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United States El Niño Impacts

By this point, most of you have heard that it looks like El Niño is coming, and maybe you’re wondering why you should care.  After all, why should it matter if the tropical Pacific Ocean becomes warmer than average? That’s thousands of miles away from the continental United States.  Well, it turns out that El Niño often results in changes in the patterns of precipitation and temperature across many parts of the globe, including North America (Ropelewski and Halpert 1987, Halpert and Ropelewski 1992).

Many folks probably remember the heavy rainfall, flooding, and landslides that occurred in California in 1982/83 and again in 1997/98. As the region suffers through a devastating drought, it could be something of a relief if we knew for certain that El Niño would bring similar soaking rains. But those two events were the 2 strongest El Niños in the past 60 years, and we’ve seen many other El Niño years where California didn’t experience those types of devastating impacts. So assuming El Niño develops, what can we expect across the United States and when can we expect it?

By examining seasonal climate conditions in previous El Niño years, scientists have identified a set of typical impacts associated with the phenomenon (Figure 1). “Associated with” doesn’t mean that all of these impacts happen during every El Niño episode. However, they happen more often during El Niño than you’d expect by chance, and many of them have occurred during many El Niño events.

Wintertime El Nino effects

Average location of the Pacific and Polar Jet Streams and typical temperature and precipitation impacts during the winter over North America. Map by Fiona Martin for NOAA Climate.gov.

 

In general, El Niño-related temperature and precipitation impacts across the United States occur during the cold half of the year (October through March). The most reliable of these signals (the one that has been observed most frequently) is wetter-than-average conditions along the Gulf Coast from Texas to Florida during this 6-month period. This relationship has occurred during more than 80% of the El Niño events in the past 100 years.  

In Southern California and U.S. Southwest, strength matters

Over California and the Southwest, the relationship between El Niño and above-average precipitation is weaker, and it depends significantly on the strength of the El Niño. The stronger the episode (i.e., the larger the sea surface temperature departures across the central equatorial Pacific are), the more reliable the signal in this region has been.

For instance, during the two strongest events in the past 60 years (1982/83 and 1997/98), much-above-median rainfall amounts fell across the entire state of California. Median or above-median precipitation was recorded over the entire state during strong episodes in both 1957/58 and 1972/73 (Figure 2). However, strong events in 1991/92 and 2009/10 only provided small surpluses in the southern part of the state, while precipitation during 1965/66 was generally average to below-average across the state.

Winter precip anomaly maps

Figure 2. DIfference from average (1981-2010) winter precipitation (December-February) in each U.S. climate division during strong (dark gray bar), moderate (medium gray), and weak (light gray) El Niño events since 1950. Years are ranked based on the maximum seasonal ONI index value observed. During strong El Niño events, the Gulf Coast and Southeast are consistently wetter than average. Maps by NOAA Climate.gov, based on NCDC climate division data provided by the Physical Sciences Division at NOAA ESRL.

 

For weak and moderate strength episodes (Figure 2), the relationship is even weaker, with approximately one-third of the events featuring above-average precipitation, one-third near-average precipitation, and one-third below-average precipitation.  

Elsewhere over the United States, El Niño impacts are associated with drier conditions in the Ohio Valley, and there is a less-reliable dry signal in the Pacific Northwest and the northern Rockies. Hawaii also often experiences lower-than-average rainfall totals from the late fall through early spring period.

The climate impacts linked to El Niño help forecasters make skillful seasonal outlooks. While not guaranteed, the changes in temperature and precipitation across the United States are fairly reliable and often provide enough lead time for emergency managers, businesses, government officials, and the public to properly prepare and make smart decisions to save lives and protect livelihoods.

Definitions

Weak El Niño: Episode when the peak Oceanic Niño Index (ONI) is greater than or equal to 0.5°C and less than or equal to 0.9°C.

Moderate El Niño: Episode when the peak Oceanic Niño Index (ONI) is greater than or equal to 1.0°C and less than or equal to 1.4°C.

Strong El Niño: Episode when the peak Oceanic Niño Index (ONI) is greater than or equal to 1.5°C.

References

Halpert, M.S. and C.F. Ropelewski, 1992: Surface Temperature Patterns Associated with the Southern Oscillation, J. Clim., 5, 577-593.

Ropelewski, C.F. and M.S. Halpert, 1987: Global and Regional Scale Precipitation Patterns Associated with the El Nino/Southern Oscillation, Mon. Wea. Rev., 115, 1606-1626

--- Emily Becker, lead reviewer

Comments

As mentioned earlier, the relationship between El Nino and weather/climate in New England is not very strong.  The Climate Prediction Center does have a webpage that shows U. S. seasonal composites of temperature, precipitation, and snowfall that may be of interest.  However, there is no level of significance associated with these composites, other than the frequency with which these departures have occurred in the past.  These figures do show a tendency for snowier El Nino winters New England.

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/composites/

In reply to by ariel

what effect will El Nino have on the Ohio (central) weather this coming Winter (2014-15)?

El Nino tends to favor a drier than average winter in most of Ohio, and the CPC seasonal outlooks for DJF and especially JFM reflect that.

In reply to by T. Shields

While I can understand the warming of the Pacific can and will affect our weather I do not see a definitive data set based on the graphs you put up. Some times it is wet and sometimes it is dry. Why all the fuss? Seems you don't really know what is going to happen. When you do, let us know. Until then you guys seem to be trying to hype the next storm that may or may not happen.

Since El Nino is not the factor that affects the climate, none of the relationships discussed here occur every time.  What El Nino does enable us to do is to issue outlooks that favor either wetter or drier, warmer or cooler weather, than average over certain regions of the country during certain seasons.  These outlooks also say nothing about the specific variabiltiy of the weather during the season, so you're correct in that we're not able to say anything about a particular storm.  That would be a weather forecast and at this time, meteorologists are able to skillfully (not perfectly) forecast the weather out to to about 7 days.

In reply to by Jon Doe

This developing El Nino has lost some steam but the MJO is in active phase so there might be another opportunity for another westerly wind burst to trigger a Kelvin Wave. Also its not mention often but there is some amount of correlation between ENSO and PDO and since January 2014 the PDO have enter a positive phase. The current PDO index is 1.80 recorded in May, so this could be the sign of a warm phase have started.

So, what should the P. NW expect over the next several months into Fall & Winter? Hopefully not another hot Summer...We can't take it! Thanks.

I know that we need rain here in California, however, I am very concerned that it is going to rain continually day after day after day, possibly for weeks at a time. I would appreciate some feedback as we are all worried here. Thanks!

Thank you for the very informative article. However figure 2 classification scheme is interesting. You used "difference from average precipitation" with 6 and 12 inches of variance as rough demarcation values. Yet of course, 'average precipitation' varies markedly across the nation. Drier areas such as the Inter-Mountain West and Desert Southwest will never show strong variance with this classification scheme because annual precipitation there is lower overall. In other words 6 inches is a large amount for these areas, whereas 6 inches for the West Coast and Gulf Coast is a smaller variance from normal. A classification scheme that shows something like "percentage of difference from average precipitation" would be more normalized and thus give a more accurate representation of El Nino impacts for regions. Thank you.

I hear about the warming oceans because of climate change and now it is from El Nino. How can you differentiate between the two? If the whole world is warming as they say, could this be falsely identified as El Nino? Can the forecasted El Nino overcome the current dry cycle phases we are in (for southwest anyways) of the AMO and PDO?

Weather has been escalating about 5 to 15 percent each or every two or three years for the past 25 years but has been in transition about 50 years where it has worsened but more so in the past 25 years. I am not saying it has gotten so bad that it is not predictable but it is more likely to be outside prediction ranges than before but for the reason weather forcasters has extended the range and improved accuracy, not because they have improved but becasue they have opened their eyes and see longer, even with improved technology but i say it is intuitiveness. Weather prediction has either gotten more scientific and accurate or it has become more predictable so that accuracy is more probable. Weather has gotten bigger, badder and more of it and so has disaster events on a larger scale. I think the solar collection magnitude is also causing some of this. It is taking away solar introductions and not allowing the solar introductions do their job of vetting weather so it can mediate a more predictable ability. Long range prediction is more common place but so is weather being more predictable in the long run, Why I question weather prediction accuracy or weather patterns being more probable toward accuracy. It says May is the all time high for global temperature surplus, oceans are warmer but so is landsites even if covered with ice and snow. A few years ago a mountain slope in Alaska slipped of its crown, about 25 miles of it and the USGS person who had the duty to talk about this said, "what we don't understand about it is it did not melt from the top down, it melted from the bottom up and it has happened in other parts of the ice covered regions. Why the land temperatures are rising, Due to warm-up of lands without any shade on it, farm landnot growing anything in the winter time. Why the oceans are warming up? Due to total atmospheric range and content, it is more dense, deeper than ever so it collects more solar energy so solar energy range is also out of sequence with all the biomass and release of microscopic material that has a lighter specific gravity than air so our upper atmosphere is also growing at alarming rates into our upper atmosphere.range. Sun light moves in a straight line, but total earth atmosphere dimension has grown more in the past 25 years than in all time. Why? Because of the thrust and movement of energy of items going out of and returning into it, pull on exit and splash on reentry has change it, mostly enlarged it substantially, not with aerosl of air but with aerosols of items lighter and less specific gravity than air and water vapors.

How would the El Nino affect the weather in the Northern Rockies- specifically northern Idaho/northwest Montana- during the upcoming fall and winter? Thank you.

Will Dallas have alot of snow like the winter of 2010 around the super bowl super

I live in SE Az downstream from where a 222,000 acre forest fire burned in 2011 and the veg is not recovered much. Will those portable rain gauges and RAWS be put out again if it looks like it's going to be a stormy winter? The data from these gets online really fast, or did when they were deployed during the 2011 monsoon and was very useful to nervous residents.

Hello, I plan to visit California from S.F. to L.A. first week of October, I worry about raining all day and night long for a week... Is this possible ?

How will el nino affect florida....keep one thing in mind.... florida was hit pretty hard in 1997-1998... in 1998 feb... ground hog day tornadoes hit central over night.... lake county, fl was spared... but when when the dry season came that year florida had a out break of wildfires... are we going see that in this year el nino... i hope not

If this El Niño continues, should we expect the current milder, drier winter forecast to morph into a colder, wetter winter?

What can the U P of Michigan expect this winter?

It appears there may be good news for central Texas if we get much-needed rain this winter. Does this mean central Texas will be also cooler than normal? Thanks so much for all the good info.

I am really hoping for an active winter for the southern states, there is a very good chance for a VERY active one, more active than last year! I hope the temperatures are frigid, and the conditions favorable for a few significant snowfalls! The humidity is going to be low, the moistness of the air high, it's all pointing towards a fortunate-to-not-so-fortunate winter for us. In my eyes, it's fortunate, school in the Deep South is cancelled with just sleet! Also, it is a risk, as opposed to my hopes, since us southerners do not get snow very often, and we are not prepared for it, last year our pipes froze 4 times and it was tragic, people had to stay inside for the first time in forever. Also, the forecast says it will be a wet one, which is favorable for snow, and last year, the lows got down to THIRTEEN DEGREES Fahrenheit, which is something you see, like, once every few decades. It was nice, though we had to go to school at the peak of the frigid temperatures, it was like being stuck in a giant freezer, though everything looks normal. If anyone could please reply to this comment, it would be greatly appreciated :)

Do you expect enough rainfall in North Texas to fill lakes? Now it seems east and south Texas is getting more.

will el nino affect north carolina weather will it be mild or cold in north carolina the winter of 2013 2014 was terrible it snowed in febuary followed by a ice storm in march twice in 10 days it was brutally cold this past winter i hope it will be a mild winter i had enough of winter i hate cold air the el nino of 1997 1998 was a major one it rained in 2003 it rained peidmont triad international airport the official reporting station recorded a record 62.36 inches of rain in 2003

If there is a weak El Nino in 2014/15, as predicted, there is no particular predictable effect on precipitation in the the piedmont portion of North Carolina during winter. To the west there would be a tilt of the odds toward below normal precipitation, while to the east (and south) there would be slightly enhanced probability for above normal. As for temperature, there would likewise be no strong expected preference for anomalies in central North Carolina, although not far to the south there would be an expectation of slightly below normal temperature (and slightly above normal precipitation). So we don't expect a repetition of the severe winter of one year ago.

In reply to by tim benett

Does ENSO warm the Pacific Ocean and cool the Atlantic Ocean simultaneously as El Nino builds up strength with time?

Often the Atlantic will warm(not cool) to some degree after the Pacific has warmed, in response to changes in the circulation throughout the Tropics. 

In reply to by Nabil Swedan

We are having one of the worse lake drought in North Texas for past 3 to 4 years. Will El Nino help our lakes?

Thus far, this is proving to be a very wet May 2015 for TX due to El Nino - any thoughts how long El Nino will continue to be a factor for the southern region of the US?

The usual effect of El Nino on Texas rainfall is to increase the chance of above average rainfall during winter and spring (up until about May), and then have little or no effect through summer and much of the fall, and then to increase it again as winter approaches. So your above-average rainfall could be due to the weak El Nino conditions we have had over the last few months. But since El Nino's influence on Texas rainfall is minimal after about May, I would not expect a continuation of your high rainfall going into June. If it does continue, it would be due to factors other than the El Nino. Then, if this El Nino is still going on next November or so (and current model forecasts indicate that it will), you may see a wet winter in 2015-16.

Yes, the El Nino does change the persistent high pressure observed in the southwest over the last several years. As illustrated in the last figure of Emily's blog post a week or two ago, http://www.climate.gov/news-features/blogs/enso/june-el-ni%C3%B1o-updat…, during El Nino the Pacific jet stream usually is extended so as to encroach on the southwestern US, bringing its storm track with it. This means that even if there is still a tendency toward a high pressure ridge over the western US, there could be repeated interruptions as low pressure systems undercut the ridge on its southern side over southern California and Arizona. So there is hope for some relief from the drought, especially south of 35 N latitude, and if it turns out to be a very strong event, the better rainfall (especially in late winter, Jan-Mar) could benefit central or even northern California as well.

Does the record rainfall in May mean that the colder and wetter than average forecast that goes with the South will reach up to Oklahoma this coming winter? Oklahoma is on the border of where you expect changes, but since the extreme precipitation reached up in May, could that mean this El Nino is just little higher on the map? Also, when you say colder and wetter in the south, how much colder and wetter can Phoenix get? One more... cloud cover and precipitation are different. We had extreme cloud cover this last winter though our precipitation numbers were not out of the ordinary. Does El Nino affect that as well? Cold wet Texas means very cloudy Oklahoma? I need to make plans to be out of this area if it's going to be colder and wetter and cloud covered. These kinds of things affect people with Seasonal Affective disorder. So please let me know what you think.

Given the July update to the ONI's, was wondering if you've updated the awesome graphic illustrating the various categories of El Niño? Also wondering if you have also added a "very strong" category? RF

We have not updated the image above showing the various categories of El Nino. While the transition to using ERSSTv4 did change designations of strength for some events, overall the changes were not drastic when it comes to the image in this blog post. 

To answer your last question, no we have not added a "very strong" category. The categories remain three monthly averaged ONI values as follows:

> 0.5C - Weak

>1.0C - Moderate

>1.5C - Strong

There are a majority comments on specific areas, why is fine but most everyone should be more concerned on how we can save the planet and get the check and balances back on scale. Unless there are some immediate drastic measures, our children and their children are screwed because we didn't face reality and took action. Striker

I've always been a fan of El Nino, so anxiously awaiting to see her effects on the Lake Superior snow belts this round. Thanks for all the great work that NOAA does keeping this amateur weather dork inspired.

I live in Western Kentucky. Our last 2 winters have been snow filled. Does this mean we can hope for a drier winter? Last year we missed 2.5 weeks of school. It was horrible!

Yes, western Kentucky is part of the "Ohio Valley" region that typically gets somewhat less than average winter precipitation during El Nino, while getting near-normal to just slightly above-normal temperature. You're likely to get some relief from a harsh winer this year.

In reply to by Kentucky Girl

So is el nino a storm or is it just warm ocean water?

What effect with ElNino have on East Tennessee this winter. (2015-2016)

You can find CPC's January-March forecast here.  There doesn't appear to be a great signal for East Tennessee.

In reply to by Mary R

How can you have negative precipitation?

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