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Illustration of a warm front. The warm air behind the front is slowly overtaking the cold air ahead of the front, which is moving more slowly in the same direction. The warmer air, due to lower density, rises over the colder air as it moves. As a result of its increased altitude, it cools off and its
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also appears, there is greater airmass instability approaching ahead of the front. When these high clouds progressively invade the sky and the barometric pressure begins to fall, precipitation associated with the disturbance is likely about 6 to 8 hours away. A thickening and lowering of these high
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can also occur preceding a warm frontal passage. Clearing and warming is usually rapid after frontal passage. If the warm air mass is unstable, thunderstorms may be embedded among the stratiform clouds ahead of the front, and after frontal passage thundershowers may continue. On
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A warm front is also defined as the transition zone where a warmer air mass is replacing a cooler air mass. Warm fronts generally move from southwest to northeast. If the warmer air originates over the ocean, it is not only warmer but also more moist than the air ahead of it.
63:, and move more slowly than the cold fronts which usually follow because cold air is denser and less easy to remove from the Earth's surface. This also forces temperature differences across warm fronts to be broader in scale. Clouds ahead of the warm front are mostly
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is a good sign the warm front or low has moved closer and precipitation may begin within less than six hours. Once the clouds have thickened to 2,500 metres (8,200 ft) from the earth’s surface, precipitation can begin to fall from heavy
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that form over source regions. The warm air mass behind a warm front is not only warmer, but often (but not always) also higher in humidity than the colder air preceding it. Because of a warm air mass’s higher temperature and thus lesser
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Usually none, but in summer or warm temperatures, cumulus congestus may continue to exist under cirrostratus and altostratus creating light to moderate showers.
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Persistent rain, usually moderate with some lighter periods and some heavier bursts. In winter, snow may turn to rain after passing through
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will increase until the front reaches the location, at which time the clouds can extend all the way to the earth’s surface as
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Different air masses that affect North
America, as well as other continents, tend to be separated by frontal boundaries.
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typically forms in precipitation falling from the thick nimbostratus layer. Often in warm temperatures, rain bearing
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a shift from winds blowing from northeast to northwest. Common characteristics associated with warm fronts include:
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As the air mass rises into regions of lower pressure, it expands and cools. As it cools, any
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cover. The first clouds that indicate an approaching warm front tend to be mostly high
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clouds if convection is sufficient. In cold humid conditions, low airmass stratus or
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with or instead of altostratus (particularly if the front is weak), and occasionally
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may precede and follow the front and temperature changes will be larger.
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584:(8th ed.). Belmont, Calif.: Thomson/Brooks/Cole. pp. 298–300.
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along with or instead of nimbostratus in summer. Additionally,
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often appears underneath the main altostratus deck and stratus
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Air masses are large bodies of air with similar properties of
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moisture condenses, forming clouds and possibly precipitation.
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clouds can appear under the cirrostratus, and more rarely
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Warm Front: transition zone from cold air to warm air
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258:North to northwest (backing) (southern hemisphere)
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245:North to northeast (veering) (southern hemisphere)
242:South to southeast (backing) (northern hemisphere)
55:located at the leading edge of a homogeneous warm
185:blowing from southeast to southwest, and in the
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642:AIR MASSES AND FRONTS - THE WARM FRONT (1962)
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612:: CS1 maint: multiple names: authors list (
550:The environment: principles and applications
418:characteristics, this air is susceptive to
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506:Hydrometeorological Prediction Center
341:may obscure the main frontal clouds.
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433:A surface weather analysis for the
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282:Light drizzle, gradually ceasing.
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553:. Psychology Press. p. 309.
499:"Unified Surface Analysis Manual"
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580:Donald, Ahrens, C. (2007).
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218:Warmer, then leveling off
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133:clouds into middle-stage
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335:altocumulus castellanus
547:Chris C. Park (2001).
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195:Weather phenomenon
187:southern hemisphere
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391:Rise, then steady
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560:978-0-415-21771-2
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509:. Retrieved
448:weather maps
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385:Steady rise
349:cumulonimbus
347:, sometimes
345:Nimbostratus
319:cumulonimbus
311:cirrocumulus
303:nimbostratus
295:cirrostratus
209:Temperature
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144:nimbostratus
130:cirrocumulus
126:cirrostratus
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74:weather maps
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636:Warm Fronts
532:21 November
398:Warm sector
366:Visibility
315:altocumulus
299:altostratus
273:ice pellets
139:altocumulus
135:altostratus
110:water vapor
94:temperature
80:Development
61:cold fronts
18:Warm sector
566:2010-12-17
511:2010-12-17
481:References
460:Cold front
408:cold front
65:stratiform
49:warm front
608:cite book
442:Depiction
381:Dew point
250:Variable
655:Category
600:66911677
454:See also
404:air mass
305:, then
168:air mass
160:rainfall
114:condense
98:humidity
57:air mass
388:Steady
355:stratus
327:fractus
307:stratus
287:Clouds
177:In the
103:density
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375:Sunny
291:Cirrus
237:Winds
122:cirrus
502:(PDF)
416:humid
369:Poor
212:Cool
118:cloud
51:is a
614:link
596:OCLC
586:ISBN
555:ISBN
534:2013
357:and
275:and
183:wind
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446:On
339:fog
164:fog
137:or
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