{"id":1586,"date":"2022-07-10T11:18:04","date_gmt":"2024-07-10T11:16:04","guid":{"rendered":"http:\/\/ialert.com\/blog\/?p=1586"},"modified":"2026-04-28T01:53:59","modified_gmt":"2026-04-28T01:53:59","slug":"glossary-of-weather-terms-beginning-with-k","status":"publish","type":"post","link":"https:\/\/ialert.com\/blog\/weather-articles\/weather-glossary\/glossary-of-weather-terms-beginning-with-k\/","title":{"rendered":"Glossary of Weather Terms – Beginning with “K”"},"content":{"rendered":"

Wondering what a katabatic wind is<\/strong> and why Santa Ana conditions are so dangerous for wildfires? Curious about knots in weather forecasts<\/strong>, what the K-Index<\/strong> tells meteorologists about thunderstorm potential, or how the Kelvin temperature scale<\/strong> is used in atmospheric science?<\/p>\n

Jump to weather terms beginning with the letter:<\/h3>\n

A<\/a> | B<\/a> | C<\/a> | D<\/a> | E<\/a> | F<\/a> | G<\/a> | H<\/a> | I<\/a> | J<\/a> | K<\/a> | L<\/a> | M<\/a> | N<\/a> | O<\/a> | P<\/a> | Q<\/a> | R<\/a> | S<\/a> | T<\/a> | U<\/a> | V<\/a> | W<\/a> | X<\/a> | Y<\/a> | Z<\/a><\/p>\n

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Weather Terms Beginning with “K”<\/strong><\/h3>\n

Katabatic Wind<\/strong><\/h4>\n

A katabatic wind is a drainage wind that flows downhill due to the negative buoyancy of cold, dense air that has cooled by direct contact with an elevated surface such as a glacier, snowfield, or high plateau. The name derives from the Greek “katabatikos,” meaning “going downhill.” As cold, dense air accumulates on high terrain overnight, gravity pulls it downslope into lower valleys and coastal zones. Katabatic winds can reach extreme speeds, up to 100 mph or more in Antarctica and Greenland, where vast elevated ice sheets chill enormous volumes of air, and are responsible for some of the most powerful sustained winds recorded on Earth. Notable katabatic or katabatic-influenced winds include the Bora on the Adriatic coast of Croatia and Slovenia, the Mistral of southern France, and the Santa Ana winds of Southern California. The Chinook winds of the Rocky Mountain lee slopes are a warming katabatic variant, the air warms by adiabatic compression as it descends, arriving far warmer than when it started. Katabatic winds are a constant, defining weather feature of Antarctic coastal stations, where they drain relentlessly off the polar ice sheet. See also: What is the Beaufort Wind Scale?<\/a><\/p>\n\n\n\n\n\n\n\n\n\n\n
Katabatic Wind vs Anabatic Wind<\/caption>\n
Feature<\/th>\nKatabatic Wind<\/th>\nAnabatic Wind<\/th>\n<\/tr>\n<\/thead>\n
Direction<\/td>\nDownslope (downhill)<\/td>\nUpslope (uphill)<\/td>\n<\/tr>\n
When It Forms<\/td>\nNighttime \/ cold surfaces \/ cold drainage<\/td>\nDaytime solar heating of slopes<\/td>\n<\/tr>\n
Temperature<\/td>\nCold (dense, sinking air)<\/td>\nWarm (buoyant, rising air)<\/td>\n<\/tr>\n
Speed<\/td>\n10-100+ mph (can be severe)<\/td>\nUsually 5-15 mph (gentle)<\/td>\n<\/tr>\n
Notable Examples<\/td>\nSanta Ana winds, Bora, Antarctic drainage<\/td>\nValley fog burns off, afternoon slope thermals<\/td>\n<\/tr>\n
Weather Effect<\/td>\nFire danger (dry, warm in valleys), wind damage<\/td>\nAfternoon cumulus development; glider flying<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Kelvin Temperature Scale<\/strong><\/h4>\n

The Kelvin temperature scale is the absolute temperature scale used throughout scientific meteorology and atmospheric science. Unlike the Celsius and Fahrenheit scales, which are based on the freezing and boiling points of water, the Kelvin scale begins at absolute zero, the theoretical temperature at which all molecular thermal motion ceases, equal to -459.67\u00b0F or -273.15\u00b0C. There are no negative Kelvin temperatures. Conversion between Celsius and Kelvin is straightforward: K = \u00b0C + 273.15 (so 0\u00b0C = 273.15K, -40\u00b0C = 233.15K, and 100\u00b0C = 373.15K). Kelvin is used in atmospheric thermodynamics because equations governing radiation, energy transfer, and gas laws require an absolute temperature scale to produce physically meaningful results. The Stefan-Boltzmann law, which governs how much energy any object radiates as a function of temperature, requires Kelvin. Satellite remote sensing instruments measure atmospheric and surface temperatures in Kelvin. Climate models, radiative transfer calculations, and thermodynamic calculations are all performed in Kelvin. In operational weather forecasting, Celsius and Fahrenheit are used in public products, but the science underlying those forecasts is done in Kelvin.<\/p>\n

K-Index<\/strong><\/h4>\n

The K-Index is a measure of the thunderstorm potential of the atmosphere derived from radiosonde (weather balloon) data. It is calculated using the temperature at 850 millibars (roughly 5,000 feet), 700 millibars (roughly 10,000 feet), and 500 millibars (roughly 18,000 feet), along with the dew point temperature at 850 and 700 millibars, parameters that together capture both the instability and moisture content of the lower troposphere. Higher K-Index values indicate greater moisture through the low and mid levels of the atmosphere combined with a larger temperature difference between lower and upper levels, conditions favorable for deep, moist convection and thunderstorm development. Interpretation thresholds: a K-Index under 20 indicates little or no thunderstorm potential; 20-25 suggests isolated thunderstorm potential; 26-30 points to scattered thunderstorms; 31-35 indicates numerous thunderstorms; and above 35 represents extreme instability with widespread severe thunderstorm potential. Aviation meteorologists and NWS forecasters use the K-Index alongside CAPE, lifted index values, and shear data to build a full picture of daily severe weather risk. Unlike CAPE, the K-Index is derived from a straightforward formula without requiring the parcel-lifting calculations that make CAPE more computationally intensive.<\/p>\n

Knot (kn)<\/strong><\/h4>\n

A knot is the standard unit of wind speed used in aviation weather and marine meteorology, equal to one nautical mile per hour. One knot equals approximately 1.15 statute miles per hour or 1.85 kilometers per hour. To convert knots to mph, multiply by 1.15; to convert mph to knots, divide by 1.15. The unit originated from the historical maritime practice of measuring a sailing ship’s speed by tossing a knotted rope overboard and counting how many knots passed through a sailor’s hands in a fixed time interval, an early form of the ship’s log. NWS marine forecasts, aviation weather products, and all tropical storm and hurricane advisories report wind speeds in knots. Tropical storm force winds begin at 34 knots (39 mph); hurricane force winds begin at 64 knots (74 mph); a Category 5 hurricane has sustained winds of 137 knots (157 mph) or greater. Pilot weather briefings and aviation routine weather reports (METARs) always express wind speed in knots, which is why a working understanding of knot-to-mph conversion is useful for interpreting aviation and coastal weather products.<\/p>\n

Kona Storm<\/strong><\/h4>\n

A Kona storm is a low-pressure system that brings unusually wet and sometimes severe weather to the Hawaiian Islands. The name comes from the Kona coast, the leeward (southwest) side of the Big Island of Hawaii, which is normally protected from the dominant northeast trade winds and remains relatively dry. When a Kona storm develops, the normal trade wind pattern breaks down and winds shift to a more southerly or westerly direction, driving moisture from the south-southwest into areas that are ordinarily in a rain shadow. The disruption allows heavy rainfall to fall on normally dry leeward coastlines, while the windward (northeast-facing) slopes that normally receive the most rain may see relatively less. Kona storms can produce heavy rainfall, strong winds, high surf on unusual coastlines, and flash flooding across all islands. They occur most frequently between November and April, when upper-level troughs from the mid-Pacific are more likely to penetrate close to the islands. Major Kona storms are relatively infrequent, perhaps several times per decade, but when they occur they can produce the most significant flooding events on the leeward sides of the Hawaiian Islands.<\/p>\n

Santa Ana Winds<\/strong><\/h4>\n

Santa Ana winds are a specific katabatic and offshore wind pattern affecting Southern California, one of the most consequential weather phenomena in the western US because of its direct link to catastrophic wildfire. Santa Ana events form when high pressure over the Great Basin (the arid plateau between the Sierra Nevada and Rocky Mountains) forces air downslope and offshore through mountain passes and canyons in the Transverse and Peninsular Ranges. As the air descends in elevation, often from 5,000 to 6,000 feet above sea level down to sea level, it compresses and warms adiabatically at roughly 5.5\u00b0F per 1,000 feet of descent. The result is air that arrives in Southern California’s valleys and coastal areas hot (temperatures of 90 to 110\u00b0F are common in October and November when the surrounding region is normally cooling), extremely dry (relative humidity frequently drops to single digits, below 10% and sometimes below 5%), and gusty (sustained winds of 30 to 50 mph with gusts of 60 to 80 mph or higher in mountain passes). The combination of low humidity, high heat, and powerful winds creates extreme fire weather conditions: vegetation that may have been dried by months without rain ignites easily and fires can spread at several miles per hour. The NWS issues Red Flag Warnings during major Santa Ana events. These winds were responsible for conditions during California’s most destructive wildfires, including the 2003 Cedar Fire (280,000 acres), the 2007 Southern California firestorm (500,000+ acres across multiple fires), and contributed to conditions during the 2018 Camp Fire.<\/p>\n

Kp-Index (Geomagnetic Activity)<\/strong><\/h4>\n

The Kp-index is a global measure of geomagnetic activity that quantifies disturbances in Earth’s magnetic field caused by solar wind and coronal mass ejections (CMEs) from the sun. It is expressed on a scale from 0 to 9: Kp 0 indicates completely quiet geomagnetic conditions; Kp 5 indicates a minor geomagnetic storm (NOAA G1 level); Kp 7 indicates a strong storm (G3); Kp 9 indicates an extreme storm (G5), the most severe classification. The Kp-index is updated every 3 hours by NOAA’s Space Weather Prediction Center and is derived from ground-based magnetometer readings at stations around the world. Aurora visibility is directly tied to Kp levels: at Kp 5, auroras are typically visible from northern states such as Minnesota, Michigan, and Maine under clear, dark skies; at Kp 7, they can be seen as far south as the mid-Atlantic states and the northern Plains; at Kp 9 (extreme storms, which are rare, perhaps once per solar cycle), auroras may be visible as far south as Florida and the Gulf Coast. The most intense geomagnetic storms can also disrupt power grids, satellite operations, GPS accuracy, and high-frequency radio communications. The Carrington Event of 1859, estimated at an extreme Kp level beyond the modern scale, caused telegraph equipment to spark and catch fire across North America and Europe.<\/p>\n

Koppen Climate Classification<\/strong><\/h4>\n

The Koppen climate classification is the most widely used system in the world for categorizing and mapping the Earth’s climates. It was developed by Russian-German climatologist Wladimir Koppen in 1884 and refined with Rudolf Geiger in the 1950s. The system divides the world’s climates into five primary groups, identified by capital letters, based on temperature and precipitation patterns: Group A (tropical: always warm, no true winter, abundant rainfall), Group B (arid: dry, evaporation exceeds precipitation), Group C (temperate: mild winters, warm to hot summers), Group D (continental: cold winters, warm summers, significant seasonal precipitation), and Group E (polar: extremely cold year-round, no warm season). Each primary group is further subdivided by additional letters indicating precipitation distribution and temperature extremes. The contiguous United States spans an unusually wide range of Koppen climate types: the humid subtropical (Cfa) climate dominates the Southeast; Mediterranean (Csa\/Csb) climates appear on the California coast; the humid continental (Dfa\/Dfb) climate covers the northern Plains, Great Lakes, and New England; the semi-arid steppe (BSk) covers the central Great Plains; and the hot desert (BWh) defines the Sonoran and Mojave Deserts of the Southwest. The Koppen system is used in agriculture, building design, insurance risk modeling, and climate change impact studies because it directly links climate type to vegetation, water availability, and human infrastructure requirements.<\/p>\n

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Frequently Asked Questions, “K” Weather Terms<\/strong><\/h3>\n

What is a katabatic wind?<\/h4>\n

A katabatic wind is a cold, dense wind that drains downhill from elevated surfaces such as glaciers, snowfields, or high plateaus. As cold air on high terrain becomes denser than surrounding air, gravity pulls it downslope. Katabatic winds can reach extreme speeds, up to 100 mph or more in Greenland and Antarctica, and are responsible for some of the most powerful winds on Earth. In the US, the Santa Ana winds of Southern California are a katabatic-type flow that brings hot, dry, fast-moving air down from the Great Basin through mountain passes, creating extreme fire weather conditions with single-digit humidity and gusts exceeding 80 mph.<\/p>\n

What is a knot in weather forecasting?<\/h4>\n

A knot is a unit of speed equal to one nautical mile per hour, approximately 1.15 mph. It is the standard unit used in aviation weather and marine weather forecasts. The NWS reports tropical storm and hurricane winds in knots: a tropical storm begins at 34 knots (39 mph), and hurricane force winds begin at 64 knots (74 mph). To convert knots to mph, multiply by 1.15. So a 50-knot wind equals about 58 mph. The unit comes from the historical nautical practice of measuring ship speed using a knotted rope thrown overboard to measure how fast the vessel was moving through the water.<\/p>\n

What is the K-Index in weather?<\/h4>\n

The K-Index is a measure of thunderstorm potential calculated from weather balloon data. It uses temperature and dew point readings at multiple atmospheric levels to assess both instability and moisture availability in the lower troposphere. A K-Index under 20 indicates little thunderstorm potential; 20-25 suggests isolated thunderstorms; 26-30 points to scattered thunderstorms; above 35 indicates extreme instability with widespread severe thunderstorm potential. Aviation meteorologists and NWS forecasters use it alongside CAPE values to build a complete picture of daily severe weather risk.<\/p>\n

What are Santa Ana winds and why are they dangerous?<\/h4>\n

Santa Ana winds are a katabatic offshore wind pattern affecting Southern California, typically from September through April. They form when high pressure over the Great Basin forces air downslope through mountain passes. As the air descends, it warms by adiabatic compression and arrives at the coast hot (90 to 110\u00b0F in fall), extremely dry (humidity under 10%), and very gusty (gusts of 60 to 80+ mph in passes). These conditions, heat, extreme low humidity, and high winds, create extreme fire weather. Santa Ana events triggered the 2003 Cedar Fire, the 2007 Southern California firestorm, and contributed to conditions during the 2018 Camp Fire, making them one of the most consequential weather patterns in the US for property loss.<\/p>\n

What is the Koppen climate classification system?<\/h4>\n

The Koppen climate classification is the most widely used system for categorizing the world’s climates, dividing them into five main groups: A (tropical, always warm and wet), B (arid, dry), C (temperate, mild winters), D (continental, cold winters), and E (polar). The US spans multiple climate types: humid subtropical (C) in the Southeast, Mediterranean (C) on the California coast, humid continental (D) across the northern Plains and Northeast, semi-arid steppe (B) on the Great Plains, and desert (B) in the Southwest. This system explains why building codes, agriculture, and weather hazards vary so dramatically across the country and is used in climate change impact research.<\/p>\n

What is the Kp-index and what does it mean for auroras?<\/h4>\n

The Kp-index measures the intensity of geomagnetic activity on a scale from 0 (completely quiet) to 9 (extreme storm). It is used to predict aurora visibility, the aurora borealis becomes visible at lower latitudes as the Kp-index rises. At Kp 5 (minor geomagnetic storm), auroras are typically visible from northern US states. At Kp 7, they can be seen as far south as the mid-Atlantic and northern Plains. At Kp 9 (an extreme and rare event), auroras may appear as far south as the Gulf Coast. NOAA’s Space Weather Prediction Center issues aurora alerts and updates the Kp-index every 3 hours based on magnetometer data from stations worldwide.<\/p>\n

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