(CNN) -
Contrasting temperatures will dominate the weather pattern this week in the continental United States, according to the forecast.
The West will have warmer-than-average temperatures throughout the week, with nearly 30 possible record highs.
In the East, the arrival of autumn air will mean a drop in temperatures in many large cities.
The jet stream, a fast-moving air highway that acts as a barrier between hot and cold temperatures, will take a more extreme form this week allowing heat to linger in the West and intrusions of cooler air in the East. .
From the Midwest to the Northeast and down to the Gulf Coast, a decline in the jet stream is expected to generate temperatures 5 to 8 ° C below average.
In Chicago, Monday's high of 25.5 ° C will be in stark contrast to the end of the week, when the forecast is expected to peak at just around 13 ° C.
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Even in Florida, temperatures and humidity levels will drop.
The greater Tampa area is expected to drop from around 32C at the beginning of the week to around 25C on Wednesday and Thursday.
The cooling in the East will follow possible rains, showers and some thunderstorms.
Heavy local rains could lead to flooding in flooded mid-Atlantic states Tuesday through Wednesday.
Heat Forecast in the Western US
Meanwhile, in the West the heat will increase.
Nearly 30 all-time highs could be reached or exceeded this week, according to Weathermodels.com.
Persistent heat with high temperatures 5-8 ° C above average will last all week.
Medford, Oregon, will potentially break its all-time highs on Monday and Tuesday as it flirts with the century mark.
The high temperatures will be combined with dry air, no rain and gusty offshore winds, creating critical fire conditions.
This pattern of heat in the West and cooler weather in the East is forecast to persist through the first weekend of October and into the following week.
