Spooky month is nearly over across the United States, yet fall leaves and pumpkins have been overshadowed by snow and smoke across the West. Incredibly dangerous fires have continued to blaze across Southern California, while record-breaking snow has fallen across much of Colorado and the Rockies. As someone who just moved to the mile-high state, the impending ski season all of this snow will bring is exciting to me. However, dangerous consequences such as hazardous roads and persistent wildfires are likely, and a dominating weather pattern is to blame.

So what’s causing all of this?

Upper level winds



A deep wave in the upper levels of the atmosphere (Roughly the altitude where planes fly and the jet stream is located) is currently present over the western and central U.S., pulling cold polar air from Canada southward. Air at these levels often behaves like a river, undulating and flowing in alternating waves. The current southward bend in the wave is like the corner of a race track. As cars enter the turn, they slow and converge on one another and as they exit the turn, they accelerate and spread out. Air behaves the same way.

Jet stream diagram



At the surface, conservation of mass results in air sinking below the area of convergence (region of surface high pressure), and air rising to fill the void below the area of divergence (region of surface low pressure). This unstable low pressure area over the mountains resulted in the snow storm that brought over 8 to 16 inches to parts of Colorado, making this month the 12th snowiest October on record. Temperatures also fell to the single digits, well below average for the month.

On the flip side of this atmospheric wave, the surface high pressure is bringing northeasterly winds across southern California, creating record-breaking Santa Ana winds that could intensify the already raging wildfires. This heavy, cold air pulled in from the surface high dries out over the desert, and is then funneled through the mountains East of Los Angeles, creating incredible sustained wind speeds in excess of 30 mph, with gusts above 50 mph.

Santa Ana winds



As this dry, fast-moving air flows over wildfires, it can act to spread them and fuel them further, limiting moisture and making fire-fighting efforts very difficult. Currently, the National Weather Service has issued a rare “extreme red flag warning” for potential wind gusts over 80 mph this week, with strong Santa Ana winds forecast through Thursday morning. For the Getty Fire, which is only 27% contained as of Wednesday morning with 745 acres already burned, this life threatening blaze could continue to spread into the L.A. metro area and beyond.

Will these extremes continue?

As Earth continues to warm over time, the temperature contrast between the arctic and the equator lessens, and this allows the jet stream to dip and meander more often. Although October snow in Colorado is not unheard of, and wildfire season across California remains, the conjunction of the two extremes due to this amplified weather pattern has created dangerous conditions that could become more common in the coming years.