A minor to light snowfall event on the way tonight as a rare southern US snowstorm is underway. Areas of Delmarva will see the extreme northern extend of the precipitation shield bringing areas of snow showers tonight, in particular across the VA counties. With extremely cold temperatures in place, this will be a very light and fluffy snow as temperatures are expected to be in the teens by the time the snow arrives later this evening. Most of the snowfall accumulations will be occurring across Northampton and Accomack counties where a short duration 1 to 2 inches are possible. Even though the amount of precipitation is very little of a tenth of a inch or less, temperatures are playing a huge role for “high ratio snowfall”
The snow-to-liquid ratio is a quantitative measurement of how fluffy or heavy new fallen snow is. It’s reported as the number of inches of snow that comes from 1 inch of liquid precipitation. Typical snow-to-liquid ratios vary by region and by the weather pattern producing the snowfall. Air temperature, humidity, and wind speed influence how dense new fallen snow is. The highest snow ratios (or lowest density snow) are usually formed by temperatures that are roughly between 0°F and 10°F, in what is called the “Dendritic Growth Zone.” This is the regime for forming large dendrites that accumulate with abundant air space between crystals. New snow grains that are smaller and pack together better form denser snow. Snow that forms outside of the Dendritic Growth Zone regime will be denser, as will snow that falls through warmer layers or is subject to riming. Stronger winds will batter snowflakes together as they fall, which breaks down snow crystals into smaller, denser grains.
...WINTER WEATHER ADVISORY IN EFFECT FROM 5 PM THIS AFTERNOON TO 7 AM EST WEDNESDAY... * WHAT...Snow expected. Total snow accumulations of 1 to 2 inches. * WHERE...Portions of northeast North Carolina and eastern and southeast Virginia. * WHEN...From 5 PM this afternoon to 7 AM EST Wednesday. * IMPACTS...Plan on slippery road conditions. The hazardous conditions could impact the Tuesday evening and Wednesday morning commutes.