El Nino, Blob, & Winter – The CliffsNotes Version

Average El Nino Impacts

My previous posts about El Nino, The Blob, and what they mean spurred a lot of questions. The main question was: so, what is the answer? The posts were necessarily long – it takes some words to explain the latest conditions, pertinent research, and to reach a conclusion. I still suggest you read them both to get a feeling for the whole story, but people are busy, so I thought it might be worth it to just give you the shortish answer.

So, here is the CliffsNotes version:

On average, we’ve had a strong ridge over the northeast Pacific Ocean for about two years which caused all of the following things: the Blob, the relatively warm, dry weather in western North America, and the cold, snowy winters in eastern North America. Research clearly links all these things together. The latest data show that the ridge and The Blob are going away. Two weeks after my original post, and all of these things are still happening. That’s got to be a good sign, right? :)

If this continues, and there is reason to think it will, we will be at the mercy of El Nino, alone (no ridge, no blob). On average, El Nino results in warmer than normal weather across much of the northern United States, and a stronger than normal sub-tropical jet along with wetter than normal weather across the southern United States. The east is trickier, but they should not experience as cold of a winter as they have the last two. Here is a graphic showing the “normal” El Nino conditions:


Average El Nino Impacts

Average El Nino Impacts


Of course, this only tells us what conditions to expect on average – there can still be individual storms that are cold and wet in the north, or warm, dry periods in the south. Be wary of anybody that tells you about individual storms or specific weather conditions beyond about 2 weeks in advance – it can’t be done reliably – and anybody who says otherwise is selling snake oil. Trust me, I’ve been doing this for a living for 20 years.



Remember, that I showed some charts and statistics in this post that indicate what we’ve seen with past El Ninos in the Pacific Northwest. Even though past performance is no guarantee of future performance, it is worth a look.



Evolution Of El Nino & The Blob – What It May Mean For This Winter


In the western United States, we’ve experienced two warmer and drier than normal winters in a row, while the eastern United States has seen brutally cold, snowy winter weather during the same span. The proximate cause of this has been in a very persistent blocking pattern in the atmosphere with ridging over or just offshore of the U.S. west coast/Gulf of Alaska and a downstream trough from the Rockies eastward. This atmospheric ridging (high pressure) also contributed to warm weather in the west via a very large area of warmer than normal water over the northeast Pacific, which has been affectionately named “The Blob.” The Blob tempered the last couple of winters over the west and eventually spread into the coast, which helped to fuel the warmest summer ever recorded in many locations over the west.

With an El Nino already in progress and forecasts that indicate it will develop into a strong El Nino and persist into the spring of 2016, the questions are: what can we expect this winter? Will the blocking pattern/blob screw us over again? What effect will The Blob have on El Nino? Will it be cold in the east again?

Of course, there is no way to answer these questions with certainty, but looking at the latest data in the light of recent research can give us some clues.

First, the blocking ridge. Here is a chart showing the mean 500 mb height anomalies for last year and a half (Jan 2014 through Jul 2015), which includes the last two winters.

H5 anomalies

Figure 1: 500 millibar anomalies (meters) from Jan 2014 to Jul 2015

The strong positive anomaly (ridging) over west coast of North America jumps off the page, as does the strong negative anomalies (troughing) over eastern Canada and the eastern United States. Given that this pattern has been the norm for the last two years, it’s no wonder it’s been so cold in the east and warm in the west.

Recent research (referenced below) makes some important conclusions about the persistent ridging and associated abnormal weather patterns those of us in the west have experienced for the last two years, including: The blocking ridge itself is caused by abnormally warm water in the tropical west Pacific1, the ridge is the cause of The Blob2, and all of these things together are responsible for the dramatically cold winters in the east3.

Knowing these things, what does this mean in light of recent trends? Here are charts showing the 500 mb height anomalies for just the last month followed by the anomaly for the last week:



Figure 2: 500 mb height anomalies (decameters) for 01Aug-30Aug2015




Figure 3: 500 mb height anomalies (decameters) for 24-30Aug2015


Over the course of the last month, the blocking pattern weakened significantly, while in the last week it has disappeared, and now we have negative height anomalies (troughing) off the west coast. You will also notice that the area of strong positive anomalies has shifted way west out into the Aleutians. Of course, that doesn’t really mean anything, necessarily, as weather can certainly vary. But in the context of what else is occurring, there is reason to think this may not be just a transitory shift.

Before I get to that, let’s talk about The Blob. As I mentioned earlier, research suggests that the ridge is caused by positive temperature anomalies in the tropical western Pacific and the ridge then causes The Blob. Here are the SST anomalies as the blocking ridge began to form two winters ago:


SST anomalies (°C) on 02 Jan 2014

Figure 4: SST anomalies (°C) on 02 Jan 2014

There were clearly positive SST anomalies in the tropical western Pacific, and you can see the blob developing off western Canada. The Blob morphed and grew over the last few years with peaks in the summer months of both 2014 and 2015. I would estimate from visual inspection of the SST charts (not scientific) that the blob peaked overall in late June or early July of this year (2015). But let’s see how the blob has changed over just the last month:


SST anomaly (°C) from 03Aug2015 (top) and 27 Aug 2015 (bottom)

Figure 5: SST anomaly (°C) from 03 Aug 2015 (top) and 27 Aug 2015 (bottom)


As the ridging moved west over the last month, the blob has also shifted westward. Also notice that water temperatures over the tropical west Pacific have cooled dramatically in the last month. Was this the reason the ridge/blob shifted? Possibly. And will this continue? Also, possibly. If El Nino strengthens as forecast, I would think so, because as warm water continues to be drawn east away from the west Pacific (typical of El Ninos), upwelling replaces it with cooler water. And as we learned earlier, the blocking ridge is forced by warm SSTs in the west Pacific, thus cooler SSTs should at least no longer support it, if not result in its opposite.

For example, in early September 1997, the SST anomalies looked very similar to how they look now. But look at SST anomalies during the height of the 1997/98 El Nino (late Dec, 1997):


SST anomalies (°C) from 30 Dec 1997

Figure 6: SST anomalies (°C) from 30 Dec 1997


The Blob had all but disappeared and water in the tropical west Pacific was cooler than normal. Does that mean it will happen this way again? No. But it shows that it can happen that way.


It is already apparent that water in the west Pacific is cooling and the atmospheric blocking pattern is diminishing. The Blob has already shifted west as a result, and this may lead to its eventual demise. There is certainly no guarantee these trends will continue, but if they do, it is likely that conditions across North America will be much different than the last few winters. Specifically, there is reason to think that the eastern U.S. will not experience another brutally cold and snowy winter like the last two. Furthermore, in the absence of The Blob, the west may experience an unfettered El Nino. What that brings is open to debate and was the subject of an earlier blog.


1 The pattern of SST across the Pacific (specifically, warm water in the west Pacific) is the cause of the blocking pattern we experienced over the last few years [Hartmann et al., 2015]. To quote Hartmann: “Although the pattern of SST anomaly is very strong in the North Pacific, it is virtually certain that the forcing for these anomalies originates with warm SST in the tropical west Pacific.” The mechanism for this is explained as Rossby wave energy that propogates northward from increased tropical convection owing to warmer SSTs [Wang et al., 2014]. In other words: because the ocean is warmer than normal, there is more convection than normal, and the energy from this convection is carried north and induces a ridge over the northeast Pacific.

2 The Blob owes its existence to the persistent atmospheric blocking ridge [Bond et al., 2015]. Persistent high pressure over the northeast Pacific blocks storms from the area, reduces upwelling, lowers the rate of heat loss, and results in relatively weak cold advection in the upper ocean. To quote Bond: “Based on a mixed layer temperature budget, these anomalies were caused by lower than normal rates of the loss of heat from the ocean to the atmosphere and of relatively weak cold advection in the upper ocean. Both of these mechanisms can be attributed to an unusually strong and persistent weather pattern featuring much higher than normal sea level pressure over the waters of interest.” The higher than normal sea level pressure was caused by the strong upper level blocking ridge.

3 It is fairly obvious that the blocking pattern was at least partially responsible for the very cold and snowy recent winters in the east. Nevertheless, both Hartmann and Wang make this abundantly clear. Hartmann states: “This pattern (the SST pattern, and by extension, the blocking ridge) is associated with high pressure in the northeast Pacific and low pressure and low surface temperatures over central North America.” And from Wang: “This persistent source of Rossby wave energy arguably contributed to the emergence of the anticyclone over the Gulf of Alaska that persisted and, subsequently, blocked the winter storms from reaching the West Coast. Also noteworthy is the Rossby wave energy dispersed downwind from this ridge, which amplified the trough stationed over northeast North America leading to the so-called ‘polar vortex.’”



Bond, N. A., M. F. Cronin, H. Freeland, and N. Mantua (2015), Causes and impacts of the 2014 warm anomaly in the NE Pacific. Geophys. Res. Lett., 42, 3414–3420. doi: 10.1002/2015GL063306.

Hartmann, D. L. (2015), Pacific sea surface temperature and the winter of 2014. Geophys. Res. Lett., 42, 1894–1902. doi: 10.1002/2015GL063083.

Wang, S. Y., L. Hipps, R. R. Gillies, and J.-H. Yoon(2014), Probable causes of the abnormal ridge accompanying the 2013–2014 California drought: ENSO precursor and anthropogenic warming footprint, Geophys. Res. Lett.41, 3220–3226, doi:10.1002/2014GL059748.


El Nino, The Blob, and Winter Weather in the Pacific Northwest

Enter El Nino & The Blob

An El Nino is already in progress, and it’s looking like a pretty good one. Sea surface temperature anomalies in the Nino 3.4 region have been above 0.5°C for seven of the last eight 3-month periods, and it currently sits at a very respectable +1.0°C. For reference, 1.0°C is the highest May/June/July positive anomaly since 1997 – which you may remember as the beginning of the strongest El Nino we’ve ever measured (1997/1998).

SST anoms

Figure 1: August global sea surface temperature (SST) anomalies from 2015 (top) and 1997 (bottom). Yellow and red are positive, blues are negative.

The current SST anomalies across the globe (Figure 1, top) do look strikingly similar to how they did in August of 1997 (Figure 1, bottom). Two things that are different are 1. the SST anomalies along the equator in the east Pacific are not currently as extreme as in 1997 and 2. An area of very warm water off the Pacific Northwest coast, which has been named “The Blob,” is much warmer and much larger this year than in 1997.

So, what’s going to happen? In short, we don’t know, exactly. First, we have to forecast the evolution of El Nino correctly. Second, the actual weather that results from each El Nino isn’t always the same. And, third, we aren’t sure what affect The Blob might have on all of this, because we haven’t really seen such a large Blob before.

The Evolution of El Nino

The track record of predicting the state of ENSO in the future isn’t perfect. What long range forecast is? The latest model forecasts predict a strong El Nino lasting into 2016, all experts seem to agree on some version of this scenario, and it sure looks like it to me.

What Will The Weather Do?

If we believe these El Nino forecasts, and I do, the next challenge is to say what that means. Unfortunately, the news isn’t really better on that front. Because no two El Ninos are ever the same, and because the effects of El Nino on the global circulation pattern (and vice versa) are so complex, there is really nothing we can say, specifically.

For example, despite the common belief that El Ninos are always stormy and wet and California, it isn’t always so. To see what I mean, consider the following charts, which show the precipitation patterns that have resulted from all El Ninos we’ve measured.

ENSO impacts

Figure 2: ENSO precipitation anomalies for historical El Ninos – from strong at the top to weak at the bottom.

See? It isn’t the same for all El Ninos, not even for all strong El Ninos. What we can say is that most El Ninos are wet and stormy in California, but not all. The NWS Climate Prediction Center said it well in their latest ENSO post: “El Nino ’tilts the odds’ for weather and climate impacts.” Which is to say that it tilts the odds that we’ll see impacts like this:

Average El Nino Impacts

Figure 3: Impacts averaged over all El Ninos for North America

What About Blob?

This is where it gets interesting. I plan to flesh this out in a following post, but recent research from my alma mater, the University of Washington, suggests that The Blob is caused by persistent high pressure over the northeast Pacific which is caused by abnormally high water temperatures in the tropical west Pacific. Unusually warm water was present in the west Pacific last winter as the Blob formed.

This has interesting implications, because if this El Nino evolves like its evil twin from 1997, the warm water in the tropical west Pacific may disappear, which should cause The Blob to disappear. It did in 1997. Here is the SST anomaly from Dec 30, 1997:

SST Anoms Dec 30, 1997

Figure 4: SST Anomalies on Dec 30, 1997

You can see that by the end of 1997, the Blob was completely gone and had been replaced by cooler than normal SSTs over the entire NE Pacific. Furthermore, the waters in the tropical west Pacific had also cooled below normal, which was almost certainly an artifact of the development of the strong El Nino in 1997/1998.

If this happens again this time, we might be able to expect impacts from this El Nino like the ones we saw in 1997. Precipitation anomalies from 1997/98 El Nino are shown in Figure 5, below. Unfortunately, I don’t have SST data from the 1982/83 El Nino. It was also a very strong El Nino, and I’d sure like to compare it to our current situation, because that one was outlandishly wet up and down the Pacific Coast.

Precipitation anomalies from the 1997/1998 El Nino

Figure 5: Precipitation anomalies from the 1997/1998 El Nino

Of course, the destruction of the The Blob in 1997/1998 is no assurance that it will happen the same way this time. After all, The Blob is much more pronounced this year than back in 1997. I’m just saying that there are reasons to think it could happen this way again. This also has implications for the eastern part of our continent which was ravaged by cold and snow over the last couple of winters. I’ll explain my theory on this in my next post.

What About The Pacific Northwest?

Unfortunately, there is no clear signal for what to expect in the Pacific Northwest during an El Nino. As we saw in Figure 2 (above), precipitation in the PacNW can vary from very wet to very dry, even during strong El Ninos. I’ve poured over rainfall/snowfall records for many locations from California to BC, and below is a bullet list of the most interesting things I found.


We are in the midst of a developing strong El Nino. Conditions right now are very similar to August 1997, which was the strongest El Nino that we’ve ever measured. Because no two El Ninos are exactly alike and The Blob may complicate things, we can’t say exactly what will happen. But the scales should be tipped toward wet weather across the southern U.S. this winter, with warmer than normal weather to the north. In the north, precipitation could amount to anything.

Interesting Things I Found From Past El Ninos

I’ve analyzed climate data from many sites over the western U.S. back to 1950 (the period for which I have SST data to compare to). Here are some of the things I found interesting:

  • Seattle, Portland, and Medford get much less snow during El Ninos than non El Nino years, especially since 1982 (what I call the modern era). Prior to 1982, they got a lot more snow overall, including during El Nino years.
  • In the modern era, Medford, OR has gotten only 1.5 inches of snow during all strong El Nino years combined. In non-El Nino years during the same period, they’ve averaged almost 4 inches per year. Prior to 1982, Medford did have some above average snow years during El Ninos.
  • Seattle, WA* averages just 1.6 inches of snow during El Nino years and 6.7 inches in non El Nino years in the modern era. During strong El Ninos, it’s even worse with an average of just 0.8 inch.
  • Ironically, the biggest snow season since 1950 in Seattle* occurred during the 1968-69 El Nino. I was born in Seattle, during this season! :)
  • Portland, OR has averaged just 1.1 inches of snow during modern era El Ninos versus 6.0 inches during non El Nino years. They also haven’t received any snow during strong El Ninos in the modern era.
  • Spokane, WA has received an average of 25.1 inches of snow during all El Ninos in the modern era. This is less than half of the average during non-El Nino years in the same period (51.8″).
  • Snowfall in the mountains during El Ninos is generally much less than during non El Nino years in the north. As we move south, the difference diminishes until it’s basically gone in California. See the following chart. I didn’t get a chance to look for mountain locations further south, but I suspect I’d find a reversal of that trend.
Average snowfall during

Figure 6: Average snowfall during El Nino years (blue) and non El Nino years (red) since 1950. **Records missing between 1989 and 1998. ^Data ends in 2000.



I get these records from the Western Regional Climate Center. I do the math myself. :)

*This is based on a reconstruction I made of Puget Sound snowfall. In the decade between roughly 1997 and 2007, climate records for Western Washington (snow record, in particular) are very sketchy to non-existent. I have no idea why the records are missing, but I made my own record using a composite of records from around the area. See here for more details.


A Reconstruction Of The Snow Record For Seattle, WA



In doing research about snowfall during El Nino years in the Pacific Northwest, I found records up north – the Seattle area, in particular – severely lacking. I checked several official sites, and it was always the same: large periods of the record missing. In particular, snow data was missing from the very important 1997-98 Super El Nino period. I don’t know why this is, but it is very frustrating.

So, lacking official records, I took it upon myself to make my own record, which is shown below.


My method was very simple: I scoured all the records around the Puget Sound and simply patched them together. By doing this, I got reliable data from some site for each year. Then, for each year of my record, I took the average snow for all sites that had data for that year. I also made one with the maximum snowfall for the year. I don’t know if this would be considered a proper way to do a reconstruction by smart people, but, frankly, I don’t care. It suited my purposes, and I feel fairly comfortable that it is a useful dataset.

Here are the sites I used in the reconstruction: Bothel, Jackson Park, Seattle Naval Air Station, NWS Sand Point, UW, Seattle City Office, Portage Bay, Boeing Field, SeaTac, Kent, Bremerton, Tacoma City Hall, Puyallup, McMillin Reservoir, Wauna, Shelton, Olympia, Quilcene Everett, and Vashon Island. You can find all these data at the Western Regional Climate Center.

My Seattle-area Snowfall Reconstruction Chart (averaging method)


My Seattle-area Snowfall Reconstruction Chart (maximum method)


My Seattle-area Snowfall Reconstruction Data

Season Avg Snow In Puget Sound (inches) Max
1950-51 14 27
1951-52 9 25
1952-53 1 3
1953-54 18 30
1954-55 6 16
1955-56 20 40
1956-57 17 25
1957-58 1 1
1958-59 8 21
1959-60 7 16
1960-61 4 9
1961-62 9 16
1962-63 2 4
1963-64 2 4
1964-65 20 44
1965-66 14 42
1966-67 6 11
1967-68 12 25
1968-69 42 82
1969-70 2 3
1970-71 17 36
1971-72 23 55
1972-73 6 10
1973-74 4 10
1974-75 8 23
1975-76 4 16
1976-77 1 3
1977-78 2 5
1978-79 9 19
1979-80 15 36
1980-81 2 4
1981-82 7 22
1982-83 0 0
1983-84 2 5
1984-85 11 19
1985-86 15 25
1986-87 2 4
1987-88 1 1
1988-89 13 30
1989-90 11 29
1990-91 6 10
1991-92 0 0
1992-93 8 14
1993-94 1 2
1994-95 5 9
1995-96 4 11
1996-97 16 23
1997-98 3 4
1998-99 4 7
1999-00 1 1
2000-01 5 10
2001-02 1 1
2002-03 0 0
2003-04 17 17
2004-05 0 0
2005-06 3 9
2006-07 5 6
2007-08 3 6
2008-09 16 28
2009-10 0 0
2010-11 7 10
2011-12 12 17
2012-13 0 1
2013-14 3 4
2014-15 1 1

We May Finally Break The Heat Wave

GFS 10-day

We’ve had a stretch of heat over the Pacific Northwest the likes of which I can scarcely remember from growing up in the area and which I’ve certainly not seen in the 4 years I’ve lived in southern Oregon. Temperatures reached 110F at times at my house over the last couple of weeks, and many records have been broken. In fact, one site in Washington State may have broken the all-time state record.

But it looks like we may finally get a break in the heat wave over the next week or so. A monster ridge of high pressure has been the culprit in the heat wave, but some long range models show the ridge retrograding offshore and allowing a trough to drop in over the PacNW. Here is the GFS 500 mb ensemble mean and spread for 10 days from now:

GFS 10-day

GFS Ensemble Mean (lines) and spread (fill), Valid 09July2015

The spread is actually pretty low for that far out, and thus troughing seems like a good bet over the west coast. This probably wouldn’t mean cool weather, but at least the oppressive heat we’ve seen should be gone.

The fly in the ointment, however, is the European Forecast. I don’t have access to its ensembles right now, but its deterministic forecast shows a brief troughy interlude followed by the ridge rebounding over the area.

Of course, we’ll have to wait and see, but at least there is some hope for those of us who don’t like living in ovens.


Potential Wind Storm In PacNW

We’ve been through a lot of boring weather through early winter, but we’re finally getting some storms again.



McMinnville, OR Tornado Rated EF1

Following up on the post I made yesterday about the tornado touchdown in McMinnville, OR, the NWS survey team rated it as an EF1. This means the damage was indicative of winds of 86-90 mph.

I have seen some video of the tornado (here and here) but they aren’t great. In fact, I can’t really see much at all. But the following photo was posted on the NWS Portland Facebook page, and it shows the tornado pretty well.

Tor pic

Tornado near McMinnville, OR on 13Jun2013. Photo taken by Bonnie Helpenstell and grabbed from NWS Portland Facebook page.

By the way, this tornado was entirely different than the big ones out in the central and eastern U.S. This kind is called a cold air funnel and is formed by processes different than the big ones that come from supercells. A violently rotating column of air reaching from a convective cloud to the ground is a tornado no matter what the mechanism. But they’re different. It will be easier to explain in a video, so I’ll do that some time.


Tornado In McMinnville, OR

Funnel cloud from Harrisburg, OR today (13Jun2013)

An NWS storm survey team confirmed that a tornado touched down in McMinnville, OR this afternoon. They have yet to say what rating the tornado was on the F-scale, but there was significant damage to some buildings.

I have heard there is video of the whole thing, but I’ve yet to see it. I will post a link when it comes out. However, I did find this photo of a funnel cloud from Harrisburg, OR this afternoon:

Funnel cloud from Harrisburg, OR today (13Jun2013)

Funnel cloud from Harrisburg, OR today (13Jun2013)

Tornado confirmed and a cool photo of a funnel cloud…in western Oregon no less! Check.

Of course, that’s not enough for me. I like to investigate why these things happen (not surprising, I suppose, since it is my job to forecast these things). Here are the radar images from around the time of the reported tornado in McMinnville:

KRTX 0.5 degree reflectivity

KRTX 0.5 degree reflectivity valid 13Jun2013/2333Z

The cell that caused the twister is fairly obvious. It had a ~60dbz core which is pretty good, but at this distance from the radar, we are sampling at ~3,700 feet above ground level. In other words: we’re not seeing much, if any, of the portion of the cell that contained the tornado.


The cell also had a **very** weak rotation at that level. Green indicates movement toward the radar (which is located in Portland – toward the upper right) and red is away. The values in there are pretty lame, like 10 knots in each direction, but that rotation is cyclonic. Again, though, we’re overshooting most of it at this range.

Finally, here is the sounding from Salem, OR. It is quite close by and, as luck would have it, taken at right around the same time:


There is some **weak** cyclonic rotation on this sounding as well – notice how the wind barbs show southerly wind at the surface and then it gradually turns toward the west/northwest with height (called veering). It’s also pretty moist in the low levels and there is some very marginal instability.

None of this information screams tornado, and I never would have forecast it to occur based solely on what I’ve seen so far. But it’s not hard to see how it happened in hindsight.

This is yet another learning experience and a pretty unusual and neat occurrence to boot.


Tropical Storm Andrea Is Born

We are about to get our first named tropical storm of the season this afternoon. Hurricane hunter aircraft reportedly found a well-defined circulation with the cloud shield seen southwest of Tampa on the following satellite photo. She will be called Andrea. June seems a little early for this! :)


Visible satellite image of tropical system currently forming in the Gulf of  Mexico, valid 05Jun2013/2115Z. It will be called Andrea.


Photos Of Wildfire In Grants Pass, OR today

Wildfire rolled up the hills just east of Grants Pass, OR this afternoon. My understanding is that it’s called the Beacon Hill Fire and was started by a truck throwing sparks as it move along I-5. It was close enough to my home that I was able to check it out for myself. I took the following photos from Grants Pass this afternoon.



There was isolated extreme fire behavior, including pockets of torching. Luckily it wasn’t windier today. I wasn’t able to photograph the worst of it, but the I did get the one below. It’s not terribly dramatic, but those flames are half as tall as the nearby telephone pole. You can also see how close this was to Interstate-5. I would have loved to get in closer to see what was going on, but then I’d just be part of the problem. 😉