How this year's bitterly cold July is ending a hot streak
Two weeks ago, I wrote a column that said that we shouldn't give up on July just yet. There were a few recent examples of previous Julys which had started slow yet still finished nicely.
Well, here we are, two weeks later, two chilly weekends have gone by, and July of 2015 is slowly and steadily inching closer to becoming one for the record books …for all the wrong reasons.
What a run ...
This July is not only shaping up to be the coldest since 1993, it will very likely end an amazing run of 21 straight years where the average July high was 20 Celsius or warmer.
It's even more impressive when you look back between 1942-1993 and find that the previous longest trend of 20 C or warmer was just four years in row.
While we still have about a third of this month to go, with a less than impressive long range forecast, time is quickly running out for this July to get "back on the rails."
Through July 19, the weather station at St. John's International Airport has recorded an average high of 17.6, with just 5 days at 20 C or warmer.
It's an almost unreal contrast from last July (the warmest on record) when we had 17 days at 20°+ through July 19th and finished with 29 of 31 days reaching that magic 20° mark. We also finished last July with a record breaking average high of 25.3°!
The chart shows average temperatures for July from 1942 through 2015 at St. John's International Airport. The red columns mark years where the average temperature was 20 C or higher. The blue columns are 19.9 C or cooler. The purple bar on the right marks this year.
From hot to cold
So could we be going from the hottest on record to the coldest? While still possible, St. John's has witnessed some absolutely terrible Julys. In fact, the most recent were the back to back years of 1992 and 1993, when average highs were 3 C to 3.5 C below seasonal.
The coldest on record was the July 1962, which saw average high of 16.1 and just five days at 20 or warmer.
A little good news
When I looked back at the top five coldest Julys — they were 1962, 1993, 1992, 1986 and 1969, respectively — all were followed by a warmer August. While all five months were still below the 20 C August average, they were certainly an improvement, and the number of 20-degree days also increased.
Blame the blocking high
So what's going on? Why the cold? It all comes back to that pesky blocking high over Greenland and Iceland. This blocking high or negative NAO (North Atlantic Oscillation) pattern is something you have heard me talk about before.
Remember "Juneuary" and the summer of 2011? This same block high pattern was a huge factor in ruining that summer for us as well.
When the pressure is higher than normal over Greenland and Iceland, it increases the chances of cool northerly or easterly onshore winds from the chilly North Atlantic.
It also leads to a weaker or displaced Bermuda High, which is the main driver of the warm southerly winds that we want this time of year.
Waiting for a pattern change
And so we wait for a pattern shift. While the next seven to 10 days shows little sign of some sustained warm air, the longer range outlooks do indicate this blocking pattern will ease as we near the end of July and beginning of August.
If it does, that will increase our chances of taping into some of that warmer air for August, for more than just a few days at a time.
Let's all keep our fingers crossed.
Thanks to Rodney Barney from Environment Canada's Newfoundland and Labrador weather office for giving me a hand gathering and confirming these numbers over the past few days.