* Geographic and topographic maps created from the USGS/ESRI ArcGIS mapping software and database
Seasonal snowfall varies greatly within the city and it's surrounding communities. The mean (average) seasonal snowfall at the National Weather Service Forecast Office in Duluth near the Duluth International Airport is 90.2 inches based on records for the 30-year period of 1991 to 2020. The previous 30-year average for the period of 1981 to 2020 was 86.1 inches. The National Centers for Environmental Information updates climatological averages every 10 years by dropping the oldest 10 years and adding the most recent 10 years. Please note that the office was moved a very short distance in 1996 from the airport to its current location along Miller Trunk Highway so some of the measurements included in the average are from the airport location. Snowfall averages which include periods of record longer than 30 years, but do not include measurements taken prior to the office being moved from downtown Duluth to the airport in 1950, are also near or above 80 inches. The National Weather Service location gets more snow than most of the city of Duluth. The office is at a higher elevation and is farther away from the warming influence of Lake Superior but is still close enough to get the added moisture. For more information on Duluth's weather station history, go to the National Weather Service's office history page.
After 19 or more years of making personal observations, examining snowfall reports given to the National Weather Service, and talking to people who live in the area, seasonal snowfall appears to be 20 to 30 inches greater on top of the hill than at the bottom near the lakefront. The lower elevations of the far western communities such as Gary-New Duluth get around 60 inches while the higher areas several miles inland get from 85 inches to around 90 inches.
Clippers
The presence of an upper-level high pressure ridge over the west coast of the Canadian province of British Columbia forces storms north into southeast Alaska, the Yukon Territory, and northern British Columbia. The remains of the storms then dive to the southeast through the Canadian provinces of Alberta or Saskatchewan and then into the northern United States where they turn east across the Great Lakes. Sometimes turn east sooner and stay in southern Canada. Sometimes they drop much further south into the Middle Mississippi Valley states, such as Missouri or Iowa, before turning east. Clippers are usually fast-moving weather systems that lack access to moisture even if they are fairly strong.
Pacific Northwest storms
Pacific Northwest storms are those that enter Washington State or Oregon and sometimes southern British Columbia and northern California. They move east across the northern half of the United States and typically produce 3 to 5 inches in Duluth as they pass through. The storms sometimes amplify and slow down, allowing them to ingest more moisture, then produce snowfalls of 6 inches or more.
Southwest storms
Strong southwest storms produce the majority of larger snowstorms in Duluth of 8 inches or more. They originate in the southern Rockies, the southern half of the Plains, or the middle to lower Mississippi Valley. Many southwest storms are hybrids where an upper trough in a southern branch of the jet stream phases in (that is combines) with an upper trough in a northern branch to create a larger, stronger storm with access to both cold air from the north and moisture from the Gulf of Mexico to the south.
Southwest storm blocking patterns
Concerning snow producing storms that approach from the southwest, a northern branch of the jet stream can dip far enough south to block a southern storm system from moving far enough north to spread snow into the Duluth, MN and Superior, WI area. One particularly annoying blocking pattern is when a trough embedded in the northern jet sits over Hudson Bay with northwest wind flow aimed into the Western Great Lakes on the west side of the trough. In this case, the snow-producing southern storm system is deflected or sheared off to the east. Sometimes if the southern storm is moving slow enough, the northern jet stream trough will pass to the north and only temporarily suppress snow to the south. The southern storm and the snow it produces will then have a chance to slip northeast behind the exiting northern jet stream trough. Also, if another trough in the northern jet is approaching from the west, that trough can draw the southern storm to the northeast.
The April 13 to 16, 2018 snowstorm that hit Minnesota and Wisconsin hard with widespread 12 to 24 inches of snowfall accumulation is a case where the scenario just described played out. The onset of continuous accumulating snow in Duluth, MN, and Superior, WI was initially held to the south by a northern jet stream upper-level trough north of the Great Lakes. As the trough moved to the east, the next trough in the northern jet sank southeast into the West Coast of the United States. That next trough appeared to help push the southern storm to the northeast in the break between the two northern jet stream troughs. A summary of the April 13 to 16, 2018 snowstorm includes more details.
Lake-effect storms
Lake-effect storms are not really a storm track. A dominantly lake-effect storm is one where the main production of snow is from the lake rather than a larger scale (synoptic scale) storm system which could also be producing snow at the same time. Snow from synoptic-scale storms can help moisten the air over the lake so that less dry air has to be overcome before clouds and snow can form. Snow from a synoptic-scale storm can also seed clouds that already exist over the lake. When a synoptic-scale storm is the primary snow producer, snow from the lake is usually referred to as lake enhancement rather than lake-effect.
Back-Door Storms
This term is borrowed from the concept of the back-door cold front. A back-door cold front is one that comes from the east or northeast. Back door storms are those that would approach from any east component direction, but usually from the southeast. Back-door storms tend to be hybrids of southwest storms. They have a strong left turn that causes their track to bend west of due north as they move into the western part of the Great Lakes region. A snowstorm that dumped heavy snow on Duluth the day before Christmas in December 2007 is an example.
More information
Sometimes Pacific Northwest storms and even clippers produce major snowstorms. In these cases, the upper trough embedded in the jet stream amplifies and slows down. The surface low pressure center intensifies or may redevelop farther south then intensify as it moves northeast. Amplification of the trough could result from being blocked by a strong high pressure ridge to the east. The slower movement allows the storm more time to ingest moisture and increases the duration of the snowfall.
March 13, 2004 (snow and snow pellet mix) January 1, 2005 (5 inches in two hours) March 1, 2007 April 5, 2008 (cloud-to-ground lightning observed) April 11, 2008 (cloud-to-ground lightning observed) November 13, 2010 April 15, 2011 April 11, 2013 April 14, 2013 February 20, 2014 November 18, 2016 (sleet, then snow-sleet mix, then snow) May 8, 2019 March 28, 2020 December 14, 2022The list of thunder observations does not include thunder that may have been officially recorded or observed by other residents in the area. For example, a small cluster of convection passed over and just south of Duluth from approximately 11:30 PM CST March 4, 2023 to 12:15 AM CST March 5, 2023. The storms produced mixed precipitation including snow, snow pellets, and hail based on personal observation, weather reported by the ASOS at the Duluth International Airport, and reports from the public given to the National Weather Service Forecast Office. Lightning was visible mainly toward the south from Duluth including in the remarks section of the official weather observations. Did not personally hear thunder but it may have been heard by other residents.
Since 2001-2002, five snow seasons in Duluth, MN have exceeded 100 inches as recorded by the National Weather Service. Three snow seasons failed to exceed 50 inches. Using the Oceanic Niño Index as a guide, the data for each season includes a description of the ENSO conditions that influenced the season. A stronger El Niño is one that generally peaks around or above an index of 2.0. A stronger La Niña is indicated by index values around or below -2.0. Other indexes are also available such as the Multivariate ENSO Index (MEI). The index appears to generally support the assessment of the Oceanic Niño Index for this particular analysis.
High Snow Seasons
2003-2004 109.9 Near Neutral
2012-2013 129.4 Near Neutral
2013-2014 131.0 Near Neutral
2018-2019 106.8 Weak El Niño
2022-2023 140.1 Weakening La Niña especially after December
Low Snow Seasons
2011-2012 49.7 Moderate La Niña
2014-2015 49.2 Weak El Niño
2023-2024 38.7 Moderate to almost strong El Niño
*This value includes snow that fell during all of the days the storm affected the region, not just the blizzard conditions that occurred from late evening December 13 into December 15.
Personal measurements for the same storms in the same order are 27.6, 20.0, 28.0, 22.0, 19.0, and 21.8.