{"id":1613,"date":"2022-07-10T11:06:58","date_gmt":"2024-07-10T11:25:58","guid":{"rendered":"http:\/\/ialert.com\/blog\/?p=1613"},"modified":"2026-04-28T02:15:03","modified_gmt":"2026-04-28T02:15:03","slug":"glossary-of-weather-terms-beginning-with-x","status":"publish","type":"post","link":"https:\/\/ialert.com\/blog\/weather-articles\/weather-glossary\/glossary-of-weather-terms-beginning-with-x\/","title":{"rendered":"Glossary of Weather Terms – Beginning with “X”"},"content":{"rendered":"

Wondering what X-band radar<\/strong> is and how it differs from the NEXRAD network, how Doppler weather radar actually works<\/strong>, what weather radar frequency bands<\/strong> mean for storm detection, what METAR abbreviations<\/strong> mean in an aviation weather report, or how solar X-ray flares<\/strong> affect GPS and radio communications? Few meteorological terms begin with X, but the ones that do touch on the radar technology that underpins nearly every severe weather warning issued in the United States.<\/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 “X”<\/strong><\/h3>\n

X-Band Radar<\/strong><\/h4>\n

X-band radar is a type of weather radar that operates at microwave frequencies of 8-12 GHz, corresponding to a wavelength of approximately 2.5-4 cm. For comparison, the NWS WSR-88D NEXRAD national network operates in the S-band (2-4 GHz, approximately 10 cm wavelength), and Terminal Doppler Weather Radar (TDWR) at airports operates in the C-band (4-8 GHz, approximately 5 cm). X-band radars are significantly smaller, lighter, and less expensive than S-band systems, making them practical for portable deployment, gap-filling coverage in mountainous terrain where NEXRAD is blocked by topography, and urban area supplemental monitoring. The tradeoff is signal attenuation: X-band radar signals weaken significantly in heavy rain (the shorter wavelength is more readily scattered and absorbed by large raindrops), reducing the radar’s effective range and reliability during the most intense precipitation events, precisely when accurate storm detection is most critical. Despite this limitation, X-band radar networks are increasingly used by universities, state agencies, airports, and research organizations to supplement NEXRAD coverage and provide higher spatial resolution data than the national network.<\/p>\n

See also: Your Local Live Doppler Radar<\/a> | Criteria for a Tornado Warning<\/a><\/p>\n\n\n\n\n\n\n\n\n\n
Weather Radar Types Compared<\/caption>\n
Radar Type<\/th>\nFrequency Band<\/th>\nWavelength<\/th>\nRange<\/th>\nBest Use<\/th>\n<\/tr>\n<\/thead>\n
WSR-88D (NEXRAD)<\/td>\nS-band (2-4 GHz)<\/td>\n~10 cm<\/td>\n250 miles<\/td>\nNational network; all-weather detection<\/td>\n<\/tr>\n
Terminal Doppler (TDWR)<\/td>\nC-band (4-8 GHz)<\/td>\n~5 cm<\/td>\n~60 miles<\/td>\nAirport wind shear detection<\/td>\n<\/tr>\n
X-Band Radar<\/td>\nX-band (8-12 GHz)<\/td>\n~3 cm<\/td>\n30-50 miles<\/td>\nUrban\/mountain gap fill; portable<\/td>\n<\/tr>\n
Phased Array Radar (PAR)<\/td>\nS-band<\/td>\n~10 cm<\/td>\n250+ miles<\/td>\nNext-gen research; faster updates<\/td>\n<\/tr>\n
Dual-Pol Radar<\/td>\nS-band (WSR-88D upgrade)<\/td>\n~10 cm<\/td>\n250 miles<\/td>\nPrecipitation type discrimination<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Xenon in the Atmosphere<\/strong><\/h4>\n

Xenon (Xe) is a heavy, colorless, odorless noble gas that exists as a trace constituent of Earth’s atmosphere at approximately 0.087 parts per million (ppm) by volume, making it far less abundant than nitrogen (78%), oxygen (21%), argon (0.93%), or even carbon dioxide. While not a significant player in weather or climate, xenon serves important roles in scientific instrumentation and atmospheric research. Xenon is used in certain high-intensity weather research lights, precision scientific sensors, and as a reference gas in atmospheric composition measurements. More importantly from an atmospheric monitoring perspective, xenon-133, a radioactive isotope released by nuclear reactor operations and nuclear detonations, is monitored by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) global monitoring network of 80+ radionuclide stations. These stations detect atmospheric xenon-133 concentrations that are orders of magnitude above background levels following nuclear events, serving as a critical verification tool for arms control treaties. The same atmospheric transport modeling used by CTBTO to trace radioactive xenon is closely related to the dispersion modeling NOAA uses for nuclear accident consequence assessment and volcanic ash cloud tracking.<\/p>\n

Xeric Climate (Xerophytic Environments)<\/strong><\/h4>\n

A xeric climate is an extremely arid environment where the potential evaporation rate exceeds annual precipitation for most or all of the year, supporting primarily drought-adapted (xerophytic) vegetation such as cacti, succulents, and desert shrubs. Xeric climates cover approximately one-third of Earth’s total land surface, the single largest climate category by area. In the United States, xeric climates dominate the Mojave Desert (California\/Nevada), Sonoran Desert (Arizona\/southern California), Great Basin (Nevada\/Utah), and Chihuahuan Desert (New Mexico\/Texas). Despite receiving very little annual rainfall, xeric regions are paradoxically highly vulnerable to flash flooding: the rare but intense rainfall events that do occur hit bare, hardpacked, or caliche-sealed soils that shed water almost as rapidly as pavement, funneling runoff into dry washes and arroyos that can go from completely dry to a wall of water several feet deep within minutes. The NWS offices serving desert regions prioritize Flash Flood Warnings (including Flash Flood Emergencies for the most life-threatening events), Excessive Heat Warnings, and Blowing Dust \/ Haboob Warnings as the primary life-safety weather products for their service areas.<\/p>\n

Cross-Contour Flow and Ageostrophic Wind<\/strong><\/h4>\n

Cross-contour flow, formally called the ageostrophic wind, is the component of actual atmospheric wind that flows across height contours (isobars) rather than along them. In theory, if the atmosphere were perfectly balanced between the pressure gradient force and the Coriolis effect, wind would flow exactly parallel to isobars, this is the geostrophic wind. In the real atmosphere, the actual wind deviates from the geostrophic due to friction at the surface, curvature of the flow aloft, and acceleration and deceleration along the flow. The cross-contour ageostrophic component is responsible for the net import and export of mass that drives surface convergence and divergence, and therefore the development and movement of low-pressure systems and their associated precipitation. In jet stream entrance and exit regions, ageostrophic wind circulations create strong zones of upward motion on specific sides of the jet, these are among the most important areas of “forcing for ascent” that meteorologists identify when forecasting where storm development will occur. Understanding ageostrophic dynamics is a cornerstone of advanced dynamic meteorology and operational severe weather forecasting at the graduate level.<\/p>\n

METAR and Weather Abbreviations (Wx Codes)<\/strong><\/h4>\n

Meteorologists, pilots, and NWS forecasters use a standardized set of abbreviations in official weather observations (METAR format) and coded text forecasts to communicate conditions concisely and precisely. METAR (Meteorological Aerodrome Report) is the international standard format for hourly weather observations at airports worldwide. Common precipitation type codes in METAR: RA (rain), SN (snow), FZRA (freezing rain), PL (ice pellets\/sleet), GR (hail, diameter 6mm or larger), GS (small hail or snow pellets, under 6mm), DZ (drizzle), FZDZ (freezing drizzle), UP (unknown precipitation type from an automated sensor). Obstruction to visibility codes: FG (fog, visibility under 5\/8 mile), MIFG (shallow fog), BCFG (patchy fog), BR (mist, visibility 5\/8 to 6 miles), HZ (haze), FU (smoke), SA (sand), DU (widespread dust), VA (volcanic ash). Descriptor prefixes: TS (thunderstorm), SH (shower), FZ (freezing), MI (shallow), BC (patches), BL (blowing), DR (drifting), VC (in the vicinity, within 5-10 miles). Sky conditions are coded as CLR (clear), FEW (1\/8-2\/8 coverage), SCT (scattered, 3\/8-4\/8), BKN (broken, 5\/8-7\/8), or OVC (overcast, 8\/8), followed by the height in hundreds of feet above the airport elevation.<\/p>\n

X-Ray Solar Flares and Space Weather<\/strong><\/h4>\n

X-ray solar flares are powerful bursts of electromagnetic radiation emitted from the sun’s surface during explosive magnetic reconnection events in solar active regions. They are classified by peak X-ray intensity on a logarithmic scale with five tiers: A-class (background level), B-class, C-class (minor), M-class (moderate), and X-class (major), with each class representing a 10-fold increase in energy over the previous. Within the X-class, flares are further numbered (X1, X2, X5, X10, etc.) with no upper limit. X-class flares can have significant consequences for Earth: they cause immediate (8-minute light-travel-time) radio frequency blackouts on the sunlit side of Earth, disrupting HF communications used by aviation, maritime, and emergency services; degrade GPS accuracy by disturbing the ionosphere through which GPS signals travel; and damage satellite electronics through radiation exposure. When a major X-class flare is accompanied by a coronal mass ejection (CME), a billion-ton cloud of magnetized plasma, it can trigger a geomagnetic storm 1-3 days later that may induce damaging currents in power grids, cause widespread communications disruptions, and produce visible auroras at unusually low latitudes. NOAA’s Space Weather Prediction Center (SWPC) in Boulder, Colorado monitors solar activity around the clock and issues the space-weather equivalent of severe weather watches and warnings for significant solar events. The most powerful X-class flare ever recorded was the “Halloween Storms” X28+ event of November 2003.<\/p>\n

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

What is X-band radar and how is it different from NEXRAD?<\/h4>\n

X-band radar operates at higher frequencies (8-12 GHz) with shorter wavelengths (~3 cm) compared to the NWS NEXRAD S-band network (~10 cm wavelength). The shorter X-band wavelength makes the radar more sensitive to small precipitation particles and allows for smaller, more portable installations, useful for filling coverage gaps in mountains and urban areas where NEXRAD is blocked by terrain. However, X-band signals attenuate (weaken) significantly in heavy rain, reducing their range and reliability during intense precipitation. NEXRAD’s S-band frequency is less affected by heavy rain, making it more reliable for detecting the full extent of major storms.<\/p>\n

How does Doppler weather radar work?<\/h4>\n

Doppler weather radar works by transmitting a pulse of microwave energy and analyzing the energy that bounces back from precipitation particles. The “Doppler” part uses the shift in the returned signal’s frequency to calculate whether precipitation is moving toward the radar (compressed frequency, higher number) or away from it (stretched frequency, lower number). This velocity data reveals wind patterns inside storms, including the counter-rotating couplets that identify mesocyclones and tornadoes. The NWS WSR-88D network upgraded to dual-polarization between 2011-2013, adding a horizontal pulse to the standard vertical pulse, enabling the radar to distinguish rain from hail, snow, biological targets, and debris.<\/p>\n

What is a xeric climate?<\/h4>\n

A xeric climate is an extremely arid environment where water loss through evaporation exceeds annual precipitation for most or all of the year. In the US, xeric climates dominate the Mojave, Sonoran, Great Basin, and Chihuahuan deserts. Despite receiving very little rainfall overall, xeric regions experience intense flash floods when rare but extreme rainfall events occur on bare, hardpacked soils that shed water almost as fast as concrete. The NWS in desert regions prioritizes Flash Flood Warnings, Extreme Heat Warnings, and Dust Storm Warnings as the primary life-safety weather products.<\/p>\n

What are solar flare classes and what do they mean for Earth?<\/h4>\n

Solar flares are classified by their X-ray intensity on a logarithmic scale: A (weakest), B, C, M, and X-class (strongest). Each class is ten times more energetic than the previous. Minor C-class flares have little effect on Earth. M-class flares can cause brief HF radio blackouts on the sunlit side. X-class flares can disrupt or completely black out HF radio communications, degrade GPS accuracy, and damage satellite electronics. When an X-class flare is accompanied by a coronal mass ejection, it can trigger a geomagnetic storm 1-3 days later that may cause power grid disruptions and visible auroras at unusually low latitudes.<\/p>\n

What are common weather abbreviations in METAR reports?<\/h4>\n

METAR is the international standard format for weather observations at airports, updated hourly. Common precipitation codes include: RA (rain), SN (snow), FZRA (freezing rain), PL (ice pellets\/sleet), GR (hail), DZ (drizzle), FZDZ (freezing drizzle), and GS (small hail or snow pellets). Obstruction to visibility: FG (fog, visibility under 5\/8 mile), BR (mist, visibility 5\/8 to 6 miles), HZ (haze), FU (smoke). Descriptors: TS (thunderstorm), SH (shower), FZ (freezing), MI (shallow), BC (patchy), BL (blowing), DR (drifting). Sky conditions are coded as CLR, FEW, SCT (scattered), BKN (broken), or OVC (overcast) with the height in hundreds of feet.<\/p>\n

What is the Space Weather Prediction Center?<\/h4>\n

NOAA’s Space Weather Prediction Center (SWPC) in Boulder, Colorado monitors the sun and near-Earth space environment around the clock, issuing alerts, watches, and warnings for significant space weather events, geomagnetic storms, solar radiation storms, and radio blackouts. Space weather can disrupt GPS navigation, HF radio communications used by airlines and emergency responders, power grids, and satellite operations. SWPC issues a 3-day forecast of geomagnetic activity and alerts when solar flares or coronal mass ejections are detected. It is the space-weather equivalent of the National Weather Service for terrestrial weather.<\/p>\n

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