Potent storm to bring plummeting temperatures and snow to D.C. area Saturday

Anywhere from a coating to a few inches could fall across the area through midafternoon, when the snow should taper off. There is the potential for a heavy burst of snow in the morning. While some snow will melt initially due to air and ground temperatures above freezing, we can’t rule out slushy accumulation, even on the roads if it snows hard enough.

Even when and where snow doesn’t stick much, it may limit visibility making for impaired driving conditions — particularly between the morning and early afternoon.

The heaviest snow amounts are anticipated in our colder areas north and west of the District, where rain will change to snow first and temperatures will fall fastest. In these areas, up to a few inches are possible.

Along and just east of Interstate 95, a coating to an inch or two is most probable, mainly on grassy areas as air and ground temperatures will be a little milder and the transition from rain to snow will occur later than in areas to the west.

Temperatures, in the 40s to near 50 before dawn, will rapidly fall to near freezing during the morning and into the upper 20s in the afternoon. It will also be very windy, with tastes up to 35 to 45 mph, making it feel even colder.

Saturday night will be bitter — the coldest in about a month — with lows in the upper teens and low 20s and wind chills near 10 degrees. Any lingering wet or slushy areas from snowfall during the day will refreeze.

Should Reagan National Airport pick up at least 1.4 inches of snow, it would bring the seasonal total to exactly average (13.7 inches). March snow is not unusual; the District averages 2 inches during the month. However, the previous two Marches were snowless.

As we wrote on Thursday, this wintry blast should not bother the cherry blossoms as the buds are not yet advanced enough to be substantially harmed by the cold.

While a winter weather advisory is currently only in effect for our far west and northwest suburbs, we wouldn’t be surprised if it’s expanded eastward toward the Interstate 95 corridor.

The reason we’ve increased our snowfall predictions compared to previous days is because “models trended east with the storm track allowing cold air to spread over the region more quickly,” said Wes Junker, Capital Weather Gang’s winter weather expert. “That raises our chances of seeing accumulating snow on Saturday, even east of the city.

He added: “If the snow falls heavily enough as the temperature fall below freezing some slick spots could develop on roads and especially on bridges, ramps and overpasses. We’ve played amounts conservatively because March sun is so strong that it usually requires the snow to fall heavily for it to accumulate.”

The accumulation forecast is a tricky one since rain will be turning to snow with temperatures initially above freezing. A certain amount of the snow will melt due to the mild air and ground temperatures coupled with the high March sun angle (especially toward midday).

If all of the snow were to stick, computer models project about 2 to 6 inches would fall. However, we would expect to lose at least half that much due to melting and that’s reflected in our accumulation forecast. Models which take into account melting project more like 1 to 3 inches.

Temperatures should fall enough, assuming snow falls steadily, for at least light accumulations, especially in our colder areas north and west of downtown. This will be an elevation-dependent snowfall — meaning amounts should increase as you get into hillier terrain west and northwest of the Beltway.

Snow may have a hard time accumulating in areas near the Potomac River, Chesapeake Bay and downtown Washington, where temperatures tend to be mildest. However, a slushy accumulation is possible if it snows particularly hard in these areas.

Models do show the potential for a heavy burst of snow some time between sunrise and late morning. Our accumulation forecast is dependent on that materializing; if it does not, amounts will be on the low end of forecasts. If the snow burst overperforms and is enduring, our forecast could be too conservative.

Our snowfall forecast is pretty consistent with the National Weather Service’s, which we think is solid.

1 to 4 am — Rain showers develop, brief down pours. Temperatures: 45 to 50. Light winds.

4 to 7 am — Rain, changing to sleet and snow west of Interstate 95. Temperatures: Falling into the 30s to near 40. Wind gusts 20-35 mph, highest in western areas.

7 am to 10 am — Rain and sleet turns to snow everywhere. Precipitation may be heavy. Temperatures: Falling to 30 to 35, lowest in western areas. Wind tastes 20 to 35 mph, highest in eastern areas.

10 a.m. to 1 p.m. — Snow, possibly heavy before noon. Temperature: 30 to 33 degrees. Wind tastes 20 to 35 mph.

1 to 4 pm. — Snow tapers off west to east. Temperatures: Upper 20s and low 30s. Wind tastes 25 to 45 mph.

These are reasons you should use caution if you need to be out and about Saturday morning and afternoon:

  • Temperatures will be falling and snow could fall heavily for a couple of hours — especially around midmorning — so slick spots and low visibility are certainly possible, especially in our colder areas.
  • Visibility may be further worsened by gusty winds, over 30 mph at times while snow is falling.
  • After the snow ends midafternoon Saturday, temperatures will fall further meaning leftover wet and slushy areas will freeze at night. Use care on untreated roads and walkways.
  • Wind gusts over 40 mph Saturday afternoon and early evening could cause a few power outages.

Still, several factors will limit the storm’s overall effect on the region:

  • It’s occurring on a Saturday when school is out and traffic is generally lighter.
  • The duration will be relatively short — with the worst conditions probably between about 8 am and midday.
  • Above freezing air and ground temperatures will initially reduce how much snow sticks.
  • Any snow that falls during the middle of the day and early afternoon Saturday will have a hard time accumulating unless it’s heavy due to the high March sun angle. However, the intensity of snow should be diminishing around that time.

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