Afternoon update: The latest European, Canadian and UKMET models have come into agreement predicting about 2 to 4 inches of snow from Thursday’s system, whereas the American model still shows the possibility of a bigger storm (though it backed off the megastorm scenario it projected earlier). At the moment, a light to moderate snow event is what the bulk of the models favor. That said, with four days to go until the storm makes its closest approach, all scenarios remain on the table, from a miss to a significant snowstorm.

For the Monday event, something to watch, especially just north of Washington, is the possibility of a period of evening snow and sleet. While the American and NAM models lean toward mostly freezing rain in our colder areas Monday evening, the European and Canadian models suggest an inch or two of snow or sleet cannot be ruled out before the changeover to freezing rain.

Original post from midday: The forecast of a messy mix of precipitation Monday afternoon and night is slowly coming into focus, while big question marks remain about a possible winter storm on Thursday.

Monday’s storm is most likely to offer a combination of snow, sleet, freezing rain and rain across the region, with the potential for a light accumulation increasing as you head north and west of the Beltway. South and east of the Beltway, mostly plain rain is expected, though a little mixed precipitation can’t be ruled out.

The potential storm on Thursday is generating a lot of chatter on social media because the American (GFS) model forecasts it to be a powerhouse that produces a lot of snow. But the European model, which on average is the most accurate, is less enthusiastic about the storm’s potential.

Let’s discuss Monday’s event first.

A wintry mix Monday afternoon and night

This appears to be a nuisance to moderate winter weather event, depending where you live. Our typical colder areas north and west of the Beltway — especially north and west of Leesburg, Gaithersburg and Columbia — have the highest chance of seeing some accumulation of frozen precipitation and icy roads.

Inside the Beltway — especially to the south and east — little or no accumulation of frozen precipitation is expected, and roads should remain mostly wet.

All of this said, if it’s just a degree or two colder, it would make for an icier forecast throughout the region. On the flip side, if it’s a degree or two warmer, mostly rain would fall everywhere (except toward the Shenandoah Valley and Mason-Dixon Line).

Here’s how we see the event evolving:

Monday afternoon (noon to 6 p.m.): Rain will develop southwest to northeast, possibly mixed with snow and sleet, especially in our colder areas. Little or no accumulation of frozen precipitation is expected. Temperatures should be in the mid- to upper 30s (near 40 in southern Maryland) in the afternoon, falling back to the low to mid-30s (upper 30s in southern Maryland) by evening.

Monday evening (6 p.m. to midnight Tuesday): Mixed precipitation will change to freezing rain in our colder areas north and west of the Beltway; a glaze is possible. Elsewhere, mostly a cold rain will fall. Temperatures will range from 30 to 32 in our colder areas to 33 to 35 elsewhere (except in southern Maryland, where it should hit the upper 30s).

Tuesday morning (midnight to 6 a.m.): Freezing rain will slowly taper off in our colder areas, while rain will end elsewhere. Temperatures will hold steady between 30 and 35 degrees (except in southern Maryland, where it should hit the upper 30s).

The period of greatest concern is Monday evening into the early morning hours on Tuesday in our colder areas, where a combination of snow, sleet and freezing rain could cause an icy glaze on untreated sidewalks and roads. Freezing rain could also build up a bit on trees and power lines, but we don’t expect enough to cause power issues at this time.

Why such limited snow prospects? The track of the storm toward the Ohio Valley will draw southerly winds north, raising temperatures above freezing several thousand feet above the ground, melting any possible snowflakes.

Thursday storm

Questions remain whether a storm system approaching from the south will come far enough north to give us snow Thursday. There are a few possibilities:

  1. Strong high pressure to the north keeps the storm suppressed to the south.
  2. The high pressure relaxes enough for the storm to come north and hammer us.
  3. Something in between.

Both the European and UKMET models keep the storm suppressed far enough south to offer mostly light snow. Alternatively, American and Canadian models advertise the possibility of a more significant snowstorm.

As an illustration of the differences between the modeling, the American modeling system shows about a 50 percent chance of at least 3 inches of snow in the 24 hours ending Thursday night, whereas the European modeling system offers less than a 10 percent chance.

The differences in the modeling systems are reflected in their forecasts for the track of the storm. Most of the simulations in the American modeling system develop the storm close to the Mid-Atlantic coast, which allows it to generate snow in our region, whereas the European modeling system forecasts the storm to pass far enough to the south and southeast so that precipitation mostly misses.

The bottom line is that the late-week system still has potential to produce snow, possibly even heavy snow, but there also is the potential for the storm to completely miss us. Until the models converge toward a solution, all we can do is monitor it over the next couple of days.