Lightning strikes to increase 50% by end of century

As if we don’t have enough to worry about with climate change already, a study found that lightning strikes in the United States will likely increase by nearly 50 percent by the end of the century as the world gets warmer and wetter.

Here is an excerpt from an AP article:

[Researchers] concluded that for every degree Fahrenheit the world warms in the future, lightning strikes will go up nearly 7 percent. That’s 12 percent for every degree Celsius.

Because scientists forecast that the world may get about 7 degrees warmer (4 degrees Celsius) by the end of the century, based on current carbon dioxide emission trends, that comes to a 50 percent increase in lightning strikes, said David Romps. He’s the atmospheric scientist at the University of California Berkeley who led the study.

“When you used to have two lightning strikes, now you’ll have three,” Romps said. “It’s a substantial increase.”

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November fire weather climatology

November is typically characterized by increases in cold air intrusions across much of the United States. This also begins what is considered the dry season for much of the Plains and portions of the inter-mountain west. Rainfall begins to become more prevalent further south along the Gulf and where Gulf flow (southerly winds carrying moisture from the Gulf into the US) can become established before a storm system. This flow typically becomes established ahead of an advancing cold front, but is pushed further east than during the summer months. Multiple cold fronts with very little moisture/flow recovery time between can greatly influence fire activity for the Mississippi Valley and eastward. Wide sweeping cold fronts are common and typically drier as moisture becomes more limited, dominated by Canadian/Arctic air masses.

fire weather november

Average rainfall for the month of November (hamweather.com)

Vegetation is now dormant across most of the continental US and foliage/grasses can cure easily. The Appalachians have a vigorous deciduous tree canopy and provide new debris and additional uncompacted litter for increased fire occurrence/sustainability. Strong cold fronts tend to bring much drier air and windy conditions that only fuel fire conditions along these slopes and further to the east/southeast. The fuel load depends greatly on the water received from tropical systems during the late summer/early fall. If there is an active tropical season, fuel loads can be greatly enhanced. Therefore, the region is greatly dependent on the tropical/drought status of the area and their subsequent influences on the fire season.

Average fire density

Average fire density occurrence in November (NICC).

Overnight relative humidity recovery is typically much higher across the US than the summer. This is due in part to the lack of solar radiation. Less sunlight reaches the earth’s surface in the Northern Hemisphere during winter. This in turn prevents the surface from warming, allowing the surface temperature to drop during the overnight, approaching saturation much easier, and providing increased humidity. Therefore, often fires in late fall/early winter may make a big run in the afternoon when the surface is warm, but then easily/quickly lay down once the sun sets. There are some exceptions including strong storm systems and terrain influences, but typically this is the case.

In November, the western US is totally dependent on the Pacific winter storms. They typically begin late fall along the northern portions of the coast and gradually shift southward through the month. A late onset of the storm season can bring continued and elongated fire season, especially to those further south in California where it takes more time for the pattern to shift. Sometimes, as in recent years, the pattern doesn’t even make it that far south long enough to bring an end to fire season. This is typical with La Nina in the Pacific Ocean where high pressure tends to dominate at the latitude of California.
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Fire weather outlook, November 5 through 10

Complicated weather pattern currently across the US. A large high pressure sits over the inter-mountain West, an elongated front extends from Texas northeast into the Great Lakes, and another cold front is sweeping south into the northern Plains.

Fire weather focus is for southwestern California, where breezy off-shore winds continue Wed/Thurs in response to diverging winds of the high pressure centered over northern Utah. Sustained winds along higher terrain are expected up to 20-25mph with gusts to 45-50 (see graphic below). With these downsloping winds, very dry/warm conditions are expected with RHs in the mid-to-upper single digits. In combination with ongoing drought conditions, this will create explosive fire weather conditions Wed afternoon and Red Flag Warnings are posted. Winds are expected to weaken Thurs as high pressure moves northward. However, some areas will still see aggravated fire weather conditions with gusts exceeding 20mph in southern CA. After Thurs, winds will be much calmer for the remainder of the period but conditions will remain very dry. Daytime RH isn’t expected to exceed 15% for the entire period with very poor overnight recoveries into the weekend.

fire weather

San Diego NWS local forecast model depicting possible winds for 21z Wednesday.

Elsewhere, several cold fronts are expected to traverse the Plains and Eastern US through the period. With these frontal systems, quick periods of dry and/or windy conditions are possible. The first front is currently entering the northern Plains and will bring a period of windy conditions for central South Dakota with RH dropping to 20-25% Wed afternoon. Overnight Wed the front moves further southeast into the Mississippi Valley, reaching the Appalachians Thurs. Friday, it reaches the southeastern US and windy conditions move offshore. However, enhanced fire concerns exist with RHs ranging 20-25% from east Texas to northern Florida. Friday afternoon, another quick moving cold front enters the Plains with strong winds across the northern Plains. This second front will move eastward and repeats the process through Sunday.

A third, much stronger cold front moves south from Canada on Sunday evening. This front will bring much colder air to much of the central and eastern US early week. Very strong winds are possible with this front on Sunday/Monday in the central Plains both ahead and behind the cold front. Enhanced fire conditions are possible across the central Plains through this 48 hour period, especially for portions of eastern Colorado, Kansas, Nebraska, and Oklahoma.

fire weather

Some rainfall is likely from these fronts, however, much of it will avoid the southeastern, central, and southwestern US. Image from NWS Weather Prediction Center – 5 day rain predicted rainfall total.

Weather Highlights:

Southern CA: Red Flag Warnings for Wed, critical fire weather with strong winds (gusting to near 50mph) and very low RH (4-9%). Winds will weaken Thurs (gusting to 20mph), and become calm Fri-remaining very dry. Poor overnight RH recovery through the week, and into the weekend.

ND/SD: Enhanced fire weather conditions on Wed & Fri afternoon with strong northwest winds (gusting to 60mph) and low RH (20-25%).

TX/LA/MS/AL/GA/FL: Locally enhanced fire weather conditions on Fri-Sun afternoons with low RHs (25-35%).

Western KS, NE, OK/Eastern CO, WY: Beginning Sun morning and continuing until a cold front passage Monday afternoon, very windy conditions (gusting to 55mph) and low RHs (5-15% increasing Mon afternoon).

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Wildfire potential, November through February

The Predictive Services section at the National Interagency Fire Center has issued their Wildland Fire Potential Outlook for October through January. The data represents the cumulative forecasts of the eleven Geographic Area Predictive Services Units and the National Predictive Services Unit.

If their predictions are accurate, southern California will have above normal wildfire activity through December, along with Minnesota in November, while the rest of the United States will have normal or below normal activity.

Here are the highlights from their outlook.

November

November fire weather

  • Above normal fire potential continues across portions of central and southern California. Long  term drought and a potential for offshore winds will keep potential elevated through November.
  • Most of Minnesota along with portions of Iowa and Wisconsin will have elevated fire potential for November. This is not expected to persist into December.
  • Below normal fire potential will continue across the Gulf Coast states.

December

December fire weather

  • Fire potential will continue to diminish in California, leaving coastal areas of southern California with above normal significant fire potential.
  • Below normal fire potential will expand across most of the South and Mid-Atlantic regions.

January-February

January February wildfire weather

  • No areas of above normal fire potential are expected for this period.
  • Below normal fire potential will continue across central and southern Texas, Florida, and southern Georgia.
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Inversion traps smoke over prescribed fire

Sequoia Kings Canyon National Park

Smoke is trapped by an inversion in Sequoia Kings Canyon National Park. NPS helitack photo.

In this photo taken Wednesday, smoke is attempting to break through an inversion over the Mosquito prescribed fire in Sequoia Kings Canyon National Park in California.

Normally, as you rise in altitude, the temperature decreases due to the changes in air pressure. In a weather (or temperature) inversion, instead of getting cooler at higher temperatures, it is actually warmer higher up.

weather inversion

Cool air trapped under a warmer layer, creating an inversion. From Fortair.org.

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