Dank now, but sun returns for the weekend!
Blog and Forecast by Meteorologist Nick Morganelli
A WINTER WEATHER ADVISORY IS IN EFFECT FOR AREAS NORTH OF RHODE ISLAND FOR TODAY THROUGH THIS EVENING. IF YOU PLAN TO TRAVEL INTO WORCESTER COUNTY, UNTREATED SURFACES MAY BE SLIPPERY. FREEZING RAIN IS POSSIBLE AS GROUND TEMPERATURES HOVER NEAR 32 WITH DRIZZLE.
Our next round of wet weather moves through tomorrow morning and midday with rain showers. As this system exits Friday evening, we could see some snow showers. North of us along the MA Pike from Worcester to the New York border could get slippery with temperatures near 32.
A northwest wind will scour out the clouds and damp weather Friday night leaving us with sunshine for the weekend! It will be seasonally cold especially in the mornings with temperatures in the 20s.
The weekend will feature the return of cold air too as we get back to typical January expectations. This pattern with a dip in the jet stream winds to the south of us will only last a couple of days. We return to milder than normal conditions next week with no big storms ahead.
Today: Patchy a.m. fog and drizzle. Overcast with highs near 46.
Tonight: Continued damp. Low near 38.
Friday: Scattered morning and midday showers. High near 40.
Friday Night: Scattered snow showers / flurries. Low near 34. Breezy. NW near 10 mph.
Saturday: Sunny and seasonal, near 38.
Sunday: Sunshine. Near 42.
Hydro what? Meteorologists study hydrometeors, hence, where the name comes from. Hydrometeor (a water meteor) is just a scientific way of saying precipitation. Most precipitation begins as snow/ice crystals in clouds. As this snow falls, it encounters a variety of temperatures. It can fall through a warm layer, then cold, then warm again and vice-versa. Meteorologists look at the three-dimensional atmosphere using data from weather balloons and computer models that use physics to create a future result, or a forecast. It’s ultimately up to the scientist to determine what will happen. Will it rain? Will snow survive the fall from the cloud? Will the snowflakes melt, then refreeze? If it refreezes in the air before reaching the ground sleet pellets are created and if it rains and surfaces are very cold, below 32 degrees, that rain can freeze on contact and that’s the most dangerous condition; freezing rain. Icing is extremely dangerous and can accumulate on trees and power lines creating power outages. There is a chance for this type of precipitation today and especially tonight in Worcester county.
The forecaster needs to determine what type of precipitation will fall. With the information age, there is a multitude of data sets, computer generated forecasts, and weather data analysis at our fingertips. Looking for the temperatures at several layers of the atmosphere, and something we call ‘thickness’ of the air helps us determine if snow will fall. One key temperature is the 0 C temp at 850 millibars which is around 3000 ft above the ground. Generally a snowflake can survive a drop of 2000 ft into air above 32 F. How much snow will actually be measured? There’s a lot that is considered. Ground/soil temperatures, amount of insolation (sunlight) prior to a snow event, solar angle at the time of the snow, pre-existing snowcover, dry air intrusions in a storm, warm layers above that may change the snow from fluffy to sticky and of course how much actual precipitation will fall from the cloud.
Typically, a 1 to 10 ratio of liquid (rain) to snow is average, but the ‘fluff factor’ can create a 1 to 30 or even 40 ratio. This happens in the arctic where the air is very cold. The snow crystals (dendrites) that form stand on end with each other and there is a lot of air in between them when they land.
For more on snow science, visit this National Weather Service page!
So, an inch of liquid could give you 3 feet of snow! This isn’t typical, however. Generally an inch will yield about a foot of snow. In spring and fall, mild layers of air or mild air near the ground can give you as little as 5 inches of snow per 1 inch of liquid. This is also not typical. Another factor is whether the snow will melt as it hits the ground and for how long during the storm. When will it ‘stick’? That’s when it begins to accumulate. Ground temperatures are very important in determining this.
Bottom line, there are a lot of factors to determining what type of hydrometeor will fall and then how much of it will accumulate and it’s NOT easy!