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Light snow and ice to bring risk of slick roads Saturday, especially north and west of Washington

Enshrine

Jan. 17, 2020

A minor winter weather event will make for a messy Saturday around the Washington region, producing a mix of light snow and ice and, in milder parts of the region, rain.
Cold air streaming into the region ahead of this event means road surfaces will be cold enough for frozen precipitation to stick, especially on Saturday morning and even through the afternoon, in colder parts of the region north and west of downtown Washington.
However, precipitation will generally be light, and there is likely to be a midday pause when you can safely get around. Snow amounts should mostly range between a dusting and an inch while a light glaze of ice could fall on top of the snow in our colder areas.
“Despite the precipitation generally being light, untreated road surfaces and walkways could become slick especially in pockets of steadier precipitation,” said Wes Junker, Capital Weather Gang’s winter weather expert.
Precipitation timing and temperatures
Precipitation is likely to come in two waves, starting with snow early Saturday morning and then, following a pause, more of a mix of sleet, freezing rain, and rain in the afternoon and early evening.
Light snow could sweep through the region starting between 5 a.m. and 8 a.m. and ending between 8 a.m. and 11 a.m., from southwest to northeast, with temperatures in the 20s. The snow probably won’t last longer than a couple of hours in most locations.
Then, most models suggest a pause in precipitation between mid-to-late morning and midday or early afternoon, when temperatures rise to near freezing or a little above along and east of Interstate 95.
The second round of precipitation is most likely to start in the early afternoon and midafternoon Saturday and end in the early evening. In this round, sleet and freezing rain is most likely north and west of I-95, with more rain along and east of the interstate. Most precipitation should end between about 6 p.m. and 8 p.m. from west to east.
During the second wave of precipitation, temperatures should range from around freezing or a little above along and east of I-95, and around freezing or a little below to the west.
After the precipitation ends, temperatures should remain steady or perhaps rise a bit, so we don’t expect a hard refreeze overnight, although freezing temperatures and slick conditions could linger in the colder parts of the region.
Amounts
Snow/sleet
Because the first wave of snow will be so short-lived, just a dusting to an inch or so is most probable. Some models suggest the snow may miss our southern areas, south of Fairfax and Prince George’s County, where a dusting or less is most possible.
The band of snow may be a bit more pronounced and long-lived toward northern Maryland, where up to a couple inches could fall.
Here are forecast amounts for the District, from different models:
High-resolution NAM: Dusting
Canadian: 0.1 inches
High-resolution Canadian: 0.3 inches
NAM: 0.5 inches
HRRR: 0.5 inches
European: 0.6 inches
American (GFS): 0.7 inches
Freezing rain
During the second wave of precipitation in the afternoon into the early evening, a light glaze of freezing rain is possible, mainly west and north of the Beltway. Generally just 0.01 to 0.1 inches is possible, but we cannot rule out up to 0.2 inches or so in some of the colder pockets in upper Montgomery, western Loudoun, and Frederick (Md.) counties.
Inside the Beltway, a little freezing rain is possible (before changing to plain rain), especially on elevated surfaces and tree limbs, but we expect temperatures at the ground to rise enough that most ice should not accumulate.
Impacts
Untreated roads could briefly turn slick and snow-covered from the initial wave of snow passing by early-to-mid Saturday morning over a large part of the region, except in our far southern areas, including Southern Maryland and Stafford County.
During the second wave of mixed precipitation (sleet, freezing rain and rain), temperatures may just be cold enough for untreated roads and sidewalks to be a concern in areas west of I-95. Temperatures should rise to freezing or a little above along and east of I-95.
If the warmer computer model forecasts are right, there’s even some chance that our colder areas west of I-95 warm above freezing and see little impact from the second wave, with more rain falling than freezing rain. However, we lean toward the colder model forecasts.
On Capital Weather Gang’s winter storm impact scale , this event rates as a Category 1 or “nuisance” event for areas west and north of downtown Washington. Elsewhere, it is unrated.
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