Odd Quiet Weather Pattern This Week Producing Fog, Pollution

Aftermath of a pileup on Interstate 64 in Virginia this morning.
Fog lifted after the crash. But dense fog and ice contributed
to this crash. 

The eastern two-thirds of the United States is still oddly quiet in the weather department.

Great for travel, but not so great for air quality. Or the production of fog.

The storminess we usually see this time of year mixes the air. Strong winds dissipate and blow away any emissions we produce and most of the fog that tries to form in moist air.

But high pressure is dominating this week, so the air is relatively still. When high pressure, fair weather systems dominate in the summer, you can get pollution problems too. But the strong sun of summer mixes the air, so that helps dissipate fog and pollution.

Around now, the winter solstice, the sun is weak, of course. So you don't get the updrafts caused by the sun's heating, and the air doesn't mix. In fact, an inversion often forms, in which the air above is warmer than the air at the surface. That locks in the air, not allowing fog and pollution to escape.

That's why it's hazy from the Plains through the Midwest to the East Coast this weekend. I noticed this while flying from Burlington, Vermont to Sioux Falls, South Dakota on Saturday. During a stopover in Chicago, it was actually kind of smoggy.

As my plane took off from O'Hare, you can see a brown smudge enveloping the air over the Windy City, which was anything but windy on Saturday.

Some places are worse than others. There's an air quality alert in southwestern New Hampshire, as air pollution is accumulating in low elevations there.

Elswhere, dense fog advisories were up for large parts of the central Plains this morning. Where I am this morning in Yankton, South Dakota, the sun is out, but you can see haze accumulating in the atmosphere.

Sometimes, this situation can get dangerous. Fog can get thick, and in the winter, the moisture from the fog can ice up bridges and highways. Motorists start sliding on the ice, and can't see each other in the dense fog.

Such was the case early this morning in Virginia. Dense fog and ice contributed to a 45-car pileup on I-64  and many people are injured, according to Virgina State Police.

Weather conditions will slowly begin to get more active on and after Christmas, so the haze and fog will start to decline, only to be replaced by our usual winter hazards of snow and ice, at least in some parts of the country.