Flash Flood Watch:  Indicates conditions are favorable for heavy rain across the watch area which may lead to rapid rises in local streams, rivers and creeks whereas the water overflows the banks and floods surrounding areas.  Plans should be prepared for evacuation in flood prone areas in the event of a warning.  Coverage area:  multiple counties to entire states.  Length of watch:  a few hours to a few days.
 
Flash Flood Warning:  Indicates recent or occurring heavy rain has caused or will very soon cause rapid rises in local streams, rivers and creeks whereas the water has or will soon overflow their banks and flood surrounding areas.  Evacuation of flood prone areas should be considered immediately.  Coverage area:  Individual counties.  Length of warning:  a few hours.
 
Flood Watch:  Indicates conditions are favorable for long lasting rain across the watch area which may lead to slow yet steady rises in local streams, rivers and creeks whereas the water overflows the banks and floods surrounding areas.  Plans should be prepared for evacuation in flood prone areas in the event of a warning.  Coverage area:  multiple counties to entire states - usually along rivers.  Length of watch:  a few hours to a few days.
 
Flood Warning:  Indicates recent or occurring long lasting rain has caused or will very soon cause rises in local streams, rivers and creeks whereas the water has or will soon overflow their banks and flood surrounding areas.  Evacuation of flood prone areas should be considered immediately.  Coverage area:  Individual counties.  Length of warning:  a few hours to a few days.
 
Flood Advisory (also known as an Urban & Small Stream Flood Advisory):  Indicates ponding of water on streets, low-lying areas, highways, underpasses, urban storm drains, and elevation of creek and small stream levels is occurring or imminent.  Urban and small stream flood advisories are issued for flooding that occurs within 3 hours after the excessive rainfall.  Coverage area:  One to multiple counties.  Length of time:  Often 3 to 4 hours.