Yes you can apply now.  HealthCare.gov and all state marketplaces allow a special enrollment opportunity when people lose other coverage.  This includes loss of job-based coverage as well as loss of Medicaid.

In general, you have 60 days following the loss of other coverage to apply for a special enrollment opportunity through the Marketplace.  In HealthCare.gov and some other states, if you have advance notice of your coverage loss, you can apply for the special enrollment opportunity up to 60 days in advance.

HealthCare.gov will ask for proof of coverage loss before you can sign up for new coverage.  For example, you may have received a notice from your employer indicating that your job-based coverage will end.  You will have to submit documentation and have it approved by HealthCare.gov before you can complete your application and choose a new health plan.

In general, your new Marketplace coverage will take effect on the first of the month following the date you select your new plan.  If you apply in advance of coverage loss, in HealthCare.gov states you can elect to have new coverage begin on the first day of the month following the date your old coverage ends.

Navigators are available to help people through this process.  You can find the program closest to you at Find Local Help.