Eranorms

What Eranorms does

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• City Weather Comparison: Compare Climate in 9 City Pairs Compare typical temperature, rainfall and humidity for 9 city pairs, including New York vs. San Francisco and Miami vs. Phoenix. Find a season that suits your trip.
• Why Does It Hail in the Summer? The Physics of Warm-Season Ice Intense summer solar heating creates explosive updrafts exceeding 60 mph that shoot freezing cloud tops past 35,000 feet, allowing hailstones to grow inside −40°F air even when surface temperatures top 90°F.
• Why Does It Smell Like Rain? The Science of Petrichor Falling raindrops trap microscopic air bubbles against porous soil and rock, launching aerosolized geosmin and plant lipid terpenes into the air at concentrations detectable at 5 parts per trillion.
• Why Is It Coldest Just After Sunrise? The Science of Dawn Lows Net radiative cooling continues to strip heat from the ground even as the sun peeks over the horizon, causing surface air temperatures to reach their daily minimum 15 to 30 minutes after sunrise.
• What Is an Atmospheric River and How Much Rain Does It Carry? Atmospheric rivers transport 7 to 22 times the Mississippi River discharge in water vapor, supplying 30% to 50% of West Coast annual water across 5 defined intensity categories.
• Graupel vs. Hail: How to Tell Soft Snow Pellets Apart from Ice Rimed snowflakes crush between your fingers at 2–5 mm when supercooled cloud droplets freeze on contact, while true hailstones build hard, concentric ice rings inside violent thunderstorm updrafts exceeding 50 mph.
• Polar Vortex vs. Arctic Blast: Jet Stream Waviness, Rossby Waves, and Stratospheric Warming Circumpolar stratospheric winds 30 km aloft differ fundamentally from tropospheric cold fronts; Sudden Stratospheric Warming triggers high-amplitude Rossby wave buckling that spills Arctic cold into mid-latitudes.
• Temperature Inversions vs. Normal Lapse Rates: How Boundary Layer Trapping Stagnates Winter Air Nocturnal radiational cooling caps valley air under a warm inversion lid, trapping particulate matter and stalling dispersion until convective mixing breaks the cap.
• Katabatic Winds vs. Foehn and Chinook Warming: Gravity Drainage vs. Compressional Heating Gravity-driven drainage chills valleys under radiative cooling, while adiabatic compression superheats lee slopes during downslope foehn events.
• Wet vs. Dry Microburst Soundings: Inverted-V Profiles and 70 mph Downbursts Atmospheric soundings explain why dry microbursts produce 70+ mph surface winds with zero rain as sub-cloud virga evaporates across a deep 2,500m dry layer, compared to precipitation-loaded wet downbursts.
• Radiation Fog vs. Advection Fog: Sounding Profiles and Clearance Times Atmospheric sounding profiles show why radiation fog burns off by mid-morning within a shallow 100m ground cooling layer, whereas advection fog spans 500m under marine winds and lingers for days.
• Lake-Effect Snow Instability: Why Convection Requires a 13°C Water-to-Air Gap NWS mesoscale sounding analyses show why lake-effect snow requires a 13°C gap between lake water and 850 hPa air to trigger boundary layer convection, producing 2–5 in/hr squalls along long-axis fetch corridors.
• Wind Chill vs. Actual Temperature: Why 20°F in Wind Cools Faster Than 0°F Calm NWS boundary layer biophysics shows why 20°F air with 30 mph wind strips insulating facial air and loses 1,050 W/m² of heat, cooling exposed skin faster than calm 0°F air.
• Heat Index vs. Wet-Bulb Temperature: Why 95°F Wet-Bulb Is Universally Lethal NWS heat stress models show why a 95°F heat index is uncomfortable in shade, whereas a 95°F wet-bulb temperature collapses the skin vapor gradient and induces fatal hyperthermia within 6 hours.
• Freezing Rain vs. Sleet: How Warm Layers Aloft Dictate Surface Icing NWS sounding data shows why a deep warm nose aloft melts snow into rain, producing destructive glaze when surface cold is too shallow to refreeze drops into sleet.
• El Niño Winter Temperature History: What Strong Events Mean for Northern States Historical NCEI station records across four benchmark strong El Niño winters show Minneapolis averaging +4.1°F and Chicago +3.2°F above normal, while southern states trend near average.
• Dew Point vs. Relative Humidity: Why 60% Humidity Feels Different at 50°F and 85°F Learn why 60% relative humidity feels crisp at 50°F (36°F dew point) and oppressive at 85°F (70°F dew point), using the National Weather Service summer comfort scale.
• Drought History by State, 2000–2026: Where It Stays and When It Spreads Every state's weekly U.S. Drought Monitor index since 2000 in one chart: the Southwest's long droughts, the 2002, 2012 and 2021–22 spreads, and 2026 so far.
• Winter Lows at Six U.S. Airports: 66 Winters in Context Compare 66 winters of NOAA daily lows at six U.S. airports, with station moves, quality flags and a clear explanation of what the record can tell you.
• What Are Climate Normals? A Simple Guide to 30-Year Weather Averages Climate normals are 30-year weather averages. Learn what they reveal about a city, what they cannot forecast, and how to compare them correctly.
• Average Rainfall by Month: How to Read a City's Wet Season Average rainfall by month explains when a city is usually wet or dry. Learn how totals, rainy days, temperature and seasonal patterns work together.
• Hottest Day on Record vs. Average Summer: What Each Number Means A city's hottest day on record and its average summer temperatures answer different questions. Learn which weather measures matter for travel, moving and heat planning.
• What Climate Stripes Actually Show You Climate stripes show annual temperatures relative to a baseline. Learn what their colours mean, how local charts differ, and what to check before comparing them.

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