A "Perfect" Storm Hits the Northwest

If you were to order a "storm" for the Northwest, you would request one that drops lots of rain over the crest and eastern side of the Cascades, decisively ending the wildfire season and providing needed moisture to late-season crops.

To do so would require an upper-level low centered along the northern Oregon or southern Washington coast, which would swing moisture in from south into eastern Oregon and Washington.  

Exactly what is happening this weekend (see upper-level map for 2 PM Saturday).

Upper-level chart (500 hPa pressure level) for 2 PM Saturday. 

The resulting clouds swirling around the low are impressive:

As was the radar image last night.

Consider the  "storm" precipitation totals as of this morning around 6 AM (below).

Nearly an inch at some locations east of the Cascade crest as moist air swung around the low and rose on the eastern slope.

Looking forward, the total precipitation predicted through 5 AM Monday (by the UW WRF model) is quite impressive, with several inches forecast east of the Cascades, exactly where we need it to end the fire season

And believe it or not, it is cold enough aloft to result in some snow at higher elevations (see below)

We will have a warm/dry period this week, followed by the return to much heavier precipitation in ten days.  Welcome to autumn.

The Effects of "Super" El Ninos Are Surprisingly Different Than Some Suggest

It is now clear that a very strong or "super" El Niño will be in place this year.  

Some are even calling it a GODZILLA El Niño.

Several media outlets and amateur YouTube channels/social media sites suggest the impacts will be like a regular El Niño on steroids: very warm, wet, with a low snowpack.

For example, Oregon Public Radio:

The Bellington Herald throws caution to the wind, predicting drought and floods!  Plus fires. Devastating impacts for Whatcom County.  Meteorological "end times".

But there is pushback on these apocalyptic predictions.  

For example, the Summit at Snoqualmie folks looked at the snow statistics associated with very strong El Niño years and found snow totals near normal (link here)

And in my previous blog on very strong El Niños, I found the same thing: Northwest snowpack can be quite decent during "super" El Niño years.

So how can this be?   

Why do moderate El Niños cause one impact and "super" El Niños result in something different?   

Let's figure this out using real data.

The figure below shows precipitation associated with moderate, strong, and very strong ("super" or Godzilla) El Niño years for October through March.

The difference from normal is shown, with blue and purple indicating above-normal, and yellow and red indicating below-normal precipitation.  

Moderate and strong El Niño years are drier than normal over the Northwest, but "super" years, like this year, are WETTER than normal.

No drought expected.  Plenty of water for our region.

Surface air temperature?

Moderate and strong years are close to normal over the Northwest (below).  For "super" years like this one, temperatures are very modestly warmer (about 0.5 C or about 1F; see the blowup below). 

No wonder snowpacks remain decent for Super El Niño years:   only slightly warmer but with much more precipitation.

The Snoqualmie Pass folks were on to something!

Finally, can we explain these differences in a more fundamental way?  

To do so, below are upper-level weather charts (500 hPa heights; think of these as pressure around 18,000 ft)

All El Niño events are associated with an enhanced low-pressure system over the northeast Pacific (the purple colors).  Air circulates counterclockwise around lows.

For the moderate El Niños, the low is centered well offshore. Strong events have the low much closer to the coast, which is not favorable for precipitation over our region.  But for the "super" events, the low is more offshore, producing more moist southerly flow over our region.

Just right.

In summary, past events suggest that the Northwest impacts of a very strong El Niño are quite different from its moderate relatives.  

Importantly, Northwest drought conditions are not expected with a very strong El Niño, and there is good reason to hope for a near-normal snowpack.

Media and social media predictions of some kind of meteorological "end of times" are without support.