This winter will be warm and dry in much of the United States, federal meteorologists said yesterday.

But much about the December-to-February winter outlook released yesterday by the National Oceanic and Atmospheric Administration is uncertain, in part because a developing El Niño weather pattern seems to have abruptly fizzled.

"This year's winter outlook has proven to be quite challenging, largely due to an indecisive El Niño," said Mike Halpert, deputy director of NOAA's Climate Prediction Center. "Typically by mid-October, we've got a good picture of the climate factors that will influence the winter season."

But this year, he said, "that has not been the case."

Conditions in the tropical Pacific Ocean, where El Niño forms, appeared to favor the development of a weak to moderate El Niño this year. Surface waters were warmer than normal for much of the summer, the hallmark of an El Niño.

In June, federal forecasters projected a 50 percent chance that a weak-to-moderate El Niño would emerge this winter.

But last month the development of the weather pattern fizzled, Halpert said, and sea surface temperatures in the tropical Pacific are back to normal.

The switch has puzzled scientists who study El Niño and its counterpart, La Niña.

"This is unique in roughly 60 years of data," Halpert said. "Why it's happening is something that we really don't know at this point. Certainly, our models didn't pick up on that. Our computer models, dynamical models, really favored this to develop."

And that uncertainty over the fate of El Niño is one of several factors that led to a winter outlook that shows much of the country facing roughly equal chances for conditions that are hotter or colder than normal, or drier or wetter than normal, over the next few months.

An El Niño year normally brings cooler and wetter weather in the southern United States, drier weather in the Pacific Northwest and wetter weather in Southern California.

Winter wheat may fade, too

The outlook released yesterday projects a warmer-than-average winter in much of the country, including most of Texas; the Central and Northern Plains; the Southwest; the Northern Rockies; northern Alaska; and eastern portions of Washington, Oregon and California.

It sees cooler-than-average temperatures for Hawaii and most of Florida, and wetter-than-average conditions across the Gulf Coast from northern Florida to eastern Texas.

A persistent drought now troubles the winter wheat crop in the upper Midwest. Click the map to watch a six-week animation. Photo courtesy of the University of Nebraska, Lincoln.

Hawaii; the Pacific Northwest; Northern California; Idaho; western Montana; and parts of Wyoming, Utah and Nevada will be drier than average.

The forecast offers little immediate hope for relief from the drought that has devastated the central United States.

"Above-normal temperatures, including episodes of record and near-record warmth, have been consistent since last fall," said Deke Arndt, chief of climate monitoring at NOAA's National Climatic Data Center. "It appears likely that 2012 will be the warmest [year] in the 118-year record for the contiguous United States."

The year to date is the warmest period on record in 25 states, including many in the Plains and Rockies, he said, and much of the country has been unusually dry this year.

The U.S. Drought Monitor's latest update, issued yesterday, shows that the total footprint of the current drought in the lower 48 states has shrunk slightly for the third straight week, falling from 63.55 percent last week to 62.39 percent this week.

The unusually dry conditions are hampering the growth of the country's winter wheat crop.

In South Dakota, where 57 percent of the state is suffering "extreme" or "exceptional" drought, just 11 percent of the winter wheat crop has emerged. That is 56 percentage points below the five-year average, according to statistics compiled by the Agriculture Department's Office of the Chief Economist.

The growth of this year's winter wheat is 30 percentage points below average in Nebraska, 21 points below average in Colorado and 28 points below average in Montana, the agency said.