Energy

Halloween Extremes – Explaining The California Wildfires And Frigid Cold In The U.S. This Week


According forecasts and reports, temperatures could approach or fall below zero in places like Denver, Colorado this week. For Denver, the record low temperature for October is -2 degrees F so it could definitely be broken. Record cold temperatures are expected from the Rockies to the Midwest as Halloween approaches. Meanwhile, California residents are facing devastating wildfires. NBA star Lebron James and former California Governor Arnold Schwarzenegger were forced to evacuate their homes as were many people that don’t have famous names. What’s the meteorology behind these two extremes?

I pose this question because it is always fascinating to watch people make sweeping statements and assumptions about weather or climate because it is extremely hot or cold in a particular week. Our weather is strongly governed by a series of undulating wave patterns in the atmosphere comprised of troughs and ridges. I will deal with the cold temperatures first. The Earth is within one of its seasonal transition periods, Fall. Slowly, the Northern Hemisphere is starting to tilt away from the Sun as we transition to winter. This means that cooler temperatures and snowstorms become more common in the forecasts. There is nothing weird about cold temperatures or snow at this time of the year even as Alaska and the eastern U.S. are warmer than normal right now (graphic below). Extreme cold events are determined by the amplitude of those “valleys” or troughs in the atmospheric wave patterns. The amplitude of a wave can be thought of as a representation of the amount of energy in the wave or how far the “hill” (ridge) or “valley” (trough) is from the base or rest position.

The current weather map shows that there is a significant trough in the western half of the United States right now (below). This trough allows cold, polar air, which is relatively dense, to ooze into the this portion of the country. Areas under ridges are associated with warmer conditions. The meandering train of waves is often delineated in our atmosphere by the jet stream. Forecast models move the wave pattern along and into the Great Plains and Midwest such that the upper level trough and associated surface cold front will cause temperatures to plummet in the coming days.

Meanwhile in California, NBA star Lebron James recently tweeted,

Man these LA (fires) aren’t no joke. Had to emergency evacuate my house and I’ve been driving around with my family trying to get rooms. No luck so far!

Lebron James on Twitter

The Kincade fire just north of San Francisco and the Getty fire near the Los Angeles area are being fanned by near “perfect” fire weather conditions. Red flag warning have been issued for these areas. According to the California government website, “A Red Flag Warning is issued for weather events which may result in extreme fire behavior that will occur within 24 hours.” The fires, once ignited by a source (human or natural) are being fanned by Santa Ana winds, which I have explained previously in Forbes. In that piece National Weather Service meteorologist Curt Kaplan told me,

There are several factors that can generate a Santa Ana event in Southern California. The majority of our weak to moderate Santa Ana events are driven by pressure gradients (difference in pressure over a given distance). When the high pressure is to the east of the region, the winds are impacted by the terrain-induced friction. Santa Ana events tend to have cold air at higher levels, typically associated with an upper-level low-pressure system.  

NWS meteorologist Curt Kaplan

Winss from the northeast (typical of Santa Ana events) have been gusting to 20-65 mph in the region. The region is also experiencing single digit humidities, which means it is very dry, and temperatures in the upper 80s and 90s. Kaplan, on social media, said that such conditions breed “the potential for very rapid fire growth and extreme fire behavior.”

These conditions in California and the interior of the United States are very scary (and dangerous) and not because it is the Halloween season. If you live in these regions, please be aware of the risks associated with extreme fires or extreme cold, respectively.



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