Eastern Washington wildfires make for smoky skies across Seattle
SEATTLE -- I know we're not too used to seeing the sun around here, but did it look a bit discolored Thursday morning?
Some of the smoke from wildfires burning near Mt. Adams in Eastern Washington are is now blowing this way, thanks to some easterly winds aloft.
Recent weather balloons launched form Forks showed easterly winds from about 3,000 to 10,000 feet, enough to carry the smoke from fires burning near Mt. Adams west into southwestern Washington. Then once the smoke reached 10,000 feet, the upper level winds veered to from the south, carrying that smoke north through the Puget Sound region.
You can see this process happen here:
As we get into Friday, the upper level winds will veer back to the west/southwest and carrying the smoke away back over to Eastern Washington.
Red Flag Warning remains in effect
Meanwhile, fire danger remains critically high in Western Washington as well. A Red Flag Warning remains in effect for much of the Western Washington lowlands, including the Seattle-Tacoma area, through early Friday morning.
The warning means that conditions are ripe for wildfires and if one were to be sparked, weather conditions would provide explosive growth potential.
An east winds are expected to continue to gust as high as 20 mph. In addition, as that wind comes down the western slopes of the Cascades, the sinking motion causes the air to dry further -- relative humidity is expected to be in the 15-25 percent range. Third, the atmosphere is expected to be somewhat unstable, allowing heat and smoke from any fire to rise further and spread horizontally.
Put it all together, and it makes for extreme wildfire danger.
The National Weather Service asks that you avoid tossing any burning materials out of vehicles, avoid any outdoor burning, tie up any loose chains involved with towing operations on roadways to avoid sparks, avoid driving over any grassy areas where hot undersides of vehicles can spark the dry vegetation, and obviously -- no fireworks.
What does a high "Haines Index" mean?
If you've ever read the Red Flag Warnings or similar fire weather bulletins, you might see them reference something called the "Haines Index".
It's a measurement combining two atmospheric factors: moisture and stability. The moisture is simply a measure of humidity -- obviously the drier the air, the easier a fire can spread. Stability is how much potential a fire and smoke column would rise. If the atmosphere is unstable, it means heat can rise more easily making for greater plumes of smoke and heat, and greater risk of fire spread.
You can visualize this by thinking of the big water fountain at Seattle Center. When the fountain is on just a little bit, only the immediate area around the fountain gets wet. But if the fountain is on full blast and the water shoots high into the air, the spray from the water reaches out farther. Think of the same with smoke, heat and embers -- a larger smoke plume cam spread these embers over a wider area, giving more potential for fire growth.
Both the stability factor and moisture factor are given ratings from 1 (low) to 3 (high). Add the two together and you get the Haines Index, which is then on a scale of 2-6. 2-3 is considered very low, 4 is low, 5 is moderate and 6 is very high. For Seattle's current Red Flag Warning, the Haines Index is at a 5.