Winter and Spring 2017, Arctic Ice

Weather and Climate Review: Winter 2017 (December-February)

By Sean D. Birkel, Maine State Climatologist, June 5, 2017

Winter 2017 was warm and wet. The statewide average winter temperature was 20.1 °F, ranking fifteenth warmest against the season mean for the 20th century. This follows record warmth in winter 2016.

Figure 1. Temperature maps and time series for winter 2017.
Figure 1. Temperature maps and time series for winter 2017.

Winter 2017 precipitation was 2.3 inches more than normal, totaling 11.7 inches water equivalent, contributing to an end of the 2016 drought.

Figure 2. Precipitation maps and time series for winter 2017.
Figure 2. Precipitation maps and time series for winter 2017.

One particularly notable event from winter 2017 was a major nor’easter February 12-13 that delivered over 30” snowfall to some areas of central Maine and Downeast.

Figure 3. Total snowfall map issued by the Caribou office of the National Weather Service for the February 12-13 storm.
Figure 3. Total snowfall map issued by the Caribou office of the National Weather Service for the February 12-13 storm.

As with other recent warm winters (most notably 2010, 2012, 2016), winter 2017 for the southern half of the state saw several rainfall events that degraded the snowpack. However, nearly all of the state retained snow cover by the end of February, thus providing an important starting condition for spring that contributes to groundwater and lake levels.

Figure 4. Comparison of February 28 snowpack for 2016 and 2017. Image from the NWS National Hydrologic Remote Sensing Center.
Figure 4. Comparison of February 28 snowpack for 2016 and 2017. Image from the NWS National Hydrologic Remote Sensing Center.

Spring (March-May)

Spring 2017 was generally cool and wet. The statewide average spring temperature was 38 °F, ranking slightly below than the season mean for the 20th century. This ranking is mostly due to March, which was the third coldest since 1984 behind 2015 and 2014. April was warmer than normal; May was near normal.

Figure 5. Temperature maps and timeseries for spring 2017.
Figure 5. Temperature maps and time series for spring 2017.

A heat wave developed Thursday, May 18, when daytime high temperature across the state soared into the 80s (northern and western) and low 90s (southern and central), breaking some records. The event was short-lived, however, due to a cold front that advanced across the state the next day (highs in the 70s Friday, May 19, 50s and 60s over the weekend).

Figure 6. Temperature forecast map for Thursday, May 18, 2017, from the North American Mesoscale Model (NAM). Image from Climate Reanalyzer website. Click on image to view 60-hour forecast animation showing heat wave followed by cold front.

May temperatures reaching above 90 °F is rare, but not in itself exceptional for the southern half of Maine from a historical perspective. However, so far in 2017 record maximum daily temperature in Bangor was matched (to within 1 degree) or exceeded on 9 occasions between January 1 and May 31, whereas record minimum daily temperature was matched or exceeded only three times. Thus, 2017 continues the trend of a warming climate.

Figure 7. Daily temperature for Bangor, ME from the Global Historical Climatology Network (GHCN).
Figure 7. Daily temperature for Bangor, ME from the Global Historical Climatology Network (GHCN).

Spring 2017 precipitation was 2.5 inches more than normal, totaling of 12.3 inches water equivalent.

Figure 8. Precipitation maps and time series for spring 2017.
Figure 8. Precipitation maps and time series for spring 2017.

Increased snowfall and a longer snow season compared to last year contributed to easing of the 2016 drought.

Figure 9. Comparison of April 1 snowpack for 2016 and 2017. Image from the NWS National Hydrologic Remote Sensing Center (https://www.nohrsc.noaa.gov/nsa/index.html).
Figure 9. Comparison of April 1 snowpack for 2016 and 2017. Image from the NWS National Hydrologic Remote Sensing Center.

The National Drought Mitigation Center and National Weather Service reported in the third week in April in the article, Maine is awash, bringing yearlong drought to an end (April 27, 2017, Portland Press Herald), that groundwater levels were back to normal across most of the state, and therefore drought was effectively over.

The latest U.S. Seasonal Drought Outlook (National Weather Service Climate Prediction Center) published on May 18 by NOAA projects drought conditions for only limited sections of the southeastern and southwestern U.S. this summer.

Figure 10. NOAA seasonal drought outlook map for May 18 – August 31 published May 18, 2017.
Figure 10. NOAA seasonal drought outlook map for May 18 – August 31 published May 18, 2017.

Keep an Eye on the Arctic

Climate in Maine and across the Northern Hemisphere is heavily impacted by the declining extent and thickness of Arctic sea ice. Sea-ice loss caused by warming temperatures presents feedback, where each summer less ice enables more solar radiation to be absorbed by the Arctic Ocean, which warms the waters and promotes further ice loss; the fall season is then extended as the thinner, less extensive ice affords more heat release from the ocean to the atmosphere. A lengthened fall furthermore means a delayed winter, which ultimately results in a reduced accumulation of freezing degrees under which ice thickens. Ultimately, reduction in the extent and thickness of Arctic sea ice alters difference in temperature between the equator and pole, which then changes the circulation of the atmosphere.

Figure 11. Satellite observed sea-ice concentration at the end of the summer melt season in 1980 and 2012.
Figure 11. Satellite-observed sea-ice concentration at the end of the summer melt season in 1980 and 2012.

There remains disagreement among scientists as to the precise way in which circulation is being altered, but a prominent view suggests a linkage between Arctic sea-ice loss and an increase in the incidence of extreme climate events – heat and cold waves, record rain and snowfall – that has been observed across the Northern Hemisphere in the past decade.

It is noteworthy that the 2016-2017 winter was the warmest on record across the Arctic Basin with the least number of accumulated freezing degrees.

Figure 12. The difference in accumulated freezing degrees for the 2016-2017 Arctic winter (November-March) compared to 1979-2000 climatology. From NCEP CFSR reanalysis.
Figure 12. The difference in accumulated freezing degrees for the 2016-2017 Arctic winter (November-March) compared to 1979-2000 climatology. From NCEP CFSR reanalysis.

Record low minimum sea-ice extents were attained in 2007 and 2012 when the ice area stood at less than half the typical minimum extents observed prior to the 1980s. The 2017 melt season has started off with much thinner ice than any year yet in the era of daily satellite observations beginning in late 1978, which has scientists speculating in the article Arctic Sea Ice Primed for Phenomenal Melt Season, Bob Henson, June 9, 2017 (WU, Weather Underground website) that come September there will be yet a new record minimum extent.

Figure 13. Comparison of Arctic sea-ice thickness forecasts for June 19, 2012 and June 19, 2017 simulated by the HYCOM model used by the U.S. Navy.
Figure 13. Comparison of Arctic sea-ice thickness forecasts for June 19, 2012 and June 19, 2017 simulated by the HYCOM model used by the U.S. Navy.

What will this mean for Maine? Time will tell.