2019 Was Warmer and Wetter Than Average

The year 2019 ended with a 24-hour corrected mean temperature of 49.2F, which was 1.6F warmer than the 120-year (1891-2010) long-term mean and 0.3F above the 30-year (1981-2010) normal. The annual average maximum temperature of 58.0F was 1.1F warmer than the long-term mean, while the annual average minimum temperature of 41.0F was 1.2F warmer than the long-term mean. The year started with largely seasonable temperatures and below average snowfall in January and February, and the coldest temperature of the year of -2F was observed on January 21st and 31st. The high temperature on the 21st was only 3F, which surpassed the previous record for the date of 9F set in 1985. This was the coldest daily maximum temperature in January or any month since a high of 2F was observed on January 8th, 1968. Harsh winter weather returned on February 26th, which started an 11-day period that featured below average temperatures and a total of 23.5 inches of snow over six consecutive days from February 27th that ended with a 15.8 inch snowstorm, the largest of the year, on March 3rd-4th. Warmth returned in April, though May was cooler than average with a few warm days. July was the third warmest on record, and although there were no heat waves during 2019, July featured the two warmest periods with high temperatures from 87F to 90F from July 3rd to 6th and 89F to 93F on July 28th to 31st. The highest temperatures of the year were readings of 93F on July 20th and 30th. September started cooler than average, then ended warm including a three-day period with high temperatures of 83F, 85F and 88F on the 21st to 23rd. Warm weather continued in October and was followed by cooler temperatures in November. The coldest day featured a high temperature of only 28F on November 13th, which was third earliest maximum temperature below 30F on the entire period of record and the first this early since November 1894. December started cold, but it ended slightly warmer than average with very variable temperatures.

Due to the cold and snowy start to March, Ponkapoag Pond was not considered free of ice until March 19th and Houghton’s Pond followed on March 22nd. These dates are a few days later than the average thaw dates. The first ripe blueberries were observed on the summit of Great Blue Hill on June 28th, which was a week later than the average date due to the cool weather in May. Late in the year, Ponkapoag Pond froze over on December 3rd and Houghton’s Pond followed on December 8th, before thawing again in mid-December and freezing over again later in the month.

Despite a dry late summer and early fall, annual precipitation was very high and totaled 56.89 inches, which was more than 8 inches wetter than the long-term mean and three and a half inches more than the 30-year normal. The highest precipitation totals occurred in April, which was the sixth wettest on record, October and December, though seven months during 2019 exceeded the long-term average precipitation. The driest period of the year from August to September saw only 3.10 inches of rain. There were several significant storms during the year. These included the largest snowfall of the year of 15.8 inches on March 3rd-4th and a rain storm that brought 3.00 inches of rain on April 22nd-23rd, including 2.60 inches on April 22nd, which was the fourth wettest calendar day ever recorded in April. On September 6th-7th, Hurricane Dorian, one of the strongest tropical cyclones ever to form in the western Atlantic, brought 0.30 inches of rain and a wind gust to 43 mph from the north to the Observatory as the storm passed offshore as a weakening Category 1 hurricane. October brought three significant rainfall events, each totaling more than an inch, including 1.64 inches with a wind gust to 41 mph from the northeast from Tropical Storm Melissa, which formed offshore on October 11th, then began moving out to sea on the 12th. The first three days of December were very snowy with a total of 13.1 inches of snow and 2.43 inches of melted precipitation. The snowiest month of the year was March with 23.1 inches, and the greatest snow depth on the ground during 2019 of 19 inches was reached on March 4th. The total snowfall for the calendar year was 59.9 inches, just an inch below the long-term average.

The mean station pressure during 2019 at the elevation of the mercury barometer at the Observatory was 29.32 inches, which was 0.03 inches higher than the long-term annual mean of 29.29 inches. The maximum sea-level pressure during the year was 30.71 inches on December 12th. The lowest sea-level pressure during 2019 of 28.82 inches occurred on October 17th during a powerful storm that passed over the area bringing 1.96 inches of rain and a peak wind gust of 61 mph from the east. This reading was the lowest sea-level pressure ever recorded in the month of October at Blue Hill, and it was the lowest pressure in any month since 28.70 inches was observed on February 25th, 2010.

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 10.3 mb (0.304 inches) during 2019. This value is higher than the long-term average of 9.8 mb and continues a trend of higher vapor pressures in recent decades. 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.

The annual mean wind speed of 12.1 mph tied with 2018 as 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 this trend has leveled off in recent years. The peak wind gust during 2019 was 77 mph from the south during a warm, windy rain storm on January 24th.

Bright sunshine for the year was 52 percent of possible, which was exactly equal to the long-term average. The least sunny months, April, October and December were also the wettest and had, respectively, just 35, 36 and 37 percent of the possible sunshine. The sunniest period of the year was July through September, which had a combined 68 percent of the possible bright sunshine, which tied as the fourth sunniest July to September on the entire period of record.

BHO Lowest Annual Mean Wind Speed, mph (1885-2019):

1) 11.8 in 2012
2) 12.1 in 2018
   12.1 in 2019
4) 12.2 in 2013
   12.2 in 2015
   12.2 in 2017
7) 12.3 in 2014
   12.3 in 2016

Mike Iacono
Chief Scientist
Blue Hill Observatory