Friday, January 27, 2017

Dry North, Wet South: The Expected Winter Precipitation Anomalies Are Reversed

The forecasts by the NOAA Climate Prediction Center and many modeling centers were fairly unanimous last fall, expecting that this winter would see above normal precipitation over the Northwest and below-normal precipitation over California (see example).

The reason for this prediction was clear--a weak to moderate La Nina would be in place for most of the cool season, which often leads to such a wet north/dry south pattern.

But reality turned out very different.  The upper level flow pattern was dominated by a low-pressure anomaly (difference from normal) over the Pacific Northwest, that drove the jet stream into California and colder, but drier, air into the Northwest (see 500 hPa upper level height anomaly below, the purple area represents much lower than normal heights/pressures).

Lets look at the actual precipitation reaching the ground over the western U.S.  The percentage of average precipitation for the last three months over the region (see below) clearly shows drier than normal conditions over Washington State and northern Oregon, but a way wet situation over California (150% and more!).

 Looking at the actual difference in precipitation from normal (not percent, but inches), some parts of the Sierra Mountains and coastal range of California are more than 20 inches above normal---amazing.   A real drought buster.

 What about the next week?   Over the next few days, a high-amplitude ridge of high pressure will build along the West Coast, drying out the entire region (see below).

 But it won't last!  A weak trough of low pressure will move through the Northwest on Sunday, bringing some light rain, followed by a return to the pesky troughing, which will again result in the jet stream heading into California (see below).

The result, as illustrated by the UW WRF model precipitation totals for the 72 h ending 4 AM Friday, is lots of rain to the south of Washington State. The saga continues.

Finally, this winter's busted long-range forecast is ANOTHER good illustration that my profession has only minimal skill for our seasonal predictions.   Last year did not work out well either.  Clearly, a subject suitable for lots of research.


Bruce Kay said...

The butterfly effect can be undervalued when we get all excited about a single overhyped factor, such as the the current barely there La Nina that everyone expected so much from.

Perhaps we should have just expected the predictable - the unpredictability of normal

Moral Individual said...

Great article Cliff! The rise of everyday forecasters on Youtube is not good and is spreading misinformation like wildfire. You see many on Youtube, some with actual skill, and others that have no clue. I find it quite insane when these "sources" are putting out predictions in October for the winter season, just doesn't make any bit of sense. And then never update each month as conditions are changing.

At least NOAA has become more adapting this year, as they do update seasonal and monthly forecasts several times a month. When we had the monster El Nino last year, NOAA did not do this. Instead they used the same graph for the country about 5-6 months in a row, not accounting for the trend to wet in our state, and the lack of wet in California. I am glad to hear California is getting drought relief, but I wonder if Washington is going to end up too dry this year, unlike last year. And is it not true that the drier the snow is (because of severe cold) the less moisture it has? Just curious. The latest figures are in the link for Washington water supply and many places are falling below normal, not all though.

Bottom line, weather is massively unpredictable these days, end of story.

Moral Individual said...

Bruce Kay: Just wanted to mention, even though NOAA hasn't said, La Nina is dead What worries me is the fact that the probability for another El Nino keeps rising, to happen again possibly in late fall.

Earthwater said...

NWS refers to a Rex Block - a provocative term! Is that what is happening here? I see the high off Haida Gwai and the lows off the PNW diverting flow to the south.

WQR said...

Moral Individual: The thought of dry snow and less moisture sort of makes my head hurt. Snow is primarily water. Water as a liquid is more dense than ice which is more dense than snow. Wet snow is denser than dry snow; so if you melt 3' of ice or wet snow it would certainly contain more water than 3' of loosely packed dry snow but 1 lb of ice and 1 lb of snow both contain the same amount of water. How do you want to compare the moisture content of water?

Buddy said...

Thanks for shining light on that Cliff. This is one of the drier winters of recent memory in the Cascades where I live. Yet there's considerable snow depth and the skiing industry is doing great. This year it's quality, not quantity.

Same in Eastern Washington. It's been a dry "snowy" winter. With the ground frozen this would be a great year for flooding but we just don't have the deep moisture. There's a enough for a couple days of fun runoff. And as an user of irrigation water from the Yakima I'm not going to worry either. First October was a great head start to the water year. And two it's staying cold and actually looks like we'll finally have a cool spring. And that's big because people forget the importance of how and when the snowpack melts. We want our snow to melt in May June July. Not March and April like it has the last few years. Let's hope.

Moral Individual said...

October was really wet in Eastern Washington, but dry in November, and a little below normal in December for precipitation. January is running normal for precipitation in Eastern Washington. That cold air though has taken out the moisture it seems so the snow quality does stink. One has to wonder if the cold temps are ever going to leave though, just killing the utilities this severe cold, or the severe cold that has happened.

NoAgenda said...

It's hard to imagine how climate models could be very accurate given the level of inaccuracy of these much nearer-horizon models.

Bruce Kay said...

Earth water - If the Rex Block is north of the 49th parallel, it could well be this blockhead:

tracksdc89 said...

The "Emerald City" isn't nearly as green as it would normally be at this time of year. Thank you for providing this interesting explanation!

Will our current lack of precipitation result in noticeable soil moisture problems this spring? Seeing how the environment is already reacting by being less "dazzlingly green" than usual, I am concerned that once spring kicks in, there may not be enough moiture for all the plants, flowers, and trees.

And if we have another unusually warm and dry April and May (as we did last year) that will certainly be a major concern - hopefully, this year, the dry and very warm weather will hold off until it is supposed to get here.

Candis Kiriajes said...

I always like your blog Cliff. I live in Northern CA and appreciate your views and the "ending of the CA drought" statement in your last article. We are so wet here! Rivers and lakes full and the soil very moist! I feel the same as the last comment. So many predictions for what is going to happen in the future with "global warming" but we can't even accurately predict the weather season to season!! With the Sun being quiet and so many other influences with the weather, I think a little humbleness is in order! Your writing is clear so interesting to read. Thank you.

John K. said...

I don't understand the Precipitation Departure From Average chart. It shows below average for the Cascades, but the snow pack there is at 100+%. Cliff, can you explain this?

Earthwater said...

Omg Canada's Rush Limberger

Bruce Kay said...

Candis K - I am perpetually amazed that so often when a prediction is "a bit off" it is characterized as a failure, especially if it is given a percentage of probability or similar. I can't help thinking that the attitude here is similar to any football game where the outcome expectation is a win or a loss, never a tie! In case you haven't noticed, weather forecasters and indeed climate forecasters (two entirely different things) are beholden to humility out of a professional ethic that reflects quite well the uncertainties of their job.

It is not the weather and climate professionals who fail to show humility - it is the consumer! We imply an expectation of certainty that they never claimed existed! why do we do this? Damned if I know but it is hubris whatever the reason. To the best of their abilities they state the probabilities - we are the one's who can't comprehend success or failure in that context.

As an example: while it is tempting and predictable that the drought is now judged as over, that of course is empirically true only for the moment. By this time next year just the opposite might be the case - or not at all. Either way, as any ethical climate expert will tell you, neither last year or this year taken in isolation is an indication of climate trends. The past thirty years is a climate trend that has meaning. The next thirty years will mean something too. Sixty years will be better yet.

Am I a climate expert? no I am not. You don't have to be to have at least a philosophical understanding of the potential benefit and error of statistical representation, first and foremost the rule of large numbers. The other rule is that statistics is always about probabilities, never certainty. Unfortunately, these 2 simple rules of thumb seldom register with the general public in comprehending reliability of any kind of forecasting.

If you doubt me just look at the most recent comments by Donald Trump about the NY Times....

"They are fake news because they were wrong about me!" he says. Well, if that indicates anything, Trump was wrong about himself right up till the time the polls closed, just like most anyone!

Rebecca Timson said...

Different measurements come into play when it comes to snow. Perhaps you've addressed this somewhere already, Cliff, but maybe you could give a mini-lesson here on the differences between and relationships among snow pack, snowfall, snow water equivalent, etc. There also seems to be a need for deeper understanding of the impact of when the snow falls during the season, what kind of weather occurs between snowstorms, and how spring weather affects the summer value of the snow pack.

Eric Blair said...

and here's Bruce once again telling us that the US public is essentially a bunch of complete morons. But of course, the real infants and people lacking in intelligence are often found in the same governmental agencies he'd like us to follow, blindingly:

So by all means, let us all follow the rigorous and scientific minds of the very same agency that has as it's core mission the safety of the air, water and soil of our country. No matter the challenges, I'm sure they're more than able to do their jobs like actual adults.

Bruce Kay said...

No Eric, most of the public are neither dumb or don't care. What is true, and this is measurable just about anywhere, is that despite good intentions, the popular understanding of "prediction" is flawed. No one should find this fact to be a surprise. Why else do you think statistical analysis is such a demanding skill domain? If only a 40 hour course was required to become fully functional in statistics, we would all be retired by now.

I got a question for you Eric. Why do you think common sense is called common sense?

Organic Farmer said...

It seems the long range models have been more accurate with tempeture than precipitation the past two winters.?

I can see where precipitation in the form of atmospheric rivers can be very difficult to predict. (Sorta like a loose fire hose spraying the west coast in what appears to be a nearly random pattern.)

Great work Cliff.

Gary said...

Could someone help me understand this: Twice Cliff states that low pressure over the PNW drives or results in the jet stream's heading toward CA:

"The upper level flow pattern was dominated by a low-pressure anomaly (difference from normal) over the Pacific Northwest, that drove the jet stream into California . . . "


" . . . a return to the pesky troughing, which will again result in the jet stream heading into California . . . "

I'm not seeing why this is true or what the relationship is, which seems to be one of cause-effect.

Scott Dakers said...


I'd like your thoughts on this article in The Mail about NOAA. If it's true, it is a bit of a bombshell. In short, it's one of NOAA's top scientists stating that NOAA used dodgy, unverifiable data to produce a report on global warming.

I'm stunned.