← Back to course
Weather Lab 6-8 / Week 08 / Friday
5/6
Week 08 · Air Masses and Fronts

Friday

Reading the evening forecast
// Where weather changes come from
⏱ about 20 min

Friday: Reading the Evening Forecast

The evening forecast glows on the lab screen: "Cold front arrives overnight. Chance of showers 50 percent, then clearing and cooler."

"Translate," Rocket says. "Do I need a raincoat tomorrow or a sweater?"

Raven reads it line by line. "What do you notice about the order of events?"

"Showers first, then clearing, then cooler," Rocket says. "That is exactly Thursday's table."

Nova dims the lights and shows a blue front line sliding toward a dot labeled Station Rooftop.

"Fifty percent means a fifty percent chance of measurable rain right here at the station," she says. "What will you pack?"

Rocket grabs both. "Raincoat for tonight. Sweater for tomorrow. The front gets both."

From map to plan

A forecast is a story about air masses. "Cold front overnight" means cold, drier air is on the way.

"Chance of showers, 50 percent" means a 50 percent chance of at least 0.01 inch of rain at your spot. It is not a share of the area.

"Clearing and cooler" is the air behind the cold front. Winds often shift, and the sky clears.

Reading the air mass behind the front tells you about tomorrow before tomorrow arrives.

TRANSLATE THE FORECAST
  • Read the question.
  • Tap your answer.
"Warm front approaching, rain likely." What should you expect?
"Cold front this evening, then clearing." What happens to the temperature tomorrow?
A 70 percent chance of rain is what forecast word?
Which air mass most likely arrives behind a winter cold front from the north?

Why forecasts use percents

Air masses are huge, but showers are small. A forecaster can be sure a front is coming and still not know which street gets wet.

So the forecast gives a probability for your point, and words like "chance" and "likely" to match.

A 30 percent chance that stays dry is not a wrong forecast. Seven times out of ten, it will stay dry.

Week reviewTrue or false?
An air mass takes its temperature and moisture from where it formed.?
A front is the boundary between two air masses.?
A warm front is drawn as a blue line with triangles.?
The cold front moves faster and can overtake the warm front.?
A 40 percent chance of rain means it will rain for 40 percent of the day.?
WHY THIS EXERCISEThese five ideas turn a forecast from a guess into a plan.
A COLD FRONT DAY, IN ORDER
  • ?A line of showers or thunderstorms arrives with the front.
  • ?Skies clear and the temperature falls.
  • ?The wind shifts to the northwest.
  • ?Warm, gusty south wind ahead of the front.
WHY THIS EXERCISESpotting this order in your own log means you have caught a front.
What do we call the boundary where two air masses meet? Type one word.
WHY THIS EXERCISEThe front is where most of the week's weather action happens.
Try it
Listen to or read tonight's forecast with a grown-up. Write down every percent and every air mass clue you hear.
Then predict tomorrow's wind direction and temperature change. Check your log tomorrow evening.

Next week you learn what thunderstorms, tornadoes and hurricanes are, and the safety rules that keep families ready.

Draw tomorrow's forecast as a surface map: a low, its fronts, your area as a dot and the percent chance of rain.

Excellent week, forecaster. Tomorrow is Station Day: your family hunts for a front.

← Thursday