It appears WN has already cancelled morning flights from MDW tomorrow and (currently) have flights leaving 13:00 or so still scheduled for departure.
https://www.southwest.com/html/advis...052449128.html
Based on the forecasted weather conditions for the cities listed below, our scheduled service on Thursday-Friday, February 8-9, may be disrupted (flights may be delayed, diverted, and/or cancelled):
Buffalo (BUF)
Chicago (MDW)
Cleveland (CLE)
Detroit (DTW)
Flint (FNT)
Grand Rapids (GRR)
Milwaukee (MKE)
Rochester (ROC)