Air Masses Arctic Maritime Polar Continental Returning Polar

Air Masses Arctic Maritime Polar Continental Returning Polar Maritime Tropical Continental

Norwegian Model

Norwegian Model

Passage of a warm front … Before Wind Dew point Pressure Temperature Cloud Visibility Weather On After Backs slowly Slow increase Usually falls Little effect Sharp veer Steady again Sharper rise Steady Usually steady Steady Fall in rain Milder than before Increases & lowers as rain approaches Thick layers Good becoming moderate Rain turning heavy Poor in rain Thin layer cloud with some breaks possible Moderate or poor Short burst Damp, drizzly of heavy rain

Passage of a cold front. . . Before On After Wind Dew point Pressure Temperature Cloud Steady Mild usually Sharp veer Steady (gusty) Falling Fall continues for a bit Pressure ‘kick’ Rises Fall in rain Usually falls Thin low cloud some breaks Thick layers Convective cloud embedded Cb develops after a bit Visibility Moderate or poor Poor in rain Weather Light rain or drizzle Very good Short burst Dry then showers of heavy rain

The Station Circle Type of medium and high cloud. Decode over page Windspeed and direction Wind from direction of the shaft Triangle = 50 kts Full feather =10 kts Half feather = 5 kts Just shaft < 3 kts Screen temperature in tenths of a degree e. g. . . 167 = 16. 7 C 167 Visibility 01 to 50 add 00 for visibility in metres 56 to 89 subtract 50 for visibility in km Present weather Symbols Fog Showers Snow Drizzle Rain Thunderstorm Phenomena occurred in past hour. 181 64 10 045 Dew point in tenths of a degree e. g. . 045 = 4. 5 C 1/30 Cloud amount and height ( Low, Medium and High) Amount of cloud in eighths /height of cloud in feet 01 to 50 add 00 for height in feet 56 to 89 subtract 50 for height in thousands of feet Mean sea level pressure Last 3 figures of the MSL Pressure e. g. . . 181 = 1018. 1 h. Pa Change in pressure (tendency) Difference in pressure from 3 hours in tenths of h. Pa and direction of up or down. Decode over page Past weather Symbols as Present weather Period covered 0000, 0600, 1200, 1800 last 6 hrs 0300, 0900, 1500, 2100 last 3 hrs All other hours last hour Type of low cloud

Observations 8 75 4 007 06 , 11 30 11 997 15 11 45 , 11 997 20 , 10 50 9 001 35 9 012 65 7 24

Tephigrams & Stability The position of the ELR gives the stability of the ascent at that point DALR > ELR > SALR Conditionally Unstable DALR > SALR > ELR Absolutely Stable ELR > DALR > SALR Absolutely Unstable Any point on an ascent