June 10--As temperatures hit the 90s Wednesday with a chance of rain, people across the Chicago area likely checked their smartphones for guidance on when to head outside.
But just how reliable are weather apps? As local users can attest, different apps can report Chicago temperatures that vary by 20 degrees, or show rain clouds when you are standing in full sunshine.
"If you downloaded a bunch of different weather apps, you could have a variety of opinions as to what the weather could be," said Jim Menard, general manager for Weather Underground, an online weather service that also offers mobile apps.
Some of the variance among apps stems from where they pull their temperature readings. Less sophisticated apps may take a reading from a single Chicago location such as O'Hare International Airport. Other app companies use GPS technology to offer temperatures closer to where you are, Menard said, noting that Weather Underground uses more than 100,000 weather stations around the world.
"You really don't know that as a user because you're just given a number," Menard said.
Weather apps also are limited by how much detail they can offer on a small screen. So while app developers do their best to offer a general forecast and an hourly breakdown, sometimes you will see that little rain cloud icon when the skies are expected to clear within the hour, Menard said.
"You certainly do have challenges because nobody is on the other end sort of explaining it to you like you would on the evening news," Menard said.
Meteorologists also are willing to share some of the blame for forecast inaccuracy, which, they say, is a recurring issue this time of year.
During winter, forecasters can track a large storm system a day in advance, then say with high confidence that it will snow. But summer months are harder to predict, said Ricky Castro, a meteorologist with the National Weather Service in Romeoville.
During warm weather months, small-scale thunderstorms and showers pop up frequently through warm and humid air masses. Lake breezes also cause unexpected storms, Castro said.
All this said, Castro predicted that temperatures would hit 90 Wednesday for the first time this year across the Chicago area, in keeping with the week in June that thermometers typically reach that mark, according to weather service statistics.
If the heat feels a little unfamiliar, that's because in 2014 temperatures reached the 90s just three times -- twice in June and once in July. On average, the Chicago area usually gets 16 days each year with 90-plus temperatures, Castro said.
For the rest of the week, Chicago-area residents can expect highs of around 80, and cooler by the lake. There will be chances of storms each day until Saturday, when skies are expected to remain clear and temperatures could be in the 70s inland, and the mid-60s on the lakefront, he said.
But don't be surprised if this all changes, Castro added.
"This time of year, people want to know the weather because there are so many outdoor activities," he said. "But even as advanced as our field has become ... it's one of those things that we can't say with certainty."
vortiz@tribpub.com
