Cliff Mass Weather and Climate Blog

New Podcast: Why is November the Stormiest Period of the Year and the Forecast for Next Week

Believe it or Not!

On average, we are now past the worst weather of the winter! Shocking but true. And in the second segment of my podcast, I tell you why.

Take a look at the daily probability of experiencing .25 inches or more in Seattle (below). Mid to late November is the time of the year when you have best chance to "enjoy" such a wet day and the probabilities actually drop in December and November.

What about a plot of daily extreme rainfall in Seattle? November has the most with December being relatively more benign (below).

There is a reason for this situation and it has to do with the strength and position of the jet stream. Check my podcast to find out.

And the podcast also includes the forecast for this week, which will include unusually dry, sunny conditions and powerful easterly flow on the western side of the Cascades.

An Extraordinary Front And The Thanksgiving Day Forecast

I received a half-dozen emails yesterday about a very odd feature apparent on the National Weather Service radar at Hoquium. Let me just show you!

Here is the lowest elevation radar image at 1:30 PM yesterday (Wednesday). Red indicates very, very heavy rain, with yellow and orange just plain heavy. What a bizarre looking feature crossing the coast, with undulations and regular gaps between heavy precipitation segments!

We learned about this features during the 1970s when the first radars were placed on the coast during some weather field experiments.

The feature in question is a narrow cold front rainband, associated with an unusually strong cold front crossing the coast.

Impressively, our high resolution forecast models were able to predict this strong front, as illustrated by the predicted surface winds, sea level pressure, and temperatures around 800 m above the surface at 1 PM (see below). A very strong pressure trough (area of low pressure) is evident as is a very sharp wind shift from southwesterly to northwesterly flow and a decline in temperature. A front you can not ignore.

What I really couldn't believe is that a simulated radar image from the forecast model actually produced a realistic corrugated narrow cold frontal rainband just like the one observed by the radar. We have come a long way.

Sharp fronts like this one can produce severe low-level turbulence. During an atmospheric field program called COAST, a bunch of atmospheric scientists flew through such a front at low-levels (~2000 ft). The plane experienced several g's up and down and the interior of the aircraft was left in disarray. The pilots made it clear---never again.

But you won't to worry about such a front on Thanksgiving Day!

Tomorrow, an upper level ridge of high pressure/heights will develop over the region--and such features produce sinking air and dry conditions (see upper level map--500 hPa, roughly at 18,000 ft--at 1 PM Thursday)

The total precipitation for the 24h ending 4 AM Friday shows nothing over Seattle and

eastern Washington and only a passing sprinkle for the rest.

Plenty of clouds on Thursday, with some passing sun breaks. Highs in the upper 40s.

Good enough to get a nice walk or run before enjoying your holiday meal.

An Important Finding about the September Labor Day Wildfires

One reason why research is so much fun is that once in a while you learn something important that is unexpected. A new and highly significant finding.

I had such a "wow" experience recently regarding the September wildfires that caused so much damage and smoke on the western slopes of the Cascades.

Currently, I have a research grant form the National Science Foundation, and smaller grants with the USDA Forest Service and WA DNR, to work on wildfire/weather issues. Recently, our group has completed three papers on the intersection of weather/climate with wildfires: on the Wine Country Fires of 2017, the Camp Fire of 2019, and Diablo downslope winds of northern CA.

I was working on a paper on the meteorology of the great western Oregon/Washington wildfires, when the big Labor Day Oregon wildfire siege occurred. So naturally my group turned to understand the event.

Why did this major event happen? How did it evolve? Was something unusual going on? How well was it forecast? These and other questions were on the table.

We knew the strong easterly (from the east) winds during the event were critical for initiating and/or spreading the fires. In fact, my initial work suggested that ALL major fires on the western slopes of the Oregon and Washington Cascades are associated with powerful easterly winds.

I asked research meteorologist David Ovens to take a look at the upper air weather observing sites in the region, locations where balloon-lifted weather stations (radiosondes) are launched twice a day to give us winds and other weather variables aloft.

Of particular interest was the Salem, Oregon radiosonde data at the first standard elevation above the surface (925 hPa--around 800 meters above the surface). This elevation is very relevant to winds observed over the nearby western slopes of the Oregon Cascades.

The record at Salem goes back 64 years to 1956, long enough to tell us a great deal about how unusual the situation was this September. It did not take Dave long to send me a figure with the requested information and I had my wow moment.

Below is the figure. Let me explain it.

I asked him to only plot the 925 hPa (again about 800 m about sea level) winds and to limit the analysis to August and September, since those are the months of historical big fires on the western slopes of the Cascades. Each observation during the 64 years during those months was plotted, with the associated wind direction indicated by the x-axis and the wind speed on the y-axis.

You will notice two major peaks in strong winds during those late summer months: (1) northerly to north-northeasterly and (2) south to southwesterly. The northerly wind peak occurs when high pressure builds over the eastern Pacific and the southwesterly powerful winds occur when a strong trough or low-pressure system approaches the coast. The southwesterly winds are the strongest (up to 51 knots!), but they are associated with clouds and rain, so little fire danger from them.

I asked Dave to identify the observations taken during the Oregon fire storm period with red dots--- and that is when the wow moment came.

Look at the red dot for September 8th at 1200 UTC--5 AM (2020-09-08 12z)---just when the fires were accelerating over western Oregon (indicated by red arrow).

Just extraordinary. The winds at that time were THE STRONGEST EVER OBSERVED at the site during those months for any wind direction from the north, east, southeast, or northwest.

The stronger the winds the greater the potential for rapid fire growth, and the greater the potential for fire ignition by failing electrical infrastructure and other causes.

Importantly, these were the strongest winds by far from the east and thus downslope on the western slopes of the Oregon Cascades. Downslope winds from the east are inevitably very dry and the air progressively became drier the longer they blow from that direction.

So why were the easterly winds so strong?

Our research identified the reason: unusually cold air and accompanying high pressure moving to the east of the Cascades.

The pressure analysis 5 AM Sept 8th is shown below, with a measure of the difference from normal shown by colors. High pressure was centered over Idaho and extended into eastern Oregon. The colors indicate the pressure was VERY unusual--up to 4-5 standard deviations from the mean for that date. To give you an idea of how unusual, if the deviation was 4.5, this would indicte an event that would occur once in 147,000 times.

The air was so cold that it brought record cold and snow to the Front Range of Colorado and environs.

So the whole situation is ironic and interesting: record cold to the east brought record fires to the west.

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California Wildfires: Is Global Warming Producing a New Normal? Part 1: Are CA Wildfires Becoming More Frequent?

With major fires burning in California, the media is abuzz with stories suggesting or stating that global warming is the key driver of these big burns. Some media reports state that the number of California fires and the annual burn area are increasing and that global warming is the cause. California's Governor Jerry Brown is absolutely explicit about the climate-wildfire connection, claiming that global warming is creating a "new normal" of increased wildfires and that the population will have to get used to it.

Are these claims really true? What does actually fire data show? The truth may surprise many.

In this blog, we will consider whether the number of fires and the acreage burned in California have increased dramatically during recent years.

If this is true, we can discuss why--- it could be climate change, mismanagement of forests, change in fire suppression policy, increased human ignition of fires, people living in places they had not before, invasive flammable species, are some possibilities.

If there is no trend in wildfires, we can examine why.

Let us first consider the wildfire statistics by CALFIRE, the official group in the State of California responsible for the numbers, which suggests a very different story provided by the media and many politicians. The numbers I will show include the entire state.

CALFIRES statisitics show that the numbers of California wildfires over the past 30 years has declined--dropping roughly in half.

For the same 30 years (1987-2016), wildfire area has grown slightly, with huge transient peaks and troughs (see below). With such variability, I suspect the trend would not be significant. Final statistics for 2017 are not yet available on the CALFIRE website.

A longer-period (one century) view of wildfire frequency and area in California is found in a nice paper by Keeley and Syphard in the International Journal of Wildfire Science: “Different historical fire–climate patterns in California”. They break down the fires in two blocks: (1) areas managed by the US Forest Service (USFS) and (2) the State of California (CAL FIRE). Their results (see below) suggest a maximum number of fires in the 1970s, followed by a substantial decline during the past decades.

Repeat: less fires recently.

“Different historical fire–climate patterns in California” by Jon E. Keeley and Alexandra D. Syphard.

They also examined the areas burned during the last century. For the US Forest Service areas (mainly the higher elevation regions) that encompass the northern part of the CA (where the big fires are burning now), the acreage was as large or larger at the beginning of the 20th century as now (see below), with a minimum around 1960. For the southern part of the state, the highest values are during the past few decades, with a secondary maximum early in the 20th century.

In contrast, for the Cal Fire areas, which encompasses lower elevations with greater overlap with human populations, the largest areas burned occurred in the early part of the 20th century. The only exception to this pattern is the south coast, where there is little trend.

The bottom line of the real fire data produced by the State of California and in the peer-reviewed literature is clear: there has been no upward trend in the number of wildfires in California during the past decades. In fact, the frequency of fires has declined.

And in most of the state, there has not been an increasing trend in area burned during the past several decades.

Yes....this and last year had some big fires, but a few years does not make a trend.

So there is a lot misinformation going around in the media, some environmental advocacy groups, and some politicians. The story can't be a simply that warming is increasing the numbers of wildfires in California because the number of fires is declining. And area burned has not been increasing either.

But now we get into the real interesting questions that many are not considering. What is driving the ups and downs in wildfires? There are so many factors that must be considered, such as:

1. The fact that extensive fires are a natural historical part of the ecology of the region
2. The impacts of a huge increase of human population, creating increasing vulnerability while humans are starting most of the fires.
3. Climate change that causes warming and changing the precipitation patterns (both wetter and drier) that influence fire frequency and size.
4. Mismanagement of our forests and wild areas, allowing tree and debris-choked landscapes
5. Invasive and often highly flammable non-native species brought in by man (e.g., cheatgrass and Eucalyptus)

Clearly, climate change is only one possible factor in controlling fire frequency and may not be the most important.

More in future blogs.

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Major Change in Northwest Weather: Rain Moves in, Smoke Moves Out

A strong upper level trough will move inland over the region tonight and tomorrow morning bringing cooling weather, clouds, some precipitation, and the removable of the smoke layer aloft.

To start, here are the upper-level (500-hPa, about 18,000 ft) charts for the next few days.

This morning (5 AM) shows a big ridge over the western U.S., but a strong closed low/trough offshore.

Tomorrow morning at 5 AM, the trough/low is moving into our coast.

The trough moves through on Saturday and then moves northeastward into Canada on Sunday (11 PM Sunday is shown below)

The initial approach of the trough is associated with enhanced southerly flow that brought up smoke from California, but as it passes, the winds will turn more westerly, driving the smoke to the east. This progression is shown by the HRRR-SMOKE model output. This morning at 10 AM, there was fairly dense smoke aloft (see figure), but far less at the surface.

But by 2 AM, western Washington is clear, as the densest smoke moves over eastern WA and Idaho.

Precipitation should start moving in by 5 AM, illustrated by the UW WRF model precipitation for the 3-h period ending that time.

Heavier rain is predicted during the subsequent three hours, particularly along the coast, the Olympics, and SW Washington.

The showers move to the Cascades during the afternoon.

And continue while slowly declining during Saturday evening.

Seattle will not got a lot from this event and we do expect some embedded thunderstorms. Sunday should be dry and warmer (around 80F).

Finally, it is interesting to look back at the temperatures at Seattle Tacoma Airport during the last 12 weeks compared to the normal highs (purple) and normal lows (cyan). We have had a series of heat waves during the past two months, with some intervening cool periods.

Clearly, this summer was warmer than normal, something shown graphically with the following map of the temperature differences from normal over the past 60 days. Western WA has been 1-3F above normal, with California being even warmer (perhaps 3-4F above normal for the period).

Dense Canadian Smoke Veil Moves Southward over Washington State

There are many Canadian imports we value, such as maple syrup and wood products, but one we would rather do without: smoke from major wildfires in British Columbia. And a major push southward of Canadian smoke is occurring as I write this.

The smoke was obvious in the MODIS satellite image around noon, with low clouds beneath the smoke, west of the Cascade crest.

Most of these clouds subsequently burned off, with lots of smoke still aloft (see picture for the GOES satellite around 4 PM)

The smoke was quite dense but was mainly aloft, leaving air quality decent near the surface. But the sky is very hazy and the sun has that weakened yellow/red look to it. For example, the latest image from the Seattle PanoCam shows the smoke clearly.

And those hiking at Sunrise on Mt. Rainier did not see blue skies.

Yesterday in contrast had very, very clear skies. What happened?

The passage of an upper level low and trough.

Prior to the low passage, there was lots of Canadian smoke aloft, since southerly flow precedes the upper level low (see my previous blog). As the low passed yesterday, the winds aloft first were first southwesterly/westerly, bringing in clean air from off the Pacific). But as the low passed by, the winds became northerly aloft which moved smoke from fires in BC southward (see upper level, 500 hPa, about 18,000 ft, map at 5 AM Sunday, winds are shown by the wind barbs)

And the upper level map for tomorrow morning (11 AM Monday) shows that the northerly flow is not over.

As many of you know by now, I am a great enthusiast for the wonderful experimental HRRR-SMOKE model run by NOAA ESRL. Here is the vertical total of smoke amount for 2 PM Sunday from HRRR-Smoke. Red is very smoky. You can see lots of smoke moving southward into NW Washington, with cleaner air over northern Oregon. The California smoke wa heading to the east and then northeast, missing us.

By 9 AM Monday, substantial smoke is over all of WA state and CA smoke is moving northward again into Oregon.

And by late Monday evening, the two smoke sources combine, producing substantial haze over the entire Northwest.

And now the bad news: the winds over the Cascades will become easterly tomorrow and eastern WA smoke will push westward over the Cascades, with smoke pushing down to the surface (see surface smoke forecast for tomorrow at 7PM). Our decent air quality may be over---so if you are vulnerable, take the appropriate precautions.

The Great Irony: Cooler Weather in the West Means More Wildfires in the East

It always seems a great irony to me. During the mid to late summer when western Washington cools down, wildfires explode over the eastern slopes of the Cascades.

But it all makes sense and is explained by lightning and winds.

By the time we get to mid-summer (after approximately July 15th), many of the "fuels" along eastern slopes of the Cascades (e.g., dry grasses, bushes, logging slash, dead trees) are dry enough to burn.

To get a fire, first one need an igniter. Humans start some fires: from fireworks, practice shooting, cars, cook fires, failing electrical systems, thrown cigarettes, and even arson. These fires tend to be in relatively accessible locations (e.g., roadsides) that can be controlled quickly.

Lightning fires are the other major source of ignition in our region and these fires are often in inaccessible locations and often in larger timber.

This week there was lightning over Washington and southern BC, just as western Washington went through a cool down period.

For example, the 24 hr ending 1 AM August 27th.

More range on the 28th.

Lots over the Cascades for the 29th.

And substantial amounts of southern BC for the 24 hours ending 1 AM on August 1.

The lightning resulted from the passage of an upper level trough (see map for 500 hPa on July 28th at 8 AM) that produced upward motion and unstable conditions over us.

This trough produced some cooling and the lightning initiated some fires. Then another trough moved in yesterday (see below) and resulted in a deepening marine layer, with the enhanced layer of cool air associated with high pressure over the western portion of the state and a larger pressure difference (gradient) across the State. Winds accelerated in gaps in the Cascades, the Cascade crest and the lee slopes on the eastern side.

To illustrate here are the max winds yesterday across WA state. Light winds over the west (gusts to 10-15 mph), but lots of 30-40 mph on the eastern side of the mountains, with some getting to 50 mph!

Max temperatures were way cool yesterday over the western half of Washington, but still toasty (90sF) over the east (see below). Relative humidities remained low over eastern WA as well.

So troughs brought lightning initiation of fires and then produced strong, gusty winds that stoked and drove the fires during the last few days.

How many fires now? Here is the latest map from the NW Wildfire Interagency Coordination Center. Several of the ones along the eastern slopes of the Cascades are the lightning/wind fires.

As the west warms during the weekend, the winds should weaken and the only lightning expected will be with some weak thunderstorms over the Cascade crest.
So conditions will be generally favorable for controlling the current fires and hopefully not initiating new ones.

It is essential for humans not to initiate fires in this period when lightning will be subdued.