Strong winds and extreme wildfire danger predicted for Southern California this week

This Santa Ana wind event will likely be the strongest and longest duration one we have seen so far this fire season. Red Flag Warnings have been issued for Sunday night through Thursday.

Above: Red Flag Warnings issued for Southern California December 3, 2017.

(Originally published at 9:31 a.m. PST December 3, 2017)

The strongest Santa Ana wind event so far this fire season is in the forecast for the coastal and mountain areas of Southern California this week. The National Weather Service has issued Red Flag Warnings for Sunday night through Thursday for areas within the counties of Santa Barbara, San Bernardino, Riverside, and San Diego.

It is unusual for a Red Flag Warning to extend over parts of five days. And this one has the possibility of being extended for an additional one or two days into the weekend.

The exact timing and speeds will vary by location, but generally, powerful winds will begin Sunday night out of the north and on Monday will be from the northeast at 25 to 40 mph with gusts of 50 to 65, reaching 80 at some peaks and exposed areas.

The NWS forecast includes this statement:

If fire ignition occurs, there will be the potential for rapid spread of wildfire with extreme fire behavior that could lead to a threat to life and property.

The strong winds and low relative humidities (5 to 15 percent)  should continue at least through Thursday. Long range computer models are showing the possibility that the Santa Ana winds could persist into Friday or Saturday, which may require the extension of the Red Flag Warnings.

Wind Gusts Tuesday california santa winds wildfire

Wildfire potential, December through March

Dry offshore winds predicted for Southern California next week.

Above: wildfire potential for December, 2017.

(Originally published at 8:12 a.m. MDT December 2, 2017)

On December 1 the Predictive Services section at the National Interagency Fire Center issued their Wildland Fire Potential Outlook for December 2017 through March 2018. The data represents the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit.

If the prediction is accurate, Southern California and Southern Kansas should see higher than normal wildfire activity, with increasing potential in New Mexico, Texas, and Oklahoma in the latter part of the period.

Below are:

  • The highlights of the NIFC report;
  • NIFC’s graphical outlooks;
  • NOAA’s long range temperature and precipitation forecasts; and
  • Drought Monitor.

“Warm and dry conditions continued across Southern California and the Southwest in November. The wind events observed across Southern California in October ended in early November. Periodic wind episodes in mid-to-late November led to slight increases in fire activity in New Mexico. In the Southeast, the autumn fire season was held in check by the passage of occasional, precipitation-bearing frontal systems that kept fire danger indices from reaching levels similar to what was observed in November 2016. Across the remainder of the country, regions were generally out of fire season as fire activity remained low.

“Temperatures across the Southwest and California were generally above average in November as high pressure off the coast of Baja California dominated. New England also experienced above average temperatures. Alaska experienced temperatures that were well above average for the first half of the month but saw a pattern shift during the middle portion of the month that allowed for below average temperatures to develop. The remainder of the country experienced near average temperatures through the month. Precipitation deficits mounted across the Southwest and Southern California as the weak La Nina-like conditions persisted. The overall dry, westerly flow across the Great Plains also allowed for pockets of drought conditions to emerge. Wetter-than-average precipitation continued across the northwestern portion of the country and across the Great Lakes region. In Alaska, precipitation was near average.

“Latest data shows that the patterns observed in November persisting through the winter months across the nation. Mountain snowpack should be at least near average except across the Southwest where below average snowpack is expected. The potential for above normal snowpack exists from the northern Sierras north to the Canadian border. An elevated potential for significant snowfall also exists across the Great Lakes region. Temperature departures should be stratified with the northern tier of the country experiencing overall colder-than-average temperatures and the southern tier of the country experiencing warmer-than-average temperatures.”

Wildfire potential January

Wildfire potential February March

temperature precipitation long range forecase

drought monitor weather

Researchers develop model to predict wildfire occurrence

Their model uses temperature and precipitation to determine probability

A team of researchers from the University of Missouri and the U.S. Forest Service are continuing an effort to research how climate influences wildfire frequency. The model focuses on two variables – temperature and precipitation – to understand how climate drives wildfire across the world.

After acquiring historic fire occurrence data from tree ring and other studies they developed a mathematical model using temperature and precipitation as the two variables. In validation runs, the predictions the model generated were close to actual fire patterns.  As they continued to collect additional historic data from locations around the world during the last several years, they refined the model making it more accurate.

research wildfire probability temperature precipitation
A Combustion-Climate diagram (CCd) of climate influences on fire probability. Climate simulated fire probabilities for ‘natural’ ecosystems using mean maximum temperature and annual precipitation in the PC2FM. This rate diagram explains two temporal differences related to the combustion of ecosystems. Temperature and precipitation affect the reaction rate at the time the reaction occurs while the rate of fuel production determines the fuel concentration and its combustion rate. These two timing conditions differentially determine the rates of the two components of the PC2FM model: ARterm and the PTrc3. (From the team’s research)

“You can see patterns in global wildfire frequency that are obviously predictable,” Michael Stambaugh, an associate research professor in forestry, said. “For example, ¹Greenland doesn’t burn. It’s too icy and wet. It’s on one end of the spectrum. The other end of the spectrum is a place like the Sahara Desert, which doesn’t burn either. It’s too dry and there’s not enough fuel. Between those two extremes, we were confident that there was a way to describe the transition.”

The work is being done by Richard Guyette, Michael Stambaugh, Daniel Dey, and Rose-Marie Muzika who developed what they call the “Physical Chemical Fire Frequency Model (PC2FM)”.

More information about their research.

 

¹Note from Bill: To be clear, Greenland RARELY burns

Wildfire potential, November through February

On November 1 the Predictive Services section at the National Interagency Fire Center issued their Wildland Fire Potential Outlook for November through February. The data represents the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit.

If the prediction is accurate, Southern California should see higher than normal wildfire activity well into next year.

Below are:

  • The highlights of the NIFC report;
  • NIFC’s graphical outlooks;
  • NOAA’s long range temperature and precipitation forecasts; and
  • Drought Monitor.

“Warm and dry conditions continued across California and the Southwest in October. Several easterly, multi-day wind events coupled with high heat and very low humidity values contributed to significant bursts of fire activity California mid-month. A passing front at the end of the third week of the month brought much needed moisture to the dry fuels across the northern half of the state. The southern half of the Great Basin also saw an increase in grass fire activity during the month due to the warm, dry, and occasionally breezy conditions.

“Looking elsewhere, most of the rest of the nation exited the core fire season though occasional activity was observed along the Rocky Mountain Front in Montana and Wyoming. The autumn fire season in the Southeast was much quieter than the previous year due to the passage of several wet cold fronts that brought timely and occasionally abundant moisture.

“Temperatures across the East, Southwest, and California were generally above average for the month with some locations along both the East and West Coasts reaching as much as fifteen degrees above average at points. The Pacific Northwest, Northern Rockies, northern Great Basin, and central Rockies generally experienced cooler-than-average conditions though a warming trend developed near month’s end. Alaska was generally colder and wetter than average.

“Precipitation departures from average showed significant dryness across the southwestern quarter of the nation and across much of Texas. Significantly wet conditions were observed across the Northwestern quarter of the country as several very wet systems impacted the region during the middle to latter half of the month. Another wet signal for the month was observed across the Great Lakes Region and the Ohio and Tennessee River Valleys.

“Latest forecast data suggests that California will remain the focus of periodic bursts in fire activity through November and possibly into December. Portions of the Deep South may also exhibit increased activity in between precipitation events as well. By February, the focus will shift to the southern Great Plains as the antecedent dry conditions begin to take its toll.”


wildfire potential december, 2017

january february 2018 wildfire potential Continue reading “Wildfire potential, November through February”

Simulation shows winds near origins of Oct. 8 fires in Northern California may have been 75-90 mph

“Hurricane force” winds, according to the National Weather Service, are sustained winds or frequent gusts of 74 mph.

Above: Fine-scale weather model simulation (horizontal grid spacing of 370 meters) analyzing the surface wind when the Northern California fires started, 8 p.m. local time October 8, 2017. The darkest brown areas (with cross-hatching) indicate wind speeds greater than 40 m/s (~90 mph). The red shapes indicate heat from active fires first detected by a satellite (VIIRS) at 3:09 a.m. local time October 9, 2017.  Simulation by Dr. Janice Coen, a Project Scientist at the National Center for Atmospheric Research in Boulder, Colorado. Simulated with the Coupled Atmosphere Wildland Fire Environment model.

(Originally published at 10:40 a.m. MDT October 30, 2017.)

More research into the weather conditions when the devastating October 8 wildfires started in Northern California indicates that hurricane force wind was one of the factors responsiblewind speed conversion table for the extremely rapid spread of the fires that killed at least 43 people and destroyed more than 8,900 structures.

Dr. Janice Coen, a Project Scientist at the National Center for Atmospheric Research in Boulder, Colorado ran fine-scale weather model simulations (horizontal grid spacing of 370 meters) analyzing the wind during the time the fires started. Her research (see chart above) showed significantly higher surface wind speeds than previously thought — 75 to 90 mph just upwind of the major fires.

CAL FIRE has not released the causes of the October 8 conflagrations, but at about the same time firefighters were first responding to numerous fires, they also received multiple calls about fallen power lines and electrical transformers exploding.

California law dictates that power lines are supposed to be able to withstand 56 mph.

In an email Dr. Coen told us more about the October 8 wind simulation and her research related to fire weather:


“These early simulations suggest that within a wide area of strong winds, these small, local bands of extreme winds occurred where winds were perpendicular to the local ridge. And, that the location of the peaks and their peak speeds evolved throughout the event as the wind direction changed, in part due to the high pressure over the Great Basin moving along.

“I don’t have a lot of confidence that we’d be able to find evidence to prove or disprove if/when a particular simulated wind speed maximum occurred.  And, although there is a lot of theoretical and laboratory work on stably stratified flow over objects, this three-dimensional terrain is too complicated to apply much of that.

“We’ve seen a sequence of devastatingly destructive fire events each driven by strong wind events – 2007 fires in southern California driven by Santa Anas, surprising destruction from a mountain downslope wind-driven fire in Gatlinburg, TN, and now this – yet fine-scale investigations of the mechanisms producing the peak winds and how they are distributed, particularly in relation to potential ignition sources, don’t really exist. And, though our forecast models may indicate strong gusty winds are possible, explicitly predicting how extreme the winds might be and where the most dangerous spots are with the detail shown here is beyond their capabilities.

“I hope to learn and share more about the mechanics of these events by visualizing these simulations, so we can see inside these events, prepare and anticipate, contribute to firefighter awareness and safety (as Diablo winds in general are a regional fire issue), and perhaps help potential ignition sources such as utilities manage the risk.”

wind simulation october 8 fires northern california
Fine-scale weather model simulation (horizontal grid spacing of 370 meters) analyzing the weather during the time the Northern California fires started, 8 p.m. local time October 8, 2017. The darkest brown areas indicate wind speeds greater than 40 m/s (~90 mph). Simulation by Dr. Janice Coen, a Project Scientist at the National Center for Atmospheric Research in Boulder, Colorado.

Triple-digit temperatures in Southern California

Above: Extreme temperatures in Southern California Tuesday afternoon, October 24, 2017.

(Originally published at 2:05 p.m. PDT October 24, 2017)

Weather conditions appear conducive to wildland fires in Southern California today. The temperature even reached 96 degrees on San Clemente Island, and triple digits in some inland areas. Meanwhile, it’s only 93 in Phoenix.

red flag weather conditions
Weather conditions at 2:27 p.m. PDT October 24, 2017 in Southern California.
Red Flag Warnings and Fire Weather Watches
Red Flag Warnings and Fire Weather Watches , October 24, 2017.