Although the current El Nino may be entering its declining stage, the sea surface temperatures in the tropical Pacific are still quite war, and thus the impacts of the El Nino continue.
The evidence is very strong that this El Nino is the key driver of the low mountain snowpack this winter. Let me show you.
Below is the latest snowpack situation from the SNOTEL network. The western U.S. snowpack water content is below normal over the coastal states, ranging from about 80% of normal in California and Oregon to around 60% over Washington State.
So why this snowfall pattern?
The precipitation difference from normal for the past 60 days shows a relatively wet California and Oregon, but drier than normal conditions in western Washington and the Cascades.
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And most of the west has been warmer than normal. It all fits. The temperature and precipitation pattern explains the snow distribution.
But can we blame this on El Nino?
NOAA has a nice webpage in which they show the typical winter conditions associated with El Ninos based on many events.
Precipitation? Wet California, dry western Washington. Looks like this winter!
The temperature during El Nino winters? Warmer than normal over the West Coast. Just like this year.
So the precipitation and temperature anomalies from normal fit the El Nino expectations like glove.
Do you want even more evidence that the low snowpack has the fingerprints of El Nino all over it?
The warm western U.S. and wet California situation this year has been caused by persistent low pressure off the West Coast. Here is a map of the difference from normal of the heights at 500 hPa pressure (about 18,000 ft) for December 1-February 5.
An anomalous low is found offshore. Such lows have warm southwesterly flow on their southern and eastern flanks. This explains the warmth of this winter and wet conditions over California. Note the higher-than-normal heights (pressures) over the northern Plains.
This is exactly the kind of pattern typical of El Nino years. Want proof? Another NOAA website has a composite of El Nino years for the same level. Same pattern Strong low offshore.
Some local media are blaming the lack of Northwest snow on global warming, but they are wrong. The cause is the naturally varying El Nino/La Nina oscillation.
A strong El Nino is the enemy of Northwest mountain snows.
But this enemy has only months to live. Wise reservoir managers understand that in such El Nino years, they must store as much water as possible during the rainy season. The managers of the City of Seattle reservoir system are some of the wise ones– Seattle’s reservoirs are now well above normal! (see below).
