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).

Chip

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.

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.

Monitor near-real time Red Flag weather conditions in LA area

Observations from weather stations in the Los Angeles area
Observations from weather stations in the Los Angeles area that “flirt with” or meet Red Flag criteria. (Click to enlarge.)

The National Weather service has developed an excellent site for monitoring the near-real time weather conditions in the Los Angeles area, and how those observations from weather stations “flirt with” or meet the criteria for Red Flag conditions. It is a very useful site, refreshing automatically every five minutes. It includes the following parameters: RH, wind speed, gusts, duration for meeting the Red Flag criteria, fuel moisture, temperature, and elevation.

When you visit the site, hovering your mouse pointer over a station brings up the last 12 observations at that station.

Other areas in the country should develop similar sites. If you are aware of more, let us know in the comments below.

Wildfire potential, October through January

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, California will be the only area with above normal wildfire activity.

Here are the highlights from their outlook.

October

September wildfire outlook

  • Above normal fire potential continues across some portions of northern, central and southern California. Long term drought coupled with increasing potential for offshore winds will keep potential elevated through October.
  • Below normal fire potential is expected for central Texas as well as the southern Atlantic Coast.
  • Elsewhere normal fire potential is expected as many areas transition to out of season conditions for the winter.

November

November wildfire outlook

  • Above normal fire potential will be alleviated in the north, leaving central and southern California as the only areas with continuing threats from dry fuels coupled with offshore flow.
  • Below normal fire potential will expand to include an area stretching from Texas to the Atlantic Coast.
  • Most other areas are out of season during November.

December and January

December January wildfire outlook

  • The last remaining areas of above normal potential in California will transition to normal during December, leaving only normal to below normal conditions.
  • Below normal fire potential will continue from Texas to the Atlantic Coast.
  • Most other areas are out of season December through January.

U.S. Forest Service launches new tool for fire preparedness

Santa Ana header

RIVERSIDE, September 17, 2014 — The USDA Forest Service, in collaboration with San Diego Gas & Electric (SDG&E) and UCLA, today unveiled a new web-based tool to classify the fire threat potential of a weather phenomenon unique to Southern California — the powerful, hot, dry Santa Ana winds that can turn a spark into an inferno.

The Santa Ana Wildfire Threat Index, which includes four classification levels from “Marginal” to “Extreme,” will be used to help fire agencies, other first-responders and the public determine the appropriate actions to take based on the likelihood of a catastrophic wildfire fueled by high winds.

“Given the current state of fuel conditions, we have the potential to see devastating fires this fall should significant Santa Ana winds occur,” said Forest Service Meteorologist Tom Rolinski. “This tool will directly benefit fire agencies by allowing us to better anticipate what kinds of resources may be needed, as well as where and when we could face the greatest challenges.”

Since the 2007 wildfires in San Diego County, SDG&E has been a partner in enhancing local fire preparedness and has taken major steps to strengthen its overhead electrical system – changing out wooden power poles for steel – to make the grid more wind- and fire-resistant. The utility also hired in-house meteorologists and installed 150 weather stations across its service area to gather real-time information about the impact of weather on utility equipment – all to improve situational awareness during emergencies.

SDG&E’s Dave Geier, vice president of electric transmission and system engineering, considered other ways to leverage this significant amount of weather data and to share it broadly.

“I asked my team to come up with something similar to the categories to rate hurricanes that could be used to classify Santa Ana wind events based on their potential to spread a major fire, which would help us in making operational decisions to protect our system and our customers,” said Geier. “The goal was to develop a uniform and recognizable system that also could be used to alert fire agencies and communities in time to prepare and take appropriate action.”

As luck would have it, Rolinski already had been working on a similar concept and was eager to share ideas and information. Initially, SDG&E’s meteorologists compiled hourly weather data for the last 30 years in Southern California — information that was used as a basis for the models that eventually led to the four-level wildfire threat index. The utility reached out to regional fire agencies, including the Forest Service and CAL FIRE, along with universities in Southern California, to partner in the development of the index. SDG&E also provided funding for state-of-the-art computing hardware and software to help turn the raw data into a manageable tool.

The actual “number crunching” was done by a team from UCLA, led by Dr. Robert Fovell, Ph.D., chair of the university’s Department of Atmospheric and Oceanic Sciences, who applauded SDG&E’s weather network for “its unprecedented station density and uniformity.”

“We not only have a new, deeper understanding of how the San Diego-area terrain influences weather, especially wind, which is crucial to SDG&E’s operations, but we also have been able to make improvements in weather modeling that will benefit forecasters worldwide,” said Dr. Fovell.

The threat index includes four levels of increasingly severe fire potential:

Santa Ana legend

The National Weather Service (NWS) is the agency that issues a Red Flag Warning when weather conditions indicate the development of a strong Santa Ana. Forecasters look at fuel moisture, humidity levels, temperature and topography, as well as wind speed, to determine whether to declare a Red Flag Warning, which typically means high fire danger with increased probability of a quickly spreading vegetation fire in the area within 24 hours.

“This index will help forecasters to quantify a Red Flag Warning and the public to better understand the risk,” said Roger Pierce, director of the NWS in San Diego. “We believe this new tool will support and complement our forecasts and provide even more information to help the public to be better prepared.”

The Santa Ana Wildfire Threat Index is intended to be used by fire agencies, emergency responders, the media and the public. The Forest Service “owns” the tool and is the agency responsible for determining and issuing the alerts, which can be found on the agency’s website at: www.santaanawildfirethreat.com

“Each of the levels includes recommended ‘calls to action’ that escalate as the chance of a catastrophic fire becomes more likely,” said Rolinski.

Recommended actions for the public include closely monitoring fire conditions, making sure cell phones are charged and vehicle gas tanks are full, as well as reviewing emergency evacuation plans at work and at home and registering phones to receive reverse-911 warnings for the latest information about an emergency.

Rising temperature trend in California, January through August

California, average temperature, January through August
California, average temperature, January through August

The NOAA data above showing the trend in temperature in California during the first eight months of the year, is impressive. The average temperature this year shattered the record. It illustrates that you should not get excited about the weather on one day, or one season, or even one decade. There is a great deal of variability. The long-term trend has the big picture.

Fire Weather Outlook September 8 through 13

An upper level trough is crossing the western US Monday. This is enhancing the pressure gradient across central WA/OR this afternoon, generating gusty winds in excess of 35mph. Combined with very dry vegetation and relative humidity between 15-20%, red flag warnings have been posted. Weak cold front will cross the region overnight, weakening winds for Tues with slightly cooler conditions and higher RH. A few pockets of lingering gusty winds will persist for northern CA/southern ID/southern OR and the northern Great Basin on Tues. Southern ID will see the strongest winds with an enhanced fire risk. Farther west, very dry vegetation and RHs < 15%, especially for northern NV/north CA will promote fire growth as well, but winds are expected to be weaker. These conditions will still promote continued suppression difficulties of large wildfires in the region.
A disturbance will round the trough as it moves east, passing over the northwest US on Wed. In response, a strong high pressure is expected to develop on the backside of this disturbance across the northern Rockies. This will once again create strong easterly surface flow for much of the west. As winds flow downslope of the Rockies, warm/dry air will situate itself over the western states with above normal temperatures and dry conditions. Some localized breezy conditions are possible Thurs across WA/OR/ID, however they will dwindle Fri as the high moves east with a weakening pressure gradient. Upper level ridging builds back in across the western US this weekend and above average temperatures with very dry conditions are anticipated to continue into next week.
Heavy monsoonal rains (and moisture from ex-hurricane Norbert) will remain possible through Tues in the desert southwest and eventually diminish mid-week. Some very widely scattered dry thunderstorms possible in south/south-central CA. Drying trend will continue into the weekend before another round of monsoonal moisture pushes into NM/NV/UT/CA by early week. This may also be enhanced by another tropical system by mid-week.
Weather Highlights:
CA: Few isolated storms south Mon/Tues, otherwise continued above normal temperatures and very dry conditions. Isolated breezy winds Tues/Thurs for northern CA.
OR/WA: Red Flag Warning Mon. Breezy winds with critically low RH Mon with improving conditions into Tues. Another period of localized breezy conditions Thurs with a warming trend into the weekend. Expect continued very dry conditions, especially for southern OR.
Great Basin/southern ID: Heavy rain possible for the southern Great Basin through Tues. Enhanced fire weather Tues with gusty winds and low RH for northern Great Basin/ID. Dry and warm through the period.
Chip