Weather Calculators
Calculate weather, storm, and climate quantities, then verify continuous, binary, probabilistic, categorical, ensemble, and interval forecasts with explicit conventions.
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Temperature20 calculators
Daily Temperature Range Calculator
Find the difference between a day’s highest and lowest observed temperature.
Mean Daily Temperature Calculator
Average the daily maximum and minimum using the conventional midpoint method.
Time-Weighted Average Temperature Calculator
Weight three temperature observations by the time represented by each one.
Temperature Change Rate Calculator
Calculate how quickly temperature rose or fell over a measured interval.
Temperature Anomaly Calculator
Measure departure from a chosen reference temperature.
Heating Degree Days Calculator
Estimate heating demand from temperature below a selected base.
Cooling Degree Days Calculator
Estimate cooling demand from temperature above a selected base.
Growing Degree Days Calculator
Calculate one day of heat accumulation between selected biological thresholds.
Heat Index Calculator
Estimate how hot shaded, light-wind conditions feel from temperature and humidity.
Wind Chill Calculator
Estimate cold exposure from air temperature and wind speed.
Humidex Calculator
Combine Celsius temperature and dew point into the Canadian humidex index.
Apparent Temperature Calculator
Estimate perceived temperature from air temperature, humidity, and wind.
Wet-Bulb Globe Temperature Calculator
Combine natural wet-bulb, globe, and dry-bulb temperatures for an outdoor WBGT estimate.
Wet-Bulb Temperature Calculator
Approximate psychrometric wet-bulb temperature from Celsius temperature and relative humidity.
Temperature Inversion Strength Calculator
Measure the temperature increase between a lower and an upper observation.
Atmospheric Lapse Rate Calculator
Calculate the observed rate of temperature decrease with height.
Freezing-Level Height Calculator
Estimate the elevation where a positive station temperature reaches 0°C.
Overnight Cooling Rate Calculator
Average the fall in temperature across an overnight observation period.
Temperature Threshold Duration Calculator
Convert a count of qualifying observations into time above or below a threshold.
Degree-Hour Exposure Calculator
Combine temperature departure above a threshold with exposure time.
Humidity20 calculators
Dew Point Calculator
Estimate dew point from Celsius air temperature and relative humidity.
Relative Humidity from Temperature and Dew Point Calculator
Calculate relative humidity from simultaneous air temperature and dew point.
Relative Humidity from Dry-Bulb and Wet-Bulb Calculator
Estimate relative humidity from ventilated dry-bulb and wet-bulb readings plus pressure.
Dew Point Depression Calculator
Find the temperature–dew point spread for an atmospheric observation.
Wet-Bulb Depression Calculator
Measure the difference between paired dry-bulb and wet-bulb temperatures.
Absolute Humidity Calculator
Estimate the mass of water vapor in each cubic metre of moist air.
Specific Humidity Calculator
Calculate water-vapor mass per kilogram of moist air from vapor pressure and total pressure.
Humidity Ratio Calculator
Estimate water-vapor mass per kilogram of dry air from temperature, humidity, and pressure.
Water Vapor Mixing Ratio Calculator
Calculate water-vapor mass per kilogram of dry air from measured vapor pressure.
Actual Vapor Pressure Calculator
Convert temperature and relative humidity into the partial pressure of water vapor.
Saturation Vapor Pressure Calculator
Estimate equilibrium water-vapor pressure over liquid water at a chosen temperature.
Atmospheric Vapor Pressure Deficit Calculator
Calculate the atmospheric difference between saturation and actual vapor pressure.
Frost Point Calculator
Estimate the temperature at which water vapor reaches saturation with respect to ice.
Condensation Temperature Margin Calculator
Measure how far a surface temperature remains above or below the air’s dew point.
Fog Formation Margin Calculator
Compare a forecast minimum temperature with the current dew point as a fog-screening margin.
Lifted Condensation Level Calculator
Estimate lifted condensation level height from the surface temperature–dew point spread.
Dew Accumulation Duration Calculator
Convert qualifying observation intervals into potential hours of dew conditions.
Precipitable Water Estimate Calculator
Estimate the liquid-water depth represented by vapor in a uniform atmospheric layer.
Air Moisture Mass Calculator
Estimate water-vapor mass contained in a stated air volume.
Relative Humidity After Temperature Change Calculator
Estimate relative humidity after sensible temperature change with unchanged vapor content.
Wind20 calculators
Crosswind Component Calculator
Resolve wind speed perpendicular to a selected heading or fixed axis.
Headwind and Tailwind Component Calculator
Calculate the signed wind component along a travel heading.
Wind Vector Components Calculator
Convert meteorological wind speed and direction into Cartesian air-motion components.
Wind Speed and Direction from Components Calculator
Recover horizontal wind speed and meteorological wind-from direction from Cartesian components.
Vector Average Wind Calculator
Average two winds as vectors rather than averaging their compass bearings directly.
Wind Gust Factor Calculator
Divide a peak gust by its paired mean wind speed using compatible observation periods.
Wind Gust Spread Calculator
Find the absolute speed difference between a peak gust and its paired mean wind.
Wind Run Calculator
Convert a mean wind speed and elapsed time into the equivalent air-passage distance.
Beaufort Scale Calculator
Classify a mean wind speed into Beaufort force 0 through 12 using stated thresholds.
Wind Pressure Calculator
Estimate ideal dynamic pressure from air density and wind speed.
Wind Speed Height Adjustment Calculator
Adjust wind speed between heights with a selected power-law shear exponent.
Logarithmic Wind Profile Calculator
Scale neutral-profile wind speed between heights using aerodynamic roughness length.
Vertical Wind Speed Shear Calculator
Calculate the change in scalar wind speed per metre of increasing height.
Wind Directional Shear Calculator
Calculate the signed shortest angular change in meteorological wind direction with height.
Apparent Wind Calculator
Find the wind experienced by a moving observer from true wind and observer velocity vectors.
Downwind Travel Time Calculator
Estimate time to cover a downwind distance at a constant speed equal to the entered wind.
Wind Drift Distance Calculator
Multiply a constant crosswind component by exposure time to estimate lateral displacement.
Prevailing Wind Percentage Calculator
Calculate the share of valid direction observations falling within a defined prevailing sector.
Calm Wind Percentage Calculator
Calculate the percentage of valid wind observations meeting a stated calm threshold.
Wind Variability Coefficient Calculator
Express directional cancellation as one minus vector-mean speed divided by scalar-mean speed.
Precipitation20 calculators
Storm Rainfall Total Calculator
Sum interval rainfall depths for one defined storm event.
Average Rainfall Intensity Calculator
Calculate mean rainfall rate across a stated event duration.
Peak-to-Average Rainfall Ratio Calculator
Compare a peak interval rainfall rate with the event-average rate.
Rain Event Duration Calculator
Find elapsed time between the declared beginning and ending of a rain event.
Hourly Rainfall Accumulation Calculator
Convert a constant rainfall rate into depth accumulated during part or all of an hour.
Rolling Rainfall Accumulation Calculator
Sum the four most recent non-overlapping rainfall intervals in a rolling window.
Tipping-Bucket Rainfall Total Calculator
Convert a valid tipping-bucket count into accumulated rainfall depth.
Rain Gauge Catch Correction Calculator
Adjust measured gauge catch for a stated collection efficiency.
Arithmetic Mean Areal Rainfall Calculator
Average four gauge depths with equal weight to estimate areal rainfall.
Weighted Areal Precipitation Calculator
Combine three precipitation depths using area weights that total 100%.
Inverse-Distance Rain Gauge Estimate Calculator
Estimate precipitation at a target using inverse-distance weights from three gauges.
Liquid Water Equivalent Calculator
Convert frozen precipitation depth to liquid-water-equivalent depth using a stated ratio.
Precipitation Percent of Normal Calculator
Express observed precipitation as a percentage of a compatible climatological normal.
Precipitation Anomaly Calculator
Calculate signed departure of observed precipitation from a selected reference amount.
Rainfall Deficit Calculator
Calculate the nonnegative shortfall of observed rainfall below a target amount.
Wet-Day Frequency Calculator
Calculate the percentage of valid days meeting a declared precipitation threshold.
Multi-Period Rain Probability Calculator
Estimate the chance of rain in at least one of several independent equal-probability periods.
Expected Precipitation Amount Calculator
Calculate a two-outcome expected precipitation amount from probability and conditional mean.
Annual Exceedance Probability Calculator
Convert a return period into annual probability of equaling or exceeding a specified level.
Precipitation Return Period Calculator
Convert annual exceedance probability into its reciprocal return period.
Snow and Ice20 calculators
Snow Water Equivalent Calculator
Convert snow depth and bulk density into liquid-water-equivalent depth.
Snow Depth from Water Equivalent Calculator
Estimate snow depth from water equivalent and an assumed bulk density.
Snow-to-Liquid Ratio Calculator
Calculate snow depth divided by liquid-water-equivalent depth.
Fresh Snow Density Calculator
Estimate fresh snow density from paired depth and water-equivalent observations.
Layered Snowpack Density Calculator
Combine three snow-layer densities using layer depth as volume weight.
Snowfall Rate Calculator
Calculate average snowfall depth rate over a stated interval.
Snowfall Accumulation Calculator
Estimate depth accumulated at a constant snowfall rate over time.
Compaction-Adjusted Snow Depth Calculator
Reduce initial snow depth by a stated fractional compaction.
Snowpack Settlement Calculator
Measure snowpack depth loss and its percentage of initial depth.
Temperature-Index Snowmelt Calculator
Estimate meltwater depth with a selected degree-day factor and base temperature.
Rain-on-Snow Melt Calculator
Estimate snowmelt supplied by sensible heat as rain cools to 0°C.
Snowmelt Water Volume Calculator
Convert a spatially uniform meltwater depth into water volume.
Snow Load Calculator
Convert snow water equivalent into ideal vertical weight per horizontal area.
Drifting Snow Depth Calculator
Estimate a scenario drift depth using an explicitly selected concentration factor.
Snow-Line Elevation Calculator
Estimate the elevation where a linear temperature profile reaches 0°C.
Freezing Rain Ice Accretion Calculator
Estimate flat-surface ice thickness from liquid depth, accretion efficiency, and ice density.
Freezing Degree-Hour Ice Growth Calculator
Estimate ice growth with a selected square-root freezing-degree-hour coefficient.
Road Surface Freezing Margin Calculator
Compare road surface temperature with an assumed effective freezing point.
Black Ice Risk Index Calculator
Combine subfreezing margin, moisture evidence, and dew-point proximity into a nonstandard screening score.
Blizzard Visibility Estimate Calculator
Estimate meteorological optical range from combined snow extinction coefficients.
Atmosphere20 calculators
Station Pressure to Sea-Level Pressure Calculator
Reduce a measured station pressure to an idealized sea-level value with the hypsometric equation.
Sea-Level Pressure to Station Pressure Calculator
Estimate station pressure from sea-level pressure, elevation, and a representative layer temperature.
Pressure Altitude Calculator
Convert pressure to ISA pressure altitude within the standard tropospheric model.
Density Altitude Calculator
Estimate density altitude from pressure altitude and outside air temperature with the common 120-foot rule.
Altimeter Setting Calculator
Convert station pressure to an approximate standard-atmosphere altimeter setting.
Standard Atmosphere Pressure Calculator
Calculate standard-atmosphere pressure through the ISA troposphere.
Standard Atmosphere Temperature Calculator
Calculate ISA tropospheric temperature from geopotential altitude.
Air Density Calculator
Calculate dry-air density from absolute pressure and temperature using the ideal gas law.
Virtual Temperature Calculator
Calculate approximate virtual temperature from air temperature and specific humidity.
Potential Temperature Calculator
Calculate dry potential temperature referenced to 1,000 hPa.
Equivalent Potential Temperature Calculator
Estimate equivalent potential temperature with a Bolton-style parcel approximation.
Hypsometric Thickness Calculator
Calculate hydrostatic thickness between two pressure surfaces.
Geopotential Height Calculator
Convert geometric height to geopotential height with a spherical-Earth gravity approximation.
Atmospheric Scale Height Calculator
Calculate the local isothermal pressure scale height for dry-air gas constant and standard gravity.
Barometric Pressure Change Rate Calculator
Calculate signed average barometric pressure change per hour.
Three-Hour Pressure Tendency Calculator
Calculate the signed net pressure change over a fixed three-hour interval.
Horizontal Pressure Gradient Calculator
Calculate the magnitude of horizontal pressure difference per 100 kilometres.
Geostrophic Wind Calculator
Estimate geostrophic wind speed from pressure-gradient magnitude, air density, and latitude.
Atmospheric Column Mass Calculator
Convert surface pressure to ideal atmospheric column mass per unit horizontal area.
Boiling Point from Atmospheric Pressure Calculator
Estimate the normal boiling point of pure water from atmospheric pressure using an Antoine equation.
Clouds and Visibility20 calculators
Cloud Base Height Calculator
Estimate convective cloud-base height above ground from surface temperature and dew-point spread.
Cloud Ceiling Selection Calculator
Select the lowest entered broken-or-overcast layer using a five-okta ceiling threshold.
Cloud Cover Percentage from Oktas Calculator
Convert cloud cover in eighths of the sky to percentage.
Cloud Oktas from Percentage Calculator
Convert cloud-cover percentage to the nearest whole okta.
Random-Overlap Total Cloud Cover Calculator
Combine three independent cloud-layer fractions with the random-overlap assumption.
Maximum-Overlap Total Cloud Cover Calculator
Combine three layers under complete maximum vertical overlap.
Weighted Cloud Cover Calculator
Average three cloud-cover estimates using explicit nonnegative weights.
Sunshine Duration Percentage Calculator
Express recorded bright-sunshine duration as a percentage of possible sunshine time.
Cloud Solar Attenuation Calculator
Apply a transparent linear cloud-cover attenuation scenario to clear-sky irradiance.
Visibility from Extinction Coefficient Calculator
Calculate contrast-limited path visibility from extinction and a selected threshold.
Extinction Coefficient from Visibility Calculator
Infer a uniform-path extinction coefficient from visibility and contrast threshold.
Meteorological Optical Range Calculator
Calculate meteorological optical range using the standard two-percent contrast convention.
Fog Visibility Calculator
Estimate fog optical range from liquid water content and effective droplet radius in a geometric-optics model.
Haze Visibility Loss Calculator
Express visibility reduction relative to a selected clear-air reference.
Runway Visual Range Estimate Calculator
Estimate a daytime contrast range along a runway path from extinction and threshold.
Solar Elevation Calculator
Calculate geometric solar elevation from latitude, declination, and solar hour angle.
Solar Azimuth Calculator
Calculate solar azimuth clockwise from true north using astronomical hour-angle convention.
Extraterrestrial Solar Radiation Calculator
Estimate top-of-atmosphere solar irradiance normal to the rays from day of year.
Clear-Sky Solar Radiation Calculator
Estimate horizontal clear-sky irradiance with a simple optical-air-mass transmission model.
Cloud-Adjusted Solar Radiation Calculator
Apply a nonlinear empirical cloud-cover correction to clear-sky irradiance.
Storms20 calculators
Lightning Distance Calculator
Estimate lightning distance from flash-to-thunder delay and temperature-adjusted sound speed.
Storm Arrival Time Calculator
Estimate travel time from along-track storm distance and constant translation speed.
Storm Travel Distance Calculator
Calculate constant-motion storm travel distance from speed and duration.
Storm Motion Vector Calculator
Resolve storm motion into eastward and northward components using a direction-toward convention.
Barometric Pressure Fall Rate Calculator
Calculate signed average pressure fall per hour over a stated interval.
Cyclone Pressure Deficit Calculator
Calculate cyclone central pressure deficit relative to a selected environment.
Hurricane Wind Category Calculator
Classify a wind speed with Saffir–Simpson hurricane wind thresholds.
Cyclone Pressure-Wind Estimate Calculator
Estimate tropical-cyclone maximum wind from central pressure with an Atkinson–Holliday-type empirical relationship.
Hurricane Wind Pressure Calculator
Calculate ideal wind dynamic pressure from hurricane-range speed and air density.
Cyclone Translation Speed Calculator
Calculate average cyclone-centre translation speed from displacement and time.
Tornado Path Length Calculator
Calculate straight-line tornado endpoint displacement from eastward and northward components.
Tornado Path Area Calculator
Estimate rectangular-equivalent tornado path area from length and mean width.
Hail Kinetic Energy Calculator
Calculate kinetic energy of one spherical hailstone from diameter, density, and speed.
Hail Terminal Velocity Calculator
Estimate spherical hail terminal velocity from drag-weight balance.
Lifted Index Calculator
Calculate Lifted Index from environmental and lifted-parcel temperatures at 500 hPa.
K Index Calculator
Calculate K Index from 850, 700, and 500 hPa temperature and moisture values.
Total Totals Index Calculator
Calculate Total Totals Index from 850 hPa temperature and dew point plus 500 hPa temperature.
Simplified CAPE Calculator
Estimate CAPE for a uniform buoyant layer from mean parcel and environmental temperatures.
Bulk Richardson Number Calculator
Calculate a simplified bulk Richardson number from CAPE and bulk vector shear magnitude.
Storm-Relative Helicity Calculator
Calculate signed storm-relative helicity for one straight hodograph segment.
Climate20 calculators
Monthly Mean Temperature Calculator
Average five daily mean temperatures as a compact monthly-mean worksheet.
Climatological Normal Average Calculator
Average three comparable climatological-normal values.
Standardized Temperature Anomaly Calculator
Standardize a temperature anomaly by a reference standard deviation.
Temperature Percentile Rank Calculator
Calculate a midrank temperature percentile from counts below and equal to a target.
Record Temperature Departure Calculator
Calculate signed departure from a selected temperature record.
Average Diurnal Temperature Range Calculator
Average maximum-minus-minimum temperature range across three days.
Frost-Free Season Length Calculator
Calculate days between last spring frost and first autumn frost within one year.
First Frost Probability Calculator
Estimate cumulative first-autumn-frost probability with a normal date model.
Last Frost Probability Calculator
Estimate cumulative last-spring-frost probability with a normal date model.
Seasonal Precipitation Total Calculator
Sum four non-overlapping precipitation periods into a seasonal total.
Standardized Precipitation Index Calculator
Calculate a simplified normal-z precipitation index for one accumulation scale.
UNEP Aridity Index Calculator
Calculate the UNEP-style precipitation-to-potential-evapotranspiration ratio.
De Martonne Aridity Index Calculator
Calculate the annual De Martonne precipitation-temperature aridity index.
Climate Moisture Index Calculator
Express annual precipitation surplus or deficit relative to potential evapotranspiration.
Hargreaves Potential Evapotranspiration Calculator
Estimate daily reference evapotranspiration with the Hargreaves temperature-range method.
Thornthwaite Potential Evapotranspiration Calculator
Estimate monthly PET with Thornthwaite heat-index and daylight correction.
Consecutive Dry Days Calculator
Find the longest dry-day run in a seven-day precipitation sequence.
Consecutive Wet Days Calculator
Find the longest wet-day run in a seven-day precipitation sequence.
Snow Season Length Calculator
Calculate the interval between first and final snow dates within one calendar-year segment.
Climate Trend Slope Calculator
Calculate an endpoint slope for a climate statistic over elapsed years.
Forecast Verification20 calculators
Temperature Forecast Absolute Error Calculator
Calculate unsigned temperature forecast error for one matched case.
Weather Forecast Bias Calculator
Calculate signed mean forecast-minus-observation error across three cases.
Weather Forecast Mean Absolute Error Calculator
Average absolute errors across three matched weather forecasts.
Weather Forecast Root Mean Square Error Calculator
Calculate square-error-weighted forecast error across three cases.
Precipitation Amount Forecast Error Calculator
Calculate signed precipitation-amount error for one accumulation.
Weather Forecast Brier Score Calculator
Calculate the Brier score for one binary probability forecast.
Weather Forecast Brier Skill Score Calculator
Compare a forecast Brier score with a declared reference score.
Probability Forecast Calibration Error Calculator
Average absolute reliability differences across three probability bins using case counts.
Weather Event Forecast Accuracy Calculator
Calculate overall binary-event accuracy from a contingency table.
Weather Event Probability of Detection Calculator
Calculate the fraction of observed events that were forecast.
Weather Event False Alarm Ratio Calculator
Calculate the fraction of forecast events that did not occur.
Weather Event Critical Success Index Calculator
Calculate threat score from hits, misses, and false alarms.
Weather Event Equitable Threat Score Calculator
Calculate threat score adjusted for expected random hits.
Weather Forecast Heidke Skill Score Calculator
Calculate chance-corrected Heidke skill from a binary contingency table.
Weather Forecast Peirce Skill Score Calculator
Calculate true skill statistic from hit rate minus false alarm rate.
Weather Event Frequency Bias Calculator
Compare frequency of forecast events with observed events.
Weather Forecast Ranked Probability Score Calculator
Calculate ranked probability score for three ordered categories.
Weather Ensemble Mean Calculator
Average five equally weighted ensemble members.
Weather Ensemble Spread Calculator
Calculate sample standard deviation of five ensemble members.
Weather Forecast Confidence Interval Calculator
Construct a symmetric mean interval from standard error and selected critical value.
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Weather calculations with their assumptions exposed
Weather calculations and forecast scores depend on location, exposure, valid time, lead, reference period, spatial matching, event threshold, aggregation, units, observations, and model assumptions. Each page identifies the working relationship and the record needed to reproduce it.
Apparent-temperature, moisture, fog-margin, and exposure calculations are screening tools rather than personal guarantees or official forecasts. Consult current observations, forecasts, watches, warnings, workplace procedures, and activity-specific guidance when weather may be hazardous.