Washington, D.C., area faces freezing rain, sleet and slick roads Saturday

Models projections and our interpretation of them are more or less on track for Saturday’s wintry mix. A few developments:

• Model simulations suggest precipitation may break out on the early side of our timeline (see below), between roughly 6 and 9 a.m. For this reason, the National Weather Service updated the winter weather advisory to start at 7 a.m., rather than 10 a.m.
• Precipitation may start as snow, especially from the District north, with a quick coating possible before a changeover to sleet by mid-morning.
• In a positive development, around the immediate area more sleet may fall then freezing rain. As noted below, sleet provides a bit more traction than freezing rain. However, as Saturday afternoon progresses, the sleet may change to freezing rain or drizzle. Unfortunately, toward Southern Maryland and north central Virginia, under an ice storm warning, freezing rain will probably dominate.
• Just as precipitation may start early, it may wind down quickly, during the late afternoon or early evening. However, after any steady precipitation ends, patchy freezing drizzle may linger well into Saturday night or even early Sunday morning.

Please take it easy tomorrow and, if and when frozen precipitation is falling, avoid traveling if you can. We’ll begin updates early Saturday morning.

5:45 p.m. — Afternoon models keep forecast on track

Our detailed forecast and discussion provided below continues to hold for Saturday. Models continue to show a patchy mix of precipitation developing early in the morning and increasing in coverage between mid-morning and midday. A few snowflakes are not out of the question at the onset before precipitation transitions to sleet and freezing rain, especially from the District north.

For this evening and tonight, skies remain mostly cloudy. A few flurries or some spotty freezing drizzle can’t be ruled out. Odds of wintry mix rise toward sunrise. Lows are in the 20s.

Our next update will come around 10 p.m. after some new model data is in. Be sure to check back.

3:35 p.m. — Winter weather advisory issued for immediate D.C. area Saturday, ice storm warning to south

Given the threat of icing and dangerous travel Saturday and Saturday night, the National Weather Service has issued a winter weather advisory for the immediate D.C. area, including the District as well as Fairfax, Montgomery, and Prince George’s counties. The advisory also includes Prince William and Fauquier counties to the south and Loudoun, southern Baltimore, Howard, Anne Arundel and Calvert counties to the north and east. In this zone, the Weather Service predicts up to a tenth or two of ice accumulation.

To the south, the situation is potentially more serious, and an ice storm warning has been issued for Stafford and Charles counties and to the south. Here, at least a quarter of an inch of ice could accumulate. “Power outages and tree damage are likely due to the ice,” the Weather Service writes. “Travel could be nearly impossible.”

A dash of snow fell south of the District on Thursday night and to the north on Wednesday night. Now, much of the region braces for icy precipitation that could make roads and walkways hazardous at times between Saturday and Sunday mornings.

Conditions may be most treacherous between midmorning Saturday and Saturday evening, but spotty freezing rain and/or sleet could begin as soon as early Saturday morning and linger as late as early Sunday morning.

Especially in the southern and eastern part of our region, this could be the most significant ice threat since Feb. 14, 2007, when serious icing affected Washington’s southeast suburbs.

As we’re right on the edge of this particular weather system, there is an outside chance that most of the precipitation misses the immediate area to the south and southeast. For this reason, it may not become clear if we’re looking at widespread, impactful icing in the immediate metro area until Friday evening or even early Saturday.

But the concern is the following: Cold air has become firmly established over the Washington and Baltimore regions, with temperatures in the mid-20s to near 30. These readings will not budge, remaining subfreezing until Sunday morning or midday. This means any icy precipitation, in the form of either freezing rain or sleet, will accumulate on untreated surfaces.

• Anytime you see precipitation falling Saturday, assume roads and sidewalks might be slick. Surfaces that appear just wet could be deceptively slippery due to black ice. Well-traveled and treated roads may be passable and just wet, but use particular caution on ramps, bridges and overpasses.
• If possible, do not travel if icy precipitation is falling.
• The risk of icy roads will become more acute in the late afternoon and evening on Saturday when the sun goes down, and ice accumulates more readily.

The weather system that will be responsible for the freezing rain and sleet will develop along an Arctic front stalled out to our southeast. It will first cause frozen precipitation to develop in Virginia and Maryland, especially east of the mountains.

Current projections suggest the heaviest precipitation and best chances for significant icing, which could damage trees and power lines, will be along and especially east of Interstate 95, where a winter storm watch is in place. Some areas, especially west of Fairfax County, may only see spotty, intermittent light freezing rain or freezing drizzle.

However, all it takes is for a light glaze of ice for untreated roads and walkways to become dangerous so even areas that receive only light, patchy frozen precipitation are at risk.

In the immediate Washington region, ice accumulation will probably not be heavy enough to cause tree damage and power outages. Most models simulate around 0.2 inches of ice, some of that in the form of sleet, which does not cling to trees and power lines like freezing rain. But toward Southern Maryland, Virginia’s Northern Neck and around Richmond, more serious icing (up to 0.25 to 0.5 inches) could cause outage concerns.

The more sleet that falls the better, in terms of the ice hazard. Freezing rain is more dangerous because the icy glaze it leaves behind provides little friction, making streets and sidewalks like ice skating rinks, whereas sleet tends to offer more traction for your feet and vehicles.

As a reminder, sleet describes tiny ice grains that ping on our window panes and accumulate as an opaque, crunchy layer on the ground. Freezing rain describes liquid water drops that fall to frozen ground, then freeze into a clear coating on impact.

Conditions should improve during the day Sunday, when temperatures should rise above freezing by late midday.

Here’s how we see this ice event playing out. Note that the predicted temperatures will tend to be lowest in our northwestern areas and highest near downtown Washington and to the southeast.

4 to 8 a.m. Saturday: Spotty snow, sleet and freezing drizzle. Temperatures 25 to 30.

8 a.m. to noon: Chance of sleet or freezing drizzle in the immediate D.C. area. Freezing rain becomes more steady south and east of the Beltway. Temperatures 26 to 31.

Noon to 4 p.m.: Freezing rain likely, especially in the immediate D.C. area and points south and east. Chance of sleet and freezing rain to the west and northwest. Temperatures 27 to 31.

4 to 8 p.m.: Freezing rain, especially near and east of I-95. Chance of freezing drizzle to the west. Temperatures 26 to 31.

8 p.m. Saturday to 8 a.m. Sunday: Chance of lingering, patchy freezing drizzle. Temperatures 26 to 31.

8 a.m. to noon Sunday: Any freezing drizzle dissipates. Temperature rise into the mid-30s.

On Capital Weather Gang’s winter storm impact scale, this event rates as a Category 2, or “disruptive” event. While precipitation is not expected to be particularly heavy, the cold air in place before and during the event means untreated surfaces will be slick and hazardous.

We expect the possibility of airport delays and some cancellations for any in-person activities Saturday into Sunday morning.

The uncertainty in the coverage of significant ice and amounts that are expected to be under 0.25 inches in the immediate area prevent a higher rating. This rating may change if the forecast shifts to indicate greater precipitation totals.

Two more winter storms are likely to affect the Washington region next week, the first, slated for late Monday into Tuesday, and the second looks to come Thursday into Friday. Both will draw large amounts of moisture out of the Gulf of Mexico and produce heavier precipitation than Saturday’s storm.

However, there are significant questions about how cold temperatures will be for both events.

The storm on Monday into Tuesday could produce serious amounts of ice or, if warmer model projections are correct, perhaps only a light amount of ice before changing to plain rain. For this storm, the likelihood of significant frozen precipitation will increase as you head west and northwest of Washington.

Models then differ substantially in their simulations for the storm on Thursday into Friday. The American model projects more of rainstorm, as it tracks well to our west and northwest drawing in mild air. However, the European model simulates a more southerly track and shows the potential for significant sleet and/or snow.

We’re in a pattern right now where models are struggling to accurately simulate exactly how far south and east Arctic air will penetrate. This led to very challenging snow forecasts in previous days and may mean we’re unable to nail down forecast specifics (such as where the snow/ice/rain lines set up) until a day or so before precipitation begins.

On Thursday night, accumulating snow fell mainly south of the Beltway, with amounts increasing toward north central Virginia and southern Maryland.

Reports show a coating to an inch fell in the vicinity of southern Fairfax, Prince William and northern and central Charles counties. Through Stafford and southern Charles counties about one to three inches fell. Then, from around Fredericksburg into central and southern St. Mary’s counties three to five inches were reported (full list of reports).

These amounts were consistent with what we predicted on Thursday, although a few spots in our southernmost areas received an inch or two more than we expected, even topping the boom expectation.