You're about to walk your dog, but the sky looks ominous. You pull out your phone, open your favorite weather app, and see that it's about to pour. You wait for the rain to pass.

Or maybe you planned a summer vacation at the beach. A week before you're supposed to leave, you hear a weather alert on the radio in your car. There's a hurricane headed toward the coast. You have plenty of time to make new plans — and spend your vacation out of harm's way.

Millions of Americans rely on weather forecasts every day. And accurate weather forecasts have never been easier to access. Hourly outlooks and severe weather warnings are available on smartphone apps and weather websites, TV and radio broadcasts and in newspapers.

But how are these forecasts made? Where does the underlying information come from?

We break it down, and explain how some of that weather information might be interrupted this year.

Weather forecast Step 1: Make lots of measurements

Basic measurements about the weather are the fuel for accurate forecasts. That includes information about how fast and in what direction the wind is blowing, where it is raining or snowing and how much precipitation is falling, what the barometric pressure is and whether there are clouds.

And accurate weather forecasts require data from all over the world, says Alex Lamers, Forecast Operations Branch chief for the National Oceanic and Atmospheric Administration's Weather Prediction Center. "Weather happens in the atmosphere, and the atmosphere is connected globally. It doesn't happen in isolation over one specific location," he explains.

One of the most powerful ways to collect global data about the weather is through satellites and Doppler radar towers.

Satellites offer big-picture information. For example, weather satellites can track hurricanes as they move across the ocean, and wildfire smoke as it spreads across large swaths of land. Weather satellites also measure lightning activity, cloud cover, the temperature of the ocean surface and humidity in the atmosphere.

The U.S. government, through NASA and the National Oceanic and Atmospheric Administration (NOAA), operates multiple weather satellites and makes all the data they collect available to the public for free. Private weather forecasting companies, like the ones that operate weather websites and smartphone weather apps, use that data to inform their weather forecasts.

"Whatever weather app you might have on your phone, the view of clouds and precipitation from Doppler radar, that's probably NOAA data," Lamers says.

The National Weather Service also operates more than 150 Doppler radar towers across the country and shares the data with the public for free. Like satellites, Doppler radar collects big-picture information about rain, snow, sleet and hail, wind speed and direction and the clouds associated with thunderstorms. It can also detect debris in the air from tornadoes, which is very helpful for tracking where a tornado is and where it's going.

Having continuous information from radar and satellites is crucial during storms, including severe thunderstorms, tornado outbreaks and atmospheric rivers, Lamers explains. "That's really important for us to monitor storms as they develop," he says, "(to) be able to monitor the current state of the storm, where the most intense parts are, and be able to monitor that around the clock."

In an open letter in May, all five living former weather service directors expressed concern that those radar installations could be impacted by the Trump administration's federal hiring freeze and budget cuts, because radar instruments require maintenance by highly skilled technicians and there are many vacant positions.

The proposed White House budget would slash funding for NOAA by about a third and virtually eliminate weather research, ocean observations and work on new satellites.

Many of those measurements happen at automated weather stations. NOAA runs about 900 weather stations all over the country. You might have seen one at an airport or next to a government building. One of the most obvious instruments is a rotating wheel with little cups on the end that measures wind speed.

Ocean information is also important because a lot of dangerous weather systems, including hurricanes and atmospheric rivers, form over the ocean before they affect the U.S.

But operating weather-monitoring instruments in the ocean takes a lot of work, because the conditions on the open sea are so harsh. The federal government maintains about 200 ocean buoys, as well as gliders and other instruments that can measure what's happening below the surface of the ocean. Research ships, military vessels and some cargo ships also contribute weather data for the public.

"Obviously we cannot cover the entire globe, the entire surface of the Earth, with all these instruments, so we have to be smart," says Vijay Tallapragada, a weather modeling expert for NOAA's Environmental Modeling Center. For example, weather sensors are strategically located in parts of the ocean where severe weather is more likely to form.

The last, and arguably most crucial, piece of the puzzle is information about the atmosphere. Every day, employees at the National Weather Service launch weather balloons with sensors attached to them. Until recently, that was happening at least twice a day at 90 locations across the country, and more often in places that were expecting severe weather such as tornadoes.

But multiple National Weather Service offices have cut back on balloon launches this spring because of staffing shortages. The Trump administration has moved to lay off hundreds of weather workers and left hundreds of other critical forecasting positions vacant after workers retired.

The weather service addressed such disruptions in a written statement. "The National Weather Service is adjusting some services due to temporary staffing changes at our local forecast offices throughout the country in order to best meet the needs of the public, our partners and stakeholders in each office's local area," the statement says. "These adjustments are also temporary and we will continue to fulfill our core mission of providing life-saving forecasts, warnings, and decision support services."

Tallapragada says balloon data, and other aerial measurements from planes, are the single most impactful source of data for weather forecasting computer models. In addition to providing real-time information about what's happening in the atmosphere, forecasters rely on balloon measurements to calibrate satellite data. So, without balloon measurements, satellite measurements are less useful.

"We definitely know that aircraft measurements and balloon data have the largest impact on the forecasts," Tallapragada explains.

Weather forecast Step 2: Put all the data into a weather supercomputer

A weather forecast is basically the solution to a really complicated math problem. Supercomputers can solve that problem. They take all the information about what's going on in the atmosphere and oceans and use it to predict and track weather that will happen in the coming weeks.

The supercomputers doing this task for the U.S. are run by NOAA.

Those computers run multiple weather models, tailored to different types of weather. For example, hurricane models to predict when and where hurricanes will hit land, and how damaging they will be when they arrive.

Developing and running the computer models is quite labor-intensive, Tallapragada explains. "Each of these models require continuous improvement and maintenance," he says.

The incoming weather information changes all the time. Instruments on buoys and planes are replaced or recalibrated. Old satellites are decommissioned and new ones are launched. Private companies and weather services for other nations agree to share data, or change which data they're providing. Every little change must be accounted for in the computer models.

"So we need people to process, understand, calibrate and characterize those datasets so they can be assembled and used in a meaningful way," Tallapragada says.

Weather forecast Step 3: Translate the forecast from computer-speak to human-speak

The supercomputer is great at math, but it's not great at communicating with humans. When it is done crunching the numbers, it spits out a forecast result that's still mostly math.

Human forecasters then have to interpret the result and translate it into an actual weather forecast. For example, a string of numbers and probabilities becomes a map showing how much rain is expected to fall over a certain area in the next three days, and what the temperature will be each hour.

That work is done by professional weather forecasters, including meteorologists at more than 100 National Weather Service offices around the country. Local National Weather Service offices provide free, detailed local forecasts every few hours.

Meteorologists at private companies, including those who work for TV, radio and newspaper outlets, also rely on public weather model information to inform their local weather forecasts.

And if there's severe weather headed your way, like a hurricane, heavy rainstorm or tornado, the local National Weather Service office will put out a warning. That warning automatically shows up and makes an alarm sound on all the smartphones in the area. Warnings also play on the radio and on local television news stations, and they show up on weather apps and websites.

In their open letter this spring, former weather service directors warned that severe staffing shortages at local weather service offices could lead to less accurate and detailed forecasts this summer.

"Work is underway to restore services at local forecast offices around the country," according to a statement from the National Weather Service.

The summer and fall months are a busy time of year for severe weather in the U.S., from heat waves and hurricanes to heavy downpours and hailstorms. And climate change is causing dangerous weather to get more common.