What Does El Niño Mean for Utah?

Tuesday, July 14, 2015 at 10:24 am

Monday, 7/20/2015 Update:  Over the past week, El Nino has continued its rapid intensification, adding even more certainty that this will be a “strong” event as we head into winter….WSF

————————————————————————————————————————

If you think the El Niño hype is bad now, it will only get worse as we get closer to winter.  Not that it isn’t warranted — this is almost certainly going to be the strongest El Niño event we’ve had in 18 years.  It is possible it could be the strongest ever.  However, there seems to be a lot of confusion regarding what El Niño means for Utah.  It’s easy to buy into the hype and assume we are destined for an epic winter.  Unfortunately, that’s not the case.

Accuweather

Accuweather

The map above does a good job of demonstrating how an unusually strong southern branch of the jet stream promotes wetter-than-normal winters for California and much of the southwest during an El Niño.  Southern Utah can also benefit greatly from El Niño.  Northern Utah (including the Wasatch and Uinta mountains) is less favored.  You can see that we lie in between typical wet areas to our southwest and the warmer and drier region of the upper plains and Northern Rockies.

When the ONI value is greater than +1.5 in the ENSO 3.4 region of the equatorial Eastern Pacific, it is considered a strong El Niño.  This past week (July 13), we crossed that threshold into “strong” category.   This is very early in the season to be reaching that level and virtually all models continue to show further strengthening, some showing ONI values approaching +3 this Fall (which would be a record).  So the Super El Niño hype is real, but that doesn’t necessarily mean that much for us just yet…. especially when you consider that the +PDO (warm blob of water off North American pacific coast), which has likely contributed to California’s drought, is still a factor.

Since 1950, we have seen five El Niño events in which the ONI has been +1.5 or greater when entering winter (using the Oct-Nov-Dec averages).  Using the UAC’s data from UDOT’s Alta Guard station in LCC, I decided to look at the these 5 events and their seasonal snowfall:

nino_table

 

Obviously, this is only one location, but you can see that El Niño can be a mixed bag.  Two of the events were below Alta-Guard’s seasonal average of 499″ (1965-66, 1972-73).  The other three seasons were above average with 1982-83 being well above average!  Overall, we have averaged 540″ of snow in strong El Niño seasons, greater than 40″ more than normal.  An important distinction is that if you look at the three seasons in which the ONI was greater than 2.0 (super strong) for the OND avg, the seasonal average for those seasons is 570″.

The big takeaways should be:

(1)  El Niño is NOT A GUARANTEE OF ANYTHING.  We’ve seen both above and below average seasons in a very small sample size.  While it may tilt the odds in your favor, California, nothing in seasonal forecasting is absolute.  That should be obvious by now! ;-)

(2) Southern Utah is the place in our state most likely to feel the effects of Niño.  Brian Head trips may be on the menu at times this season!

(3) Stronger is better.  The table above seems to indicate the stronger El Niño events provide a greater opportunity for Northern Utah to see above average snowfall.  C’mon El Niño! Keep strengthening!

(4) Cautious optimism…

I’ll be talking about El Niño A LOT for the rest of Summer and into the Fall, mostly because it is the single biggest player in worldwide weather patterns, particularly in a strong state as we are currently seeing develop.  This post is designed to be a disclaimer I can refer to throughout the coming months that separates hype from reality.

WSF