el_nino

NOAA update

see el_linko for cool graphics and march-may '05 forecast details...

The Latest Word on El Niño
February 28, 2005

El Niño is a disruption of the ocean/atmosphere relationship in the Pacific Ocean that can have significant impacts on global weather patterns. Eastern and central Pacific equatorial ocean temperatures rise, deep tropical convective activity shifts eastward with the warmer temperatures, and surrounding weather patterns are altered. (El Niño conditions officially exist when equatorial Pacific Ocean temperatures equal or exceed 0.5° C above normal for three consecutive months).

Weak El Niño conditions have existed in the tropical Pacific since the Summer of 2004. Through mid January, however, there little effect on the global atmospheric circulation and precipitation patterns. However, in early February 2005, the atmosphere finally began to react. Precipitation over the warm waters of the west-central Pacific Ocean increased and became more persistent.

(In contrast, the culprits for the severe Winter weather in the West during January was due to the combination of the Madden Julian Oscillation (MJO) and a blocking ridge of high pressure. Though not related to El Niño, the MJO is a cyclical period of disturbed weather patterns over the central Pacific Ocean. On a time scale of 30 to 60 days, it is marked by warmer sea surface temperatures and an increase in deep atmospheric moisture.

Moisture is then carried eastward across the ocean by a unique jet stream trajectory called the "Pineapple Express". The recent MJO episode resulted in a three week period of rapidly moving disturbances that brought heavy precipitation to much of the western U.S. between Christmas and mid January. A break down of this pattern then occurred during the last half of January.

By mid February, the Pacific Jet Stream began to respond to the current weak El Niño conditions by strengthening and extending eastward into the eastern North Pacific, contributing to the storminess in Southern California.

Latest El Niño Forecast:

Equatorial sea surface temperatures are forecast to continue a cooling trend, and a transition from a weak El Niño to neutral conditions is expected during the next three months. Despite this weakening, convection near the International Date Line may continue to influence the circulation and precipitation patterns over the eastern North Pacific Ocean into the Spring. This is reflected in the latest 90 day outlook, which suggests a wetter than normal period for eastern Utah and western Colorado.