Around the fifth century, the European Celts believed that animals had certain supernatural powers on special days that were halfway between the Winter Solstice and Spring Equinox.  Folklore from Germany and France indicated that when marmots and bears came out of their winter dens too early, they were frightened by their shadow and retreated back inside for four to six weeks.  This was adopted by the Romans as Hedgehog Day.  When Christianity came into being, the formerly pagan observance also came to be called Candlemas. The earliest known American reference to Groundhog Day can be found at the Historical Society of Berks County in Reading, Pa.  The reference was made on February 4, 1841, in Morgantown, Berks County (Pennsylvania) storekeeper James Morris’ diary:  Last Tuesday, the 2nd, was Candlemas Day, the day on which, according to the Germans, the Groundhog peeps out of his winter quarters and if he sees his shadow he pops back for another six weeks nap, but if the day be cloudy he remains out, as the weather is to be moderate.

In 2024, the NWS groundhogs did see their shadow.  It was 30°F with partly cloudy skies.

In the U.S. the tradition derives from a Scottish poem:

In western countries in the Northern Hemisphere, the official first day of Spring is about six weeks after Groundhog Day, on March 20 or 21.  About 1,000 years ago, before the adoption of the Gregorian calendar when the date of the equinox drifted in the Julian calendar, the spring equinox fell on March 16 instead.  This was exactly six weeks after February 2.  Assuming that the equinox marked the first day of spring in certain medieval cultures, as it does now in western countries, Groundhog Day occurred exactly six weeks before spring. Therefore, if the groundhog saw his shadow on Groundhog Day there would be six more weeks of winter. If he didn’t, there would be 42 more days of winter. In other words, the Groundhog Day tradition may have begun as a bit of folk humor.

Alternatively, the custom could have been a folk embodiment of the confusion created by the collision of two calendrical systems.  Some ancient traditions marked the change of season at cross-quarter days such as Imbolc when daylight first makes significant progress against the night.  Other traditions held that Spring did not begin until the length of daylight overtook night at the Vernal Equinox.  So an arbiter, the groundhog/hedgehog, was incorporated as a yearly custom to settle the two traditions.  Sometimes Spring begins at Imbolc, and sometimes Winter lasts 6 more weeks until the Equinox.

For more information on the various prognosticating groundhogs across North America click here. 

Groundhog Climate Statistics:
 

Below are some Groundhog Day weather statistics for La Crosse, WI, and Rochester, MN.

La Crosse, WI:

The following statistics comprise 151 years of data. From 1873 through 1950, the data came from various locations in downtown La Crosse. Since 1950, the data has been gathered at La Crosse Regional Airport.

The odds of having any precipitation at all on Groundhog Day is 51% (77 out of 151).  There has been measurable (0.01" or greater) precipitation on 42 Groundhog Days (27.8%) and trace amounts (less than 0.01") of precipitation on 35 Groundhog Days (23.2%). 

Since 1893, it has snowed on 62 out of 127 (48.8%) Groundhog Days.  Measurable snow (0.1" or greater) has fallen on 31 Groundhog Days (24.4%) and a trace of snow (a dusting) has fallen on another 31 Groundhog Days (24.4%)

Since 1893, residents have woken up with measurable snow (1/2" or greater) on the ground 113 times (86.3%), no snow 13 times (9.9%), and trace amounts (less than a 1/2" inch) 5 times (3.8%).

In 2023, the high temperature was 20°F and the low temperature was -2°F. No precipitation fell. There was 5" of snow on the ground at 6 AM.  The average wind speed was 12.8 mph.

Rochester, MN:

The following statistics comprise 112 years of data. From 1887 through 1931, the data came from several cooperative observers in the Rochester area. Since 1932, the data has been gathered at Rochester International Airport. No data was taken on Groundhog Day from 1890, 1891, 1908, 1909, from 1921 to 1928.

The odds of having any precipitation at all on Groundhog Day is 47.7% (52 out of 109).  There has been measurable (0.01" or greater) precipitation on 26 Groundhog Days (23.9%) and trace amounts (less than 0.01") of precipitation on 26 Groundhog Days (23.9%). 

Since 1929, it has snowed on 50 out of 104 (47.5%) Groundhog Days.  Measurable snow (0.1" or greater) has fallen on 26 Groundhog Days (24.8%) and a trace of snow (a dusting) has fallen on another 24 Groundhog Days (22.9%). 

Since 1939, residents have woken up with measurable snow (1/2" or greater) on the ground 79 times (89.8%), no snow 5 times (5.7%), and trace amounts (less than a 1/2") 4 times (4.5%).

In 2023, the high temperature was 16°F and the low temperature was -10°F.  A trace of snow fell.  There was 6" of snow on the ground.  The average wind speed was 18.2 mph.

Groundhog Weather History:

Below are some weather events that took place on this day:

• In 1951, a strong arctic cold front moved through central Wisconsin. Temperatures at Alma, WI fell from a high temperature of 41 to -12 by the end of the day. This 53-degree difference between the high and low temperatures tied 3/22/1951 for Alma's greatest diurnal temperature change.
   
• In 1956, Osage, IA received 6" of snow.
   
• In 1965, Theilman, MN had its coldest February temperature (-38°F).
   
• In 1970, a strong arctic cold front moved through the region. Temperatures ahead of the cold front were mainly in the 30s. Once the cold front moved through, temperatures fell throughout the day, falling below zero by the end of the day. One of the greatest temperature changes occurred at La Crescent, MN. They had a high temperature of 38°F and a low temperature of -8°F. This 46-degree diurnal temperature difference is the greatest ever recorded there.
   
• In 1973, Theilman, MN received 6" of snow.
   
• In 1983, a snowstorm brought heavy snows to the region: In IA: Oelwein (10"), Decorah (9"), Marble Rock (9"), Waukon (8.5"), Charles City (7"), Elkader (7"), Waucoma (7"), Fayette (6.1"), and Osage (6"). In MN: Rochester (9.3"), Austin (8"), Grand Meadow (6"), La Crescent (6"), and Minnesota City (6"). In WI: La Crosse (10"), Mondovi (9"), Hillsboro (8.5"), Cashton (8"), Mauston (8"), Muscoda (8"), Necedah (8"), Platteville (6.3"), and Lancaster (6").
   
• In 1996, record low temperatures for February were set in: Cresco, IA (-36°F, also the coldest day on record), Austin, MN (-34°F), Osage, IA (-34°F, also the coldest day on record), Charles City, IA (-32°F), and Lancaster, WI ( -31°F, also tied with 1/23/1963 for the coldest day on record).
   
• In 1998, a snowstorm produced heavy snow in Alma, WI (7"), Harmony, MN (6"), Lanesboro, MN (6"), Neillsville, WI (6"), and Osage, IA (6").
   
• In 2004, an area of low pressure tracked northeast from the southern Plains on the 1st, to across the eastern Great Lakes by the 3rd. An inverted surface trough north of the low brought widespread snow to the region, with the bulk of the precipitation falling on the 2nd. The heaviest snow fell across southeast Minnesota and north-central Wisconsin, with 8-12" common. Amounts south and east of there were in the 4-8" range. Some specific totals from the event: In IA: Osage (8.7"), New Hampton (8"), Charles City (7.5"), Mason City (6"), Oelwein (4.5"), Fayette (4.3"), Decorah (4"), and Elkader (4"). In MN: Austin (12"), Grand Meadow (11"), Theilman (9.9"), Rochester (9.4"), Owatonna (8.5"), Preston (5.4"), Caledonia (5.3"), and Zumbrota (5"). In WI: Mondovi (7.6"), Alma (7"), Hatfield (7"), Cashton (6"), Neillsville (6"), Viroqua (6"), La Crosse (5.9"), Genoa (4"), Lynxville (4"), Mauston (4"), and Richland Center (4").
   
• In 2016, a winter storm moved through the region. Snow spread across Iowa early that morning, with the heavy snow reaching the Interstate 90 corridor mid to late morning.  Snowfall rates of 2" per hour were common during the peak, which led to snow-covered roads very quickly. Hazardous travel conditions developed shortly after snow onset. Snow let up for a time late in the day, but returned overnight and early the next day adding to the snowfall totals.  Several more inches of snow fell from a few bands that developed before the storm moved off to the east. Warm air became a factor as well, leading to lower snowfall totals in parts of northeast Iowa and southwest Wisconsin.  A wintry mix or just rain fell at times. Strong winds, with gusts of 35 to 45 mph, led to blowing and drifting snow, especially in open terrain and ridge tops.  The warmer temperatures lowered the blowing snow threat for some areas though, especially along and south of Highway 18 in southern Wisconsin and northern Iowa.
   

• In 2018, temperatures warmed dramatically across the area.  After early morning low temperatures in the single digits and teens, temperatures quickly warmed to around 40°F.  This resulted in widespread dense fog across the area.

• In 2020, there was an unseasonably warm air mass over the region.  The high temperature was 42°F (5th warmest Groundhog Day) at Rochester MN and 50°F (second warmest - only 2006 was warmer with a high temperature of 51°F) at La Crosse WI.