Researchers find that nearly half of lightning down strikes in California occur with little or no rain

Researchers studied the climatology of dry lightning in California

Dry Lightning, California
(B) Total number of dry lightning flashes across three elevation zones (<1000 m, 1000–2000 m, >2000 m) within the domain for each month between 1987–2020. Text indicates the area of each elevation zone, and inset map shows the geographic distribution of the elevation zones and major mountain ranges. (D) The three elevation zones for each month (bars). Dashed lines in (D) indicate the dry lightning fraction averaged across all months for each zone. Blue dashes in (D) represent the dry lightning fraction computed from all months and elevation zones. (From the paper)

A group of six researchers who studied the occurrence and characteristics of cloud to ground lightning in Central and Northern California found that nearly half, 46 percent, was dry, accompanied by less than 0.1 inch of precipitation.

Of course dry lightning is the bane of land managers and is much more likely to ignite a wildfire than a wet thunderstorm. And on the occasions when there are thousands of down strikes, it can overwhelm the capacity to suppress what can be hundreds of fires.

The six scientists used daily gridded lightning and precipitation observations (1987–2020) in combination with atmospheric reanalyses, to characterize the climatology of dry lightning and the associated meteorological conditions during the warm season (May–October) when wildfire risk is highest.

The paper the group produced is available as open source: “Meteorological and geographical factors associated with dry lightning in central and northern California.”

Daniel Swain, a prolific user of Twitter, used the platform today to highlight some of the group’s findings. In the tweet below, click on “read reply” to see more discussion and illustrations.

The six researchers who participated in the project were Dmitri A. Kalashnikov, John T. Abatzoglou, Nicholas J. Nauslar, Daniel L. Swain, Danielle Touma, and Deepti Singh.

Prediction issued for this summer’s wildfire potential

July wildfire outlook weather fuels

The forecast for wildland fire potential issued July 1 by the National Interagency Fire Center predicts that in July it will increase to higher than “normal” this summer in Alaska, Texas, Northern California, and the eastern portions of Washington and Oregon. In August added to the list will be parts of Montana, the Black Hills, and the Northern Plains. Hawaii will be above normal for the next four months.

The fire potential text and maps from NIFC shown here represent the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit. Additional graphics are included from other sources.

Below:

  • Excerpts from the NIFC narrative report for the next four months;
  • Additional NIFC monthly graphical outlooks;
  • NOAA’s three-month temperature and precipitation forecasts;
  • Drought Monitor;
  • Keetch-Byram Drought Index;
  • Soil moisture.

“Most of the West, Plains, and Texas remain in drought, with areas of extreme to exceptional drought across the southwestern US. Drought developed across southwest Alaska and expanded or increased in severity across the Southeast and Hawai’i. Temperatures were above normal across the southern tier of the US and the Plains, with near to below normal temperatures across the northwestern US and the Northeast.

“Climate outlooks indicate below normal precipitation is likely across much of the Plains through the central Rockies into the Inland Pacific Northwest, with above normal temperatures likely across most of the contiguous US (CONUS) through summer. A robust North American Monsoon is expected to continue through July into August across the Southwest and portions of the broader Four Corners region. Alaska is likely to remain warm, with near normal precipitation likely through summer.

“Above normal significant fire potential is forecast for the southern Plains through October, spreading across Texas, the Lower to Mid-Mississippi, Missouri, and Ohio Valleys by fall. Much of the central and northern High Plains, including the Black Hills, are likely to have above normal potential through summer. The Southwest, southern Great Basin, and Colorado Rockies have returned to near normal potential.

“Southwest, south-central, and Interior Alaska will have above normal significant fire potential through August, although portions of southwest Alaska will likely return to near normal potential during August. Much of the Sierra and Coast Ranges in California will have above normal significant potential by August, continuing through September. Offshore wind prone areas in California will likely retain above normal potential in October as well. Along and east of the Cascades into much of the western and northern Great Basin is expected to have above normal potential this summer due to above normal fine fuel loading and long-term drought, with southwest Oregon likely to have increasing potential by August. Leeward sides of the Hawai’ian Islands will have above normal potential through October due to ongoing drought and likely enhanced trade winds.”


August wildfire outlook weather fuels September wildfire outlook weather fuels October wildfire outlook weather fuels

90-day temp & precip outlook Drought Monitor, June 28, 2022 KBDI June 30, 2022 Soil moisture, June 30, 2022

With near-record setting wildfire activity, Alaska moves to Preparedness Level 5

This weekend temperatures in the state could be 20 degrees above average

Alaska daily cumulative acres burned, by year
Alaska daily cumulative acres burned, by year. The black line is 2022.  Accessed June 29, 2022. University of Alaska Fairbanks.

With near record-setting wildfire activity early in Alaska’s fire season and a looming heat wave, on Thursday the Alaska Interagency Coordination Center moved to wildland fire Planning Level 5, the highest level. Currently there are multiple large fires that require incident management teams in several areas simultaneously. PL5 status means most of the initial and extended attack firefighting resources are committed to new and existing fires. Nationally the PL is 2, according to the National Interagency Coordination Center, but each geographic area establishes their own based on local conditions.

current fires, July 1, 2022 map fires
Red areas represent current fires, July 1, 2022

There are currently 160 fires in Alaska, and 17 are staffed. With the predicted hot dry weather, lightning, and Red Flag warnings, the fire risk is very high. In addition, fire smoke is at health advisory levels in parts of the state.

Red Flag Warnings, Alaska, July 1, 2022 fires
Red Flag Warnings, Alaska, July 1, 2022

More than 1,646,895 acres have burned so far this season. Since mid-June the cumulative acres burned to date has been hovering at record levels or above. As of June 29 the only year with more acres burned to date was 2015. The average total burned each year in Alaska from 1992 through 2021 was 1,192,909 acres.

Alaska heat wave, AccuWeather

Forecasters say a heat dome will settle over Alaska Friday through Monday that will challenge daily record high temperatures. Fairbanks is expected to hit an abnormally high 85 on Friday. That would be three degrees below the July 1 temperature record of 88, which was set just last year.

The abnormal heat will pile on to already abnormally dry vegetation, or as known to firefighters, fuels. In Anchorage, just 7 percent of the city’s normal June rainfall fell, while Fairbanks saw 36 percent of its typical June rainfall totals.

Red Flag Warnings in six states Sunday

Possible dry lightning in New Mexico and Arizona

Storm Prediction Center June 12, 2022 forecast lightning thunderstorms
Red flag warnings are in effect Sunday for locations in Nevada, Utah, Colorado, Texas, New Mexico, and Arizona. In New Mexico most of the warnings will last until Monday evening.

The forecast calls for winds gusting at more than 40 mph with single-digit relative humidity.

In addition, the NOAA Storm Prediction Center warns that isolated thunderstorms with little or no rain could occur in portions of New Mexico, Colorado, and Arizona.

Red Flag Warnings June 12, 2022 fire wildfire
Red Flag Warnings June 12, 2022.

Why are we still using the Haines Index?

We look at an alternative

South Moccasin Fire in Montana, October, 2021
South Moccasin Fire in Montana, October, 2021. Photo by Lauren Kokinda, BLM.

When Don Haines developed what became his namesake index, he never intended it to be used operationally. As a meteorologist for the US Forest Service, at one point he was given two tasks — determine how weather conditions led to the escape of the 1980 Crane Lake prescribed burn in Michigan, and create a fire weather tool to prevent future tragedies. The escaped prescribed burn became the Mack Lake Fire which killed one person, destroyed 44 structures, and burned 20,000 acres.

In 1988 the result of his work was published in National Weather Digest, titled “A lower atmospheric severity index for wildland fire.” He retired shortly after, but made it clear he intended his work to be the beginning, not the finished product, of the development of a fire weather index after refinement and feedback from subject matter specialists.

It became known as the Haines Index, described by NOAA as “Based on the stability and moisture content of the lower atmosphere that measures the potential for existing fires to become large fires.”

Example of the Haines Index
Example of the Haines Index being cited in a spot weather forecast for the Riverview Fire In the Pike National Forest southwest of Denver, Colorado, issued June 5, 2022 by the National Weather Service.

It is widely used and often included in fire briefings and weather forecasts. It is based on two components, the temperature difference between two prescribed pressure levels; and the moisture component, the dew point depression at a prescribed pressure level. Some may think of it as a measure of atmospheric stability, but as you will see below, that may not be appropriate. With an unstable atmosphere there is less resistance to the vertical movement of air, which can make it easier for a convection column of rapidly rising air and smoke to form over an intensely burning fire, affecting the rate of spread. Add a strong wind, high mixing level, low humidity, low fuel moisture, and steep slopes and a fire can be over the hill before you can get the wind gauge out of your pocket.

“Fire science is not rocket science—it’s way more complicated.”
Robert Essenhigh, Professor Emeritus, Mechanical and Aerospace Engineering, Ohio State University.

In “The Haines Index — it’s time to replace it” published in 2018 in the International Journal of Wildland Fire, Dr. Brian Potter, a Research Meteorologist with the US Forest Service wrote:

Subsequent studies have sought to evaluate the Index, with results that do not support its use in the original form. Yet it is used operationally across the United States, and elsewhere. Mills and McCaw (2010) produced a modified Index, following the sort of refinement Haines stated was necessary. In its present form, the Haines Index cannot be considered a scientifically designed, complete or verified metric that provides any information on fire behaviour or fire danger.

Dr. Potter also wrote a more detailed analysis of the Haines Index published the same year in MDPI Atmosphere, “Quantitative Evaluation of the Haines Index’s Ability to Predict Fire Growth Events.”

On June 3 Darren Clabo, the State Fire Meteorologist for South Dakota, posted two seven-minute videos on YouTube, Part 1 and Part 2 of “Don’t Use the Haines Index.”

“The idea for these videos grew out of conversations with many of my colleagues across the country, with notable head nods to Dr. Brian Potter and Larry Van Bussum,” Mr. Clabo told Wildfire Today. “Dr. Potter has been working to rid the field of the Haines Index for two decades now and these videos are just an extension of that work.”

Hot-Dry-Windy Index

A possible alternative to the Haines Index which was introduced in 2019 is the Hot-Dry-Windy Index. It is described as being very simple and only considers the atmospheric factors of heat, moisture, and wind. To be more precise, it is a multiplication of the maximum wind speed and maximum vapor pressure deficit (VPD) in the lowest 50 or so millibars in the atmosphere.

Hot-Dry-Windy Index
Hot-Dry-Windy Index for a location in north-central Colorado, obtained June 7, 2022.

In 2019 McKenzie G. Kulseth, a graduate student at Michigan State University, wrote her thesis about the HDW Index, titled “An evaluation of the Hot-Dry-Windy Index using historical fire events and meteorological analysis datasets.” She concluded:

The results of this study suggest that the original HDW formulation is capable of identifying the largest fire spread day for between 56.5 to 78.3% of the twenty-three wildland fire events used in this study.

On a website bearing the logos of the U.S. Forest Service, Michigan State University, and St. Cloud State University, you can click on the map to display the HDW for any 0.5-degree long/lat grid spacing area in the contiguous United States. Then the displayed chart shows the index for the preceding 10 days and the forecast for the next 7 days, compared to a 30-year average for each day. For the current and following days you will see results of the Global Ensemble Forecast System (GEFS), which is a weather forecast model made up of 21 separate forecasts, one control (in red) and twenty perturbations. The reasoning for showing 21 different forecasts is to quantify the amount of uncertainty in a forecast by generating an ensemble of multiple forecasts, each minutely different, or perturbed, from the original observations.

The HDW only only uses weather information – fuels and topography are not considered by HDW at all. If the fuels are wet or have a high live or dead moisture content it will not be reflected in the data.

We asked Mr. Clabo, since he ruled out the use of the Haines Index, what should firefighters use, the HDWI?

“We need to first ask the question, what are we looking for?” he said. “If you are interested in a first-glance product for situational awareness, I think the Hot-Dry-Windy Index is a fantastic tool. If you are trying to diagnose the potential for plume-dominated fire growth, I think you need to critically assess your fuel moisture/fuel loading and terrain first and then look to see if the atmospheric conditions are favorable for pyrocumulus or pyrocumulonimbus development. If you are trying to assess whether or not large fire growth is likely, it might be better for you to look at maximum wind speeds.”

Our take

The lack of a fuel component limits the use of the HDW. If, for instance, it was used on a daily basis in mass media, it would not be practical to explain, for example, “Even though it shows we’re at the 95th percentile today, it rained yesterday so ignore the scary-looking chart.”

However, it could be useful among fire and weather professionals who monitor the daily fire danger and weather, can factor in current fuel moisture data, and understand how to interpret the analysis.

Increasing wildfire potential predicted for Northern California and Plains over next four months

Fire potential outlook, June, 2022

The forecast for wildland fire potential issued June 1 by the National Interagency Fire Center predicts that the potential for wildfires will increase to higher than “normal” this summer in Northern California, the Plains states, and Northern Rockies.

The U.S. Drought Monitor reported May 24 that in California “snow cover is virtually non-existent below 8,000 feet; peak flow through area rivers and inflow into the reservoirs has already occurred or will occur soon, weeks ahead of normal; and applications for grants for well drilling, purchasing tanks, and bottled water recipients are increasing.” According to its most recent weekly report, 76 percent of land in the western United States is in severe drought or worse, up from 72 percent at the same time last year.

NOAA reported that the period from January to April was the driest on record in California. The Southwest region, which includes Arizona, New Mexico, Utah, and Colorado, experienced its driest period on record from May 2020 to April 2022.

The fire potential text and maps from NIFC shown here represent the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit. Additional graphics are included from other sources.

Below:

  • Excerpts from the NIFC narrative report for the next four months;
  • Additional NIFC monthly graphical outlooks;
  • NOAA’s three-month temperature and precipitation forecasts;
  • Drought Monitor;
  • Keetch-Byram Drought Index;
  • Soil moisture.

“Most of the West, Plains, and Texas remain in drought, with areas of drought in the Southeast and Hawai’i. Temperatures were above normal across the Southwest, Texas, and east of the Mississippi River, with below normal temperatures across much of the northern Intermountain West. Little snow remains across California and the southern Rockies, but snowpack in Washington and the northern Rockies is above normal for the end of May due to cool, moist storms thus far this spring.

“Climate outlooks indicate below normal precipitation is likely across much of the Plains through the central Rockies to the Northwest, with above normal temperatures likely across most of the contiguous US (CONUS) through summer. Critically windy and dry periods are likely to continue through mid-June for the Southwest and southern Great Basin. The North American Monsoon is likely to arrive on time and be robust this summer, but potential early moisture surges during June could result in periods of lightning across the Southwest, Colorado, and the southern Great Basin.

“Above normal significant fire potential is forecast for the southern High Plains through September, spreading across much of the Plains by August into September. Drier than normal conditions forecast in summer may lead to above normal potential developing across the western Mid to Upper Mississippi Valley in July and August.

“Most of the Southwest, southern Great Basin, and southern Colorado is forecast to have above normal significant fire potential in June, before returning to normal in July. Above normal significant fire potential is forecast across northern California and the lee sides of the Hawai’ian Islands through September, with above normal potential spreading into the southern Sierra and Coast Ranges of southern California in August and September. Above normal potential for central Oregon in June will expand across most of the Northwest by August, with above normal potential remaining in the Cascades and western Oregon in September. Central and eastern Montana east of the Continental Divide and much of Wyoming are forecast to have above normal potential July through September as well. Portions of southern and eastern Idaho are also forecast to increase to above normal potential in August and September.”


Fire potential outlook, July, 2022 Fire potential outlook, August, 2022 Fire potential outlook, September 2022

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