[{"data":1,"prerenderedAt":285},["ShallowReactive",2],{"learn-\u002Flearn\u002Fjet-stream-and-clear-air-turbulence":3,"learn-nav-\u002Flearn\u002Fjet-stream-and-clear-air-turbulence":261},{"id":4,"title":5,"body":6,"date":200,"description":201,"draft":202,"extension":203,"faqs":204,"howTo":214,"keyTakeaways":215,"meta":220,"navigation":221,"path":222,"quiz":223,"seo":248,"series":214,"seriesOrder":214,"sources":249,"stem":258,"topic":259,"__hash__":260},"learn\u002Flearn\u002Fjet-stream-and-clear-air-turbulence.md","The jet stream and clear-air turbulence",{"type":7,"value":8,"toc":190},"minimark",[9,13,19,24,33,66,70,86,101,105,108,133,137,140,143,147,173,177],[10,11,12],"p",{},"Cruise can be glass-smooth for an hour and then, with a clear sky ahead and nothing on the radar, the aircraft starts to buck. More often than not the cause is the jet stream, and understanding it turns a nasty surprise into something you can plan around.",[14,15,16],"blockquote",{},[10,17,18],{},"This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.",[20,21,23],"h2",{"id":22},"what-a-jet-stream-is","What a jet stream is",[10,25,26,27,32],{},"A jet stream is a narrow, fast-flowing river of air high in the atmosphere, near the ",[28,29,31],"a",{"href":30},"\u002Flearn\u002Fthe-tropopause","tropopause",". It forms where there is a strong horizontal temperature contrast, such as the boundary between cold polar air and warmer mid-latitude air, and it can wind for thousands of miles around the globe while being only a few hundred miles wide and a few thousand feet deep.",[10,34,35,36,42,43,47,48,51,52,55,56,61,62,65],{},"As the ",[28,37,41],{"href":38,"rel":39},"https:\u002F\u002Fwww.faa.gov\u002Fregulationspolicies\u002Fhandbooksmanuals\u002Faviation\u002Ffaa-h-8083-28b-aviation-weather-handbook",[40],"nofollow","FAA Aviation Weather Handbook"," describes, the cores are commonly 100 knots or more. The two that matter most at mid-latitudes are the ",[44,45,46],"strong",{},"polar-front jet",", which is lower and stronger and shifts with the seasons, and the ",[44,49,50],{},"subtropical jet",", which is higher and further toward the equator. On the high-level ",[44,53,54],{},"significant weather charts"," built to the ",[28,57,60],{"href":58,"rel":59},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fannex-3-meteorological-service-for-international-air-navigation-1",[40],"ICAO Annex 3"," convention, a jet is drawn as a bold arrow when its core wind speed is ",[44,63,64],{},"80 knots or more",", with the core height and speed labelled.",[20,67,69],{"id":68},"why-the-shear-turns-into-turbulence","Why the shear turns into turbulence",[10,71,72,73,81,82,85],{},"The danger is not the strong wind itself, which an aircraft flies through happily, but the way the wind speed changes around the core. The fast core sits next to much slower air above, below and to either side, so over a short distance the wind speed and direction change sharply. That change is ",[44,74,75],{},[28,76,80],{"href":77,"className":78},"\u002Flearn\u002Fglossary#gt-wind-shear",[79],"glossary-link","wind shear",", and where it is strong enough it breaks down into ",[44,83,84],{},"clear-air turbulence (CAT)",".",[10,87,88,89,94,95,100],{},"The word \"clear-air\" is the whole problem. As the ",[28,90,93],{"href":91,"rel":92},"https:\u002F\u002Fwww.faa.gov\u002Fair_traffic\u002Fpublications\u002Fatpubs\u002Faim_html\u002Fchap7_section_1.html",[40],"FAA AIM"," and ",[28,96,99],{"href":97,"rel":98},"https:\u002F\u002Fskybrary.aero\u002Farticles\u002Fclear-air-turbulence-cat",[40],"SKYbrary"," note, CAT forms in cloud-free air, so there is no cloud to mark it and weather radar, which sees precipitation, does not detect it. You feel it before you can see anything.",[20,102,104],{"id":103},"where-to-expect-it","Where to expect it",[10,106,107],{},"CAT is not scattered at random. It clusters in predictable places relative to the jet:",[109,110,111,123,130],"ul",{},[112,113,114,115,118,119,122],"li",{},"on the ",[44,116,117],{},"cold (poleward) side"," of the core and just ",[44,120,121],{},"below"," it, where the shear is sharpest;",[112,124,125,126,129],{},"near ",[44,127,128],{},"sharp upper troughs"," and where the jet curves tightly or two jets cross;",[112,131,132],{},"in the shear zone just under the tropopause.",[20,134,136],{"id":135},"a-worked-example","A worked example",[10,138,139],{},"Suppose your route crosses a polar-front jet and the forecast winds aloft show the core at FL340 running 130 knots, while the level you are planning, FL300, shows 70 knots from a slightly different direction. That is a change of roughly 60 knots and a shift in direction across only 4000 feet of height: a classic strong-shear signature on the cold side and below the core.",[10,141,142],{},"Nothing on the satellite picture or the radar marks it, but the significant weather chart draws the jet arrow there and the shear is exactly where CAT lives. The practical move is the same one professional crews make: note it at the planning stage, keep the seatbelt sign on through the band, and if the ride deteriorates, a change of a few thousand feet up or down often climbs out of the worst shear layer. A pilot report passed on helps the aircraft behind you.",[20,144,146],{"id":145},"common-pitfalls","Common pitfalls",[109,148,149,155,167],{},[112,150,151,154],{},[44,152,153],{},"Radar will not save you."," Weather radar paints precipitation, not the dry shear of CAT, so a clear screen is no promise of a smooth ride near a jet.",[112,156,157,160,161,166],{},[44,158,159],{},"The strong wind is not the hazard; the change in it is."," A steady 120-",[28,162,165],{"href":163,"className":164},"\u002Flearn\u002Fglossary#gt-knot",[79],"knot"," wind is smooth; it is the gradient at the edges of the core that bites.",[112,168,169,172],{},[44,170,171],{},"It is a cruise-level phenomenon."," Because jets sit near the tropopause, CAT is mostly a concern at the higher levels, not in the circuit.",[20,174,176],{"id":175},"in-pilot-efb","In Pilot EFB",[10,178,179,180,184,185,189],{},"Pilot EFB helps you read the ",[28,181,183],{"href":182},"\u002Flearn\u002Freading-winds-and-temperatures-aloft","winds and temperatures aloft"," and the forecasts that flag where shear is likely, so the jet is on your mind before the flight rather than a mid-cruise surprise, and it keeps the ",[28,186,188],{"href":187},"\u002Flearn\u002Fhow-to-read-a-pirep","pilot reports"," and significant weather products you have pulled together in one place. A briefing you have already pulled stays readable with no signal; fetching fresh forecasts needs a connection. Pilot EFB is not a certified Electronic Flight Bag, so treat it as a study and planning aid and brief from your official source of record.",{"title":191,"searchDepth":192,"depth":192,"links":193},"",2,[194,195,196,197,198,199],{"id":22,"depth":192,"text":23},{"id":68,"depth":192,"text":69},{"id":103,"depth":192,"text":104},{"id":135,"depth":192,"text":136},{"id":145,"depth":192,"text":146},{"id":175,"depth":192,"text":176},"2026-06-22","What a jet stream is, where it sits near the tropopause, and why the wind shear around it produces clear-air turbulence that arrives with no cloud to warn you.",false,"md",[205,208,211],{"q":206,"a":207},"What is a jet stream?","A jet stream is a narrow, fast-flowing band of wind high in the atmosphere, near the tropopause, with cores that are often 100 knots or more. On the high-level significant weather charts pilots use, a jet is drawn when its core wind speed is 80 knots or more. The two that matter most at mid-latitudes are the polar-front jet and the subtropical jet.",{"q":209,"a":210},"Why does the jet stream cause turbulence in clear air?","The strong winds in the core sit next to much slower air above, below and to the sides, and that sharp change of wind speed and direction over a short distance is wind shear. Where the shear is strong enough it breaks down into clear-air turbulence. It is called clear-air because it forms in cloud-free air, so there is no visual cue and often no warning until you feel it.",{"q":212,"a":213},"Where around a jet stream is clear-air turbulence most likely?","It is most common on the cold (poleward) side of the jet and just below the core, and near sharp upper troughs and where jet streams curve or cross. Because there is rarely any cloud to mark it, pilots rely on forecasts, significant weather charts and pilot reports rather than what they can see.",null,[216,217,218,219],"A jet stream is a narrow band of very strong wind near the tropopause, with cores often 100 knots or more.","The sharp change in wind speed and direction around the core is wind shear, and strong shear breaks down into turbulence.","Clear-air turbulence forms in cloud-free air, so there is no visual warning; it is most likely on the cold side of and below the core and near sharp troughs.","High-level significant weather charts draw a jet when its core is 80 knots or more, and pilots plan around it with forecasts and pilot reports.",{},true,"\u002Flearn\u002Fjet-stream-and-clear-air-turbulence",[224,233,240],{"q":225,"options":226,"answer":231,"explanation":232},"Roughly where in the atmosphere does the jet stream sit?",[227,228,229,230],"Just above the surface, in the friction layer","Near the tropopause, around the top of the troposphere","Deep in the stratosphere, above all weather","Exactly at 18,000 feet, the transition altitude",1,"Jet streams flow near the tropopause, the boundary at the top of the troposphere, which is why they are a cruise-level rather than a low-level phenomenon.",{"q":234,"options":235,"answer":192,"explanation":239},"On a high-level significant weather chart, a jet stream is drawn when its core wind speed reaches what value?",[236,237,64,238],"40 knots or more","60 knots or more","120 knots or more","The ICAO significant weather chart convention depicts a jet stream when the core wind speed is 80 knots or more; cores are frequently well above that.",{"q":241,"options":242,"answer":231,"explanation":247},"Why is clear-air turbulence hard to avoid by looking outside?",[243,244,245,246],"It only happens at night","It forms in cloud-free air, so there is no visual cue","It is always marked by lenticular cloud","It only occurs inside thunderstorms","Clear-air turbulence forms in cloud-free air from wind shear near the jet, so there is nothing to see; pilots rely on forecasts, charts and pilot reports.",{"title":5,"description":201},[250,252,254,256],{"label":251,"url":38},"FAA Aviation Weather Handbook (FAA-H-8083-28B)",{"label":253,"url":91},"FAA Aeronautical Information Manual, Chapter 7 Section 1 (Meteorology)",{"label":255,"url":58},"ICAO Annex 3: Meteorological Service for International Air Navigation",{"label":257,"url":97},"SKYbrary: Clear Air Turbulence","learn\u002Fjet-stream-and-clear-air-turbulence","Weather","FIlSXqc0qlSKQ4MPQtICfOnMPWSRVHYurCQFauq2BH8",{"related":262,"newer":263,"older":279,"series":214},[263,268,273],{"path":264,"title":265,"description":266,"date":200,"topic":259,"draft":202,"minutes":267,"series":214,"seriesOrder":214},"\u002Flearn\u002Fcloud-types-explained","Cloud types and what they tell a pilot","The ten cloud genera grouped into high, middle and low, the difference between heaped and layered cloud, and how to read what each type is telling you about stability, moisture and the weather ahead.",3,{"path":269,"title":270,"description":271,"date":200,"topic":259,"draft":202,"minutes":272,"series":214,"seriesOrder":214},"\u002Flearn\u002Fmountain-waves-and-rotor","Mountain waves and rotor","How stable air flowing over high ground sets up standing mountain waves and the violent rotor beneath them, the cloud signs that give them away, and why the turbulence and downdraughts deserve respect.",4,{"path":274,"title":275,"description":276,"date":200,"topic":259,"draft":202,"minutes":272,"series":277,"seriesOrder":278},"\u002Flearn\u002Ftaf-change-groups","TAF change groups: TEMPO, BECMG, PROB and FM","A deeper look at the change groups that make a TAF a forecast rather than a snapshot, with the exact meaning of FM, BECMG, TEMPO and PROB and a worked example that decodes them in order.","decode-the-weather",6,{"path":280,"title":281,"description":282,"date":200,"topic":283,"draft":202,"minutes":267,"series":284,"seriesOrder":278},"\u002Flearn\u002Fminimum-safe-altitudes-msa-mora-mea-moca","Minimum safe altitudes: MSA, MORA, MEA, MOCA and MEF","The family of minimum altitudes that keep you clear of terrain and obstacles, what each one guarantees, and the difference between an altitude that also promises navigation signal and a chart figure that only tells you the highest obstacle.","Operations","plan-a-vfr-cross-country",1782089963505]