INTERPRETING A SKEWT LOGP AEROLOGICAL DIAGRAM Locate pressure

• Locate pressure level (and matching ICAO Height) • 400 m ASL •

• Read off T and Tdp from that level • T = 32°C

• Follow Tdp upwards along line of constant mixing ratio. • Mixing ratio

• Follow T upwards along dry adiabat. • Potential temperature = 307 K

• Lines cross at Lifting Condensation Level = cloud base. • LCL =

• Dry adiabat is cooler than Environmental Lapse Rate (right-hand red line) at

• Between the surface and 900 h. Pa the reversed ELR shows the

• Now… Let’s add heat to the surface air with a fire (no

• Potential temperature = 323 K • LCL = 540 h. Pa •

• Dry adiabat is warmer than ELR – air is unstable. • Above

• Dynamic inversion when saturated adiabat and ELR cross. • P = 250

• Winds at surface • 35 kts (60 km/hr) from N

• Winds at LCL • 30 kts (50 km/hr) from NW

• Winds at dynamic (plume) inversion. • 55 kts (100 km/hr) from W

• So under these conditions a hot backburn would move to the south,

• Additionally, pyro-cumulus clouds would form within the plume at 5000 m. •

• CALCULATING HAINES INDEX • T 850=27°C • T 700=12°C • DP 850=-1°C

• CALCULATING CONTINUOUS HAINES INDEX (CH) • CA = (T 850 -T 700)/2

• CALCULATING FUEL MOISTURE CONTENT • FMI = 21 -(2*TTdp)/4 • FMI=7% •

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INTERPRETING A SKEW-T LOG-P AEROLOGICAL DIAGRAM

• Locate pressure level (and matching ICAO Height) • 400 m ASL • 970 h. Pa

• Read off T and Tdp from that level • T = 32°C • Tdp = 7°C

• Follow Tdp upwards along line of constant mixing ratio. • Mixing ratio = 6. 5 g/kg

• Follow T upwards along dry adiabat. • Potential temperature = 307 K = 34°C

• Lines cross at Lifting Condensation Level = cloud base. • LCL = 670 h. Pa • LCL = 3400 m (ICAO)

• Dry adiabat is cooler than Environmental Lapse Rate (right-hand red line) at all levels. • Air is stable

• Between the surface and 900 h. Pa the reversed ELR shows the mixing layer. • As the day heats up this will move to the right, to the grey line.

• Now… Let’s add heat to the surface air with a fire (no additional moisture). • T = 50°C

• Potential temperature = 323 K • LCL = 540 h. Pa • LCL = 5000 m (ICAO) • T @ LCL = -2°C

• Dry adiabat is warmer than ELR – air is unstable. • Above LCL air rises along Saturated Adiabat.

• Dynamic inversion when saturated adiabat and ELR cross. • P = 250 h. Pa • Height = 10500 m (ICAO) • T = -42°C

• Winds at surface • 35 kts (60 km/hr) from N

• Winds at LCL • 30 kts (50 km/hr) from NW

• Winds at dynamic (plume) inversion. • 55 kts (100 km/hr) from W

• So under these conditions a hot backburn would move to the south, but its plume, rising to 10 km height, would increasingly rotate to the left as it rose.

• Additionally, pyro-cumulus clouds would form within the plume at 5000 m. • We have no information on fuels, and so cannot assess how much cloud.

• CALCULATING HAINES INDEX • T 850=27°C • T 700=12°C • DP 850=-1°C • Stability term = 3 (range of 15°) • Moisture term = 3 (range of 28°) • Index = 3+3 = 6

• CALCULATING CONTINUOUS HAINES INDEX (CH) • CA = (T 850 -T 700)/2 -2 • CA = 5. 5 • CB = (T 850 -DP 850)/3 -1 • If(CB > 9) then CB = 9 • If(CB > 5) then CB = 5+(CB-5)/2 • CH=CA+CB • CB=6. 7 • CH=12. 2 • 95% HI = 8. 5

• CALCULATING FUEL MOISTURE CONTENT • FMI = 21 -(2*TTdp)/4 • FMI=7% • FMC=7*FMI/DF • If DF = 10, FMC = 5%