Liquid equivalent versus snow
WEST MICHIGAN — The image attached to this story shows how much liquid precipitation fell across our area Saturday night in to Sunday. The area circled shows where the heaviest fell. Most locations were between .40″ and .60″ (of an inch).
If this had been all snow as our models indicated and we forecast, that would have translated to between four and six inches of snow…right on the mark! Unfortunately, for those of you expecting the snow, warmer air was still in place Saturday evening with temperatures in the upper 30s to near 40…so the changeover never occurred until after 11 PM in Grand Rapids. That reduced our snow totals substantially to between two and five inches from Grand Rapids off to the north/west.
Weather is a science! It’s not an exact science and things can change. Some would consider ourselves lucky that we picked up smaller amounts of snow. As the image shows, Grand Rapids had more than a half inch of rain, Lansing more than six tenths, and many other places almost a half inch. Our forecast models were consistent in producing four to six inches of snow, some were even showing seven to eight inches. That said, if the cold air arrives a few hours later or the storm tracks a little further one way or the other, the outcome changes. In this case, we held on to the warm air about five or six hours longer than expected.
Liquid to snow ratio is generally about 10:1. That means for every tenth of an inch of liquid precipitation we see about one inch of snow. To put it another way, every one inch of rain would be ten inches of snow. That’s a general rule. In Arctic air outbreaks and lake-effect snow events, that ratio can be more on the order of 20:1 or even 30:1 signifying a much lower moisture content.
The other thing worth noting that was visibly embedded within the band of precipitation were two small scale low pressure areas (called meso-lows). Note the radar image below valid just before 11 PM Saturday night. These lows, while independent from the main low, could have helped to keep warmer air in place for a longer period of time to keep things all rain. Remember the circulation around these lows…in a counterclockwise fashion…helping to filter in milder air from the south and mitigate the cold air intrusion as planned. It’s unlikely a forecast model would ever pick this type of feature up, nor can we as Meteorologists forecast when and where these will occur. I should also mention that despite the radar showing snow in Grand Rapids at this time, the city was still mainly see rain or a rain/snow mix. It’s also possible the main low pressure area tracked further north/west, which kept the warmer air in place longer.
I would suggest that everyone remove the snow from the driveways, sidewalks, and porches BEFORE the core of the real Arctic air arrives today. Once we head in to the deep freeze and stay there the next several days, you’ll be chipping the ice away in order to remove it! Watch out for winds too. Expect a northwest wind at 15 – 25 mph with gusts to 40. That will produce wind chills in the single digits and eventually below zero.
More accumulating snow arrives Monday night in to Tuesday. Get the forecast at www.fox17online.com/weather.