It’s been a beautifully boring couple of weeks in the Pacific Northwest. Boring in the sense that there has been NO active weather since the first weekend of November. Beautiful in that we have seen tons of sunshine ever since then, with seasonably cool days and cold, crisp nights. As of November 18, PDX is running 4.0 degrees colder than normal, and most of the cold departures have occurred since the 7th of the month (the last day with measurable rainfall). There’s nothing unusual about cool departures during November dry spells. The long nights and weak sun allow chilly air to linger in the lowlands, even if the upper-level pattern is warm and ridgy. In this regard, November behaves very differently than September or October do – and it’s not much of a stretch to think of November as an “early winter month” in our climate. Normal daytime temps are cooler in November than they are in March, and it’s easier to get low-elevation snow in the Gorge and the eastern lowlands as well.

These temperature inversions also explain why winter-like east wind begins to develop in November whenever we have a ridge overhead: cool and dense air begins to pool in the Columbia Basin to our east, resulting in prolonged episodes of high surface pressure over there. The high pressure then pushes the chilly air through the Columbia River Gorge and into NW Oregon & SW Washington. Last week we saw gusts as high as 94 mph at Crown Point Vista House east of Corbett!

Last week from Sunday through Tuesday morning, I visited Bend, Oregon for the second time this year. I absolutely love the charm of that area, both for its natural beauty and its thriving modern culture. But the weather is another attraction of Central Oregon’s high desert. The region is one of the sunniest areas in the greater Pacific Northwest, at least for places with an appreciable human population. (To be sure, the southeast corner of Oregon is slightly sunnier still, but almost nobody lives there!) It is even sunnier than The Dalles or the Columbia Basin, though last Monday was a cold and foggy exception to the rule. And best of all, it doesn’t have the miserably hot days and stuffy warm nights that plague lower eastside elevations in the summertime.

You might think that cities like Redmond, Bend and Sunriver would be numbingly cold and buried in snow for half of the year. After all, they are between 3,000 and 4,000 feet in elevation, and are east of the Cascade Mountains where there is far less marine influence. But the reality is far more nuanced than that!

CLIMATE DATA

Before looking at the data for the high-desert cities of Central Oregon, let’s review the data for The Dalles – or rather, the airport across the river in Dallesport.  It lies at 213′ elevation, and is the best low-elevation proxy for the region that we have.  (All charts below are from NWS Pendleton NOWDATA, www.weather.gov/wrh/climate?wfo=pqr)

DALLESPORT (213′ elevation)

Normal high temperatures range from the low 40s in December/January, to the upper 80s for July and August.  It has a classic four-season temperature regime, with very warm to hot conditions in the summer and cold enough in the winter for periods of snow most years.  The precip regime is mostly semiarid, but has a distinctly “Mediterranean” pattern of dry summers and moderately damp winters.

Next, let’s look at Bend, Oregon.  It lies at about 3,600′ above sea level:

Bend is actually slightly drier than The Dalles.  It still has a dry summer/wet winter pattern, but not quite as clearly defined.  There is actually a second ‘wet season’ centered around the month of May, though it is very subtle.  This is likely due to more thunderstorm activity during the spring and summer months (better storm chasing opportunities!).  

As for temperature, the nights are definitely much colder across all months, and the frost-free gardening season is very short (3-4 months as opposed to 6 1/2).  Days are also cooler than The Dalles in spring, summer and early fall.  But look closely at the normal high temps in December and January:  they are almost exactly the same!  Despite being nearly 3,500 feet higher, winter days are hardly any colder up there.  

 

Next is Redmond, 15 miles north of Bend at about 3,100′ elevation:

Redmond is even drier than Bend.  Its precipitation exhibits less of a seasonal cycle, and May is actually the wettest month.  Nighttime temps are nearly the same as Bend, but days average about 3 degrees F warmer across the year.  In fact, July and August days are nearly as warm as The Dalles.  And now for the biggest twist of all:  December and January days are actually WARMER!  That’s right…a full 3,000′ higher in elevation, yet you gain 1-2 degrees in daytime temperature during the winter.  

What the heck is going on here?  I don’t know enough to give an official explanation, but a clue may be found in what I discussed earlier in this blog.  Remember what I said about the inversion season in the Columbia Basin?  Well…The Dalles and points east get quite a lot of inversion days between mid-November and mid-February, and they often are accompanied by low stratus clouds that pool in the eastern lowlands.  Growing up in The Dalles, I always found the inversion pattern to be the most frustrating weather of all:  it’s chilly and dark, but we don’t get any excitement out of it in the form of snow or even heavy rain.

Sometimes the cold pool becomes deep enough that it also engulfs the Bend and Redmond area; this happened when I was visiting last Monday 11/14.  But more often than not, much of central Oregon remains above the inversion.  When this happens, days can be mostly sunny and quite mild…though nights still get freezing cold.  In fact, on Wednesday (the day AFTER I left Bend), The Dalles was socked in with low clouds and a high of only 37, a full 13 degrees below normal.  Meanwhile, Redmond had mostly sunny skies and a high of 48!  And that was after a morning low temperature of 14; I’m sure the diurnal contrast made that 48 feel especially nice to anyone living or visiting there.  

It’s important to note that this is not always the case. When we have a cool trough overhead and the air is well “mixed,” the high desert is almost always colder and snowier than the lowlands. But inversion scenarios are obviously common enough to neutralize much of the average temperature disparity that we would otherwise expect with increased elevation. 

Of course, Bend and Redmond are also more than 100 miles south of The Dalles, so I’m sure that the difference in latitude has at least a marginal effect on temperature, all else equal.  For a second angle of comparison we can look at Eugene, Oregon – which is nearly the same latitude as Bend and Redmond but much closer to sea level AND west of the Cascades.  (Source:  NWS Portland NOWDATA)

December and January days are milder than they are in Bend and Redmond…but only by about 4-6 degrees.  And that’s with both much lower elevation AND marine influence working in Eugene’s favor.  This clearly tells me that something is going on besides the usual formula of higher elevation + inland location = colder winters.  Keep in mind that this doesn’t really apply at night; Bend and Redmond are unambiguously colder in that respect.  But the data clearly hint that winter sunshine is able to work a certain degree of magic in central Oregon, that it cannot do in inversion-prone lowlands.

 

Finally….if you really want more cold and snow in central Oregon, Sunriver is the place for you.  It’s about 25 miles southwest of Bend, at nearly 4,200′ elevation:

Sunriver gets more precip than Bend or Redmond due to being tucked in closer to the actual Cascade Mountains.  In the wintertime that takes the form of additional snowfall – an average of 60″ per season, nearly double that of Bend!  The winter sun can still warm Sunriver up somewhat, but they are starting from a colder nighttime temperature so everything generally stays more frozen there.

You can also get to more extreme cold by going east from Bend and over Horse Ridge.  This area is a very high-elevation basin, with almost no slope to allow cold-air drainage at night.  Temperatures in this isolated area can seriously plummet – in fact, Horse Ridge dropped to -3F in early November this year!

So there you have it.  Central Oregon is a clear winner when it comes to winter snow, winter sunshine, and cool, crisp summer nights.  I look forward to spending significantly more time there in the not-too-distant future.

Karl