|Visible Satellite 1/23/14|
That white area in the middle of the picture is the fog and stratus that has filled in the Columbia Basin of eastern Washington and north-central Oregon. You can see some mountains above the fog near the Washington/BC border, as well as the Washington Cascades.
Why are we stuck in this pattern? High pressure over the western US is steering storms away from our area. As we've discussed in past blogs, this is causing a severe drought in the western US. But for many in the West, they're enjoying sunshine and warmth. Take a look at this satellite image to see what we mean:
|Western US Visible Satellite picture 1/23/14|
So why are we so cloudy while the rest of the West is sunny? Professor Cliff Mass of the University of Washington wrote about this in his blog. You can find it at: http://cliffmass.blogspot.com/2014/01/cloud-bowl-of-eastern-washington.html We highly recommend it.
But in short, the reason is three-fold. First, the Columbia Basin acts as a topographic bowl.
The Columbia Basin is bordered by the Cascades to the west, the Selkirks to the north, the Panhandle mountains to the east, and the central-Oregon mountains to the south. A perfect bowl. Note in the above picture of the western US, the Central Valley of California also provides a nice elongated topographic bowl.
Second, you need moisture in order to form fog. And while we have been very dry, we still have had weather systems providing some moisture. Coupled with the cold nights, and you get fog and stratus to form. The Central Valley of California has been so dry this winter, they can't even produce fog!
The third ingredient is a lid to put on the bowl of fog, to prevent it from going anywhere. This is provided by the ridge of high pressure. High pressure results in sinking air. Sinking air warms. So while at the surface we're stuck in cold, sub-freezing temperatures, the air above us is much warmer. Locations in the mountains as high as 5000-6500'' have been reaching the mid-40s each day. The high pressure also keeps storms away from our area. Storms mean wind, and wind mixes the air which dissipates fog. Below is a temperature and moisture sounding or profile taken at our office on 1/23 at 3 pm. There are two pink lines on this chart, the one on the right denotes how the temperature changes with height. The line on the left is the moisture profile. The farther away the two lines are from one another, the drier the air. So on this sounding, most of the atmosphere is clear and dry. The exception is near the ground where our temperatures have been stuck in the mid 20s to lower 30s for days and the sun has been a rather rare site. Notice how the temperature increases with height and peaks at 47° at an elevation around 6500'. So if you seeking sun and warmth, the mountains are the place to go.
|Spokane temperature sounding 3pm Thursday. Light pink line or right denotes the temperature profile.|
One positive of this weather has been the beautiful natural flocking which has adorned most of the objects stuck in fog for the past week. This flocking is being produced from the deposition of small sub-freezing water droplets on objects resulting in riming. The rime in this event is covering everything from trees, fences and power lines. We wrote about this back in December. You can read about it at: http://inlandnorthwestweather.blogspot.com/2013/12/another-kind-of-white-weather.html
Here's some pictures from our office:
So this kind of weather can't last forever, can it? No, but it can last for a few weeks. This episode started on January 16th, and today is the 24th. Yep, it's only been going on for a week. Seems like a month though. Have we seen longer episodes in the past? Of course. One of them occurred during the 1976/77 drought. After a few storms brought rain and snow to the area in the middle of January 1977, a huge area of high pressure developed over the area, just like our current episode. Spokane and the Inland NW were stuck in the fog from the 19th of January through February 10th. That's 22 days! Although there were a few peaks of bright sunshine during that streak they quite brief. A weak weather system moved through at the start of February, but it was too weak to get rid of the fog. Instead, they had some freezing rain.
How long will our current episode last? Aside from a few possible sun breaks, we're likely stuck in the fog through the weekend and into early next week. There's a outside chance that some locations in the Panhandle and northeast Washington will see more sun on Monday. This is due to an arctic high pressure system centered over eastern Montana and the Dakotas that may push a bit of drier air into our area from the east.
|7am 1/27/14 precipitation and sea-level pressure forecast from GFS model.|
Despite the presence of the weak system notice the 500 mb ridge (below) remains very amplified and basically centered over the Pacific Northwest.
500 mb pattern for 7am 1/27/14 GFS model.
Starting on Tuesday, some very weak Pacific weather fronts might be able to break up the low clouds as well as bring us a dusting of snow as the ridge gets progressively weaker each day. By the end of next week, there is more confidence that the weather pattern will have changed and we can get a respite from the fog and low clouds.
|4am 1/28/14 500 mb map from GFS. |
Ridge gets flattened a little by weak front.
|7am 1/30/14 500 mb map from GFS. |
Ridge is virtually gone now over PacNW and is replaced by a trough off the coast.
And this ridge breakdown could actually persist for more than a couple days. The map below is the mean 500 mb pattern projected for the period from January 30th-February 3rd. Notice the ridge has generally shifted into western Alaska and has left a broader trough over most of the US, including our area. The 8-14 day outlook (bottom image) through February 7th looks similar as well.
|8-14 day outlook., Mean 500 mb map|