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Welcome to Tech News Briefing. It's Thursday, December 5th. I'm Danny Lewis for the Wall Street Journal. Have you ever had a weather app swear it wasn't raining in the middle of a downpour? We'll find out why you can't always trust your weather app and ways to get better predictions.

And then, for years, many U.S. tech companies kept the defense industry at arm's length.

Now, one of the biggest names in artificial intelligence development, OpenAI, is getting into the business of war. The chat GPT maker has struck a deal with defense startup

and Dero. Our reporter Deepa Sitha Raman explains how this is the latest example of Silicon

Valley's efforts to forge deeper ties with the Pentagon. But first, weather apps are a convenient

way to get a glimpse at the day's forecast so you know

what to wear. But they can be fickle and aren't always accurate. Our personal tech columnist

Nicole Nguyen dug into why this happens and how to get better weather predictions. She joins us

now. Nicole, why aren't weather apps always accurate? Weather apps use data from these

publicly available models. And these models spit out a bunch of numbers, and it's up to our

weather apps to simplify those numbers and turn it into an icon, say, cloudy, rainy, et cetera. It doesn't have much

nuance. So it's making its best guess, and when that guess is wrong, you are stuck in the rain,

unfortunately. How has weather forecasting tech changed in recent years?

The underlying models are these very complicated mathematical models that require super

computers all around the world to crunch the numbers, and it's so intensive that some only

crunch the numbers every six hours. And those computers themselves have become faster, more

competent, and so they can run more types of mathematical equations for more

grids across the planet faster.

And that means that the accuracy has gone from a good forecast looking ahead three days to

...