While snowflakes are possible anywhere in the region, potentially coinciding with the Wednesday morning commute, our colder areas northwest of the Beltway have the best chance for a slushy accumulation and even a few slick spots on the roads before the precipitation exits by midmorning.
How this event may unfold
Temperatures max out Tuesday between midmorning and midday, between 55 and 60 degrees (possibly topping 60 in a few spots, especially along and east of Interstate 95). But then the cold front sweeps through, producing rain showers and sharply falling temperatures, plunging into the 40s by sunset or shortly thereafter. By midnight, many areas dip below 40.
Between around midnight and predawn Wednesday, rain showers are likely to mix with and change to snow from northwest to southeast, as temperatures drop back several more degrees.
The farther northwest you live from Washington, the higher the chance the snow falls heavily enough and long enough for a bit of accumulation. There could even be some slushy roads and school delays.
Along and east of Interstate 95, the window for snowfall will be pretty short. However, it’s not out of the question that a heavy enough burst of snow comes through to whiten the ground and even produce a little slush on the roads.
If there’s no burst of heavy precipitation, the air probably won’t cool enough for snow to accumulate in the immediate area. In addition to air temperatures just marginally cold enough for snow, the ground will also be warm due to temperatures the previous day — so it would take rather heavy snowfall to overcome that. There’s some chance little or no snow materializes if temperatures fall less than forecast and/or precipitation is light.
How much snow we see depends on both how quickly the cold arrives Tuesday night and how long precipitation lingers over the region Wednesday morning. In addition, whether an area of heavy precipitation develops will play a role in how quickly temperatures drop and where, which has important implications for accumulation potential.
If a band of heavier snow develops toward dawn, temperatures could drop to freezing. That would allow for a quick inch or so of snow, possibly coating roads with a little slush. If no such band develops, temperatures may remain in the mid-30s with little or no accumulation.
Unfortunately, there’s no model consensus as to whether and where a localized heavier burst of snow might develop. Models are bouncing around as to its existence and location in each forecast. The NAM model run early this morning developed a heavier band of snow west of the city, which resulted in temperatures dropping low enough to support accumulation. But the next run forecast only light precipitation west of the city and somewhat heavier precipitation to the east with minimal accumulation prospects.
Beware that model snowfall accumulation forecasts posted on the Internet are likely to be highly inflated because the algorithms make unrealistic assumptions. They assume every flake will stick, which is incorrect with air and ground temperatures above freezing.
Our best guess is that our typically colder northwest suburbs have the highest chance of seeing accumulating snow simply because of lower temperatures. In most areas, this event is likely to be more of a nuisance than highly disruptive. However, a burst of snow could materialize anywhere (with the possible exception of far south and southeast areas) and coincide with the early part of rush hour Wednesday, so everyone should monitor the forecast and be prepared for the possibility of low visibility and a bit of slick travel.
This forecast could change toward snowier or less snowy outcomes over the next day, so check back for updates.