Given weather related issues, California, Maryland Rhode Island and Washington, D.C. have extended their open enrollment windows to purchase an Affordable Care Act (ACA) policy:

During the first two open enrollment periods, Healthcare.gov and most of the state-run exchanges extended the final deadline for enrollment. This time around, Healthcare.gov did not extend enrollment, other than to help people complete enrollments that were begun by midnight on January 31.

Just four state-run exchanges announced open enrollment extensions, and at least two of them only apply to people who began their enrollments by January 31:

Maryland: The exchange tweeted that anyone who begins the process by January 31 but is unable to finish on time due to the recent snowstorm, will have until February 5 to complete the enrollment. Enrollments had to be started by January 31, and enrollees must attest that the January blizzard interrupted their ability to finish enrolling by the end of January.
California: The exchange issued a press release stating that anyone who begins the process by January 31 but is unable to finish on time will have until February 6 to complete the enrollment.
Washington DC: Due to the blizzard on the east coast in late January, the DC exchange is giving all residents an additional two days to enroll. The new deadline is February 2 at 11:59pm. Enrollments completed by February 2 in DC will have coverage effective March 1.
Rhode Island: The exchange has a notice on their home page, indicating that people who weren’t able to get through to the call center have until February 8 to enroll. It’s unclear whether this applies to everyone, or just to people who began the enrollment process by January 31. We’ll update this page as more information becomes available.