If you wake up on Mother’s Day morning with flakes flying in the Great Lakes, Ohio Valley, and Interior Northeast, you might not dream. That’s because the stubborn spring cold, combined with a damp storm system, lowers the temperature just low enough for moist, sloppy snowflakes.
May snow in this region of the country is unprecedented, but rare. Chicago last recorded snow trails in May in 2004. In and around this area, measurable snow in May appears to occur about once or twice every 10 years, depending on the north-south distance of the location.
The storm system, located in central Planes, travels east overnight from Saturday to Sunday, causing severe storms in Kansas and several supercell thunderstorms that can drop tornadoes. This turns into a squall line, traveling southeast through Kansas City and St. Louis, potentially damaging gusts of over 70 mph.
On Sundays, stormy weather sinks southeast into the warm, moist air of eastern Texas, Arkansas, and Louisiana. However, the north side of the storm remains cold.
In most cases, this means stable, cold rain that runs eastward from Iowa through northern Ohio, the southern Great Lakes, and into the northeastern interior on Mother’s Day. In fact, most of the area will be rained 1-3 inches.
However, in the very narrow zones with the highest rainfall, heavy moist snowflakes are mixed. This is because if the atmosphere is cold enough on the border to snow, a phenomenon called dynamic cooling from the heavy precipitation zone itself can cool the columns. Enough to generate snow.
The secret is to accurately predict where it will be set. As of Saturday night, the model shows a very narrow band, perhaps only 30 miles wide, extending from northern Illinois to northern Indiana, northern Ohio, and northern Pennsylvania near the New York border. It may take moist flakes just outside Chicago, South Bend, Indiana, south of Cleveland, near Bradford, Pennsylvania. Basically, the places where you are most likely to find snow are far enough away from the Great Lakes to avoid the calm air near the Great Lakes and the altitudes similar to northwestern Pennsylvania.
Generally not very much, but there can be hours of wet snow heavy enough to throw away an inch of mud on a grassy surface. And the hills of northern Pennsylvania may squeeze a few inches in the blink of an eye. In most places, it only melts when it touches the ground.
Whether it snows or cold rains in these areas, it becomes raw and chilly, with overnight lows in the thirties and Mother’s Day temperatures hovering in the forties all day long.
So what is the cause of this anomalous pattern? You may have noticed that the temperature is getting colder and the grip is weaker this spring. This is due to the atmospheric conditions that meteorologists call blocking patterns near Greenland. This is when a high-pressure ridge (think of it as a mountain of warm air in the atmosphere) is stuck in the polar regions of eastern Canada and the North Atlantic.
As a result, cold air pockets, usually to the north, are pushed out and travel south beyond the northern United States. This stubborn pattern has been around since the beginning of April. In fact, this pattern can be traced back to the winter when Texas and the central United States were suffering... In climate, these block-like patterns can be difficult to break down, especially if they are as robust as those seen in this past winter.
So if you live in the Great Lakes or the northeast and wonder why it doesn’t seem to want to warm up consistently, now you know why. Looking ahead to next week or two, there’s a short warm-up, but there’s little reason to believe that this cool stubborn pattern will break. Forecasts for the next 10 days (shown to the right of the tweet above) show lower than normal temperatures in blue and green in most of the eastern United States.
Mother’s Day Weather: Rare snow can fall from Illinois to Pennsylvania
Source link Mother’s Day Weather: Rare snow can fall from Illinois to Pennsylvania