[{"data":1,"prerenderedAt":349},["ShallowReactive",2],{"learn-\u002Flearn\u002Freading-a-surface-analysis-chart":3,"learn-nav-\u002Flearn\u002Freading-a-surface-analysis-chart":320},{"id":4,"title":5,"body":6,"date":248,"description":249,"draft":250,"extension":251,"faqs":252,"howTo":262,"keyTakeaways":271,"meta":276,"navigation":277,"path":278,"quiz":279,"seo":305,"series":306,"seriesOrder":306,"sources":307,"stem":317,"topic":318,"__hash__":319},"learn\u002Flearn\u002Freading-a-surface-analysis-chart.md","How to read a surface analysis chart",{"type":7,"value":8,"toc":239},"minimark",[9,21,27,32,48,77,81,84,107,136,140,153,179,185,189,222,226],[10,11,12,13,20],"p",{},"A surface analysis chart is the weather at a glance: one map that shows where the pressure systems and fronts are, and so where the wind and the weather will be, before you ever open a single ",[14,15,19],"a",{"href":16,"className":17},"\u002Flearn\u002Fglossary#gt-metar",[18],"glossary-link","METAR",".",[22,23,24],"blockquote",{},[10,25,26],{},"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.",[28,29,31],"h2",{"id":30},"isobars-and-the-pressure-gradient","Isobars and the pressure gradient",[10,33,34,35,39,40,43,44,47],{},"The lines that cover a surface chart are ",[36,37,38],"strong",{},"isobars",": lines joining places of equal ",[36,41,42],{},"mean sea level pressure",", normally drawn every ",[36,45,46],{},"4 hectopascals",". They are the chart's most useful feature, because their spacing is a direct read on the wind.",[10,49,50,51,54,55,58,59,61,62,65,66,69,70,76],{},"Where the isobars are ",[36,52,53],{},"tightly packed",", the ",[36,56,57],{},"pressure gradient"," is steep and the wind is ",[36,60,36],{},". Where they are ",[36,63,64],{},"widely spaced",", the gradient is gentle and the wind is ",[36,67,68],{},"light",". As the ",[14,71,75],{"href":72,"rel":73},"https:\u002F\u002Fwww.faa.gov\u002Fregulationspolicies\u002Fhandbooksmanuals\u002Faviation\u002Ffaa-h-8083-28b-aviation-weather-handbook",[74],"nofollow","FAA Aviation Weather Handbook"," describes, this pressure gradient is the force that drives the wind in the first place.",[28,78,80],{"id":79},"highs-lows-and-the-wind","Highs, lows and the wind",[10,82,83],{},"Two letters mark the pressure centres:",[85,86,87,98],"ul",{},[88,89,90,93,94,97],"li",{},[36,91,92],{},"H"," is a ",[36,95,96],{},"high"," (an anticyclone): descending air, generally settled weather, light winds near the centre.",[88,99,100,93,103,106],{},[36,101,102],{},"L",[36,104,105],{},"low"," (a depression): rising air, generally unsettled weather with cloud and rain, and stronger winds.",[10,108,109,110,113,114,119,120,123,124,127,128,131,132,135],{},"The wind does not blow straight from high to low. Away from the surface it blows ",[36,111,112],{},"roughly along the isobars",", as ",[14,115,118],{"href":116,"rel":117},"https:\u002F\u002Fskybrary.aero\u002Farticles\u002Fwind",[74],"SKYbrary"," describes, a balance summed up by ",[36,121,122],{},"Buys Ballot's law",": in the northern hemisphere, stand with your back to the wind and the low pressure is on your ",[36,125,126],{},"left",". Near the ground, ",[36,129,130],{},"friction"," turns the wind to blow slightly ",[36,133,134],{},"across"," the isobars towards the lower pressure, and slows it, which is why the surface wind is backed and lighter than the wind a few thousand feet up.",[28,137,139],{"id":138},"the-fronts","The fronts",[10,141,142,143,146,147,152],{},"A front is the boundary between two air masses, and each type has a standard symbol and its own weather, covered in the ",[14,144,75],{"href":72,"rel":145},[74]," and the ",[14,148,151],{"href":149,"rel":150},"https:\u002F\u002Fwww.metoffice.gov.uk\u002Fweather\u002Fmaps-and-charts\u002Fsurface-pressure",[74],"Met Office"," chart guidance:",[85,154,155,161,167,173],{},[88,156,157,160],{},[36,158,159],{},"Warm front (red semicircles):"," warm air rising over retreating cold air, usually a long, sloping spell of layered cloud and steady rain ahead of it, then a rise in temperature.",[88,162,163,166],{},[36,164,165],{},"Cold front (blue triangles):"," cold air undercutting warm air, often a narrower band of heavier showers or thunderstorms, a wind shift and a drop in temperature.",[88,168,169,172],{},[36,170,171],{},"Occluded front (alternating purple):"," a cold front catching up with a warm front and lifting the warm air off the surface, mixing the two kinds of weather.",[88,174,175,178],{},[36,176,177],{},"Stationary front (alternating red and blue):"," a boundary that is not moving, which can keep similar weather over one place for a while.",[10,180,181,182,20],{},"The symbols always point in the direction the front is ",[36,183,184],{},"moving",[28,186,188],{"id":187},"common-pitfalls","Common pitfalls",[85,190,191,197,211],{},[88,192,193,196],{},[36,194,195],{},"A high is not a guarantee of good flying weather."," In winter, a slack high can trap fog, low cloud and poor visibility under an inversion for days.",[88,198,199,202,203,206,207,210],{},[36,200,201],{},"Analysis versus prognostic."," An analysis chart shows the ",[36,204,205],{},"observed"," situation at a time; a prognostic (forecast) chart shows an ",[36,208,209],{},"expected"," one. Check the label and the valid time.",[88,212,213,216,217,20],{},[36,214,215],{},"It is a big-picture, area product."," The chart tells you the synoptic situation, not the conditions at your runway, so always pair it with the latest METAR and ",[14,218,221],{"href":219,"className":220},"\u002Flearn\u002Fglossary#gt-taf",[18],"TAF",[28,223,225],{"id":224},"in-pilot-efb","In Pilot EFB",[10,227,228,229,232,233,238],{},"Pilot EFB decodes the ",[36,230,231],{},"text"," products that sit alongside the chart, the METAR, TAF and ",[14,234,237],{"href":235,"className":236},"\u002Flearn\u002Fglossary#gt-sigmet",[18],"SIGMET",", and always keeps the raw report so you can trace each one back to source. It does not replace the official charts and is not a certified Electronic Flight Bag; it is an offline-first personal reference, so read the surface and significant-weather charts from your official provider and use the decoded text to fill in the detail.",{"title":240,"searchDepth":241,"depth":241,"links":242},"",2,[243,244,245,246,247],{"id":30,"depth":241,"text":31},{"id":79,"depth":241,"text":80},{"id":138,"depth":241,"text":139},{"id":187,"depth":241,"text":188},{"id":224,"depth":241,"text":225},"2026-06-20","Decode a surface analysis chart: isobars and the pressure gradient, highs and lows, warm, cold and occluded fronts, and what the big picture tells you before you read the METAR.",false,"md",[253,256,259],{"q":254,"a":255},"What do the lines on a surface analysis chart mean?","They are isobars, lines joining places of equal mean sea level pressure, usually drawn every 4 hectopascals. How close together they are shows the pressure gradient: tightly packed isobars mean a strong pressure gradient and strong wind, widely spaced isobars mean light wind.",{"q":257,"a":258},"How is the wind related to the isobars?","Away from the surface the wind blows roughly along the isobars, not across them, with low pressure on the left in the northern hemisphere (Buys Ballot's law). Near the surface, friction turns the wind to blow slightly across the isobars towards the lower pressure, and slows it down.",{"q":260,"a":261},"What is the difference between a warm front and a cold front?","A warm front, drawn with red semicircles, is where warm air advances over retreating cold air, typically bringing a long spell of layered cloud and steady rain. A cold front, drawn with blue triangles, is where cold air undercuts warm air, often bringing a narrower band of heavier showers or thunderstorms and a wind shift.",{"name":263,"steps":264},"Read a surface analysis chart",[265,266,267,268,269,270],"Find the pressure centres: H marks a high (anticyclone), L marks a low (depression).","Read the isobars: note their spacing, because tightly packed isobars mean a stronger pressure gradient and stronger wind.","Estimate the surface wind: roughly along the isobars, backed slightly towards low pressure and reduced by friction near the ground.","Identify the fronts: warm (red semicircles), cold (blue triangles), occluded (alternating purple), stationary (alternating red and blue).","Picture the weather: settled near a high, unsettled with cloud and rain near a low and along the fronts.","Confirm whether the chart is an analysis (observed) or a prognostic (forecast), and pair it with the METAR and TAF for the aerodrome.",[272,273,274,275],"Isobars join points of equal mean sea level pressure; their spacing shows the pressure gradient and so the wind strength.","H marks a high (generally settled), L marks a low (generally unsettled, with cloud and rain).","Fronts have standard symbols: warm (red semicircles), cold (blue triangles), occluded (alternating purple), stationary (alternating).","A surface chart is the big picture; an analysis is observed and a prognostic is forecast, so always pair it with the METAR and TAF.",{},true,"\u002Flearn\u002Freading-a-surface-analysis-chart",[280,289,297],{"q":281,"options":282,"answer":287,"explanation":288},"On a surface analysis chart, what do tightly packed isobars indicate?",[283,284,285,286],"Light winds","A strong pressure gradient and strong winds","Clear skies","An area of high pressure",1,"Isobar spacing shows the pressure gradient. Tightly packed isobars mean a strong gradient and stronger wind; widely spaced isobars mean lighter wind.",{"q":290,"options":291,"answer":287,"explanation":296},"Which symbol marks a cold front?",[292,293,294,295],"Red semicircles","Blue triangles","Alternating purple","A capital H","Blue triangles point in the direction the cold front is moving. Red semicircles mark a warm front; alternating purple marks an occluded front.",{"q":298,"options":299,"answer":287,"explanation":304},"In the northern hemisphere, with the wind at your back, where is the lower pressure?",[300,301,302,303],"On your right","On your left","Directly ahead","Directly behind","Buys Ballot's law: in the northern hemisphere, stand with your back to the wind and lower pressure is on your left.",{"title":5,"description":249},null,[308,310,312,315],{"label":309,"url":72},"FAA Aviation Weather Handbook (FAA-H-8083-28B)",{"label":311,"url":149},"UK Met Office: surface pressure charts",{"label":313,"url":314},"NOAA \u002F NWS Weather Prediction Center: surface analysis","https:\u002F\u002Fwww.wpc.ncep.noaa.gov\u002Fhtml\u002Fsfc2.shtml",{"label":316,"url":116},"SKYbrary: Wind","learn\u002Freading-a-surface-analysis-chart","Weather","cEPiUrkwBX2sALTXHKcr1yo_-mi3zLsc-oma71XtABQ",{"related":321,"newer":340,"older":345,"series":306},[322,327,335],{"path":323,"title":324,"description":325,"date":248,"topic":318,"draft":250,"minutes":326,"series":306,"seriesOrder":306},"\u002Flearn\u002Fthe-international-standard-atmosphere","The International Standard Atmosphere (ISA)","What the ICAO International Standard Atmosphere is, its sea-level values and lapse rate, and how ISA deviation underpins altimetry, performance and density altitude.",3,{"path":328,"title":329,"description":330,"date":331,"topic":318,"draft":250,"minutes":332,"series":333,"seriesOrder":334},"\u002Flearn\u002Fhow-to-read-a-sigmet-and-airmet","How to read a SIGMET and an AIRMET","What SIGMETs and AIRMETs warn of, the phenomena codes, how long each stays valid, and a worked SIGMET decoded field by field, with the ICAO baseline and the US differences.","2026-06-18",5,"decode-the-weather",4,{"path":336,"title":337,"description":338,"date":339,"topic":318,"draft":250,"minutes":332,"series":333,"seriesOrder":287},"\u002Flearn\u002Fhow-to-read-a-metar","How to read a METAR","A plain-language guide to decoding a METAR field by field, with a worked example and the EASA\u002FUK and FAA differences that trip pilots up.","2026-06-17",{"path":341,"title":342,"description":343,"date":248,"topic":344,"draft":250,"minutes":326,"series":306,"seriesOrder":306},"\u002Flearn\u002Fmach-number-and-true-airspeed","Mach number, true airspeed and the speed of sound","How the speed of sound depends on temperature, why Mach number rises as you climb at a constant true airspeed, and how indicated, calibrated, true airspeed and Mach relate.","Operations",{"path":346,"title":347,"description":348,"date":248,"topic":344,"draft":250,"minutes":326,"series":306,"seriesOrder":306},"\u002Flearn\u002Fsquawk-codes-and-transponders","Squawk codes and transponders explained","What a transponder squawk code is, the difference between Mode A, C and S, and the emergency codes 7500, 7600 and 7700 every pilot must know.",1781989192081]