Spring Snowpack Numbers!

If you’re looking for the latest snowpack numbers for the Pacific Northwest, look no further.

In January, we reported on snowpack conditions in our region producing haves and have-nots. And while snowpack conditions have improved during February and March, this—sadly—is still a story of haves and have-nots.

In this Northwest Climate Currents, we will tell the snowpack story using tools developed by CIRC researchers, the Natural Resources Conservation Service, as well as tools found on the National Integrated Drought Information System (NIDIS) Drought Early Warming System’s (DEWS) new Snow Drought page. (See “New Snow Drought Page” in this issue of the CIRCulator.)

Washington, northern Idaho, and western Montana (the haves) are currently experiencing above normal snowpack while much of Oregon (particularly southern Oregon) is seeing below normal snowpack numbers (the have-nots). In fact, southern Oregon (as well as much of California and the southwest US) is effectively in a snow drought.

Snow droughts occur when a region receives a less-than-adequate amount of snow. This can occur when above normal temperatures force precipitation to fall as rain instead of as snow, when not enough precipitation has fallen to create an adequate amount of snow, or through a combination of warm temperatures and low precipitation levels. The latter has been the story this year. Enter Figure 1.

Figure 1:

The map on the left, taken from the Northwest Climate Toolbox run by CIRC researchers at the University of Idaho, shows total precipitation since the beginning of the water year, which started on October 1st, 2017. Notice how the total precipitation measurements split the Pacific Northwest into a wet north (see green-colored areas) and dry south (see tan-colored areas).

The map on the right shows temperatures since October 1st, 2017. Temperatures since the start of the water year have been mildly above normal (on average) over the Pacific Northwest but have shown pockets of cooler-than-normal temperatures (shown by cooler blue colors) throughout much of the region.

Now combine the two maps in your mind. The areas with warmer-than-normal temperatures (red areas) and lower-than-normal precipitation (tan areas), especially southern Oregon, have been the hardest hit in terms of this year’s snow drought. Enter Figure 2.

Figure 2.

April 1, 2018 basin-wide median snow water equivalent percent compared to historical baseline 1981–2010.

Figure 2 to the right shows April 1st snow water equivalent (SWE)—the amount of water contained in the snowpack if you were to melt it—on a basin-by-basin basis. (Here, basins are shown as 6-Digit Hydrologic Unit Codes, or HUC6’s.) The map was made using the Natural Resources Conservation Service’s interactive map tool.

Warmer colors (in the orange-to-red spectrum) depict below normal SWE numbers. While cooler colors (in the green-to-blue spectrum) depict above normal SWE numbers. The SWE conditions are taken from SNOTEL, or Snow Telemetry, data from the network of over 700 automated snowpack-monitoring sites across the American West.

As you can see from this graph, much of southern Oregon and Idaho are covered in warmer colors, meaning they are currently experiencing lower-than-normal SWE levels—these are the have-nots—whereas much of Washington, northern Idaho, and western Montana are covered in cooler colors—these are the haves.

We’re looking at these numbers now, in the second week of April, because, generally speaking, April 1st marks the point of maximum snowpack accumulation for much of the Western US.

April 1st also marks the turning point after which snowpack begins to melt. Although the exact date of peak snowpack may occur earlier or later than this—depending on factors, such as location, elevation, and year-to-year variability—streamflow forecasts using SWE numbers on April 1st have long been used for predicting summer streamflow. So much so that April 1st snowpack numbers act as a kind of bellwether for summer water supplies.

Years with low April 1st snowpack tend to be followed by low flows in rivers and streams during the summers that follow. This can sometimes lead to or exacerbate water scarcities, especially in snowmelt-dominated basins.

Now let’s look again at SWE using the UW Drought Monitoring System for the Pacific Northwest run by CIRC’s own Bart Nijssen at the University of Washington. Enter Figure 3.

Figure 3:

Percentiles of snow water equivalent (SWE)for the calendar date April 1, 2018. (Image Credit: The UW Drought Monitoring System for the Pacific Northwest.)

The map on the left shows percentiles of April 1st SWE calculated using a hydrologic model. The warmer colors denote places with exceptionally low snowpack. Cooler colors denote places with exceptionally high snowpack. You’ll notice that most of the low snowpack areas are in southern and eastern Oregon and southern Idaho, especially at the lower elevations.

So, this is again a story of haves and have-nots. However, before you start to think that we are painting an especially dire picture for the have-nots, let’s use our data to travel back in time to the snow drought of 2015.

During the 2015 snow drought, precipitation levels across the Pacific Northwest were at near normal levels. Temperatures, however, were far above normal.

In fact, 2015 was the warmest year on record for both Oregon and Washington, according to NOAA. This meant that much of the precipitation that fell during the cool months did so as rain instead of as snow. As a result, in 2015 record low April 1st snowpack measurements were set at 80% of SNOTEL sites across the American West. Here in the Pacific Northwest, 2015’s April 1st snowpack was the lowest on record for Oregon—89% below normal—and tied for the lowest on record for Washington.

(See, “Snowpack & Drought—Climate Impacts CIRC 1.0 Final Report,” “Record Low Snowpack,” “Revisiting the 2015 Snow Drought,” and “Mountain Snow Declines Past and Future.”)

So, how does the 2018 snow drought compare with the 2015 snow drought? Enter Figure 4.

Figure 4:

In 2015, basin-average snowpack conditions for April 1st were well below normal (3–58% of normal) across the Pacific Northwest region. Averaged over the region, April 1st SWE in 2015 was 37% of normal. This year, April 1st snowpack averaged across the Pacific Northwest region is 100% of normal, or just plain normal. However, averaging over the entire region washes out the contrast between abundant snow in the northern basins of the region and snow deficits in the southern basins.

The haves, in other words, hide the have-nots. However, the have-nots are not and should not be ignored.

In March, Oregon’s governor issued a drought declaration for Oregon’s southern Klamath County. Others may follow. What’s more, spring and summer streamflows are projected to be well below normal for much of Oregon, according to the Natural Resources Conservation Service. Luckily, most of the state’s irrigation reservoirs are in good shape, which may buffer some of the impacts for those with access to water. That said, water users without access to reservoir water are likely to experience water shortages this summer, particularly water users in southern and eastern Oregon.

We’ll keep monitoring the climate impacts. Stay tuned.

OSU_icon_gears_Black Resources:

At OCCRI since 2011, Meghan Dalton is a trained climate researcher with a BA in Mathematics from Linfield College and an MS in Atmospheric Science from Oregon State University. Meghan has worked closely with several Northwest communities working on Community Adaptation, including the water provider Seattle Public Utilities on the PUMA project. Meghan has worked as the lead on several regional climate assessments, including “Climate Change in the Northwest: Implications for Our Landscapes, Waters, and Communities” and “The Third Oregon Climate Assessment Report.”

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