The Northwest Sacrifices its Precipitation So New Orleans Can Experience Snow

This week I have been in New Orleans, attending the Annual Meeting of the American Meteorological Society.   I spent a lot of time in the sessions dealing with the meteorology of western wildfires--will share some of the interesting findings in future blogs.  I even gave a talk on western Washington/Oregon wildfires.

We are now experiencing and will continue to experience an unusually dry period on the West Coast, and that will be associated with cold and snow over the eastern U.S.  Snowflakes may fall on the Big Easy.

The reason?   A strong and persistent ridge of thigh pressure along the West Coast.  For example, below  is the forecast upper-level (500 hPa pressure, about 18,000 ft) heights for Tuesday morning.  Wow.

A high amplitude ridge (orange/red colors) from coastal CA into the Yukon, with a very intense trough of low pressure extends to the Gulf coast (blue and purple colors).  

Boy I am I glad I got out of New Orleans.  Got to feel sorry for the gaters, though.

This atmospheric pattern sets of strong northerly wind from the Arctic to the substropics.  A frigid atmospheric superhighway

Look at forecast temperature anomaly from normal for 1 PM PST Tueaday.   Unbelievable.

Some areas of the southeast will be 30F or more below normal.

Take a look at the predicted snowfall totals through next week.  Shockingly, New Orleans, southern Texas and northern Florida may see some flakes!

 

Now what about our region?  With winter ridges like this, large contrasts develop between lower elevations and aloft. It will be COLDER than normal at low elevations and WARMER than normal at higher elevations.

Why?

Because the light winds and relatively clear skies associated with a ridge/high aloft allow cold air to settle in, usually accompanied by low level stratus and fog.  Yuck.

To illustrate the low clouds, consider the visible satellite image early this afternoon around Washington State.  Lots of low clouds around Puget Sound and in the Columbia Basin.  There will be MUCH more  low clouds next week.

But warmth will be close at hand.  Just take a hike or drive into the mountains, where it could be as much as 20F warmer.  A strong inversion will be in place.

High pressure is actually associated with sinking warm air aloft.   In the summer, the media LOVE to talk about the "heat domes" produced by high pressure areas.   Heat domes are also there in winter--they are just aloft.

So ascend approximately 1500-1200 ft if you want sun and warmer conditions.

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Why the LA Wildfires Have Little to do With Long-Term Drought or Climate Change

Some climate activists and media outlets are claiming the drought or climate change were major contributors to the recent wildfires around Los Angeles (see sample below)

These claims can easily be shown to be false.

Long-term Drought had little impact on the LA fires.

Climate Change had little impact.  

Let me provide the facts below.

The Fuels

The vegetative fuels for the fires were predominantly light fuels such as grasses and range vegetation.  To illustrate, consider the area where the Palisades fire started (below).

Most of these fuels are 1-10 hr fuels, which means they typically dry out after 1-10 hours of drying conditions.   

The meteorological conditions immediately preceding the fires were so drying (very strong winds with  very low humidities) that even if it had rained the week before, the fire still would have occurred.

Consider a plot of the ten-hour fuel moisture at the nearby Topanga Canyon site over the past year (below).  Keep in mind that when the moisture level gets below 15% rapid fire spread is possible.  

Interestingly, even during every wet periods (such as the first part of 2024), fuel moisture levels return to burning-level fuel moisture between showers.

There has been a late start to the rainy season in southern CA, which normally begins around December 1.  So the normal green-up of regional vegetation, which works against fire, was delayed about a month when the fire started.   Obviously, local utilities knew this and should have considered the impacts (increasing fire threat)

But grasses and bushes were not the only thing that burned.  Once the wildfires got to the homes or burning embers reaches the homes, the homes THEMSELVES supplied the fuels.  

One house ignited the next.   

This is very similar to the situations of others major urban wildfires, such as the Camp Fire (Paradise, CA), Lahaina (Maui), and the Marshal Fire (Superior, CO).   Homes flammability has little to do with weather conditions.   But poorly constructed homes (e.g., flammable roofs, no screens to stop embers moving into home spaces) are major problems.

There is No Trend for Less Precipitation in Southern California

Several media and other outlets suggested climate change associated dry conditions was a contributor to the LA wildfires.   First,  as noted above, the light fuels that brought the fires to the homes did not need a drought period to be sufficiently dried to burn.  

But even if drought had been important, there is no evidence than climate change could have contributed.   How can I be be so sure?  Because there is no long-term trend for less precipitation over the region.

Consider the trends of October 1 to January 6 precipitation at Los Angeles from 1950 through this year (see below).  The trend line is UPWARDS (brown line).   More rain, not less.  Yes, the past autumn was dry, but that is not climate but normal weather variability.

Not convinced?    Below is the annual precipitation of the region since the late 1940s.  

No downward trend.  And the last several years have been wetter than normal, which would contribute to more bountiful vegetative growth and thus more fire potential.

The LA Fires Were Associated with Strong-Dry Santa Ana Winds.  Such winds are predicted to WEAKEN, NOT Strengthen under global warming.

The LA wildfires were associated with very strong (up to 100 mph) and dry Santa Ana winds, which were generally from the northeast.

There is an extensive peer-reviewed science literature indicating that global warming will reduce the strength, intensity, and frequency of such Santa Ana winds.

It makes complete sense that global warming would weaken the Santa Ana winds.  

Such winds are driven by difference in pressure between inland high pressure and lower pressure to the south and west.  This high pressure is associated with low-level cool air (cool air is denser and heavier than warm air), which will be warmed due to global warming, thus reducing the pressure difference that drives the Santa Ana winds.

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Very strong video and photographic evidence indicated the Los Angeles Eaton fire, which resulted in the most deaths was due to a faulty power line.  Clearly, this transmission line was not de-energized even with the forecast of severe Santa Ana winds.