El Niño, La Niña, La Nada...winter rainfall for 2002
Remember El Niño? La Niña? The Pineapple Express? How about La Nada?
Researchers in recent years have been able to correlate changes in ocean temperatures with rainfall patterns along the west coast.
Here's a summary of the official government review of ocean temperatures:
As of Aug. 3, 2001, "sea surface temperature anomalies continued to increase...."
In other words, we are tending towards El Niño in the Southern Oscillation effect that rotates between El Niño and La Niña. [This year has been described as "La Nada" because ocean temperatures are neither warmer nor cooler than average].
Pacific ocean temperatures in the anomalous areas are "rising to their highest levels since the 1997-98 warm (El Niño) episode."
Over the past two years there has been a gradual trend towards El Niño and away from La Niña. This increase in temperatures is likely to continue into 2002. The effect on temperatures and rainfall that result from this depend on the "intensity"--i.e., how warm this upcoming El Niño event is. Most computer models predict a weak to moderate warm El Niño by the end of 2001 and into winter of 2002.
So this is the forecast:
"A gradual transition to warm episode conditions [El Niño] is expected to continue...through early 2002.
What does this mean for Northern California in winter 2002?
Southern Oscillation events are mostly useful for predicting rainfall, not temperatures, in Northern California. But wet years tend not to have severe freezes.
Strong El Niño years tend to be wet here; some of them are the wettest on record.
Mild El Niño years tend to be "normal."
La Niña years tend to be dry, but it is not uncommon for them to have episodes of the "banana express"--warm, wet storms that cause flooding.
So, what does this winter have in store? Try the following article from a couple years back...
CAPITAL WEATHER HAS A TROPICAL INFLUENCE
From the Sacramento Bee, Jan. 2, 1999 By John D. Cox, Staff Writer
Forget El Niño, forget La Niña. Scientists say the West Coast's biggest flooding threat comes from a more obscure climate creature that can sling tropical moisture thousands of mile across the sea like a runaway fire hose. Their latest research shows how North America's winter is fed by pulses of big storms in the far western Pacific Ocean off the coast of Indonesia, a third of the way across the globe.
For the first time, climate forecasters say they can tell months in advance whether conditions are shaping up to pose a particularly high risk of flooding to Northern California. "The key is, the interaction is coming through the Pacific jet stream," said a senior research meteorologist.
[According to their research] Northern California, especially the American River watershed, is most prone to flooding during winters when the equatorial Pacific Ocean seems to be preparing itself for an El Niño the following year. These high risk winters accounted for the top three of the worst five floods on the American River in the past half-century. The other two are La Niña winters.
[Researcher Wayne Higgins] is focused on a smaller phenomenon ... caused by a rolling atmospheric wave known ... as a Madden-Julian Oscillation ... a powerful windy ripple in the atmosphere that encircles the equator about every 40 days. This MJO poses the biggest threat of flooding to the U.S. West Coast, and to Northern California in particular.
This wave of tropical storminess pumps huge amounts of warm moisture into the atmosphere and can lead to the dreaded series of torrential rain storms known as the Pineapple Express. The five worst floods on the American River since 1950 were the work of the Pineapple Express.
Said another researcher, "the intermediate periods, where nature is sort of cocking the gun just before the El Niños, actually are the ones where you tend to get the heavy rain events. "It would be a sequence like this. We would say, OK, California, no El Niño or La Niña, but the western Pacific is warmer than normal. There is some slight chance that during this coming winter you might see a Pineapple Express."
In El Niño years, the effects of the MJO are obscured by the more dominant features of warm seas and reversed winds and the towering tropical storms they spawn. In La Niña years, the unusually cool waters over the central and eastern Pacific curb the MJO's progress eastward. But the effects of the MJO ... are dramatically apparent during "neutral winters before El Niño."
You read it here first......
© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
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