bringing snow and ice to nearly 30 states and affecting nearly 160 million people, forecasters warn. The National Weather Service (NWS) expects "life-threatening cold air" to slowly track from the High Plains and Rockies in an eastward direction from Friday. Meteorologists say temperatures could plunge well below freezing in some areas. Separately, snow showers are already affecting an area of the US downwind of the Great Lakes, which span the US-Canada border, according to the NWS.

US transportation officials, including airport authorities in several major cities, are warning travellers to brace for significant as the severe weather system moves across the US over the weekend. That weather system is expected to take shape in Texas and New Mexico before moving eastward, blanketing cities including Memphis, Nashville, Washington DC, Baltimore, Philadelphia and New York with snow.

The NWS says the coldest wind chills may fall below -50F (-46C) across the Northern Plains, with a much wider area of the south-eastern US also experiencing sub-zero chills. "These wind chills will pose life-threatening risk of hypothermia and frostbite to exposed skin," the NWS warned. While it remains too early to predict exact snowfall totals in urban areas, some places are expected to see over 12in (30cm), weather experts have said. States further south may experience freezing rain, which could coat trees with ice and weigh them down, possibly leading to power outages. Hazardous travel conditions, tree damage and reduced visibility are all expected as well.

Canada is experiencing freezing temperatures of its own, and eastern and Atlantic regions could experience snowfall, meteorologist Geoff Coulson told CBC News. But Coulson said it was too soon to say how big the impacts could be . Governors in several US states, including Texas, North Carolina and South Carolina, have declared states of emergency, allowing emergency officials - including National Guard troops - to begin mobilising response efforts. "Based on current forecasts, the State of Texas is acting to ensure Texans have the resources they need before severe winter weather impacts communities across Texas," Texas Governor Greg Abbott said in a statement on Tuesday. (BBC)