MIDWEST CLIMATE: ABOUT THE SNOWFALL CLIMATOLOGY TOOL

The Midwestern Regional Climate Center is proud to present a snowfall total climatology for over 1800 stations nationwide! This climatology will answer questions such as:

Data Available

Total number of days and average days per year are available for one-day, two-day and three-day snowfall totals. Seven thresholds are available:

   • 0.1 in (Measurable snowfall)
   • 1.0 in
   • 2.0 in
   • 3.0 in
   • 6.0 in
   • 8.0 in
   • 12.0 in

Several of these thresholds were chosen based on National Weather Service criteria in many central U.S. offices for winter weather advisories and winter storm warnings.

Where do I find specific dates? Station threshold searches that include specific dates can be completed through the
cli-MATE
data portal under Station Data>>Daily>>Threshold Search.  Two- and three-day extremes can also be found using the Multi-Day Extremes tool on cli-MATE

Methodology

The climatology consists of data from the 1960-61 snow year, which began on July 1, 1960, through the most recent snow year. Stations were considered only if they had 90 percent of data available during that time frame. Stations with only some months with more than 90 percent of data were included, provided a majority of the data available came during the winter months. Averages were computed by creating a daily average snowfall value and summing those values for monthly and annual averages. This was done to ameliorate issues with missing data.

Two- and Three-Day Totals Limitations

Two- and three-day totals are a summation of snowfall over those periods. This could mean that the snowfall came from multiple events. For example, six inches falls on Day 1, zero inches fall on Day 2 and four inches fall on Day 3. The three-day total of ten inches would be considered to be above the threshold of eight inches and would count, despite coming from separate snowfall events. These totals are also counted multiple times if the one or two day threshold is already met. For example eight inches of snow falls in one day and zero inches fell in each of the previous two days and the following two days. The event will be counted three times under the eight inch threshold as three different three-day periods are considered to meet the threshold.

What are ThreadEx Stations?

Stations that are denoted by grey circles are ThreadEx stations. These stations are “threaded” through multiple stations in a city area to create a longer and more complete period of record. Read more about the cautions and limitations of using these stations here.

Point Rendering (in Web Mapping Application)

The bin intervals in the legend are calculated on-the-fly using a natural breaks method.  The use of this method results in a wider variety of colors showing on the map, compared to other classification methods such as equal interval.  This also means that the size of each bin varies, depending on the data values being symbolized.  ESRI provides descriptions of standard classification methods in ArcGIS here.

Specifically, the web mapping application uses the getClassBreaks method of FeatureLayerStatistics to calculate the class break information.

How Often Will This Climatology Be Updated?

The MRCC will update this climatology once per year after the conclusion of the snow year.