El Niño, in the central and eastern equatorial Pacific Ocean, is expected to be a dominant climate factor that will influence the December through February winter weather in the United States.
According to the 2009 Winter Outlook by NOAA’s Climate Prediction Center, El Niño could bring some big changes to Arizona.
“We expect El Niño to strengthen and persist through the winter months, providing clues as to what the weather will be like during the period,” said Mike Halpert, deputy director of the Climate Prediction Center – a division of the National Weather Service.
El Nino usually means above normal rainfall for Phoenix and above normal snowfall for the high country for the months of December through February.
Two of the last three El Nino events provided above normal rainfall for the Valley during the winter months.
The most recent El Nino was the winter of 2006-2007 where only 1.23" of rain fell across the Valley which was 1.22" below normal for that time period.
However, the El Nino events of 2002-2003 and 1997-1998 were very wet with above average rainfall for the Valley.
Rainfall for the winter of 2002-2003 ended up at 3.88" which was almost 1.5" above normal. And rainfall for the winter of 1997-1998 ended up a wet 4.11" which was 1.66" above normal.
When looking at snowfall for the high country during El Nino, we find out that there is a significant difference in the amount of snowfall for the area when the El Nino is considered strong compared to moderate or weak.
Lets focus on the Flagstaff area. The last three strong El Nino events occurred in 1997-1998, 1991-1992, and 1982-1983.
The El Nino of 1997-98 produced 136.7" of snow which is more than 27" above normal.
The El Nino of 1991-92 produced 158.9" of snow which is more than 49" above normal.
And the El Nino of 1982-83 produced 142.6" of snow which is more than 33" above normal.
The El Nino events of 2006-07 and 2002-03 were considered weak to moderate and only produced 50 percent of the normal amount of snow for the winter months.
“Other climate factors are also likely to play a role in the winter weather at times across the country,” added Halpert. “Some of these factors, such as the North Atlantic Oscillation are difficult to predict more than one to two weeks in advance. The NAO adds uncertainty to the forecast in the Northeast and Mid-Atlantic portions of the country.”
Highlights of the U.S. Winter Outlook (December through February) include:
*
Warmer-than-average temperatures are favored across much of the western and central U.S., especially in the north-central states from Montana to Wisconsin. Though temperatures may average warmer than usual, periodic outbreaks of cold air are still possible.
*
Below-average temperatures are expected across the Southeast and mid-Atlantic from southern and eastern
Texas to southern
Pennsylvania and south through
Florida.
*
Above-average precipitation is expected in the southern border states, especially
Texas and
Florida. Recent rainfall and the prospects of more should improve current drought conditions in central and southern
Texas. However, tornado records suggest that there will also be an increased chance of organized tornado activity for the
Gulf Coast region this winter.
*
Drier-than-average conditions are expected in the
Pacific Northwest and the
Ohio and Tennessee River Valleys.
* Northeast: Equal chances for above-, near-, or below-normal temperatures and precipitation. Winter weather in this region is often driven not by El Niño but by weather patterns over the northern Atlantic Ocean and Arctic, such as the North Atlantic Oscillation. These patterns are often more short-term, and are generally predictable only a week or so in advance.
* California: A slight tilt in the odds toward wetter-than-average conditions over the entire state.
* Alaska: Milder-than-average temperatures except along the western coast. Equal chances for above-, near-, or below-median precipitation for most areas except above median for the northwest.
* Hawaii: Below-average temperatures and precipitation are favored for the entire state.
This seasonal outlook does not predict where and when snowstorms may hit or total seasonal snowfall accumulations. Snow forecasts are dependent upon winter storms, which are generally not predictable more than several days in advance.
