Rare Mother’s Day snow possible from Illinois through Pennsylvania
When you wake up with flakes on Mother’s Day morning in the Great Lakes, Ohio Valley, and the Northeast, you just can’t dream. That’s because stubborn spring chill is combined with a moisture-laden storm system to bring temperatures down just low enough to create some wet, sloppy snowflakes.
Snow in May in this part of the nation is not unheard of, but rare. The last time Chicago recorded a trail of snow in May was in 2004. In and around this region, measurable snow appears to occur in May about every one or two decades, depending on how far north or south the location is.
A storm system over the states of the Central Plains will move east overnight Saturday through Sunday, causing severe storms in Kansas. Some supercell thunderstorms can throw off tornadoes. This will turn into a gust line and run southeast through Kansas City and St. Louis, with the risk of damaging gusts of wind over 100 km / h.
On Sunday, the storm sinks southeast into the warm and humid air over East Texas, Arkansas and Louisiana. But the north side of the storm will stay in the cold sector.
For most, that means steady, cold rain from Iowa east through the northern Ohio Valley, southern Great Lakes, and into the inner northeast on Mother’s Day. In fact, most of the region will soak 1 to 3 inches of rain.
In the case of a very narrow strip, which is in the heaviest precipitation, heavy, wet snowflakes mix in. When the atmosphere is borderline cold enough for snow, a phenomenon known as dynamic cooling by the heavy precipitation band itself can cool the column enough to produce snow.
The trick is to predict exactly where this will be set up. Beginning Saturday night, models are showing this very narrow band, perhaps only 30 miles wide, that stretches from northern Illinois to northern Indiana, northern Ohio and the northern Pennsylvania plain near the New York border. That can take the wet flakes just outside Chicago, South Bend, Indiana, south of Cleveland, and near Bradford, Pennsylvania. Basically, the most likely places where snow can be spotted are just far enough from the Great Lakes to avoid the milder air near them and places of elevation similar to northwestern Pennsylvania.
What happens in May if you are stuck with polar blockades and get a storm with heavy, steady rainfall? Sloppy snowflakes for Mother’s Day. Note that the snow band is very narrow – where the heaviest precipitation falls. But regardless of the raw, cool 30s / 40s tonight and tomorrow! pic.twitter.com/jojncTfPdU
– Jeff Berardelli (@WeatherProf) May 8, 2021
It won’t be much in general, but there could be enough wet snow for a couple of hours to throw a muddy inch on grassy surfaces. And the hills of northern Pennsylvania can push a few inches out. In most cases, it simply melts on contact with the ground.
Regardless of whether there is snow or cold rain in these areas, it is raw and cold, with lows in the 30s overnight and temperatures on Mother’s Day hovering in the 40s for most of the day.
What is causing this unusual pattern? You may have noticed that the cool temperatures this spring have been slow to reduce grip. That’s because there is an atmospheric condition that meteorologists near Greenland refer to as the blocking pattern. This is the case when a high pressure crest – think of it as a mountain of warm air in the atmosphere – gets stuck over the polar regions of eastern Canada and the North Atlantic.
What about that relentless spring cold in the Great Lakes and the Northeast? Well … the pattern is still blocky in Canada / Greenland. These robust glitches are hard to remove, aren’t they? @ Judah47 So the ten-day deviation from normal value (euros) on the right side remains cool! pic.twitter.com/RXLCd1wqRb
– Jeff Berardelli (@WeatherProf) May 8, 2021
The result is cold air bubbles that are usually far north and displaced south into the north of the United States. This persistent pattern has been around since early April. In fact, we can trace this pattern back to the winter when Texas and the central US suffered. In the climate, these blocky patterns are sometimes difficult to break, especially when they’re as tough as what we saw last winter.
So, if you live in the Great Lakes or the Northeast and are wondering why it doesn’t look like it is constantly warming up, now you know why. While there will be brief warm-ups ahead of the next week or two, there is little reason to believe that this cool, stubborn pattern will break. The forecast for the next 10 days – seen on the right in the tweet above – shows in most of the eastern United States under normal temperatures in blue and green