Cooler temperatures are predicted to span much of the eastern part of the United States throughout the month of August.

The first of several spells of below-average temperatures saw shorts exchanged for sweaters across the east of the country over the weekend, with lows of 60F in Chicago and Green Bay on Friday.

Those overnight lows are expected to persist in lands east of the Rockies for the next two weeks, with daytime highs ranging from the upper 70s to the low 80s, according to Weather.com.

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A map shows that a cold front is forecast to sweep across large parts of the country from the east during the first half of August, plunging temperatures below the month's average

Blue spots covering the east and Midwest show a higher chance of temperatures falling below the average for this time of year

A shift in the jet stream is expected to bring unusually cold weather and rain to territories east of the Rockies for the next two weeks, with storms on the East Coast on Monday

Lows of 60F were seen in parts of the east and Midwest over the weekend, with the weather resembling fall rather than summer (Tuesday forecast pictured)

Experts say a southward dip in the jet stream is causing the cooling effect.

This pattern will continue into the second week of August with below-average temperatures affecting much of the East Coast, Midwest, and some of the South.

The Weather Channel reports that Sunday morning saw record breaking lows in Missouri, Kentucky, Tennessee and Indiana.

Another cold front is also expected to bring thunderstorms and showers through the central and eastern states early this week.

The weather divide is visible in Wednesday's forecast, with most places west of Denver seeing sun and high temperatures, while most places east are colder than usual with rain

Forecasters say the pattern of lower temperatures in the east will continue until at least the second week in August, though could reverse after that (pictured, Thursday forecast)

New York City will be hit with showers and cloudy skies Monday morning, with temperatures staying in the high 60s.

Between spells of cold weather temperatures could return to somewhere approaching seasonal norms, but the trend is for weather to be predominantly colder than usual, according to the Washington Post.

This is expected to persist until mid-August, which could then see a reversal of fortunes and warmer-than-average temperatures until September.