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Source: THE AS­SO­CI­AT­ED PRESS

Harsh weath­er moved west on Mon­day as a po­lar vor­tex was ex­pect­ed to grip the Rock­ies and the north­ern Plains af­ter win­ter storms pum­melled the east­ern U.S. over the week­end, killing at least 10 peo­ple, in­clud­ing nine vic­tims in Ken­tucky who died dur­ing flood­ing from heavy rains.

The Na­tion­al Weath­er Ser­vice warned of “life-threat­en­ing cold” in­to Tues­day, with tem­per­a­tures in north­east­ern Mon­tana pre­dict­ed to dip as low as 45 de­grees be­low ze­ro (-42.7 de­grees Cel­sius) with wind chills down to 60 be­low (-51 de­grees Cel­sius).