Fronts Flashcards
What is a front
A place where air masses meet
Developing front symbol
Triangles with dots
Could also be called frontal-genesis
Decaying front symbol
Triangles with crosses
Could also be called frontolysis
Quasi front
Stationary front
Little movement, 5 kts
Caused by parallel isobars and geostrophic wind running parallel to the front
Very unstable
Doesn’t last very long
Polar front
Marks the boundary between polar maritime and tropical maritime air masses
Boundary between polar and Ferrell cells
Varies due to seasons and land masses
Average position is 50*N/S
Intertropical front
ITCZ
Zone of converging air-masses due to trade winds
Mediterranean front
Only in winter
Warm winds from the south meet colder winds from the European land mass
Arctic front
Only forms in winter, the temp is so low that a pressure gradient is formed
Can be very faint
Can create an arctic front jet stream
N America/america
Frontal surface
Slopping boundary between air masses
Approx 3-5km long
Summer polar front
Canada to over Scotland
Around 65* max north
Winter time polar front
Florida to SW uk
Can be as low as 35* max
Polar front depression
A low is created off the coast of Florida which could be caused by high winds.
The cold air undercuts the air, making the waves bigger down the front
Other names for PFD
Westerly waves
Frontal waves
Westerly situation
Speed of the fronts in a PFD
Cold, same speed as system
Warm, 2/3rds of the speed
To establish the speed and direction of a PFD
Use the first 2 isobars
The direction they are pointing is the direction the front is moving
The spacing between 2 isobars is the speed
Ahead of a warm front
500 - 800km/ 500 -600nm Wind - veers SW, backs in the Southern Hemisphere Temp/dp - steady low P - slow then quick decrease Cloud - ci cs, as, ns,st FEW-OVC Precipitation - DZ,RA 200nm Viz-decrease to poor fg Turb- light to mod
At the warm front
200nm Wind - sharp veer/back in Southern Hemisphere Temp/dp - sudden increase P- slow decrease Cloud - st/ns Precipitation - ra/dz poss FZRA Vis-poor, poss fg 1:150, gentle slope
In the warm front
Wind - steady W Temp/dp - steady warm P - slowly decrease Cloud in winter - BKN/OVC, st,Sc Cloud in summer - fairwx cumulus Precipitation - RA/DZ Vis-winter-poor, fg Summer - good SkC Avrg 5-6km Possible light to mod rime ice Possible carburettor ice at high levels
At the cold front
50-100m/300nm/400km Wind - sharp veer/back in Southern Hemisphere Temp/dp - sudden decrease P-decreases then slow increase Cloud - BKN/OVC, convective cloud Precipitation - shra/ts/gr/gs Vis-good outa sh Mod to severe turb and icing Steep incline 1:80
Behind a cold front
Wind - Slight veer/ back in Southern Hemisphere Temp/dp - steady low P-slowly rising Cloud-BKN,higher base, isol cu cb Precipitation- sh/shra/ts/gr/gs Vis-good out of sh
Secondary depressions
Form within the circulation of a main primary depression
May be caused by a localised effect like orographic uplift
Weather conditions are more severe
Frontal secondaries
Secondary depression that forms on the trailing cold front
What happens to the altimeter on passage of a PFD
Thinks you’re higher on passage of a warm front
Thinks your lower on passage of a cold front due to higher pressure
What happens to pressure just before the cold front
Sudden reduction
Occlusion
Cold front catches up with the warm front
All clouds are pushed together
Warm occulusion
Typically occurs in winter
Coldest air is ahead of the warm front
Forces cold above it
Rains before the warm front passes
Cold occlusion
Coldest air is behind the cold front and cuts under warm air
Typically forms in winter
Rains before and after the warm front
Biggest danger with occlusion
EMB cbs due to the clues being pushed together
Non occluded PFD
Normal PFD
Back bent occlusion
The occlusion bends backwards
Will continue to move with the depression
Stronger worst weather
Jet stream cuts through
