Blocking Ridge, Dry Pacific Northwest, and Southern California Rain

 Not a boring time for meteorologists.  New Orleans Airport is closed with record-breaking snow and cold, while the Pacific Northwest is strangely dry and southern California will get its first decent rain of the season.

The Big Easy

All because of a highly amplified upper-level wave pattern.

The upper level (500-hPa) height map (think of this as pressure around 18,000 ft) today shows a ridge of high pressure aloft over the eastern Pacific while a trough of low pressure is found over the eastern U.S. (red indicates high pressure and blue indicates low pressure).  

Ridges/high pressure are associated with sinking air and dry conditions on their eastern sides.  Like over us.   Troughs are associated with rising air and precipitation.  Between them, cold air moves southward.

By Thursday the eastern Pacific ridge becomes crazy strong.  

Keep your sunglasses handy, as it will be sunny and dry.   What a nice break in the middle of winter for us.   But cold and wet over the eastern US.

By Saturday, something interesting...and important... will occur.   A trough will develop south of the West Coast ridge, resulting in a pattern called a Rex Block.  Very stable pattern.

Such a southern California trough will produce upward motion and precipitation.   Southern California will get wet.  Significantly wet.    

Below are the forecast precipitation totals through next Monday evening.  As much as 1.5 inches in the mountains near LA.  Significant rain over the entire coastal zone.

Such rain will moisten the light fuels and greatly reduce the fire threat until the next Santa Ana.  Very good news.

 

Finally, something else occurred today that I thought was interesting.....a very energetic Chinook wind on the western side of the Rockies around Great Falls, Montana.

Two days ago,  shallow cold air was entrenched over the lower elevations of Montana, with lows of -5 to -20F. (see below)

But with high-pressure building over the east Pacific and lower pressure inland, strong winds from the west descended into eastern Montana.  As the air descended the eastern slopes of the Rockies, warming by compression occurred.   This descending air also displaced the frigid dense air that was in place.

Today's low temperatures were MUCH warmer around Great Falls and neighboring locations near the eastern slopes of the Rockies, with highs getting into the 20s!

Check out the temperature and relative humidity observations at Great Falls during the past day (below).

Yesterday morning at 7 AM, the temperature dropped to around -9F.  By noon it was 12F and by noon today is was around 36F.   All associated with air sinking on the eastern slopes of the Rockies.  

   

The UW WRF model simulated this transition well. The forecast surface temperatures for 4 AM Monday were very cold over most of Montana on Monday (white is very, very cold air).  The winds are shown by the wind arrows.  Weak at low levels.

But by 10 PM PST Monday, the white was gone as westerly winds descended the Rockies.  Blue colors are relatively warm.

Chinook winds are also Foehn winds and are sometimes referred to as "snow easters."

The Origin of The Los Angeles Wildfires

My group and scientists from the University of Albany are now studying the meteorology of the LA wildfires earlier this month and have significant early results.  At the American Meteorological Society meeting last week, I attended many wildfire meteorology sessions and talked to several colleagues who have actively studied such events. The LA fires were a topic of considerable discussion.

We have a good idea of what happened:  an extreme/unusual Santa Ana event associated with severe downslope winds.   In this blog, I will show you some early simulations and explain why this event occurred.  

I will also describe why climate change did not play a significant role.

As I will explain below, this is not only a Santa Ana event, but an unusual one, with extreme winds descending to lower elevations.  Some lower-elevation stations, such as Burbank, experienced their strongest wind gusts on record.  Model simulations suggest the development of what is known as a high-amplitude mountain wave leading to a downslope windstorm event.

Santa Ana 101

Santa Ana's are associated with strong northeasterly (from the north to east) winds over southern California.  These strong winds are accompanied by very low relative humidity and are very favorable for southern CA wildfires.   

The typical large-scale weather pattern associated with Santa Anas includes a large high-pressure area over the Great Basin, with the strongest events also having a low center to the southwest (see below). Such a pattern results in strong northeasterly winds approaching the mountains of southern CA.

The observed sea level pressure pattern at 4 PM January 7 (below) showed many of these elements, with the low to the south being particularly strong (warm colors indicate above-normal pressure, cool colors show below-normal pressures).

This pattern produced extreme, perhaps unprecedented, northeasterly winds approaching the region in the lower atmosphere.  To illustrate,  the color shading in the map below shows wind differences from normal at 925 hPa (about 2500 ft above sea level) at 10 PM Tuesday (January 7) evening.  The light gray indicates very unusual winds (more than six standard deviations from normal).  The wind direction and speed at some points are also shown.

This was not your normal Santa Ana.

High-Resolution Simulations

To understand what happened,  UW Research Scientist David Ovens, a member of my research group, ran a very high-resolution forecast/simulation of the event using the WRF model, with a grid spacing of 1.3 km (this is very high resolution).

Let me show you a surface wind gust forecast (32 hours into the prediction) for 12 AM on Wednesday, January 8.   The areas of the Palisade and Eaton fires (the two biggest ones) are shown by red outlines.   

Extreme winds (with gusts exceeding 70 knots, 81 mph) were forecast over and downwind of the San Gabriel Mountains.  HUGE threat.    Lesser, but still strong winds (50-60 mph gusts) are noted in the Palisades area extending to the west and south.   

To understand what is going on, it is useful to plot vertical cross-sections through the fire areas to show the 3-D atmospheric structure.   Below is a cross-section (at 8 PM Tuesday) through the Eaton fire; a section that crosses the San Gabriel Mountains.  The shading shows sustained winds in knots, the x-axis is the horizontal distance and the y-axis is height in pressure (700 is about 10,000 ft)

Wow.    Very strong acceleration of the air as it descends the southern slopes of the San Gabriels, with the strongest winds near Altadena, where the fire went crazy.  This was a very powerful downslope windstorm with a highly amplified mountain wave pattern.

Another cross section, this time going through the Palisades fire at 10 AM on Wed. January 8, is shown below.   Very strong winds to the lee (south) of both the interior mountains and Santa Monica mountains to the south (left side of the figure).

These and earlier simulations by the UW WRF model and NOAA/NWS models (such as the HRRR, High Resolution Rapid Refresh) consistently forecast the extreme downslope winds DAYS in advance.

It was also clear that there were unusually large amounts of dried "fuels" ready to burn.  The fuel load was particularly high after TWO unusually wet winters (2022-2023, 2023-2024).  A dry start of winter ensured massive amounts of fuels were ready to burn. 

This was clearly a situation of extraordinary extreme wildfire danger.  That is why I blogged a strong warning the day before.  Why the National Weather Service did the same.  LA officials should have know a severe threat was in place.

All that was needed was an ignition source.  For the deadly and large Eaton Fire near Pasadena, it appears that a problematic electrical transmission tower was the origin of the fire.

For the Palisades inferno, it is either some smoldering embers from a New Year's Eve fireworks blaze or the failure of some aged powerlines found north of Skull Rock.   Perhaps, arson is another possibility.  Several fire experts I talked to at the AMS wildfire meeting thought the powerlines were the most probable cause, but a definitive evaluation is not yet available.

What is clear is that LA did not shut off the power to the region even AFTER the fire was initiated and that only limited fire-fighting resources were in place before the fires began.  Not good.

Bottom Line:   A very skillfully predicted Santa Ana event with record-breaking winds hit LA earlier this month. Two wet winters resulted in unusually high levels of dried fuels. Human ignitions initiated the fires.

Influence of Global Warming

There are several media outlets and climate activists that are suggesting that LA fires were the result of global warming or significantly enhanced by human-caused warming.  

These claims are contrary to the best science, which indicates minimal impacts of human-caused warming.  

Such claims undermine the importance of key societal failures, from not shutting off power and fire-hardening homes to not having sufficient fire-fighting capabilities or adequate warnings and evacuation protocols.

Key reasons why global warming is not an important factor include:

1.  There is no evidence that global warming increases Santa Ana winds.  In fact, there are strong physical reasons (with supporting scientific literature) that global warming WEAKENS Santa Ana winds.

2.  The available fuels were unusually abundant because the two previous years have been much wetter than normal.  There is no evidence this is caused by global warming.  And there is no long-term trend for wetter winters, which would be evident if this was a climate issue.

3.  The immediately prior months were drier than normal.  This is not predicted by global warming projections and there is no historical trend to drier early winters which would occur if climate was a cause (see plot below of Los Angeles precipitation for Oct. 1-January 6 ).

3.  There are some outrageous claims that the LA fires are the result of increasing "weather whiplash" due to climate change.  This "whiplash" theory is unsupported by observations, such as the plot shown above.

I am particularly troubled by the media pushing weather/climate theories that are untrue.  A prime example is the unsupported claim that the Lahaina fire was associated with the passage of a hurricane to the south.   This was proven to be false.

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.

,,

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.

_____________________________________________

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.

Increasing Winds Threaten Southern California

 Let me say at the onset, that the threat is nothing like last week, but strong winds today and powerful winds tomorrow are a serious problem....both in dealing with current fires and for starting new ones.

The National Weather Service is again putting out a strong message (see below),

These warnings need to be taken seriously, including shutting down the power to some areas.

Winds have accelerated today, with maximum gusts reaching 60 mph in the mountains and 40-50 mph at lower elevations around Malibu (see below)

The strong wind are generally from the northeast, a classic of Santa Ana conditions.

Looking at the winds observed at Topanga Canyon near Malibu, one can see that the winds today are strong but not the equal of January 7-8.

Now lets examine the surface wind gust forecasts from the relatively high resolution HRRR model.  Keep in mind that the orange and reds indicate serious winds (50 mph and more).

Monday morning at 8 AM, shows strong winds reaching the coastal zone around Oxnard and Ventura.  Lesser but serious winds over northern Orange County.

By 10 AM Tuesday winds will be really cooking over the mountains and the lower elevation Ventura area.  The power should have been off for the previous 12 hours and for the rest of that day.

The region of strongest winds are within the responsibility of Southern CA Edison.   I hope they are more responsible than the Los Angeles folks.  That means Public Safety Power Shutoffs (PSPSs).   Their web page worries me....

Where and how did the Palisades Fire start?

 Important Update

Video evidence now available that the Eaton Fire (second biggest fire) was caused by a failing power transmission line:

https://www.powerlineblog.com/archives/2025/01/scenes-from-the-fire-line.php

________________________

I am going to go out on a limb here.   There is strong evidence on exactly how and where the Palisade Fire started.  

We know that the fire started around 10:30 AM on Tuesday.  The GOES visible satellite image at that time is shown below and you can see the smoke plume from a single fire.

Using Google Maps we can easily identify that spot, just east of the Summit Community.  Below is a close-in shot of Summit, with the red arrow indicating roughly where the fire started started based on weather satellite smoke plume.

What do we find at the location where the fire started?   Powerlines.   Hung on wood structures.  I have several pictures of the location and the powerlines (see below)

Could these structures have handled the 80-100 mph winds that occurred on Tuesday and Wednesday?

You can see the powerlines extending down to the Summit neighborhood

Not convinced the powerlines did it?    There is other evidence.   The wonderful Ting power sensor network noted disturbances in the electrical power system in the neighborhood just prior to the fire.  

Finally, the fire initiation location does not look like an area where homeless encampments would be located. Encampments where camp fires would be found. 

The big question is why the Los Angeles power authorities did not de-energize all the power lines on the hills.