Quick Reference Indoor home (general): 30 to 50 percent. ASHRAE and EPA consensus. Sleep, asthma, allergies: 30 to 50 percent. Stay below 50 to suppress dust mites and mold. Hardwood floors and furniture: 35 to 55 percent. Pianos and acoustic guitars: 40 to 50 percent. Houseplants: 40 to 60 percent. Babies and infants: 40 to

Quick Reference What it is: A long, narrow corridor of concentrated water vapor moving through the atmosphere, typically 250 to 375 miles wide and over 1,000 miles long. How much water: A strong atmospheric river transports more water vapor than the Mississippi River carries on the ground. The Pineapple Express: The most famous variety, hauling

Quick Reference Category 1: 74 to 95 mph. Some damage. Roofs, gutters, siding. Category 2: 96 to 110 mph. Extensive damage. Major roof and siding failure, mass tree damage. Category 3 (major): 111 to 129 mph. Devastating damage. Well-built homes lose roof decking. Category 4 (major): 130 to 156 mph. Catastrophic damage. Severe wall and

Quick Reference The 50-degree line. Below 50 degrees Fahrenheit, almost no warm-season seeds will germinate. Above 50, cool-season crops thrive. How to measure: Soil thermometer, 4 inches deep, in the morning, in the planting bed itself. Cool-season crops (germinate at 40-65 degrees): Lettuce, spinach, peas, kale, radishes, beets, carrots, onions, broccoli, cabbage, cauliflower. Warm-season crops

Quick Reference Humidity: Water vapor in the air, in invisible gas form. Three types: Relative humidity (a percentage), absolute humidity (grams per cubic meter), specific humidity (grams per kilogram of air). Dew point: The temperature at which the air would be 100 percent saturated. The cleaner outdoor-comfort measure. Why warm air feels mugger: Warm air

Quick Reference What it is: A blood moon is a total lunar eclipse, when Earth’s shadow falls completely across the Moon and the Moon turns deep red or copper. Why red: Earth’s atmosphere bends red wavelengths of sunlight through the shadow and onto the Moon. Same physics as a sunset. NASA terminology: NASA calls it

Quick Reference What it is: A large area of cold low-pressure air that circulates around each pole. Always there, always strongest in winter. Two layers: A stratospheric polar vortex (10 to 30 miles up) and a tropospheric polar vortex (lower, where weather happens). Strong vortex: Cold air locked at the pole. Winter cold stays north.

Quick Reference The two main numbers: Kp index (0 to 9, planetary geomagnetic activity) and the G-scale (G1 minor through G5 extreme storms). Kp 5 (G1 minor): Aurora possible across far northern US, including Maine, Michigan, Minnesota, Wisconsin, and the Dakotas. Kp 7 (G3 strong): Aurora visible as far south as Pennsylvania, Iowa, and northern

Quick Reference Severe threshold: Hail of 1 inch or larger is officially severe per the National Weather Service. 1-inch hail can dent vehicles and damage roofs. Hail size scale: Pea (0.25″), marble (0.5″), penny (0.75″), quarter (1″), golf ball (1.75″), tennis ball (2.5″), baseball (2.75″), softball (4″), grapefruit (4.5″+). Largest US hailstone: Vivian, South Dakota,

Quick Reference What it is: Body core temperature below 95 degrees Fahrenheit (35 degrees Celsius). Mild (90 to 95): Shivering, slurred speech, fast heart rate, fatigue, mild confusion. Watch for the “umbles”: stumbles, mumbles, fumbles, grumbles. Moderate (82 to 90): Violent shivering that then stops, severe confusion, drowsiness, slow weak pulse, blue lips and fingers.