If it seems like summer this year has been unseasonably cold, well, that’s because it has been.
The 90-day period from May 1 to July 29 saw the lowest daily high temperatures on average in Juneau since officials began keeping records in 1943, according to National Weather Service data.
“The average high this year so far is about 4.4 degrees below normal over those 90 days, which is pretty significant,” said NWS meteorologist Richard Lam.
This year, the average high temperature over that 90-day period was 55.9 degrees Fahrenheit. On average, it is 60.4 degrees.
Lam said this summer broke the record previously held by the summer of 1970 for the coldest May 1 to July 29 period. That year, the average high temperature was 56.3 degrees – nearly half a degree of temperature warmer than during the same period this year.
When comparing average overall temperature, rather than just average highs, that same period is the ninth coldest since record-keeping began, Lam said.
“That is still pretty significant,” Lam added.
The temperature from May 1 to July 29 averaged 50.4 degrees, colder than the average of 52.3 degrees over that same time period since 1943.
The disparity is because while average high temperatures this summer have been well below normal, average low temperatures have been roughly on par. Lam attributed that to high levels of cloud cover – 90 percent coverage on average in May and June, according to his data — blocking much of Juneau’s sunlight during the day.
Frequently, those clouds have brought rain.
“From May 1 to July 29, we are the second-wettest … 90-day period,” Lam reported. “We are six inches above normal for precipitation.”
16.71 inches of rain fell in that 90-day period this year. While that is shy of 1992’s record of 17.36 inches, it is well above the 10.70 inches averaged since 1943.
Without full records for July 30 and July 31, Lam said rainfall so far in July has been fairly typical, with 4.29 inches falling versus the average of 4.6 inches for the month.
But, Lam added, the month is not over yet, and even as he spoke Monday morning, fat drops of water ran off the eaves of the Forecast Office in the Mendenhall Valley.
“For the next few days, we are going to get more rain on our way,” said Lam.
With rain sheeting down Monday and more expected Tuesday, that means rainfall for July could actually finish well above average.
This dreary summer comes after a rather temperate start to the year.
While January was colder and snowier than average, February was markedly warmer and drier. A fairly average March gave way to a warm, virtually snowless April.
But that’s when it all changed, Lam said.
One-fifth of an inch of rain fell on April 20, after barely any precipitation over the previous month — not much on its own, but the start of a trend.
“That’s the big turning point,” said Lam, indicating the data on his screen. “Since April 20, we go from a warm, mild and dry pattern to … a wet and cool pattern.”
While Lam described the string of warm, sunny days last week as a reversion to the former pattern, he suggested the latter pattern remains dominant, with rain in the forecast for the week ahead.
Lam said summer 2012 so far has seen several more new records set.
July 9 set a daily record this year for rainfall, seeing 1.64 inches fall at Juneau International Airport, where weather measurements for the city are taken.
Mark your calendar: May 8, May 11, June 14, June 29, June 30, July 9 and July 10 all snapped daily records for lowest high temperature, while this July 12 saw a record low temperature of 38 degrees.
A trace of snow detected on three days in May was enough to break a record for amount of snowfall during the month, Lam said, though none accumulated at sea level in Juneau due to temperatures remaining well above freezing.
• Contact reporter Mark D. Miller at 523-2279 or at firstname.lastname@example.org.