The Washington and Baltimore areas face a potentially hazardous commute Monday afternoon and evening, not so much from snow but from ice. On Sunday afternoon, the National Weather Service issued a winter weather advisory highlighting the potential for a light wintry mix to glaze surfaces between 3 and 9 p.m. Monday.
We advise that motorists pay close attention to conditions Monday afternoon, consider leaving work early and allow considerable extra time for commuting. Southern Maryland is excluded from the advisory but should still use caution and monitor temperatures on Monday.
Timing: Monday from 3 to 9 p.m.
Hazard: Light freezing rain, sleet and snow that could form an icy glaze on any untreated surfaces, including roads, sidewalks, driveways and parking lots.
Impacts: Potential for multiple accidents and traffic delays from roadways that become quickly glazed in ice.
A cold front will be approaching the region on Monday afternoon, and some light precipitation is expected to break out ahead of that front. At issue here will be subfreezing temperatures and cold roads as the precipitation comes through.
After an extended period of frigid temperatures, cold air in place will probably be impossible to dislodge even as milder air tries to push north Monday ahead of the incoming front. Temperatures may briefly nudge above freezing early Monday afternoon but should drop below freezing by late afternoon or early evening as precipitation moves in. The high-resolution NAM model, shown below, suggests that temperatures will drop into the 20s in many areas Monday evening. (Other models suggest that it won’t be as cold, but — in these situations — when you have a historically cold air mass departing, the coldest models are usually correct.)
The precipitation that falls will be light and patchy. But if light freezing rain falls, that could prove more problematic vs. heavier rain, which would tend to run off more. Light freezing rain can form a thin glaze that does not readily wash away. Sleet or snow also could mix in with the precipitation.
Especially as the sun sinks lower in the sky late Monday afternoon and as darkness sets in, the potential for ice accumulation will rise.
This will not be a long-duration event, and it may be hit or miss because of the patchiness of the precipitation. But icy areas could linger into Tuesday morning, extending the duration of slick spots on untreated surfaces and leading to additional delays.
There is some uncertainty in the timing and location of any precipitation, but this event has the potential to have a significant impact, especially Monday evening. Preparation and continued monitoring of the forecast are highly advised.
Published at Sun, 07 Jan 2018 20:27:51 +000010 0