Freezing fog advisory explained as US dealt yet another extreme winter weather warning

Parts of the US are set to face even more extreme weather conditions this week.

Storm Fern brought heavy snowfall across 34 states over the weekend, triggering power outages for millions and killing dozens of people.

Boston recorded a whopping 16.7 inches of snow on Sunday (January 25), the Weather Channel reports, while the Sierra Blanca mountains above New Mexico saw upwards of 31 inches.

While temperatures have resurfaced above freezing and dangerous ice is beginning to melt away, the whacky weather isn't settling anytime soon.

Now, an advisory for freezing fog has been issued, impacting North Texas and parts of Louisiana.

The warning is in place until midday today (January 28) - but what exactly does it mean?

What is freezing fog?

Parts of the US were blanketed with snow over the weekend (Stock photo - Douglas Sacha/Getty Images)

The National Weather Service explains that freezing fog happens when tiny, supercooled liquid droplets in fog 'freeze instantly' when surface temperatures are at freezing, or below.

You might notice this effect on tree branches, and while it might look wintery and aesthetic, it's incredibly dangerous, particularly as it can also impact roads, sidewalks and vehicles.

Freezing fog can also cause difficult-to-spot black ice; a thin layer that appears invisible because you can see the road through it.

"Extreme caution should be taken if travel is necessary," the Weather Service adds. "Drive more slowly when you suspect icy conditions."

It's also noted that freezing fog can impact planes and make flying 'very dangerous.'

In the North Texas weather alert, in place from 3am until 11am, the Service warns: "Slick road conditions are possible on untreated bridges and overpasses and other untreated surfaces where visibility falls below three miles."

What has caused freezing fog today?

You might've seen freezing fog on trees before, just like this (Feifei Cui-Paoluzzo/Getty Images)

After temperatures became milder yesterday, North Texas and Louisiana then had winds from the south pulling in extra moisture, causing humidity levels and dew points to rise.

As winds calmed overnight and temperatures dropped below freezing once again, that moisture has condensed and frozen, leading to areas of freezing fog.

As CBS reports, this refreezing has then seen dangerous black ice form roads.

Rising temperatures today should help melt some of the fog and black ice.

And while milder daytime conditions are forecast this week, mornings will remain cold - so don't assume you'll be immune from black ice!

Should you drive in freezing fog?

Freezing fog and black ice makes road conditions incredibly dangerous (Mint Images RF/Getty Images)

It's best to avoid driving in freezing fog, for your own safety and that of others.

But if you have no choice but to set foot in your car before lunchtime, then be sure to heed the following advice.

The Weather Service says: "Slow down, use your low beam headlights, and leave plenty of distance between you and others."