Understanding Forecasting

Every day, meteorologists on TV and the radio give a weather "forecast." What they are actually doing is predicting what the weather will be for the next 24 hours, or even the next few days, based on the current weather conditions.

Forecasting with the Clouds

The type and number of clouds in the sky can tell you a lot about the weather to come. As you observe the clouds, look them up on the following table.

Type of Cloud	Most Likely Weather
Thickening Cirrus	Precipitation within 12-24 hours
Altocumulus	Precipitation within 6-12 hours
Altocumulus with "castle-like" appearance in the morning	Severe storms by afternoon
Altostratus	Drizzle, fog, and rain (or possibly snow and ice, if during the winter_
Stratocumulus with breaks of sun	Generally dry and cool weather
Stratocumulus overcast	Showers will develop
Nimbostratus overcast	Steady precipitation
Cumulus with no vertical development	Nice weather
Cumulus with vertical development	Showers and storms by afternoon
Cumulonimbus	Thunderstorms soon
Cumulonimbus with mammatus (curve-shaped) clouds	Severe weather in the area

Forecasting with Wind and Barometer Readings

You can also forcast the weather based on the wind speed and direction and the current barometric pressure. With this information, look up the intersection of those readings in the chart below.

Wind Direction	Sea-Level Barometric Pressure (Inches)	Most Likely Weather
SW to NW	30.10 to 30.20 steady	Fair, little temperature change for one to two days
SW to NW	30.10 to 30.20 rising rapidly	Fair, followed within two days by warmer and rain
SW to NW	30.20 and above steady	Continued fair, no marked temperature change
SW to NW	30.20 and above falling slowly	Fair with slowly rising temperatures for two days
S to SE	30.20 and above falling rapidly	Wind increasing; rain within 12-24 hours
SE to NE	30.10 to 30.20 falling slowly	Rain in 12-18 hours
SE to NE	30.10 to 30.20 falling rapidly	Increasing wind and rain within 12 hours
E to NE	30.10 and above falling slowly	In winter, rain within 24 hours. In summer, with light winds, rain may not occur for several days<
E to NE	30.10 and above falling rapidly	In winter, rain or snow with increasing winds. In summer, rain probable within 12-24 hours.
SE to NE	30.00 or below falling slowly	Rain will continue one or two days
SE to NE	30.00 or below falling rapidly	Rain with high winds followed in 36 hours by clearing, cooler
S to SW	30.00 or below rising slowly	Clearing within a few hours and fair for several days
S to E	29.80 or below falling rapidly	Severe storm soon followed within 24 hours by clearing and, in winter, colder
E to N	29.80 or below falling rapidly	Severe northeast gale and heavy precipitation. In winter, snow followed by cold wave
To W	29.80 or below rising rapidly	Clearing and colder