A rare dip of ultra-frigid temperatures in our area saw a reading of minus four degrees below zero around 3 a.m. on Christmas Eve, along with wind chills of 23 degrees below before the thermometers saw their levels start to rise slowly and a revised forecast from the National Weather Service Office in Blacksburg claims the actual temperature will leave the sub-zero range around 9 a.m.
But wind chills will keep the “feels like” cold below zero. The thermometer read three below zero at 6:30 am Saturday but it is expected to edge up to one degree above by 9 a.m. then six above at 10 a.m. and a forecasted high of 17 in the afternoon before heading back down to an overnight low of 11 for Christmas morning.
Wind chill advisories and warnings are expected to remain in place through 1 p.m. Sunday. High winds in the teens, with gusts up to 30 miles per hour have knocked power in Floyd and surrounding counties, downed trees, brought down power lines and branches, and kept slick spots on many roads.
This bitter, frigid weather comes, the weather experts say, comes from a rare winter event called a “bomb cyclone.” To make matters worse, the one is stronger and more prolonged than most.
In The New York Times, Henry Fountain says he is “always ready to write about bombogenesis:”
The storm pummeling large swaths of the United States and Canada is what forecasters call a “bomb cyclone.” While this kind of storm is not exceedingly rare, this one is very strong, with high winds that are bringing heavy snow or rain to many areas.
Storms can form when a mass of low-pressure air meets a high-pressure mass. The air flows from high pressure to low, creating winds. What defines a bomb cyclone is how rapidly the pressure drops in the low-pressure mass — by at least 24 millibars in 24 hours. This quickly increases the pressure difference, or gradient, between the two air masses, making the winds stronger. This process of rapid intensification has a name: bombogenesis.
As the winds blow, the rotation of the earth creates a cyclonic effect. The direction is counterclockwise in the Northern Hemisphere (when viewed from above).
John Moore, a meteorologist, and spokesman for the National Weather Service tells The Times: “Conditions for a bomb cyclone had been met over the Great Lakes, where frigid Arctic air from the meandering polar vortex met very warm air to the east.
“Air pressure dropped to at least 962 millibars, while elsewhere it was as high as 1047 millibars. It’s a really sharp gradient.”
In other words, an incredible PITA (Pain In The Ass).
The NWS wind chill advisory:
Make preparations per the instructions
Roanoke/Blacksburg – VA, US, National Weather Service
Portions of northwest North Carolina, southwest and west central Virginia and southeast West Virginia
…WIND CHILL WARNING REMAINS IN EFFECT UNTIL 1 PM EST THIS AFTERNOON…
…WIND CHILL ADVISORY IN EFFECT FROM 1 PM THIS AFTERNOON TO 1 PM EST SUNDAY…
WHAT…For the Wind Chill Warning, dangerously cold wind chills. Wind chills as low as 30 below zero. For the Wind Chill Advisory, very cold wind chills are expected. Wind chills as low as 15 below zero.
WHERE…Portions of northwest North Carolina, southwest and west central Virginia, and southeast West Virginia. WHEN…For the Wind Chill Warning, until 1 PM EST this afternoon. For the Wind Chill Advisory, from 1 PM this afternoon to 1 PM EST Sunday.
IMPACTS…The dangerously cold wind chills could cause frostbite on exposed skin in as little as 10 minutes.
PRECAUTIONARY/PREPAREDNESS ACTIONS… Avoid outside activities if possible. When outside, make sure you wear appropriate clothing, a hat, and gloves. Use caution while traveling outside. Wear appropriate clothing, a hat, and gloves.–Tne National Weather Service
Not a very nice way to celebrate Christmas. Stay inside if you can. If you must go out, bundled up be careful on roads, sidewalks, and parking lots.
Our best wishes for a Merry Christmas.