2018 Was the Third Wettest Year on Record

| January 11, 2019 | Reply

The year 2018 ended with a 24-hour corrected mean temperature of 50.0F, which was 2.4F warmer than the 120-year (1891-2010) long-term mean and 1.1F above the 30-year (1981-2010) normal. The annual average maximum temperature of 58.5F was 1.6F warmer than the long-term mean, while the annual average minimum temperature of 42.2F was 2.4F warmer than the long-term mean and the twelfth warmest on record. The year got off to a very cold start with four of the first seven days of the year recording minimum temperatures below 0F, including the coldest temperature of the year of -8F on January 7th. This day was the last of a 13 day period of severe cold that had started on December 26th, 2017. The rest of January and February was generally warm with only a few cold days and a few small snowfalls, and February was the warmest on record. The warmth peaked with daily record high temperatures of 68F on February 20th and 70F on February 21st with the latter approaching the highest temperature ever recorded in February of 71F observed in 2017. The warmth was interrupted in March, which was relatively cold and very stormy during the first two weeks, with the temperature dropping to a low of 10F on March 18th. For only the fifth time since 1885, and for the second consecutive year, March was colder than February. The cold weather continued well into April, reaching a low of 24F on April 9th, which was the coldest temperature that late in the season since 1997. Warmth returned in May, reaching a high of 90F on May 3rd, and May was the third warmest on record. A four-day heat wave began on June 30th, and this day was the first of five out of six days through July 5th that exceeded 90F. The highest temperature of the year was 94F on July 1st, July 3rd, and August 29th. August had 23 days warmer than average, and it was the second warmest August on record. September also started warm, though this gave way to cooler weather for the rest of the Fall months, which were also very wet and cloudy. A brief period of frigid air arrived in late November, and November 22nd was the coldest Thanksgiving Day ever observed at Blue Hill with a high of 20F and a low of 9F. December was warmer than average with a monthly high temperature of 62F setting a daily record on the 21st.

Due to the record warmth in February, Ponkapoag Pond was considered free of ice on February 20th and Houghton’s Pond followed on the 22nd. This was the third straight year that both ponds thawed in February, several weeks earlier than the long-term average date. The first ripe blueberries were observed on the summit of Great Blue Hill on June 18th, which was a few days earlier than the average date. During the short period of very cold weather in late November, Ponkapoag Pond froze over on November 23rd, before opening again a few days later. Both ponds remained partly frozen during December.

Due to several stormy periods during the year, annual precipitation was very high and totaled 67.20 inches, which was more than 18 inches wetter than the long-term mean and nearly 14 inches more than the 30-year normal. The highest precipitation totals occurred in March (mostly as snow), September and November, though eight months during 2018 exceeded the long-term average precipitation. The May through August period was slightly drier than average. There were several significant storms during the year. These included a snowfall of 16.5 inches on January 4th, during the extreme cold that started 2018, a windy rain storm that brought 3.47 inches of rain (and a little melted snow) on March 2nd, a snowfall of 15.0 inches on March 7th-8th, and a major blizzard that brought 23.0 inches of snow on March 13th. The latter storm tied for the fourth largest snowstorm ever observed March and set a new record for snowfall in a single March calendar day. The snow depth reached its high point for the year of 19 inches on March 14th following this storm. March ended as the second snowiest on record with a total of 45.5 inches, which was very close to half of the annual snowfall of 91.2 inches. The wettest period of the year was the Fall season, which brought the highest total for any season on record with 25.41 inches of rain (and melted snow), or about 38 percent of the annual total. November alone had seven significant rainfall events that combined brought over ten inches of precipitation, the most ever measured during November.

The mean station pressure during 2018 at the elevation of the mercury barometer at the Observatory was 29.34 inches, which was 0.05 inches higher than the long-term annual mean of 29.29 inches. This value ties five other years as the highest annual mean station pressure on record. The maximum sea-level pressure during the year was 30.83 inches on February 13th. The lowest sea-level pressure during 2018 of 28.84 inches occurred on January 4th during a winter snowstorm that brought 16.5 inches of snow, 1.66 inches of melted precipitation and a peak wind gust of 54 mph from the NNW. This reading was the lowest sea-level pressure at Blue Hill since 28.84 inches was observed on February 14th, 2014.

Water vapor pressure, which is derived from the dew point and is an absolute measure of the amount of moisture in the air in terms of the pressure that water vapor contributes to the total surface pressure, averaged 11.0 mb (0.325 inches) during 2018. This value ties with 2012 for the highest annual mean vapor pressure on record at Blue Hill. Another way to interpret this value is to state that water vapor on average comprised a little over one percent of the total annual mean station pressure. During the year, two months also set new records for high average vapor pressure, February at 5.9 mb (0.174 inches) and August at 22.5 mb (0.664 inches).

The annual mean wind speed of 12.1 mph was the second lowest on record behind only the 11.8 mph mean observed in 2012. This continues the several decade long trend of decreasing mean wind speeds on Blue Hill, though the trend has moderated in the last few years. The peak wind gust during 2018 was 73 mph from the NNE during the windy rain storm on March 2nd.

Bright sunshine for the year was just 48 percent of possible, which was four percent less than the long-term average, making 2018 the ninth cloudiest on record and the cloudiest year since 1992. The least sunny period of the year was the Fall season, which was the cloudiest Fall on record with only 37 percent of the possible bright sunshine.

BHO Greatest Annual Precipitation, inches (1886-2018):

1) 71.00 in 1998
2) 69.36 in 1996
3) 67.20 in 2018
4) 66.23 in 2005
5) 65.51 in 1972

BHO Highest Annual Mean Station Pressure, inches (1885-2018):

1) 29.34 in 1906
   29.34 in 1911
   29.34 in 1946
   29.34 in 1949
   29.34 in 2015
   29.34 in 2018
7) 29.33 in multiple years

BHO Highest Annual Mean Vapor Pressure, mb (1932-2018):

1) 11.0 in 2012
   11.0 in 2018
3) 10.9 in 2011
4) 10.7 in 1973
5) 10.6 in 1979
   10.6 in 2006

BHO Lowest Annual Mean Wind Speed, mph (1885-2018):

1) 11.8 in 2012
2) 12.1 in 2018
3) 12.2 in 2013
   12.2 in 2015
   12.2 in 2017
6) 12.3 in 2014
   12.3 in 2016

BHO Lowest Annual Total Bright Sunshine, hours (1886-2018):

1) 2003.2 in 1889 [47%]
2) 2026.0 in 1919 [47%]
3) 2055.9 in 1887 [48%]
4) 2056.7 in 1903 [48%]
5) 2061.2 in 1939 [48%]
6) 2064.7 in 1951 [48%]
7) 2075.7 in 1992 [48%]
8) 2080.6 in 1917 [48%]
9) 2081.4 in 2018 [48%]
10) 2089.1 in 1888 [48%]

Mike Iacono
Chief Scientist
Blue Hill Observatory

Category: Weather Summary Archives

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