Frontal Weather Flashcards
Front
boundary between air masses of different density
Frontal weather is caused by
the lifting of warm moist air by colder more dense air.
All fronts
have a temperature inversion.
4 front differences
Temperature
Dew point
Pressure - “fall then rise”
Wind shift - approx. 90°, will need drift correction to the right
–Wind speed and direction will change across a boundary
Primary factors affecting frontal weather are:
slope and speed, moisture content and stability.
During stagefield training and frontal passage, what would you expect to happen to wind direction and speed?
An approximate 90 deg shift in wind direction and wind speed based upon current pressure gradient force.
Warm Fronts
Stable Cloud Sequence
Mostly stratiform clouds in moist stable air
Warm Fronts
Unstable Cloud Sequence
CB and AC clouds in moist unstable air
Warm fronts
Affects larger surface areas (thousands of miles)
Stationary Fronts
Facts
Slope – 1:200
Clouds – Stable air lifting, ST clouds
Unstable air lifting, CU clouds
Width of weather band – Thousands of miles and very persistent
Winds – parallel to the front - 180o wind shift
Direction of movement – unpredictable
Speed – Less than 5 KTS
Symbol line of blue triangle and red balls
Stationary front
a front which is not moving. Normally considered stationary with a speed of zero to less than 5 knots.
Stationary front
Winds
except in areas of showers, winds are light and variable, but generally tend to parallel the front in opposite directions.
Cold front
The leading edge of a cold air mass normally moving to the southeast.
Cold front
Facts
Vertical cross-section
(b) Slope - 1:50 to 1:100 (average 1:80)
(c) Clouds - cumuliform predominant
(d) Weather
(1) Type – post-frontal, can be violent.
(2) Coverage – critical area is on average, 50-miles wide.
(3) Winds – generally FROM the NW behind the front, FROM the SW ahead of the front.
(4) Movement - TO the SE.
(5) Speed – average 25-35 kts. If moving faster, a squall line may form as much as 50-200 miles ahead. Squall lines may include tornadoes, hail and destructive winds.
(e) Weather chart portrayal
(1) Sectional (local) blue line
(2) Graphic depiction
Warm front
the trailing edge of a cold air mass moving generally to the northeast, being overridden by warmer air.
Warm front
Facts
(a) Vertical cross section
(b) Slope - average 1:200
(c) Clouds - stratiform predominant, but specific to stability
(d) Weather - (1) Type – low ceilings, poor visibility, rain, drizzle, fog; scattered or embedded thunderstorms in the unstable warm front; possible clear ice and/or freezing rain below inversion level depending on surface temperature.
(2) Coverage – wide spread (thousands of miles) weather ahead of surface position- prefrontal weather.
(3) Winds – generally FROM the SW behind and FROM the SE ahead of front.
(4) Movement – TO the NE.
(5) Speed – slower than cold front.
(e) Weather chart portrayal
(1) Sectional (local) red line
(2) Graphic depiction
Cold front occlusion
When the cold front runs underneath the warm front, it is called a cold-type occlusion. In this area the coldest, or more dense air, is behind the cold front. The warm or less dense air of the warm front is lifted aloft and blocked from the surface.
Warm front occlusion
When the cold front runs over the warm front, it is called a warm-type occlusion. In this area the coldest, or more dense air, is ahead of the warm front. The warm or less dense air of the cold front is lifted aloft and blocked from the surface.
A front is
the boundary between air masses of different densities
The primary cause of frontal weather is
the lifting of warm air by colder air
Fronts happen in ____pressure troughs between air masses.
low
The frontal inversion of any front always slopes over the____air and the precipitation associated with it normally occurs in the ____air.
cold
cold
The type of air masses most often associated with fronts in the US are ___ and ___ (classification abbreviations of air masses referring to temperature).
P
T
True or False
All fronts have temperature inversions
true
