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Thundersnow, Blizzard, and Heavy Snow

Duluth, MN

December 13 to 17, 2022


WSR-88D Radar, National Weather Service, Duluth, MN

* This storm summary is a work in progress and updates are being made. *

Storm discussion outline

Storm highlights

1. The storm produced excessive snow totals of 20 to 30 inches in the higher elevations of Duluth and the North Shore of Lake Superior. A few locally higher amounts also reported by weather spotters to the National Weather Service in Duluth. Would have been even more snow if it had not been mixed with sleet and freezing rain for the first few hours. Much less snow accumulated in the lower elevations of Duluth near the shore of the lake and also in the city of Superior, WI. Only one-third to one-half as much accumulated compared to the higher elevations. Warmer temperatures and more mixed precipitation held down the snow totals.

2. Respectable snow totals of 10 to 20 inches were also reported over the rest of northeast Minnesota and northwest Wisconsin. Again, some areas along the lake shore right near the water got much less snow.

3. Thundersnow occurred several times during Wednesday morning, December 14, especially between 7 AM and 8 AM.

4. East winds gusting over 40 mph helped produced occasional blizzard conditions in spite of the density of the wet snow. Peak wind gusts measured at the Duluth International Airport were 43 mph from east on December 14 and 48 mph from the east on December 15. Winds were likely stronger near the ridge crest.

5. Winds converging at the head of Lake Superior and strong orographic enhancement due to a deep layer of east to southeast onshore winds boosted snow totals along and inland of the ridge crest of the North Shore.

6. The Long duration storm spanned five calendar days with heavy snow occurring from late evening December 13 through the morning of December 14 and from late evening December 14 through the early morning of December 15.

7. Snow accumulated 10 to 12 inches in the higher elevations of Duluth during each of the two periods of heavy snow. Snowfall rates peaked around 2 inches per hour.

8. Generally light to moderate, fluffy, and highly dendritic snow fell for rest of the event and is included in the snow totals used in this storm summary. The exception was that a few heavy snow showers developed on Friday afternoon, December 16 that prompted the National Weather Service to issue several snow squall warnings.

9. This snowstorm was large in geographic coverage as it dumped heavy snow over a much larger area than just northeast Minnesota and northwest Wisconsin. One to two feet of snow fell from the rest of northern Minnesota through almost all of North Dakota and South Dakota. Noticed two reports of 48 inches in the Black Hills of South Dakota as reported to the National Weather Service in Rapid City, SD.

Widespread heavy snow

Two sequences of images from the WSR-88D Radar at the National Weather Service in Duluth, MN are shown below. The first animation shows heavy snow occurring early in the morning around sunrise on December 14 at approximately the time that thunder was reported in the weather observations for the Duluth International Airport. The second animation shows the peak of the second period of heavy snow which occurred between midnight and 6 AM on December 15. The snow continued beyond 6 AM but was lighter on average. Notice the difference in character of the two radar examples. The reflectivities for the first period of heavy precipitation are clearly more cellular. Some of the stronger reflectivities in Wisconsin denoted by the orange to red colors are due to mixed precipitation. The second period of precipitation is more consistent but still some very heavy snow indicated by the patches of yellow embedded in the large dark green areas.



Thundersnow reports

This author observed thundersnow at approximately 7:34 AM CST ( 13:34 UTC) and again at 10:27 AM CST (16:27 UTC). Meteorological Aerodrome Reports (METAR observations) for the Duluth International Airport (KDLH) showed thunder in the observations between 7:30 AM and 8:00 AM CST (13:30 UTC and 14:00 UTC). The following is a portion of the observations taken from the National Weather Service's Aviation Weather Center for KDLH in reverse chronological order with the more recent observations times listed first.

KDLH 141404Z 09023G36KT 1/4SM R09/3500V4500FT +SN BLSN VV005 M01/M02 A2976 RMK AO2 PK WND 07036/1403 TSE1358 P0001 T1006101

KDLH 141355Z 09021G35KT 1/4SM R09/2800V4500FT +TSSN BLSN OVC005CB M01/M02 A2976 RMK AO2 PK WND 09037/1333 SLP098 OCNL LTGIC SE TS SE MOV NW SNINCR 1/11 TSB35 P0007 T10061017

KDLH 141341Z 09022G37KT 1/4SM R09/2200V6000FT +TSSN BLSN OVC005CB M01/M02 A2977 RMK AO2 PK WND 09037/1333 TSB35 OCNL LTGIC SE TS SE MOV NW P0006 T10061017

Orographic enhancement

Between the periods of heavier snow, evidence of precipitation enhancement due to the higher terrain of the North Shore could be seen more easily on radar. The radar animation following this text shows the first onslaught of heavy convective snow moving away to the north but lighter precipitation continuing in Duluth. The reflectivities appear to be attached to the higher elevations. Orographic enhancement contributed to precipitation production through most of the storm.


WSR-88D Radar, National Weather Service, Duluth, MN
Time of animation centered at approximately 2:00 PM CST (20:00 UTC)


Upper air maps closest to the time of the radar show a deep layer of east to southeast winds extending through the depth of the troposphere on the northeast side of a strong vertically stacked low pressure system from the surface through 250 millibars. Maps for the surface (mean sea level), 925 millibars, 850 millibars, and 700 millibars are shown in the order listed. Click maps to see larger images.

Data Sources: The surface map was produced by the Weather Prediction Center of the National Weather Service and the upper air maps are from the map archive of the Storm Predication Center of the National Weather Service.




Heavy snow showers and Snow Squall Warnings

The two radar animations from the WSR-88D Radar of the National Weather Service in Duluth on Friday afternoon, December 16 show examples of snow showers that prompted the National Weather Service to issue Snow Squall Warnings. The red geometric objects overlaying the radar show the locations of the warnings in effect at the time.


Storm evolution from the perspective of water vapor satellite imagery

Water vapor satellite imagery helps identify the location, structure, and movement of mid to upper tropospheric weather features. Storm features for this particular storm are well correlated to the location and timing of the precipitation and its intensity. The sequence of images roughly covers the time from shortly after midnight Wednesday, December 14 to near daybreak on the morning of Thursday, December 15. The time window includes most of the two periods of heavy snow that produced most of the accumulation for the storm. The time labels for the images are at the bottom of each image and are in Coordinated Universal Time (UTC). UTC is 6 hours ahead of Central Standard Time (CST). The analysis that is given after the images translates the image times into CST.

Data Source: NESDIS - National Environmental Satellite Data and Information Service

The first satellite image at 9:11 PM CST, Tuesday evening, December 13 shows Duluth under the southern portion of the enhanced green area of moisture corresponding the the initial band of moderate to heavy precipitation that was moving north through the region at the time. In well developed mid-latitude cyclones, widespread heavy precipitation tends to occur with the upstream part, in this case southern part, of the enhanced moisture area but also in the less enhanced area trailing just behind the enhanced area. This gradient in enhancement frequently represents strong vertical motion. The center of circulation of the large closed upper-level low pressure system can be seen over central and eastern Nebraska. Through time, another band of heavy precipitation developed south of the initial band of precipitation and was more in the form of snow compared to the initial precipitation.

The second satellite image at 4:41 AM CST, Wednesday morning, December 14 shows the northern part of another band of enhanced moisture moving north over Duluth corresponding to the second band of precipitation. If you look carefully you can see a narrow region of less enhanced moisture extending from extreme northern Wisconsin into north central Minnesota. This lower enhancement represented a temporary break in the heavier precipitation although lighter precipitation continued. The enhanced clouds over the Arrowhead of Minnesota denote the location of the first band of precipitation that had previously moved through the Duluth area. The narrow dark line extending from eastern Kansas to central Iowa corresponds to the western edge of a strong jet streak that extended from central Texas through Missouri then into eastern Iowa and western Wisconsin.

On the third satellite image at 9:50 AM CST, Wednesday morning, December 14, the back edge of the stronger moisture enhancement had moved northeast of Duluth but one last patch of precipitation mostly as snow persisted. The snow was between the green enhanced area and the dark line representing the western edge of the jet streak. Even though the snow was about to end, the satellite image was already showing evidence upstream that the next round of precipitation was starting to organize. Another upper-level wave of low pressure over Texas was rounding the base of the larger upper-level low pressure system centered near the four corners intersection of Nebraska, South Dakota, Iowa, and Minnesota. Over Missouri a small patch of enhanced moisture can be seen starting to develop and was not evident on the previous satellite image.

On the fourth satellite image at 1:26 PM CST in the afternoon on Wednesday, December 14, the enhanced moisture area over Missouri had expanded northward through Illinois, eastern Iowa and the eastern two-thirds of Wisconsin. The upper-level low pressure wave was moving into eastern Oklahoma. As the low pressure wave moved northeast and began to merge more with the original upper-level low pressure system, the enhancement on the satellite imagery rapidly expanded. By the time of the fifth satellite image at 11:26 PM CST late in the evening on December 14, the enhanced moisture area was developing into a comma head feature and had spread westward into Minnesota. At this time widespread moderate to heavy precipitation had developed across Wisconsin and was spreading west through eastern Minnesota. The precipitation was in the form of snow or in the process of changing to snow.

The sixth and seventh satellite images are valid for 5:01 AM CST and 7:01 AM CST, Thursday morning, December 15. The images show the dry slot advancing rapidly northwest toward Duluth and the western tip of Lake Superior during the two hours separating the images. After 7 AM the snow was not as persistently heavy but occasionally moderate snow continued to around 10 AM, then very light snow or flurries fell through the rest of the day.

Evolution of surface and 500 mb (upper air) features

The following surface maps and upper air maps also encompass the two periods of heavy snow. The maps are displayed in pairs with surface maps and upper air maps of the same time matched with each other. The surface map is displayed first and the upper air map is displayed following the surface map. The first pair of maps is valid at 00:00 Universal Coordinated Time (UTC) December 14 and the last pair of maps is valid for 12:00 UTC December 15. Each pair of maps is separated by 12 hours. Note that 00:00 UTC December 14 translates to 6:00 PM Central Standard Time (CST) December 13. Click maps to see larger images. The discussion following after the maps translates UTC into CST.

Data Sources: The surface map was produced by the Weather Prediction Center of the National Weather Service and the upper air maps are from the map archive of the Storm Predication Center of the National Weather Service.





The first pair of maps, valid for 6 PM CST Tuesday, December 13 shows that the centers of both the surface and upper-level components of the low pressure system are located in south central Nebraska. The second pair of maps shows that the centers moved to northeast Nebraska by 6 AM CST Thursday, December 14 then stalled for twelve hours as indicated by the third pair of maps valid for 6 PM CST on the same day. The surface and upper-level low pressure centers then resumed their movement with the surface low moving northeast into southern Minnesota and western Wisconsin and the upper low moving east into central Iowa. The key feature to note on the first 500 mb upper-level map for 6 PM CST Tuesday, December 13 is the trough axis extending southwest into Arizona. While the initial storm was producing heavy snow and mixed precipitation in Minnesota and Wisconsin, this next wave of low pressure set the atmosphere up for the second round of heavy precipitation. As the upper trough rotated around the base of the main upper low and moved northeast it tended to merge with the main upper low and strengthen the overall storm system. This process correlated well with the water vapor satellite image enhancement that developed from Missouri into Wisconsin from late morning into afternoon on December 14, then rotated west into Minnesota during the evening.

A comparison between the second pair and third pair of maps shows that the surface pressures and 500 mb heights increased as the first period of heavy precipitation diminished. A comparison between the third pair and fourth pair of maps shows that the surface pressures and 500 mb heights decreased as the second period of heavy precipitation developed. The increase in values indicated weakening of the storm system. The decrease in values indicated strengthening of the storm system.

References and data sources

National Weather Service Forecast Office Duluth, MN - WSR-88D Radar and Snowfall reports

National Weather Service Forecast Office Rapid City, SD - Snowfall reports

Aviation Weather Center (AWC) of the National Weather Service - Surface observations for the Duluth International Airport

Weather Prediction Center (WPC) of the National Weather Service - High resolution surface maps

Storm Prediction Center (SPC) of the National Weather Service - Upper air maps at 500 mb

National Environmental Satellite Data and Information Service (NESDIS) - Water vapor satellite images