DES MOINES, Iowa — As another winter storm heads to Iowa, some may wonder why certain locations are placed under a Winter Storm Warning, while others fall under a Winter Weather Advisory.

The answer has to do with the forecast of course, but also with Winter Storm Warning criteria.

Criteria for Winter Storm Warnings and Winter Weather Advisories vary by the National Weather Service office. At the Des Moines National Weather Service office, that criteria includes:

  • At least 6 inches of snow in 12 hours
  • At least 8 inches of snow in 24 hours
  • 1/2 inch of sleet
  • 25 mph winds

When a Winter Storm Warning is issued, only essential travel is recommended.

Winter Weather Advisories are issued when less serious weather impacts are expected. That criteria includes:

  • 3-5 inches of snow
  • Less than 1/2 inch sleet
  • Less than 1/4 inch freezing rain

When winter weather advisories are in place, travel can still be difficult, and you’re asked to use caution.

As for this winter storm (impacting Iowa for February 15-16), Polk county and Des Moines are right on the dividing line for where the Winter Storm Warning and Winter Weather Advisory have been issued. Some have asked why Des Moines isn’t included in the Winter Storm Warning.

For this weather system, Polk county (along with surrounding counties to the west and east) is right on the edge, where snow totals will drop off. Around 3-6″ of snow is expected in Des Moines, and those totals will likely vary from northwest (less) to southeast (more) in Polk county itself.

In the end, the division line between higher and lower totals has to happen somewhere, and for this system, it just happens to fall right over Polk county!

Regardless of which warning or advisory you’re under, conditions will be slick late Wednesday night into Thursday.