Following a record-breaking wet winter, one of the coldest some parts of the Northwest have experienced in over two decades, many were looking forward to the warm and dry summer months. This summer delivered and then some.
The Northwest, British Columbia, and California experienced an exceptionally warm and surprisingly dry summer, helping create an especially busy and unexpectedly destructive fire season.
So how warm, dry, and fiery was the summer of 2017 for the Northwest? We give you the numbers in this Northwest Climate Currents.
Let’s start with a definition of summer.
Climatologists define summer as June through August, even though for most of the Northwest—that’s Oregon, Washington, Idaho, and western Montana—the first weeks of June can be gloomy and wet and the first weeks of September sunny and dry. So, let’s provide a Northwest-specific definition of summer. Let’s consider summer to be the 90-day period from June 21st to September 18th. This year during this period we are calling summer, a number of long-term records for heat were broken.
This summer, temperatures across a large portion of the Northwest have been the highest (or near highest) experienced in at least the last four decades.
Spokane set a record for the number of consecutive days where the daily high temperature was at least 90 degrees Fahrenheit. A total of 15 days in a row, from July 28th to August 11th, exceeded 90 degrees Fahrenheit, beating out the earlier record of 14 days in a row set in 1894. Salem, Oregon had 32 days above 90 degrees Fahrenheit this summer, over twice as many days as during a typical summer.
Now let’s see how these high temperatures played out on the regional map. To do that, we’ll use the Climate Mapper, a free online tool created by CIRC researchers, myself included, for The Northwest Climate Toolbox.
With the Climate Mapper we can examine raw data, anomalies, and percentiles for several meteorological variables and time periods and in so doing get a feel for how warm the summer of 2017 actually was. Check out the map below to get a sense of what this looks like.
Okay, let’s unpack this image.
What you’re seeing are this summer’s temperature measurements being compared to summer temperature measurements for the years 1979–2015. What’s happening here is a kind of sorting and ranking that allows us to contextualize how this summer compares to the summers of the recent past.
The Climate Mapper ranks and sorts by percentiles. Percentiles—you’ll no doubt remember from your college entrance examines—comprise a system, wherein the lowest value on record is 0 percentile and the highest is the 100th percentile. We’ve also colored coded this ranking to make it easier on the eyes.
Look for the multi-colored vertical bar on the right hand side of the map. This represents the percentile rankings of temperature. The blues here make up the lower percentiles and hence lower temperatures. The reds make up the higher percentiles and higher temperatures. The middle-of-the-road temperatures, what we might call “normal,” are represented by numbers hovering around the center of the distribution between the 33rd to 67th percentiles. They show up as the washed out colors at the center of the bar.
The map—as you probably noticed—is mostly red and orange. There’s not a lot of cool or neutral colors. That’s because nearly 85% of the Northwest had temperatures this past summer above the 90th percentile, according to the Climate Mapper. And while being in such a high percentile is ideal for getting into a good school, it’s not what you want when it comes to temperature. In other words, things were very hot! What’s more, they were also very dry.
The exceptional warmth across our region was accompanied this summer by well-below-normal precipitation. Now keep in mind, summers are typically the dry season here in the Northwest. Nonetheless, this summer saw some notable precipitation shortfalls. Let’s consider readings from just three cities.
Missoula, Montana saw 46 days (June 28th to August 12th) without measurable precipitation. (Here measureable is defined as at least 0.01 inches.) For Seattle, Washington it was 55 consecutive days (June 18th to August 11th). While Spokane, Washington beat them all with 80 consecutive days (June 29th to September 16th) without measurable precipitation.
These warm and dry conditions allowed much of the Northwest to slip back into shades of drought this summer after being drought free this past spring.
Now let’s consider just one key drought indicator: evapotranspiration from vegetation.
Evapotranspiration is essentially the water demand used by plants as it relates to temperature, humidity, winds, and solar radiation. Plant water demand tends to rise on warm, dry, and sunny days.
The Climate Mapper provides what’s called reference evapotranspiration, or the water demand expected from a given crop given how warm and/or dry it happens to be. The evapotranspiration is considered a reference because the mapper does not measure actual in-the-field evapotranspiration. Instead it tracks hypothetical evapotranspiration based on a reference grass crop, like your lawn. Not surprisingly, percentiles of reference evapotranspiration tracked over the summer by the Climate Mapper show exceptionally high atmospheric water demand accompanying the warm and dry conditions.
Undoubtedly, however, the most dramatic climate impact this summer was fire. Precipitation shortfalls and high temperatures helped exacerbate vegetation stress in our forests, fueling this summer’s unexpected and explosive fire season.
Wildfires in the Northwest combined with fires burning in both Northern California and British Columbia, leading to poor air quality for many cities and towns throughout the summer. The fire season, as we noted in an earlier blog, was fueled in part by the very wet winter, which along with high summer temps led to a bumper crop of flammable vegetation. However, while this year’s fire season in the Northwest was well above recent averages, it was not record breaking in terms of fire extent.
As of this writing on Friday, September 22nd, many of the wildfires burning across the Northwest have been put to bed by the much-appreciated return of the autumn rains and our courageous firefighters. As for clues to how the Northwest will fare this fall and winter, we can look to the ocean.
Climatologists like to dip their toes, so to speak, into the tropical Pacific Ocean to get a sense of climate outlooks heading into the winter. The tropical Pacific is where the origins of the El Niño-Southern Oscillation (ENSO) manifest.
ENSO is the periodic departure from normal ocean temperatures in the Pacific that includes both El Niño and La Niña events. Here in the Northwest, El Niño events tend to mean warmer and drier than normal winters while La Niña events tend to mean cooler and wetter than normal winters.
The National Oceanic and Atmospheric Administration’s Climate Prediction Center recently announced the potential development of La Niña conditions this year, as indicated by cooler than normal waters in the tropical Pacific.
Depending on your predilection for snow, a La Niña can either mean snow shoveling hell or snowboarding heaven. Our region often experiences colder and wetter winters during La Niña events. And that often means lots of snow.
Many of the seasonal climate forecast models are suggesting a wetter-than-average fall and winter for the Northwest, as is typical of La Niña conditions. However, we will have to wait another month or two to see how conditions materialize in the tropics. So, don’t pull out those shovels or boards just yet.
We’ll keep you posted in the next Northwest Climate Currents. Until then, enjoy the rains. After this summer, you’ve earned it.
Northwest Climate Currents uses the Northwest Climate Toolbox as well as other publically funded science resources to help track, unpack, and prepare for climate events in the Northwest.
The Northwest Climate Toolbox is suite of free online applications designed by CIRC researchers and intended to help foresters, farmers, and water managers respond to and prepare for climate variability and change and its impacts. Toolbox takes in raw climatological, meteorological, and hydrological information, translating them into a series of easy-to-navigate tools and interactive maps that allow users to plug in their location and visualize data for that location.
The Northwest Climate Toolbox currently has ten tools, or applications, designed around a set of climate metrics, such as temperature and precipitation. These metrics are then translated into visualizations that play out in near real time—we update these data daily—so that the information is timely and as useful as possible.
Tools in the Northwest Climate Toolbox include visualizations of short-term, seasonal forecasts (on the order of months); visualizations of historical data (going back decades); and long-term, future projections (on the order of decades to the year 2100). Still more tools track wildfire danger and how plant growing zones are expected to shift as the climate warms.
Acknowledgements: The Northwest Climate Toolbox is funded in part through the NOAA Regional Integrated Sciences and Assessments (RISA) program and National Integrated Drought Information System (NIDIS).
John Abatzoglou has been a CIRC team member since 2010. A climate and meteorology researcher at the University of Idaho and self-described “weather weenie,” John leads CIRC’s Northwest Climate Toolbox effort. He has participated in the creation of several CIRC-related Climate Tools, including Climate Engine and Integrated Scenarios. More Posts by this Author.
ResearchGate: John T. Abatzoglou