News and opinion about wildland fire
Friday’s weather includes Red Flag Warnings in the west and a hurricane on the east coast
Above: Weather forecast, current at 9 a.m. MDT September 2, 2016. Weatherunderground. Black text added by WildfireToday.
The weather map for the United States today has quite a range of conditions across the country. While Hurricane Hermine, now downgraded to a tropical storm, batters the southeast, a cold front is bringing strong winds and low humidities to some areas in the west. There is a chance of isolated dry thunderstorms in northwest Wyoming and eastern Montana.
On September 1 the Predictive Services section at the National Interagency Fire Center issued their Wildland Fire Potential Outlook for September through December, 2016. The data represents the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit. Below are highlights from the outlook.
****
September is typically a month of significant change in fire conditions, especially across the northern tier of the United States. Days shorten, lessening available solar radiation to dry and heat fuels; longer nights are cooler with generally higher humidity. These conditions slowly reduce fire activity and typically end normal fire season activity throughout the month. This is expected to be the trend this season as well.
Throughout the northern portions of the Great Basin including portions of the Northwest, Northern Rockies and Rocky Mountain Areas above normal conditions will transition through the month to normal conditions and by the end of September normal conditions indicate minimal fire activity throughout this area. Occasional dry cold fronts during September and possibly October will present the potential for large fires on the landscape to grow rapidly; however, these conditions will be short in duration followed by opportunities for successful firefighting efforts. California will remain at above normal levels of fire activity throughout much of the state as dry conditions will continue and fall will bring the increased potential for offshore flow events.
In October, November and December diminishing activity in the northern tier will transition to heightened activity across the southern tier; especially in central and southernCalifornia and the Southeast. California is not expected to see any significant events that will alleviate long term drought and very dry fuels. This will come with enhanced potential for offshore flow, increasing the potential for very dry and windy conditions. The southeastern United States is a significant wildcard moving into the fall months.
Tropical systems the Atlantic Ocean and Gulf of Mexico could provide substantial relief to some if not all of the area.
If this dry area remains, fall fire activity in the Southeast will be amplified and could become significant throughout the fall and winter. It is possible significant changes will occur, but the current conditions dictate elevated potential is likely.
NOAA’s Earth System Research Laboratory, as part of an experimental program (above), has produced a smoke forecast for 5 p.m. on Wednesday, August 31, showing that many areas in the western U.S. are affected by smoke from wildfires.
Below is their forecast for 5 p.m. MDT on Thursday, September 1, 2016.
The last map, below, predicts elevated wildfire danger on September 1 in parts of California, Nevada, Utah, Idaho, and Montana. Isolated dry thunderstorms could be in the cards for areas in Nevada, Idaho, Montana, Utah, and Wyoming.
Above: The photo above was taken from the research aircraft August 30 by Nick Guy of the University of Wyoming’s Atmospheric Science department.
The Fire Weather Research Laboratory from San Jose State University is conducting research from an aircraft flying over the Pioneer Fire in central Idaho. Today using N2UW, a twin engine 1977 Beech 200T King Air, they flew for over three hours at 27,000 feet studying the fire for the RaDFire project.
The aircraft is outfitted with a ton of instruments including Doppler radar. Craig Clements, Associate Professor in the Meteorology Dept. at SJSU, described it for us:
The radar is called the Wyoming Cloud Radar (WCR). It’s on the aircraft, points up, down, and down-forward to get horizontal winds and vertical winds. The goal of the RadFIRE (Rapid Deployments to Wildfires Campaign) is to get data on plume dynamics from ground based mobile Doppler Lidar. But we were awarded 10 flight hours to test the WCR to see if it works in smoke plumes. And it does so well, more than we can imagine!
First #SJSU RaDFIRE deployment with #NSF #Wyoming KingAir to study #wildfire plume dynamics w/ radar. #PioneerFire pic.twitter.com/VJvCqx9BAp
— SJSU FireWeatherLab (@FireWeatherLab) August 29, 2016
The group has been known to fly through the convection column. I’ve done that a few times and it’s an interesting experience — it can get a little turbulent, as you might expect.
On Monday they said the top of the pyrocumulus cloud over the fire topped out above 30,000 feet. In Tuesday’s photos it was at about 25,000 feet but toward the end of the day the top got up to at least 32,000 feet, Mr. Clements said.
The project is sponsored by the National Science Foundation and it’s being led by San Jose State University. Other collaborators on the project are David Kingsmill at the University of Colorado Boulder, and the University of Wyoming King Air team.
Since it started on July 18 the Pioneer Fire has burned over 140,000 acres.
View from 24K ft of #PioneerFire #pyrocumulonimbus yesterday before penetration. #turbulence https://t.co/2oefuOnB60 pic.twitter.com/7lLIZDhgSw
— SJSU FireWeatherLab (@FireWeatherLab) August 30, 2016
Current flight path of UWKingAir over #PioneerFire Flight crew reports explosive plume growth: 1500 ft vertical/min pic.twitter.com/PspwQjrmLG
— SJSU FireWeatherLab (@FireWeatherLab) August 30, 2016
This last photo of the convection column was not taken by the researchers. It was shot by Steve Botti in Stanley on August 29, more than 20 miles away from the fire.
Author Bill GabbertPosted on Categories Uncategorized4 Comments on Where does the moisture in a pyrocumulus cloud come from? Above: CNN Meteorologist Chad Myers explains pyrocumulus clouds. This is a screenshot from Mr. Myers’ 52-second video. The Weather Channel has a similar explanatory video.
Cumulus clouds are puffy clouds, usually having a somewhat flat base but with some vertical development that gives them rounded towers on top. They can form when the sun heats the earth, which then heats the air above it causing the warmer air to rise. Rising air cools and the relative humidity increases. If it reaches 100 percent, water vapor condenses forming a visible cloud.
Above: time-lapse video of pyrocumulus over the King Fire in California.
Clouds can also form over vegetation fires. In some cases a very intense fire can produce enough heat that the air rises very quickly. If it is not dispersed laterally by wind it can rise high enough that a cloud forms. This can look like a cumulus cloud, but when they form over a fire they are called pyrocumulus clouds.
Occasionally these clouds will produce rain or even lightning. Water requires a non-gaseous surface to make the transition from a vapor to a liquid. Smoke helps out by contributing very small particles that are used as condensation nuclei on which water droplets form, to create clouds or rain.
If pyrocumulus clouds grow large they resemble cumulonimbus, thunderstorm clouds. What goes up must come down, and if not disturbed by a strong wind during the dissipating stage the updrafts can reverse and become downdrafts. This is sometimes called a “collapsing column”. When that descending air hits the ground it spreads out, sometimes in all directions, and can quickly and drastically change the wind direction at a given point on a fire. This can be fatal if firefighters find themselves in the wrong location at the wrong time.
I had always assumed that much of the moisture that formed a pyrocumulus came from a byproduct of combustion — water vapor — something that many burning fuels create. (Some TV meteorologists also make the assumption about the sources of the moisture.) A great deal of water vapor is produced when vegetation burns, and the higher the fuel moisture the more water vapor is created.
But I wanted to confirm that assumption before I wrote this article, and it turns out I was wrong. I found two research papers that were devoted to the subject and they were mostly in agreement. As the byproducts of combustion rise above a fire the water vapor is rapidly diluted before it reaches the condensation level, or what becomes the base of the pyrocumulus. One group of researchers in Germany calculated that 10% of the moisture in a pyrocumulus comes from the fire.
Others with the Bushfire & Natural Hazards CRC in Melbourne, Victoria, Australia determined that the contribution of water vapor from the fire is negligible since it is diluted before it reaches the height of the cloud:
Fire plumes entrain large amounts of environmental air as they ascend, which greatly dilutes the plume gases, including the fire moisture. Figure 3 shows the fire moisture dilution for the moist fire simulation(right panels of Fig. 2). The lightening shades of blue with height demonstrate the fire moisture dilution. When the plume reaches the condensation level (4.5 km) there is barely any fire moisture evident to contribute to cloud development. The dilution rate may be sensitive to fire size and intensity.
Continue reading “Where does the moisture in a pyrocumulus cloud come from?”
On August 1 the Predictive Services section at the National Interagency Fire Center issued their Wildland Fire Potential Outlook for August through November, 2016. The data represents the cumulative forecasts of the ten Geographic Area Predictive Services Units and the National Predictive Services Unit. Below are highlights from the outlook.
****
“For August, significant wildland fire potential will continue to be focused in the finer fuel and brush areas of California and the Great Basin with some expansion into Oregon, Montana and Wyoming. Primary concerns continue to focus on the abundant fine fuels and their ability to carry fires more effectively than in a typical year. Additionally significant mortality will increase heavy fuel availability throughout the mountains of California, while typical summer dryness will bring fire activity in the heavier fuels of the Northwest, Northern Rockies, Rocky Mountains and Great Basin up to normal levels. Furthermore, the Southwest, Rocky Mountains and southern Great Basin will see an intermittent monsoon which will continue some level of fire activity in those areas.
“As fall begins, days shorten, temperatures cool and frontal systems become more common. This typical transition will return much of the Northwest, Northern Rockies, Rocky Mountains and Great Basin to normal fire activity through September. California will continue to see elevated potential due to long term dryness. This will occasionally be amplified through the fall and early winter as offshore flow events become more common. The southern U.S. will also see an increase to above normal significant fire potential as long term dryness couples with leaf drop and dormancy of live fuels to create a receptive environment for fall fire activity.
“By October and November much of central California will transition to normal fire potential as is seasonally expected. Southern California will continue to see elevated significant fire potential and will also see the persistent threat of offshore wind events. The southeastern states will see a broad area of increased potential as a result of long term dryness and the introduction of La Niña conditions which typically bring warmer and drier-than-normal conditions to the southern tier of states.”
