Concerns over hot and dry weather, which in Argentina grew on Monday, have spread to North America, where a dearth of rainfall and "snow-eater" winds has prompted fears for winterkill, and spring planting conditions.

"There is not much snow cover over crops, which would leave winter wheat exposed in lower temperatures," Commerzbank analyst Carsten Fritsch told Agrimoney.com on Monday.

"And the upcoming season for corn and soybean sowings could be compromised by a lack of moisture in the soil."

The comments followed a prolonged period of unusually hot and dry weather in western and northern US and parts of Canada, highlighted last week by a series of temperature records set in states from North and South Dakota to Iowa to California.

However, there is the prospect of temperatures changing, with weather service WxRisk.com warning on Monday that a "major pattern change" is on its way.

"Winter is coming," the weather service said, adding that a "bitter cold arctic air mass which is been stocked up across northern Canada and the arctic circle is to come southward at a slow but steady pace, driving arctic cold temperatures across the US-Canada border" later in January. 

'Record highs shattered'

"You'll have to excuse the western two-thirds of the US for wondering if we've skipped ahead to spring," weather service MDA Weather said, terming conditions "more indicative of March than January".

"Record highs weren't just set, they were shattered in many spots" last week, hitting 68 degrees Fahrenheit in Sioux City, Iowa, where the previous January record had been 61 degrees, and the same in Mitchell, South Dakota – 17 degrees above the previous all-time high.

Meanwhile, snow cover is a fraction of the normal levels. More than 95% of the area normally covered by snow at this time of year has less-than-usual amounts.

MDA blamed the shortfall on the prevalence of Chinook, or so-called "snow-eater", winds, which have driven temperatures far above normal levels.

'More vulnerable to drought'

Indeed, some commentators have said that farmers might soon be ready to plant corn, were it not for the lack of moisture, also evident in Canada, where the Prairies are reportedly their driest in five years.

Parts of Alberta, Manitoba and Saskatchewan saw only 40% of usual rains in the last quarter of 2011.

Crop forecaster Gail Martell warned last month that Edmonton, Alberta would need nearly twice normal rainfall "to completely restore field moisture" by the end of April, when spring sowings begin.

Furthermore, the "lack of stored field moisture makes 2012 crops more vulnerable to drought".

'A lot more breaks in the thunderstorms'

The dryness has been blamed by some commentators on the La Nina weather pattern which is also widely held responsible for the lack of rainfall which has prompted a series of downgrades to hopes for corn and soybean crops in Brazil and, especially, Argentina.

On Monday, Celeres, the consultancy, cut its forecast for Brazil's soybean crop by 1.2m tonnes to 74.4m tonnes, and its estimate for the corn harvest by 1.3m tonnes to just under 62m tonnes.

And forecasters continued to remove the levels of precipitation expected in rainfall forecast for Argentina on Tuesday and Wednesday.

The latest weather report showed "a lot more breaks in the thunderstorm areas", David Tolleris at WxRisk.com said.

"The coverage and the actual rainfall has decreased to about 50% of central and eastern Argentina."