Volume 206: From Record-Lows to Record-Highs in 6 years

Background

In January 2013, Lakes Superior and MichiganHuron were in the midst of a 14-year streak of 

below average water levels. Lake MichiganHuron’s monthly mean water level sunk to 576.02 

feet (IGLD85) that month. Not only was this level 

a record-low for the month of January, it was the 

lake’s lowest monthly mean level since 1918, the 

beginning of its period of record. 

By May 2019, just six 6 years later, the Great 

Lakes were experiencing record-high levels. Lakes 

Superior, St. Clair, Erie, and Ontario matched or 

set numerous record high monthly mean levels in 

2019. Moreover, in June 2019, Lakes Erie and 

Ontario climbed to their highest overall monthly 

mean level in their period of record dating back to 

1918, while Lake St. Clair achieved the same 

milestone a month later. Based on preliminary 

water level statistics for 2020, Lake MichiganHuron has set monthly mean record high levels for 

January, February, March, April, and May this 

year. (Lakes Michigan and Huron are considered 

as one lake hydraulically due to the connection at 

the Straits of Mackinac.)

Figures 1 through 5 show the Great Lakes’ 

monthly mean water levels from the end of the low 

water level period to 2019, plotted against their 

respective monthly long-term average (LTA) 

levels. The solid line represents the 2013 to 2019 

monthly water levels and the dashed line 

represents the LTA levels for each month.

Figure 1: Plot of Lake Superior water levels from 

2013 to 2019 versus the lake’s LTA levels.

Figure 2: Plot of Lake Michigan-Huron water 

levels from 2013 to 2019 versus the lake’s LTA 

levels.

Figure 3: Plot of Lake St. Clair water levels from 

2013 to 2019 versus the lake’s LTA levels.

Great Lakes

Update
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Figure 4: Plot of Lake Erie water levels from 

2013 to 2019 versus the lake’s LTA levels.

Figure 5: Plot of Lake Ontario water levels from 

2013 to 2019 versus the lake’s LTA levels.

This update article chronicles the shift from the 

historic low water levels of the late 90’s to the 

early ‘10s, to the historic high water levels that 

are occurring today. No discussion of long-term 

Great Lakes water level fluctuations is complete 

without an evaluation of Net Basin Supply 

(NBS). Net Basin Supply is the combined effects 

of precipitation falling on the lakes’ surface, 

runoff draining to the lakes, and evaporation from 

the lakes’ surface, and is the primary driver of 

water level changes on the Great Lakes. NBS data 

from 2009 to 2019 is preliminary, not final.

Historic El Niño Triggers Water Level Decline

The El Niño of 1997-98 was the most powerful on 

record up to that point, bringing record-high 

temperatures and significantly below normal 

precipitation throughout the region. Lake 

Superior’s winter precipitation was the second 

lowest since the early 1960s. Moreover, the much 

warmer conditions substantially reduced total 

snowfall in the basin and snowpack accumulation 

that winter.

The 1997-1998 El Niño seemed to usher in a 

transition to higher lake surface water 

temperatures and higher evaporation rates in Lakes 

Superior and Michigan-Huron. The below plots of 

Lakes Superior and Michigan-Huron’s annual 

average lake surface temperatures and annual 

evaporation data estimates from the Great Lakes 

Seasonal Hydrological Forecasting System 

(GLSHyFS) model, developed by NOAA’s Great 

Lakes Engineering & Research Laboratory

(GLERL), show a noticeable trend of generally 

higher surface temperatures and annual 

evaporation after 1997.

Figure 6: Comparison of annual evaporation and 

lake surface temperatures from 1948-2012, Lake 

Superior.

Figure 7: Comparison of annual evaporation and 

lake surface temperatures from 1948-2012, Lake 

Michigan-Huron.
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Evaporation from the lake surface is directly 

related to the difference in temperature between 

the air and lake surface. Evaporation increased 

over this time period, as did the air and surface 

temperatures, but their temperature difference did 

not. What could be the cause of the enhanced 

evaporation? Evaporation rates generally go 

higher as water temperatures go higher. 

The combination of below normal 

precipitation/snowfall, reduced snowpack 

accumulation, and somewhat increased 

evaporation in the Great Lakes basin from mid1997 through 1999 resulted in considerable water 

level decline. Lakes Michigan-Huron, St. Clair, 

and Erie’s levels plummeted 28 to 31 inches 

between July 1997 and July 1999, while Lake 

Superior fell 11 inches; Lake Ontario dropped 44 

inches in the 8-month period between April and 

December 1998. By the end of 1999, the lakes 

ranged from 2 to 14 inches below LTA.

Levels of Lower Lakes not as Extreme

It is important to note that the lower lakes (St. 

Clair, Erie, and Ontario) did not experience the 

same continuous trend of below average levels 

during this decade-and-a-half period as the upper 

lakes. The monthly levels of Lake St. Clair were 

below average from early 1999 to the end of 2008, 

but the lake achieved many months of near average 

to above average water levels in 2009 and 2011. 

Lake Erie was nearly continuously below average 

from Spring 1999 to Summer 2004, but its level 

was, in general, near average from mid-year 2004 

to early 2012. Figure 8 illustrates Erie’s levels.

Figure 8: Lake Erie water levels from 1997-2019.

Lake Ontario did not experience any multi-year

long stretch of below average water levels during 

this period. Annual NBS is the sum of monthly 

NBS in a calendar year. From 1999-2011, the 

average annual Net Basin Supply for Lakes Erie 

and Ontario was 27% and 13%, respectively, 

above normal. 2011 stands out in particular as 

Lake Erie experienced precipitation that was 49% 

above average, and for Lake Ontario, 24% above 

average. The 2011 annual NBS of Lakes Erie and 

Ontario were their highest and 4th highest, 

respectively, since 1900 (up to that point in time).

Deeper review of the Upper Lakes

It is also important to note that the annual NBS for 

Lake Michigan-Huron was 95% of average during 

the 12 years between the historically low NBS 

years of 1998 and 2012. In fact, the lake’s annual 

NBS was above average in 6 of the years in the 

1999 to 2011 time span. Precipitation was above 

normal in 9 of those years. It wasn’t that the lake’s

NBS was continually below average year after 

year after year. Rather, there were no consecutive 

year streaks of above average NBS to provide an 

upward push to the water levels. 

Another factor that impacts Lake Michigan-Huron 

water levels is the inflow into the lake from the St. 

Marys River. In 12 of the 15 years from 1998 and 

2012, the St. Marys River monthly outflow into 

Lake Michigan-Huron was below average in 10 or 
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more months. St. Marys River monthly outflow 

statistics are preliminary from 2009 onward.

For Lake Superior, the 15-year period of below 

average water levels was marked by consistently 

dry conditions. Annual precipitation was below 

average in 9 of the years between 1997 and 2012. 

Precipitation during winters was especially 

lacking. Based on the coordinated Great Lakes 

precipitation statistics, six of the ten driest winters 

since 1950 occurred during the 1998-2014 low 

water level period as shown in below Figure 9.

Figure 9: The 10 Lowest November through 

February Overbasin Precipitation Amounts for 

Lake Superior from 1950-2017.

An indicator of runoff in a watershed is soil 

moisture. Soil Moisture is the amount of pore 

space within soil occupied by water. The lower the 

soil moisture, the higher the volume of rainfall that 

can potentially percolate into the pore space of the 

soil, and less the volume of water that stays on the 

surface and runs into streams and rivers. Low soil 

moisture is an indication of low runoff.

The soil moisture map (Figure 10) of the U.S. 

from January 2003 by NOAA’s Climate 

Prediction Center shows exceptionally below 

normal soil moisture in the majority of the Great 

Lakes basin, and is representative of the low soil 

moisture, and thus low runoff, during this period.

Figure 10: NOAA’s Climate Prediction Center 

map of Soil Moisture Percentile Ranking for 

North America, January 2003.

From 1999 to 2003, Lake Superior’s average 

monthly departure from LTA levels was 7 inches

below monthly LTA. Above average NBS in 

2004 brought the lake’s level to near average in 

the cold-season months of 2004-2005. However, 

annual NBS to Lake Superior was below average

every year from 2005 to 2012. Continuous years 

of below average water supplies led to Lake 

Superior descending to record-low monthly mean 

levels in August and September 2007. During 

2008 and 2009, the lake's monthly mean levels 

were an average of 12 inches below monthly 

LTA.

The “Non-Winter” of 2011-12 

In the fall of 2011, the levels of Lakes St. Clair, 

Erie, and Ontario were near or above their LTAs. 

However, the unusual winter of 2011-12 plunged

the upper lakes into record- and near record-lows.

This winter was distinguished by far below normal 

precipitation and near-record high temperatures in 

the Great Lakes region and the nation as a whole. 

Above average temperatures persisted into the 

spring and summer. According to the GLSHyFS

model, monthly air temperatures over Lakes

Superior and Michigan-Huron were 10° F above 
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average in June and July 2012. For all lakes, air 

temperatures were above average in all months of

2012 except for Lake Ontario in November. In 

addition, according to the NWS and Environment 

and Climate Change Canada, the Great Lakes 

experienced some of their highest lake surface 

temperatures in a century in the spring and summer 

of 2012. The GLSHyFS model calculated 2012 

annual evaporation from the Great Lakes to range 

from 22% to 42% above average.

Figure 11: Drought Monitor Map from July 2012 

produced by NOAA’s Climate Prediction Center.

In 2012, severe drought conditions were felt 

nationwide (Figure 11 above). Much of the

country east of the Rocky Mountains received 

below normal snowfall in winter 2011-12.

Moreover, precipitation in the spring and summer 

seasons were below average for Lakes MichiganHuron, Erie, and Ontario. The low snowfall and 

below average spring rainfall in the Great Lakes 

basin led to decreased runoff for all of the lakes. 

The Advanced Hydrologic Prediction System 

(AHPS) model, also developed by NOAA 

GLERL, calculated runoff to Lakes Superior, 

Michigan-Huron, Erie, and Ontario to be 20% to 

33% below average in 2012. 

The dry conditions culminated in Lake Superior 

just barely missing its record-low October monthly 

mean level by 1 inch. Just a month earlier, the lake 

experienced its lowest NBS on record for the 

month of September.

Lake Michigan-Huron set new record low water 

levels during the months of December 2012 and 

January 2013. The lake’s 2012 Annual NBS was 

its 2nd lowest since 1900 and its April and 

September monthly NBS were its lowest and 2nd

lowest on record for those respective months.

Lakes St. Clair and Erie did not experience a 

seasonal rise in 2012. Their monthly mean levels

fell 20 and 22 inches, respectively, from January 

2012 to 2013. In fact, Lake Erie’s monthly mean 

level declined 10 consecutive months from 

December 2011 to October 2012. Its monthly NBS 

was at or below average 9 of 12 months in 2012. 

Lake Ontario declined 28 inches from February 

2012 to December 2012.

Water Levels Rebound in 2013, Receive Boost 

from Polar Vortex of 2013-2014

2013 proved to be a turning point. For only the 2nd

time since the high-water level year of 1996, all of 

the Great Lakes experienced above average 

precipitation in the same year. This led to above 

average rises for all the lakes in the spring and 

summer (Figure 12). Precipitation was actually 

above average throughout the basin in 2008, but in 

contrast to the low-water period, the wet year of 

2013 was succeeded by a climatological event that 

sustained the wet conditions.

The Polar Vortex winter of 2013-2014 brought 

record-low temperatures and record/near-record 

snowfall to the basin. Various cities from 

Petoskey, MI, to Toledo, OH, experienced their 

highest winter snowfall amounts on record. 

Moreover, cities like Chicago, IL and Duluth, MN, 
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received the third-highest seasonal snowfall totals 

in their histories.

The harsh winter produced record-high ice cover 

over the Great Lakes. The cooling of the lake 

surface by the bitterly cold temperatures and 

record-high ice cover lowered lake surface 

temperatures, moderately depressing evaporation 

in spring and summer. As a result of the reduced 

evaporation and the abundant runoff generated 

from the melting of the above average snow 

accumulation, all of the Great Lakes experienced 

above average Net Basin Supplies in April, May, 

and June 2014.

 

For Lake Superior, monthly NBS was above 

average in 13 of 14 months between May 2013 and 

June 2014. The annual water supplies in 2014 for 

Lakes Superior and Michigan-Huron were in

excess of 50% above average, and were their 2nd

and 4th highest Annual NBS, respectively, since 

1900. In addition, the annual NBS was over 20% 

above average for Lakes Erie and Ontario in 2014. 

Figure 12: Great Lakes Seasonal Rises in 2013 & 

2014 versus Historical Average Seasonal Rises.

Due to those seasonal rises, Lake Superior reached 

its long-term monthly average in March 2014, 

ending a 15- consecutive year period in which the 

lake was below LTA. By September 2014, Lake 

Michigan-Huron matched its LTA, the first time in 

16 years the levels of all of the Great Lakes were 

at or above average at the same time.

Generally Wet Conditions Persist Through 2019

In 2015 and 2016, NBS was moderate basin-wide, 

even somewhat below average in the lower lakes. 

The upper lakes remained above LTA those years. 

However, in 2017, Lake Ontario commenced the 

surpassing of record-high levels. The lake 

experienced above average monthly NBS 9 

months that year, and its 2017 Annual NBS was its 

highest on record. Propelled by above average 

precipitation in March, April, May, and June, 

including nearly 6 inches of rainfall in May, the 

lake rose 53 inches in 2017 and set record-high 

monthly mean levels for May and June. In 

addition, in 2019, Lake Ontario experienced above 

average monthly NBS every month except March 

and August.

Lake Superior’s Annual NBS was above average 

every year from 2013 to 2019, in contrast to the 

low water level period when Annual NBS was 

below average in 14 of the 16 years. In addition 

to its near-record 2014 Annual NBS, the lake 

experienced its 6th highest Annual NBS in 2017, 

and its 11st highest Annual NBS in 2019, since 

1900.

Lake Michigan-Huron’s Annual NBS has been 

above average in 5 of the past 7 years. The lake 

received its highest Annual NBS on record in 

2019, its 4th highest Annual NBS in 2014 and its 

8th highest Annual NBS in 2017, during this 

period. Below Figures 13 and 14 illustrate the flip 

from generally below average to generally above 

average NBS in 2013 and the water level response.

Figure 13: Annual NBS difference from LTA and 

Monthly Mean Water Levels for Lake Superior 

from 1997-2019.
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Figure 14: Annual NBS difference from LTA and 

Monthly Mean Water Levels for Lake MichiganHuron from 1997-2019.

Lake Erie’s 2017 Annual NBS was its 8th highest 

in 119 years. Its Annual NBS was above average 

in all but one year in the 2013-2019 time frame.

Continuously High NBS results in RecordBreaking 2019

Record-high water levels matched or set in 2019 

on Lakes Superior, St. Clair, Erie, and Ontario are 

shown in Figure 15 below. 

Figure 15: Table showing which months recordhigh monthly mean water levels were set in 2019.

Lake Michigan-Huron did not reach record high 

water levels in 2019. However, its record high 

2019 Annual NBS resulted in the lake being within 

an inch of record-high levels in June, July, and 

December. Its July-December water level decline 

in 2019 was just 5 inches – 50% of its historical 

average - leading to a record-high January level in 

January 2020, according to preliminary data. In 

addition, by the end of 2019, all of the lakes were 

13 to 36 inches above LTA.

Record-High Precipitation Catapults NBS

Consistently above average precipitation may be 

the most significant catalyst for the recent recordhigh NBS and water levels. Lake Superior’s 

annual precipitation was above average each year 

from 2013 to 2017, the first time it had been above 

average 5 years in a row since the record-high 

water level period of the mid-1980s. Annual 

precipitation for Lakes Erie and Ontario were 

above average 3 and 4 years, respectively, in that 

5-year stretch. Lake Michigan-Huron’s annual 

precipitation, while closer to average than the 

other lakes, was below average only one year 

during that time. USACE’s official Great Lakes 

precipitation statistics are only coordinated 

through 2017.

According to the NWS, the state of Wisconsin, of 

which significant portions lie in the Lake Superior 

and Michigan-Huron basins, experienced above 

average precipitation for 7 consecutive years 

(2013-2019). Three of the state’s top five wettest 

years have taken place in the past 5 years (2015-

2019). Moreover, the state received record-high 

annual precipitation in 2018, and again in 2019. In 

addition, estimates from the Midwest Regional 

Climate Center (MRCC) indicate that 2019 annual 

precipitation for Michigan and Minnesota were 

their highest on record. Also, the MRCC data 

indicated that precipitation in 2018 in the Midwest 

region, which includes 6 Great Lakes states, was 

the highest in the Center’s period of record. 

Remarkably, the 2019 Midwest precipitation 

exceeded the 2018 record-high.

A below plot of the 5-year running total of 

estimated precipitation in the U.S.-only portion of 

the Great Lakes basin, by NOAA's National 

Centers for Environmental Information (NCEI), 

shows the stretch of precipitation from 2015-2019 

is the highest five-year total since the beginning of 

the NCEI’s period of record in 1895. 
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Figure 16: Plot of 60-month cumulative 

precipitation totals from 1895-99 to 2015-2019 

by NOAA’s NCEI.

Several of the lowest 5-year precipitation totals, 

post the 1960’s droughts, are from the early years 

of the 1998-2014 low-water period.

Another significant factor in this current high

water level period is runoff. Soil moisture and 

streamflow can be indicators of extent of runoff. 

In contrast to the low water level period, the 

fraction of months of below normal soil moisture 

during the high-water years has been substantially 

lower, implying a shift to higher runoff. Figure 17

represents the change to higher soil moisture 

during this high-water period.

Figure 17. Soil Moisture Percentile Ranking in 

the United States, October 2019.

Streamflow is the quantity of water flowing in 

rivers in a watershed. In general, the higher the 

streamflows, the higher the runoff. The below 

map from the USGS’s 2018 Annual Summary of 

Streamflow shows the streamflows within the 

Great Lakes Basin in Water Year 2018 (October 

2017-September 2018) were the 11st highest 

since 1930.

Figure 18: Rankings of streamflow in Regional 

U.S. Watersheds in Water Year 2018 relative to 

the period of record (1930-2018).

How long will High Water Levels Continue?

Unless there are continuous dry conditions in the 

Great Lakes basin for an extended period of time, 

water levels will remain very high for the time 

being. Official forecasts of Great Lakes water 

levels extend out six months. To see the latest 6-

month forecast, visit: 

Monthly Bulletin of Great Lakes Water Levels

Beyond six months, it is difficult to say with 

certainty how high water levels will be. Water 

levels of the Great Lakes cannot be fully controlled 

through regulation of outflows. More importantly, 

the major factors that affect the water supply to the 

Great Lakes - over-lake precipitation, runoff, and 

evaporation - cannot be controlled, nor can they be 

accurately predicted in the long term. Great Lakes 

levels will continue to fluctuate from low to high 

and back, and we need to be prepared for that 

variability.