The American model forecast radar at 7 a.m. Tuesday is displayed.

Computer models are suggesting the possibility of two waves of wintry precipitation impacting the area early next week. Neither appear to be blockbuster, high-impact storms — although the second of the two could turn out rather messy.

The first round could arrive Sunday evening and brush the region with light snow and sleet, possibly mixed with rain, before ending Monday morning. But it also could pass mostly to the south with little fanfare.

A more significant round of snow, ice and rain is possible Monday night into Tuesday. The specifics of exactly how it will unfold also has a lot of question marks.

Sunday night into Monday morning: A coating of snow/sleet possible

Any precipitation from this first wave is likely to be light and the coverage may be spotty, but it could move into the area starting as soon as Sunday evening. Areas of snow and sleet, maybe mixed with rain or freezing rain at the onset, could fall gently at times into the morning commute.


The NAM model forecasts some light frozen precipitation moving into the region on Sunday evening.

The steadiest precipitation may focus south of Washington, but the coldest temperatures for supporting accumulation are likely to be to the north and west. There’s some chance the bulk of the precipitation misses the immediate region entirely and stays south (the American and Canadian models make this prediction).

If steadier precipitation develops (as predicted by the NAM and European models), temperatures would fall near freezing and a light accumulation of a coating to an inch cannot be ruled out. Minor impacts of Monday morning’s commute and school delays are also possible.

Models project whatever precipitation falls to end between 7 and 10 a.m. Monday.

Chance of at least an inch of snow: 10 to 20 percent

Overall forecast confidence: Low-Medium

Monday night into Tuesday: Some snow/ice, then rain

This second wave is likely to be the more significant of the two.

Like many of our storms, evolution of the storm is a complicated one, with a pattern that is far from perfect if you like snow. The one feature that argues for some wintry weather is the predicted high-pressure zone to our north in a very favorable location to feed cold air southward. However, most of the model runs are also predicting that the primary storm system will track to our north and west toward the Ohio Valley or Great Lakes area, drawing north mild air at the mid-levels of the atmosphere. This would argue against an all-snow event.


The American model simulation of precipitation types between Monday evening and Tuesday evening is displayed. (PivotalWeather.com/PivotalWeather.com)

Such a complicated set up can provide a number of possible scenarios.

  • If the high-pressure zone weakens and shifts eastward before the precipitation arrives, we’d see a brief period of frozen precipitation Monday night, mainly in our colder areas to the north and west. Then temperatures would probably warm enough for plain rain on Tuesday. The European model favors this scenario. (Note, however, that although the primary European model simulation predicts little snow, quite a few simulations in its larger modeling system do show at least a couple inches of accumulation. Its average forecast is in the one- to two-inch range.)
  • If the high-pressure zone holds in place, sustaining the low-level feed of cold air, and precipitation moves in quickly, a longer and more substantial frozen precipitation event would materialize. The American model favors this scenario. It suggests the potential for up to a few inches of snow and sleet late Monday night into Tuesday morning, heaviest in our coldest areas, before precipitation tapers to a drizzle or freezing drizzle Tuesday afternoon.

Either scenario is possible. The quicker the bulk of the precipitation arrives, the greater the chances of seeing accumulating snow across portions of the area. The later it comes, the better our chances are of seeing more rain. These forecast situations are always tricky, as the air right at the ground surface often stays colder than forecast by models. For that reason, some winter weather is likely, especially for folks living in colder areas north and west of the city.

Chance of at least an inch of snow: 20 to 30 percent

Overall forecast confidence: Low-Medium