January 12, 2018
10:30 AM

Multi-Impact Rain/Flooding/Icing Event Friday/Saturday


The NWS (National Weather Service) has forecasted a multi-impact rain event to occur today into Saturday.

Several bouts of heavy rain are expected to move into the region starting this morning and continuing into Saturday. Storm total rainfall amounts of 1.5 to 3 inches with locally higher amounts of up to 4 inches are forecast over the entire region. Strong 45-55 mph wind gusts could develop late today into early Saturday, especially across the south coast and the Cape and Islands. There may be periods of dense fog this morning and again this evening into Saturday.

As the heavier rain ends Saturday morning, temperatures will begin to drop from west to east, and they will rapidly dip below freezing during the afternoon and evening on Saturday, potentially resulting in flash-freezing. Any remaining precipitation will change over to freezing rain or sleet before ending altogether by Saturday evening, with resulting ice accretions of up to 1/10" to 1/4" possible.

Some areas of uncertainty still remain in the forecast:

Some rivers still have a risk for going into flood stage. These will be updated through the next 24 hours.
Dense fog could be localized.
The timing of the change to freezing rain and sleet could be off somewhat, and will ultimately determine the exact amount of icing on Saturday.


The heavy rain and associated flooding has the potential to impact this evening's commute.
The heavy rain may result in flash/urban flooding and flooding in low-lying and poor drainage areas - - these may be areas that regularly flood during heavy rain events.
Snow-clogged storm drains may result in, or exacerbate urban/street flooding and flooding in low-lying/poor drainage areas.
Rainfall combined with rapid snowmelt may result in some river and stream flooding. Smaller streams and creeks are forecast to crest tonight or early Saturday and larger streams may crest later Saturday into early Sunday.
Scattered ice jams are possible on rivers and streams. Where an ice jam forms, flooding may occur first above the location of the jam, and then as it breaks up, the rapid release of water may cause flooding below the jam.
Areas of dense fog may result in poor visibility and hazardous travel conditions.
As the temperatures fall across the region on Saturday, black ice may develop and any ice jams on rivers may freeze in place. This may cause hazardous travel conditions, especially on untreated bridges, overpasses, and secondary roadways, as well as extended river flooding.
Strong wind gusts tonight into Saturday may result in a few downed limbs or small trees and isolated power outages.

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