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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

How do you expect El Nino to potentially affect Alaska, specifically the Interior (Fairbanks) and the SE (Anchorage and the Mat-Su Valley)?

it IS maddening that none of those maps include Alaska!!

In reply to by Christine McCabe

Unfortunately, the climate division data set used to create these plots do not include divisions over Alaska.  There isn't a well defined precipitation signal over Alaska in any case.  However, winters are typically warmer than average over large parts of the state during El Nino years.

In reply to by AKflamingo

What does this mean for Texas gulf coast during the summer months?

In reply to by Christine McCabe

The link between El Nino and Texas rainfall is a cold season relationship (October - March), so the development of El Nino wouldn't be expected to impact the Texas gulf coast during the summer.

In reply to by melissa

That's weird because it is? El Niño affected Texas raising temperatures to over 110 degrees rising to 119 it killed 2 people.

In reply to by mike.halpert

How will El Nino effect the northeast like Virginia.

In reply to by Christine McCabe

How will the 2015-16 El Nino winter effect Vermont (New England area)

In reply to by Christine McCabe

New England, especially the northern part (northern Vermont & New Hampshire, and most of Maine) is likely to have above-average temperature during winter. Although there is not much effect on precipition, what little there is would be toward low-average or below average. Because of the likely warmer-than-average temperature, a little more of the precipitation would be expected to be rain than snow or other types of frozen precipitation. Of course none of these tendencies are a guarantee. What the North Atlantic Oscillation (NAO) does will exert greater weight on the climate than ENSO, and the NAO has very little predictability; ENSO has much greater predictability, especially now that we're well into summer.

In reply to by Jill Hopper

What no one seems to realize is that this El Nino is coming with a vengeance - it's going to make 82' look like a rain shower. In my 50 plus years surfing in Santa Cruz this is the warmest winter we've ever had. I was wearing a new 2mm summer suit at the end of January, and wore it for a week in Feb., and began recycling my old suits to wear so I would not wear out my summer suit before summer. I know guys are saying the water is cold up north, but here in the Monterey Bay it's been nice. We only had 2 cold spells this winter and they never lasted more than 4 days each. There were a number of days where it was warmer in the water surfing, than standing on the cliff watching the surf.

I think you must ask yourself, were the conditions you experienced due to El Nino, which has/had not formed yet, nor were it's conditions evident yet during the winter or were your conditions a result of the jet stream tracking further east which contributed greatly to the severe drought in California?

In reply to by Farley

Revised forecasts indicate a weak to moderate El Nino towards the end of the summer and into next spring. Hurricane forecasts have been upgraded in some instances to account for the expected decrease in intensity of the upcoming El Nino.

In reply to by Farley

Very warm water off the west coast is not always associated with a moderate or strong El Nino. It is usually associated with a strong positive phase Pacific Decadal Oscillation. (+PDO) The +PDO was at all time high historic levels last December through March. It is only weakening now. Strong positive phase PDO Winter's make for warm surfing conditions off the SOCAL coast Dec thru March and a warm dry west coast winters as well.

In reply to by Farley

I live in north central Texas, close to the OK border. In 82 we received 23 inches of rain in 2 weeks. Our average is 46" per year. I grew up in the 50s and 60s when the temperatures were very hot and little rain. If one snow flake fell from the sky, school was called off. Nowadays, we might miss 2 to 5 snow days...unheard of when I was growing up. I do not know how our cattle survived but they did. No one had to mow their yards after April...one perk. Interestingly, we visited Australia in July of 2013. The Outback was green because they had received more rain than usual. Bottom line is that El Nino can be good for us but bad for the Outback.

How do you expect El Niño to effect summer and fall precipitation here in south central illinois, or more importantly in the corn belt?

I see that Alaska barely shows effect, but warm. How is this really going to effect us? Our winter was mild last year, our summer is starting off slow. Does this mean we should have a hard winter also?

No impacts are guaranteed with El Nino, or really with any climate phenomena.  However, the development of El Nino will increase the odds that the winter of 2014-15 will be warmer than average over large parts of the state.

In reply to by Carolyn

Although Central California looks neutral, I wonder about the small pocket of the Santa Cruz Mountains? On one hand, we need the rain, on the other, we don't need the mudslides and washouts. Typically we get much more rain than the surrounding areas.

Precipitation impacts over California often depend on the strength of the episode.  Hard to say very much about smaller, local regions as factors such as the terrain can significantly impact local precipitation totals.

In reply to by Lori

Unfortunately, no matter how much rain you get to start with, the soil is so rock hard it will mostly run off and not soak in to the ground in the beginning. Lots of mudslides at that point. Hopefully the ground will moisten up and be able to absorb the water quickly and the danger will mostly pass. That has been true no matter what state I have lived in.

In reply to by Lori

In regards to California, even within a category (i.e., weak, moderate, strong) the average conditions are made up of a broad range of past events. See http://ggweather.com/enso/ca_enso.htm.

Is there anything at all promising for an early fall and wet winter here in the Upper Northern Ca? I'm talking Redding to Oregon boarder. Doesn't even have to be promising, a glimmer of hope would be fantastic!! Thanks for keeping us as up to date as you can!!

As the article discuses, precipitation during the winter in California often depends on the magnitude of the event.  Northern California can be an even tougher call, as often the jet stream shifts far enough south to provide suplus precipitation for southern and central California, but leaves northern California dry.  We'll have to see how this event unfolds, assuming it eventually develops.

In reply to by Marcy

Thank you for a well written article and sticking with facts. It's nice to read science where global warming in not thrown in our faces!

Thanks, Mike. Great post. The wordings of the discussions of likelihoods were excellent as were the illustrations. Best I've seen. Thanks again.

How will El Nino pattern affect New England, Massachusetts, New Hampshire? I forgot it this means more snow or warmer with more flooding rains?

Is this accurate? -- The recent data on the Jet Stream is interesting and explains this last winter very well. The pressure from the cold of the North and the warmth of the South spins the Jet Stream. Since the North is warming the pressure is waning -- causing the Jet Stream to slow and wobble. It is also too weak to hold back the power from the South from pushing up into Alaska and the Northwest. That means the ridge of cold air from the North Pole will drop across our continent when and where the push from the South dissipates. It might be that as the North Pole warms, ridges of cold air will drop farther and farther East, but the ocean currents will have effects too that might change that equation.

You don't mention much about the mid-Atlantic.....what does all this bode for us?

Can you suggest the potential effect of El Nino on the Northeast? We used to hope for El Nino when I was skiing a lot, because the scuttlebutt was that it meant a heavy snow winter...

There seems to be a lot of questions about the potential for snow next winter from the Carolinas northward through the Northeast. There was no mention in the piece about this region because quite simply, the relationship between El Nino and weather/climate 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 in the mid-Atlantic and the Northeast.

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

In reply to by louie

Has anyone done research into Tornado Alley moving north with climate change, global warming, and El Nino? There seems to be a lot of severe weather north of I-70 this year. While likely not unprecedented the storms seem to be more frequent, larger, and more severe than usual.

OK, At what point and when will you determine if it will be a STRONG, Mod, or a weak El Nino ?

The eventual strength of this event will be determined by the maximum seasonal departure in the region we refer to as Nino 3.4, a region in the equatorial central Pacific.  At CPC, we characterize an event as weak, when the maximum departure falls between 0.5 and 0.9 degrees Celsius, moderate when the departure is between 1.0 and 1.4, and strong when the maximum anomaly is 1.5 or greater. 

In reply to by Rick

Is this potentially development of El Nino is going to affect our hurricane season here in South Florida? Specially the very tip of the state Key West?

El Nino normally acts to suppress the Atlantic hurricane season and as such, the current seasonal outlook calls for a normal or below normal season.  However, this forecast is not a landfalling forecast, and it's impossible to say anything about specific regions. 

In reply to by Marty

In California we need all the rain we can get. We had so many spare the air days last winter, and still haven't had much rain here in the S.F. Bay Area.

thank you for a great article.. I too am left with questions. How will el nino affect Northern Maine/ New England?

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