Microclimates

One recent Sunday morning, Sandy Burnett looked out the window of her Rathdrum, Idaho, home and saw 2 feet of fresh snow and wondered if she’d be able to get out of her driveway to visit her friends in Spokane.

Her friends live on Spokane’s South Hill, where just a skiff of new snow had fallen overnight.

Anyone who has lived in the Inland Northwest for any amount of time has encountered these general regional weather variations, which are driven largely by topography, proximity to mountains and other big-picture geographical factors.

But there are other smaller-scale influences that result in weather variations within smaller geographic areas, like within Spokane itself – between the North and South sides of the city, between Spokane Valley and the West Plains.

Bob Quinn, professor of geography at Eastern Washington University, has made a lifetime study of the region’s weather and has been teaching all facets of meteorology at Eastern since 1967.

“If you want to know why, in a given snowstorm, you got 2 inches of snow at your house, and a half-mile away there’s just 1 inch, those are just the vagaries of the weather gods in the sky,” Quinn said. “But if you want to know why it’s generally cooler at night on the floor of the Spokane Valley than in Green Bluff or why it’s usually warmer on the Moran Prairie than on the slopes of the South Hill, there are microclimate patterns that clearly explain that.”

Generally (big picture), the higher the elevation, the colder the temperature, and the closer to the mountains, the more precipitation you get, Quinn said. Witness the latter fact with about 8 inches of annual precipitation at Moses Lake, 10 inches at Ritzville, 14 inches at Sprague, 17 inches at the Spokane airport, 25 inches at Coeur d’Alene and 35 inches in the Kellogg-Wallace area.

“Drier in the Columbia Basin, wetter going toward the Rockies,” Quinn said.

Clouds are formed by the vertical motion of air currents. There’s nothing like bumping into a mountain to force air upward, Quinn observed.

Yet within that generalization are the effects of valleys and ridges to skew the pattern.

This meso (moderate) scale effect can be seen in the airflow heading east through Spokane Valley getting squeezed or funneled by Mount Spokane on the north and Mica Peak and Browne’s Mountain to the south – what Quinn terms a slop-over effect – increasing rain and snowfall on the margins.

Similarly, the southwest-to-northeast air currents from Cheney to Four Lakes are compressed between the steptoes – the bare-hill ancestral remnants of the Rockies (like Prosser Hill, Needham Hill and Wrights Hill) – that create enough vertical motion for what Four Lakes residents know well as their narrow rain/snow belt corridor.

“It just dumps there,” Quinn said, “while at my house, a patch of paradise in the Cheney scablands, it’s so much drier. There’s no official weather station at Four Lakes, but my observations over the years show about 3 inches more precipitation there than in Cheney.”

Smaller still are the microclimate patterns that work neighborhood to neighborhood.

Spokane’s South Hill has a generally north-facing slope. Because it isn’t exposed to the midday sun as are south-facing slopes, it doesn’t dry out as fast or warm up as much.

Conversely, Spokane’s North Side, especially on the slope heading up from downtown toward Wellesley Avenue, faces toward the south and is benefited by the warming and drying sun.

These examples are reflected by vegetation differences, Quinn observes.

Because it’s cooler and moister on the South Hill, it’s more hospitable to the growth of native ponderosa pines which, in turn, grow large and intercept more of the sunlight, keeping the area cooler than the more exposed south facing slopes of the drier and warmer North Side.

The same effect is noticeable in Spokane Valley, on the north side above Trent Avenue, where the hillside has a southerly orientation and the sun exposure will make it hotter in the summer than the exact mirror location on the south side of Spokane Valley.

Cooler air settles in lower places, so valley bottoms are generally cooler at night, Quinn said.

“There can be a 5- to- 15-degree temperature difference between the bottom of a valley and 50 feet up an adjacent hill,” he observed. “That’s why all the orchards are up on Green Bluff, up on in the south-facing hills, where it stays warmer at night and provides for a longer growing season.”

Another microclimate effect at work is at the top of the South Hill, where South Regal Street reaches out to Moran Prairie and the topography flattens out.

“This exposes the ground to more direct sunlight, so it will be a bit warmer than on the slopes of the South Hill, where the ponderosa pines thrive and prosper,” Quinn said. “But in the winter, the air currents lifted by Tower Mountain will produce probably 20 inches more snow on the Moran Prairie than on the flat portions of Spokane Valley.”

Downtown Spokane has its own special microclimate pattern.

“Cities are general urban heat islands,” Quinn said, “with temperatures usually running 2 to 5 degrees warmer during the day than surrounding areas at the same elevation, but the real differences are noticeable at night. Urban areas just don’t cool off well.”

Solar energy works to evaporate moisture from the soil, Quinn explained, but there really is no soil to speak of in a downtown area, so instead of providing evaporation or cooling, that energy heats the concrete instead. At night, he said, the vertical forest (tall concrete buildings) emits infrared radiation from the side surfaces.

While some of it escapes into the atmosphere, most of it re-radiates to buildings nearby – the end result being an infrared radiation trap between buildings, which slows down the rate at which cities can cool down.

Weather differences moving north out of the central Spokane area are largely influenced by elevation changes, Quinn observed.

The general elevation of the urban areas on the North Side is not much higher, but those areas are surrounded by higher hills to the west, to the north and Mount Spokane to the east. This, Quinn said, results in more lifting of air and a higher snowfall.

Anyone living in the Wandermere area, Deer Park or the Indian Trail area can speak to the increase in snowfall.

In addition, the microclimate effect of rivers, streams, ponds and lakes helps create a moister and more temperate environment than in adjacent locations, Quinn said.

“Those who live by a river or lake experience less frost and slightly cooler days than those in the drier areas away from the water.”

As for Sandy Burnett, being on flat land snuggled up against Rathdrum Mountain, she is doomed or blessed, depending on point of view, to snowier winters than her South Hill friends. That’s just a climatological fact of life.