Question: when does rain occur in a warm front

title: Warm front
text: As the air mass rises into regions of lower pressure , it expands and cools . As it cools , any water vapor that is present will condense and form extensive cloud cover . The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first , changing to cirrostratus as the front approaches . However , if cirrocumulus 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 clouds into middle - étage altostratus or altocumulus 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 nimbostratus . If unstable altocumulus castellanus accompanies or takes the place of the main altostratus layer , cumulus congestus or cumulonimbus producing showers or thunderstorms may follow . Low stratus and stratocumulus commonly form underneath the main precipitating clouds . 

Answer: answer: The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first. If cirrocumulus 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 clouds into middle - étage altostratus or altocumulus 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 nimbostratus.
answer: The first clouds that indicate an approaching warm front tend to be mostly high cirrus at first. A thickening and lowering of these high clouds into middle - étage altostratus or altocumulus is a good sign the warm front or low has moved closer and precipitation may begin within less than six hours.