Dangerous weather alert: There will be extreme fire danger next week, so be prepared.
Dangerous Weather Warnings at Decoded Science
With this report, Decoded Science is initiating a category of weather event that includes potentially dangerous conditions of wind, rain, snow, ice, fire, drought, lightning, and disease.
An alert for dangerous weather is designed to give a little extra warning for weather patterns that are shaping up to be treacherous. It is not intended to put anyone in a panic — just to provide information.
The names of these potentially serious situations will be the names of common birds. Since there are no common birds that begin with either of the first two letters of the alphabet, this alert is named Canary.
There will be extreme fire danger next week over a wide swath of the western United States.
Hot, Dry Weather Means High Fire Danger
This is a no-brainer: Fire likes Dry; Fire likes Heat — heck Fire IS Heat. Fire also likes something to burn — grass and trees. There is plenty of that in the west.
The Persistent Weather Pattern Over The United States
For the better part of a year, the weather pattern over the US has featured high pressure in the west and low pressure in the midwest. This pattern extends to considerable height in the atmosphere; on average, the jet stream shows a ridge (high pressure) over California and a trough (low pressure) over Illinois.
The pattern sometimes breaks down, but it always returns. Decoded Science has pointed to very warm water in the Gulf of Alaska as one of the causes, but since the atmosphere is interconnected across the globe, there could be other reasons for the persistent weather.
Last Week’s And Next Week’s Jet Stream
Summer is normally a time when the jet stream relaxes with a gentle west to east flow. Not this summer. Time after time, the ridge builds in the west and the trough is reinforced in the center of the country.
The more amplified the jet stream flow becomes, the more slowly the weather tends to move. When ridges become omega blocks and troughs become cut off lows, the normal west to east movement of weather systems can come to a complete standstill.
What Will Happen Next Week?
All of the long-range weather forecasting models are in agreement: the trough in the center of the country will become a cut off low pressure center, flinging cold air deep into the south.
The ridge in the west will become an omega block, which is wind flow shaped like the greek letter omega (Ω).
Under the high pressure ‘dome,’ the air will gently sink. Sinking air heats at about five degrees per thousand feet, and the whole air mass will become very warm.
Since warm air can hold more moisture than cold, the relative humidity (the moisture in the air as a percentage of the moisture the air could hold) will fall — the air will be very dry.
Where Will Fire Danger Be Highest?
The entire western US from the Rockies to the Pacific coast will come under the influence of the omega block. High fire danger could occur anywhere in the area, probably centered on Idaho.
Local conditions are important. Locations on the east sides of mountain ranges are normally dry because the winds are generally from west to east and moisture is squeezed out as the air is forced up the west side of the mountains. So places such as the ones hit by last week’s fires in Washington and Oregon, on the east side of the Cascade Mountains, are dry to begin with.
How Long Will Canary Last?
The forecast indicates that the pattern will persist for many days, perhaps even a week or longer. Forecasts at this time range are notoriously inaccurate, but when all of the model forecasts are in synch, they are likely to be right.
When Does Fire Season End?
The fire danger subsides with the colder and rainier weather of fall. This can begin as early as late-August near the Canadian border, but not happen until late-November in southern California.