As shown here, you could write:
@echo off
set daysofweek=Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday
for /F "skip=2 tokens=2-4 delims=," %%A in ('WMIC Path Win32_LocalTime Get DayOfWeek /Format:csv') do set daynumber=%%A
for /F "tokens=%daynumber% delims=," %%B in ("%daysofweek%") do set day=%%B
echo day number %daynumber%
echo day %day%
(script copied from http://www.sysnative.com/forums/windows-tips-tricks)