Dry Through Tomorrow, Then a Soaker Approaches

PROVIDENCE, R.I. (WLNE) — Our next round of wet weather is scheduled for Thursday night and Friday. It will once again be rain with a very wet day to end the work week. For now, high pressure is building in to deliver a light wind and a blend of sun and clouds through tomorrow. Temperatures by day will continue above normal/mild. At night it’s 20s as expected for January. No surge of arctic air expected in the next 7 to 10 days!

 

Here is the area of low pressure that will develop over the plains tomorrow and track towards the eastern Great Lakes on Thursday and Friday.

We’ll remain on the mild side with a strong southerly wind and moderate to heavy rain possible especially on Friday morning.

Map

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This Evening:  Clearing sky. Temperatures falling 34-38. NW 6-10 mph.

Tonight: Mostly Clear and moonlit.  Low near 24.

Wednesday: Morning sunshine to afternoon clouds. High near 40.

Thursday: Cloudy. Chance of a light passing shower. High near 40. Becoming breezy. SE 8-12 mph.

Friday: Rain and windy, Near 52. SSE wind 15-25 mph.

Weekend: Scattered showers Saturday. Drying and colder Sunday. Highs generally in the 30s.

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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.

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Snow Crystals

For more on snow science, visit this National Weather Service page!

https://www.weather.gov/apx/snowflakescience

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!

Categories: News, Weather Forecast