![]() Severe weather watch areas are outlined by heavy dashed lines, usually in the form of a large rectangular box.Ģ2 Lifted Index Chart Provides plot of the lifted index and K index values Lifted Index is a measure of atmospheric stability – it is a comparison of predicted temperature change from the surface (2° saturated or 3° unsaturated) less actual temperature change from the surface to 500mb (18,000 msl +/-) Positive LI – colder so stable air Negative LI – warmer so less stable Zero LI – neutral stability Becomes more stable with decreased dew point, decreasing surface temperature or increasing 500 mb temperature Severe thunderstorm guide 0 to -2 weak potential -3 to -5 moderate potential ≤-6 Strong potentia Ģ3 Lifted Index Chart K Index – used mostly by meteorologistsĭuring warm season a large Ki indicates conditions favorable for thunderstorms In winter temperature terms completely dominate K index Ki 35 – Numerous thunderstormsĢ4 Lifted Index Chart Lifted Index (LI) Severe Potential K-Index *Īirmass Thunderstorm Probability 0 to -2 Weak 40 near 100% It is essential to note that an unstable Lifted Index does NOT automatically mean thunderstorms. ![]() Highest echo height in the area is shown above a short line, with the top height displayed. NB: Symbols are the same as the Surface Analysis Chartġ7 Radar Summary Chart Aids in preflight planning by identifying general areas and movement of precipitation and/or thunderstorms Issued hourly Shows: Radar echos Types of precipitation Movement of cells Tops of precipitation Severe Thunderstorm and Tornado Watch areas DOES NOT SHOW clouds or fogġ9 Radar Summary Chart Individual cell movement is indicated by an arrow with the speed in knots entered as a number at the top of the arrow head. IFR MVFR Precipitation / Vis obstructions Sky cover AGL cloud height Legend Data Wind Latitude Temp Height / pressure altitude Temp – DP spread Height change / aircraft type Satellite data Balloon / Ground station Data Temp / Isotherm Airplane observation Longitudeīroad overview of flying conditions – IFR (5sm vis >3,000 ceiling) Also shows fronts and troughs (except 10 and 23Z) Prepared 8 X per day high altitude=high pressure area) Some charts also show: isotherms – areas of equal temperature – bold dashed line isotachs – constant wind speed areas – short fine dashed line with _Kġ1 Historic (FAA) Constant Pressure Chart Contours can be interpreted in the same manner as isobars on the surface chart (e.g. ![]() 309 = 3309 meters or 10,754’ – Look at gradients - wind speed proportional to gradients (close = high winds). X Marks high/low center Issue date/time Wind Level Contour line area of = height in meters (850 MB omits 1 before and 700 omits 2 or 3 before – which ever makes the number closer to 3,000 meters) e.g. Similar to the surface analysis chart but at different pressure levels (altitudes will vary) 850 MB chart ≈ 5,000’ 700 MB chart ≈ 10,000’ 500 MB chart ≈ 18,000’ Provides a 3D view of large areas – interpolate between charts Data gathered through balloons Shows winds and temps – can identify jet stream / freezing risks for example Charts available at: Low Sea Level Pressure –4mb interval lines - Line below # is pressure trend Warm front stationary front Cold front – Pips show direction of movement High - Number adjacent is central pressure Sea Level pressure (first 10 or 9 digits omitted) or ceiling height Tropical wave Data Wind Temp Sky cover – If station symbol is square then automated data was used Dew Point Shows the “big picture” – helps plan flights around WX Depicts Sea level pressure Position of highs, lows, ridges and troughs Position of fronts Position of boundaries Overview of winds, temperatures and dew points Issued every 3 hours Valid for 6 hours Available at: Observations Surface Analysis Charts Constant Pressure Charts Weather Depiction Charts Lifted Index Charts Radar Summary Charts Forecast Charts Short Range Surface Prognostic Chart Low level Significant Weather Prognostic Chart
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