Lately, I've been having a hard time trying to put a positive spin (vorticity?) on the revival of our offshore ridge.
Who likes skiing on cream cheese or mashed potatoes?
Champagne powders dark, distant cousin.
Especially after the mega-dump of snow most of the ski resorts that were seeing drought conditions desperately needed.
But according to the 500 mb height anomaly map below, it's back with a vengeance....
Mountain ski conditions are quickly going to deteriorate with the pronounced warming in the upper levels of the atmosphere. After last week and the return to a more zonal flow, I know how disheartening it is for mountain enthusiasts to see the return to what we've been faced with for most of this fall and winter.
Facing the prospect of another spell of nasty inversions that bring low cloud/fog at the lower levels, with brilliant blue sunshine above 300 metres or so... I wanted to try to dig up an answer for you all. The Climate Prediction Centre in the United States has some answers/speculation. Skip ahead if you'd rather not here the technical details.
The persistent ridging we have seen across the northeast Pacific and along the west coast this winter has not projected (correlated) well with some of the more commonly used or discussed modes of climate variability such as the AO / NAO / PNA etc. It has, however, been somewhat more consistent with a less commonly discussed mode of variability derived from Barnston and Livezey, 1987 called the East Pacific - North Pacific pattern. A projection map is at the link below, focus on the "October" panel as this is the type or orientation of the pattern I am referring to. This mode of climate variability during December was the strongest of any of the indices we monitor, by a considerable amount.
It is unclear as to why this pattern has been so strong and persistent. We need to remember that we can't always attribute persistent climate patterns to a given climate forcing (AO, MJO, etc.) of which we currently understand. It is human nature to try and attribute features we see in the climate system to something we currently understand or are familiar with but natural variability often plays a large role at times. It would take considerable and carefully conceived modeling studies to try and attribute and understand if there is anything predictable with respect to this event. It may be in time, but it also may not be in time, due to natural variability (simply not predictable).
There have been some discussions here at CPC regarding the generally persistent enhanced convection near Indonesia and whether that potentially led to a La Nina like response (i.e. tendency for ridging, blocking across the north Pacific) and dry conditions across California. But this pattern has been quite amplified and has led to ridging and dry conditions across the Pacific Northwest where wet conditions of course prevail in this area. But this and other potential reasons are purely speculation.
Now for a secret.
Want a relatively inexpensive way to experience a tropical paradise in the Pacific Northwest that's less than a 10 hour drive from Vancouver, BC?
Hop in your car and begin your drive to Brookings, OR.
I present to you, the banana belt of the southern Oregon coast. Normally in January, when you think of our coastlines you immediately think low cloud, fog, and rain. Typical.
But tomorrow, the Brookings effect will be in full force. Cliff Mass gives an exceptional explanation in his book "The Weather of the Pacific Northwest":
"Most of the Northwest coastline has relatively low and narrow coastal mountains to the east, the southern Oregon coast in on the western flasks of the high and wide Siskiyou Mountains"
Mass also states that when the typical offshore flow pattern is replaced by an offshore flow from northeast to southeast. This occurs when high pressure builds over eastern Oregon and when low pressure reaches north up the California coast.
Consequently, the descending air over the Siskiyou mountains to sea level is compressed and warmed during the descent.
To make this even more miraculous, Eugene Oregon last month saw its coldest night in over 40 years, a bone-chilling -23C or less than a four hour drive to the Brookings - such a contrast.
According to the UW-WRF GFS model, tomorrow's high in Brookings will be approaching the mid 20's (or upper 70's for you American readers). And yeah, a low 80's reading isn't out of the question...
Remember, It's the middle of January!
For those of you who want some more technical information on the Brookings effect, Cliff Mass has written several blog posts on the matter, including this one last year.