Weather tracker: North-west US hit by snow ahead of eastern heatwave

Western states experience unseasonally low temperatures but New York and Washington DC could reach 40C by end of week

Unseasonal snow has fallen in some parts of the US, while other parts of the country brace for a heatwave this week.

A strong cold front spread into the western US from the northern Pacific over the weekend, bringing an abrupt change in conditions to a region that had been experiencing high summer temperatures amid drought. Temperatures from the Canadian border to California have widely been 5-10C below the norm since Friday, and more than 10C below in some parts farther north. The pattern is expected to remain for much of the coming week.

The cold front brought the first significant rainfall in weeks to several parts of the north-west US. Across the Rocky mountains in Idaho, Montana and Wyoming, this combined with the unseasonal cold to produce snowfall at unusually low elevations for the time of year. Whereas the snow line in summer typically sits at about 3,300 metres (11,000ft), snow fell as low as 1,800 metres on Sunday, with more due to fall on Monday. Several inches are expected to accumulate at higher altitudes.

Counterintuitively the cold front has also strongly increased the danger posed by wildfires. With much of the western US currently suffering some form of drought, lightning strikes from the leading edge of the front posed an ignition risk to the widespread dry vegetation and plant litter, while heightened winds fuelled the spread of existing fires.

The gustiest conditions over the weekend were in Utah, Colorado, and Arizona, where several major fires were already burning. The strong winds will move north into Wyoming on Monday. The 2026 fire season is shaping up to be one of the worst on record in terms of number and the extent of the areas affected.

Temperatures were a little below average across many other parts of the northern US over the latter part of last week but that is set to radically change over the next few days. A heatwave developing over the north-east in the run-up to the Fourth of July weekend will push temperatures into the high 30s celsius for several parts of the midwest and north-east.

Forecast models suggest highs could possibly reach 40C (104F) for cities including New York, Philadelphia and Washington DC on Thursday and Friday, with night-time lows struggling to drop below the high 20s celsius. By contrast, the average daily high for these cities in July varies from 29C in New York to 32C in Washington. The temperature records stand at 42C for New York and 41C for Philadelphia and Washington.