MANCHESTER, N.H. -- A flood watch was posted Friday for southern New Hampshire as a slow-moving storm threatened to bring heavy rain to the upper Northeast, television station WMUR-TV reported.

Drizzle and fog are expected give way to steadier rain by Friday afternoon. Rain will become heavy Friday evening and Saturday, the station's meteorologists predicted.

About 3 to 5 inches of rain is expected in the Monadnock Region of New Hampshire. Two to 4 inches of rain is expected in the Merrimack Valley and along the Atlantic coast, and up to 2 inches of rain is forecast for the Upper Valley, Lakes Region and parts of the White Mountains.

Localized flooding is a strong possibility over the weekend, and water may pool on roadways and low-lying areas. Smaller rivers and streams will rise quickly on Saturday and Sunday, forecasters said.

Officials warned drivers to use caution and not attempt to cross roadways covered with water.

Rain is expected to lessen across the region by Sunday, but more wet weather is expected by Tuesday, WMUR-TV reported.