December 4, 2023
There have been some changes to the NWS Winter Storm Warning Criteria. As we are heading into the winter season, the NWS thought this was worth passing along to all of their partners for overall general awareness, but also because it may have an influence on your decision making and planning.
These changes will be the same for southern Illinois, southeast Missouri, and western Kentucky.
Up until this point, the NWS would issue winter storm warnings based on 12- and 24-hour snowfall totals (other winter parameters, as well).
However, there was a nationwide overhaul of the snowfall criteria, in an effort to make NWS offices and states better aligned.
The new criteria for all of Kentucky moving forward is as follows.
Heavy snow accumulation of 4 inches or more per event (an event being up to 48 hours in duration)
AND/OR
Sleet accumulation of ½ inch or more
AND/OR
Mixed precipitation with at least one winter hazard type (blizzard, freezing rain, sleet, or snow) meeting or exceeding warning criteria
OR
High impact frozen precipitation outside of the normal winter season or during a critical situation (standard criteria not being met, but impacts are expected to be unusually significant).
There is no longer a 12- or 24-hour restriction, but rather winter storm warnings for snow are event based with a max duration of 48 hours.
How will this impact you?
Because the warning duration is now stretched to 48 hours, it may be easier to reach a 4-inch criteria in some locations, especially in our higher terrain. Therefore, there is a chance that this may result in more winter storm warnings, especially for the far southeast portion of eastern Kentucky.
Also, if you are under a winter storm warning for 4 inches or more of snow, keep in mind that it may not be a short duration event, but rather may stretch through a 2-day period. For example: we may get 2 inches of snow on one day, and 2 inches on the next day, and this is now considered to be Winter Storm Warning criteria so long as it’s within a 48-hour period.
The NWS will specify the duration, amounts, and impacts expected in our warnings to give the warning better context.
