Synoptic drivers: warm fronts

A warm front is the leading edge of a warm, lighter air mass that slowly rises over a retreating cold air mass. Because the warm air ascends gradually, it forms layered clouds (starting with high cirrus and thickening to stratus), often bringing steady rain or drizzle over a long period. The approach of a warm front is marked by a slow drop in pressure, increasing humidity, and winds that back (e.g., from east to southeast). After the front passes, temperatures rise gently, the rain eases, and pressure stabilizes or rises slowly. Warm fronts usually move slowly and bring more subtle but prolonged weather changes than cold fronts.

Example of a warm front moving eastward across Ireland, https://meteo.hr/prognoze_e.php?section=prognoze_model&param=web_fronte_sutra12

When a warm front passes, the changes are more gradual and subtle than with a cold front, but they still can have a big impact on sailing... 

A warm front is the leading edge of a warm, lighter air mass that slowly rises over a retreating cold air mass. Because the warm air ascends gradually, it forms layered clouds (starting with high cirrus and thickening to stratus), often bringing steady rain or drizzle over a long period. The approach of a warm front is marked by a slow drop in pressure, increasing humidity, and winds that back (e.g., from east to southeast). After the front passes, temperatures rise gently, the rain eases, and pressure stabilizes or rises slowly. Warm fronts usually move slowly and bring more subtle but prolonged weather changes than cold fronts.

Passage of a warm front

When a warm front passes, the changes are more gradual and subtle than with a cold front — but they still have a big impact on sailing. A warm front marks the boundary where warm air slowly overtakes and rises over cooler air.

• Temperatures: cool temperature ahead of the warm front, rising gradually over the passage of the warm front and resulting in a gradual rise of warmer and more humid temperatures after.
• Winds: initially light to moderate easterly or southeasterly, progressively backing (anticlockwise shift) to gently increasing southerly or south-westerly winds after the passage of the front.
• Pressures: slowly falling ahead of the warm front and stabilising with slight rise after the passage of the front. 
• Meteors: thickening layers of light cirrus, potentially developing in nimbostratus at the passage of the front to break to lower clouds or haze after the front. 

However, a warm front often precedes a cold front crossing, and this should be taken into consideration when looking at forecast. Other differences with cold fronts include:

• A warm front is slower (21 to 36 hours) in expressing changes in weather,
• Longer expected periods of rain or “bad” weather,
• But often announce a cold front. Watch the synoptic charts.