 02 - 271,161 cloud-to-ground flashes   Top State: Kansas

8. July 14 - 267,279 cloud-to-ground flashes   Top State: Tennessee

9. May 12 - 262,927 cloud-to-ground flashes   Top State: Texas

10. July 15 - 260,477 cloud-to-ground flashes   Top State: Texas

As might be expected in the U.S., the top days are mainly in the summer months, but the spring months of April and May appear this year, and another in early September. Previous Vaisala studies have found that two-thirds of the contiguous U.S. cloud-to-ground lightning flashes occur in June, July, and August.

Globol Top 10 Days for Lightning

Worldwide, the top ten days for lightning activity are: 

1. September 2 - 4,315,259 strokes

2. April 30 - 4,211,041 strokes

3. April 29 - 4,039,212 strokes

4. October 2 - 3,676,378 strokes

5. September 20 - 3,634,461 strokes

6. August 30 - 3,627,466 strokes

7. April 28 - 3,571,362 strokes

8. May 27 - 3,550,073 strokes

9. July 3 - 3,543,899 strokes

10. July 2 - 3,496,652 strokes

Around the world, all of the top ten days are in the Northern Hemisphere summer, and the months shortly before and afterward. This is to be expected due to its much larger land mass compared with the Southern Hemisphere. Additionally, only two days for the world are the same as for the U.S., showing how there are diverse thunderstorm systems occurring at any time around the world.

Accurate, Reliable Lightning Detection Network

The NLDN is the most accurate, reliable, and scientifically validated lightning detection network in the United States. The network has been independently verified through ground truth studies and is supported by a long history of continuous advancements in science and technology behind our lightning detection sensors and data collection methodologies.

The Vaisala Global Lightning Dataset GLD360 is a service that provides real-time lightning data for accurate and early detection and tracking of severe weather. The data provided is generated by a Vaisala owned and operated worldwide network.

While the specific days and locations of the Top 10 lightning days change from year to year, the total number of cloud-to-ground flashes remains between 20 and 25 million per year over the contiguous U.S.. Having an increased understanding of when, where, andhow much lightning occurs has been coincident with a gradual reduction in lightning fatalities and injuries in the United States. The ability of GLD360 to expand our view of lightning to a global level provides a comprehensive perspective on the lightning threat, which needs considerable attention in many areas of the world.

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