One "polar vortex" after the other, it seems like this summer is really just an extension of spring. The cool temps are causing people who live east of the Rockies to wonder if 2014 will go down as the year without a summer. As we enter the waning days of July, we can look back and see if it's true.
What we have is really a tale of two summers. On the West Coast, residents have dealt with relentless heat, drought, and fires. Towards the east, it's been a roller coaster ride between short-lived sweltering heat and abrupt and welcome cool-downs, interspersed with major severe weather outbreaks.
Why is the country split between two extremes?
The wide range in temperatures is the result of a topsy-turvy jet stream, or the fast-moving river of air around 30,000 feet. Generally, temperatures south of the jet stream remain warm while temperatures north of the stream are cool. During the summer, the jet stream usually remains far enough north that it doesn't have much of an effect on a majority of the United States.
This year, though, we're getting intense troughs (elongated areas of low pressure) and equally intense ridges (elongated areas of high pressure) swinging through the country much like we would see during the spring.
Here's the GFS (American) model forecast for the jet stream tomorrow:
The model shows a very deep ridge over the western United States, while the eastern part of the country lies within a deep trough. Ridges are conducive to heat waves and troughs usually bring cooler weather down from the north.
The trough/ridge effect is easily spotted on temperature forecast maps. Here's a 5-day forecast from the GFS showing temperature anomalies; the east is much cooler than normal under the trough, while the west is much warmer than normal under the ridge.
Where does this July stand in comparison to previous years?
Surprisingly, this July doesn't even clock in the top five coolest Julys on record in most major eastern U.S. cities. Using climatological records kept by NOAA, we can take a look at the mean monthly temperatures for the five coolest and five warmest Julys on record.
(For reference, the monthly mean temperature is the average of every temperature reading taken that month.)
As of July 27, the mean temperature in Boston for this July is 74.4 degrees. If this average holds to the end of the month, it will register as Boston's 29th warmest month out of the weather station's 79 years in service. It's stuck in the middle between hot and cold, and from what I hear, most Bostonians approve.
Boston's high maximum (highest high temperature) this month was 92, which it hit three different days, and its low maximum (lowest high temperature) was 72, which it also hit three times.
New York City
At New York City's Central Park, the mean temperature so far this month is 76.6 degrees, placing the month at #65 in the station's 144-year history. Like Boston, this July is on track to end just a little warmer than cooler in the record books.
NYC's high maximum this month was 91 (which it hit twice) and the month's low maximum was 74.
After several incredibly hot summers (and one brutal winter), this July's constant waves of cool weather were a welcome relief to residents of the D.C. metro area. Over at Dulles Airport — which I used for this study because the temperature readings at National Airport are unreliable — this July ranks 36 out of 53, making it the 17th coolest July on record since the airport opened in 1962.
The high maximum at Dulles this month was 95 degrees, and the low maximum this month was 78.
This month is on track to register as the seventh coolest July on record at O'Hare International Airport, with a mean monthly temperature of 70.6 degrees, and there's an outside chance it could snag the sixth or fifth spot if this week's temperature forecasts hold up.
The warmest high in Chicago so far this month was 90 degrees, and the city saw a high temperature of only 70 degrees on two separate days.
Out of the comfort and into the heat and wildfires we go, with Los Angeles sitting at a mean monthly temperature of 74.1 degrees as of July 27th. The month won't end with any records, but it is the 30th warmest July since the station began taking measurements 138 years ago.
The warmest high in the city this month was 92, and the coolest high was 75.
Congratulations, San Francisco! You are on track to see the warmest July ever recorded at the city's airport. This month's mean monthly temperature is 67.1 degrees, a full 1.3 degrees warmer than the previous warmest July, seen back in 2006.
The city hit 90 degrees one day (the day's average temperature was 12.1 degrees higher than normal), and 20 out of 27 days this month saw average temperatures two or more degrees above normal.
Portland is also seeing a fairly warm summer, with this July set to end as the sixth warmest on record. The mean monthly temperature is 71.2 degrees, just a few tenths of a degree shy of cracking the top five.
Portland's hottest day this month — with a high of 99 degrees — saw an average daily temperature a full 12.4 degrees above normal.
What's the verdict?
Given the data just for this July, it's clear that this is not the year without a summer. It's the year of a comfortable summer. It's the year we didn't sweat as much in comparison.
Unless you live in San Francisco, of course. Then it's the warmest July you've seen in at least 70 years. Summer plus.
For the sticklers...
Since I anticipate some pushback for just using July, I'll throw in the numbers for the full meteorological summer to date (June 1 through July 27) to illustrate that the season isn't really all that cool when compared to previous years.
- In Boston, up through last Sunday this is the 41st coolest summer out of 79.
- In NYC, this is the 59th coolest summer out of 144 years of records.
- In Washington, this is the 21st coolest summer out of 52.
- In Chicago, this is the 22nd coolest summer so far out of 56.
- In Los Angeles, this is the 57th warmest summer out of 138 on record.
- In San Francisco, so far this is the 2nd warmest summer out of 70 years of records.
- In Portland, this is the 26th warmest summer on record out of 74.
Enjoy the cool shot this week, easterners, and to those of you out west, stay cool.
[Top image via AP, all charts by the author]