Chicago’s string of mild weather will continue through the remainder of this week, before colder conditions arrive for the last weekend of the year. High temperatures on Christmas Day should top out around 40, nearly 20 degrees higher than the city’s 21-degree high recorded last Christmas. By Thursday, unseasonable warmth will arrive as Chicago area temperatures surge well into the 50s as the city lies on the warm side of a strong winter storm, slated to bring heavy snow to portions of the northern Plains and upper Midwest. Waves of rain and even some rare December thunderstorms are expected here as the city basks in its warmest weather since Halloween when the mercury peaked at 61 degrees. In the wake of the storm, colder weather will follow by the weekend as temperatures return to more seasonable levels in the lower 30s.