As residents of Chicago enjoy a partly sunny sky with a high near 69 degrees today, the National Weather Service cautions of a stark shift in weather beginning later tonight, with a 70% chance of showers and possible thunderstorms after 1 am, including a threat of heavy rainfall; northeastern winds will be blowing at 5 to 10 mph, reports the NWS forecast. Alongside this, Lake Michigan beachgoers are alerted to a high swim risk through this evening, while all mariners are advised on hazardous conditions today for small craft on Illinois and Indiana nearshore waters, according to a Hazardous Weather Outlook by the National Weather Service Chicago/Romeoville IL.