May off to chilly start in East thanks to 'Omega block' weather pattern
The first week of May is feeling rather wintry in parts of the Midwest and East due to an atmospheric traffic jam that has trapped cold air. AccuWeather forecasters say a warmup is on the horizon, however.
An atmospheric traffic jam will make the first week of May feel much cooler than average across the East, but AccuWeather forecasters say a warmup is on the horizon.
A massive atmospheric traffic jam will keep chilly air locked in over the Midwest and much of the eastern United States this week, AccuWeather meteorologists say. Forecasters warn that the same pattern set to deliver weather more typical of March rather than May will bring accumulating snow to some spots as well as another round of frosts and freezes to some locations.
A pattern in the jet stream, known as an Omega block, shaped like the Greek letter by the same name, will remain over much of North America through the middle of this week. This setup tends to prevent the normal west-to-east movement of weather systems and tends to lock in chilly, unsettled conditions in some areas, while other locations have an extended period of dry and warm conditions.
"The pattern much of this week will act like a giant pinwheel of clouds, showers and cold air in the Midwest and Northeast," AccuWeather Chief On-Air Meteorologist Bernie Rayno said.
Heavy snow in May?
Pockets of rare, heavy May snow are even in store into the middle of this week for parts of the Great Lakes and central Appalachians.
In locations where the atmosphere was cold enough for snow to fall all the way to the ground, some impressive snowfall totals were reported in Michigan. Into Tuesday evening, several cities on Michigan's Upper Peninsula recorded over 18 inches of snowfall with 32 inches piling up in Ishpenming Township.
More than 500 miles to the southeast of this zone, a separate helping of accumulating snow is in store for portions of the central Appalachians into early Wednesday. In this case, higher elevations will play a major role in providing the ideal temperature for wet snow to accumulate.
Most locations in the mountains from West Virginia to west-central Pennsylvania and southwestern New York will pick up a coating to an inch or two of snow.
However, where the temperature remains close to or below freezing much of the time through Wednesday morning in the highest elevations of West Virginia, 6–12 inches of snow will fall with an AccuWeather Local StormMax™ of 15 inches within reach. The weight of the wet snow could bring down tree limbs, which could lead to sporadic power outages. Fallen tree limbs that are large enough could also block secondary roadways.
Temperatures more typical of March than May
Aside from some occasional wet snowflakes mixed in with rain showers at intermediate elevations in the central Appalachians and the northern Great Lakes, no accumulating snow is in the offing elsewhere in the Midwest and Northeast. However, temperatures more typical of March are in store.
At the depths of the chill, which will be through Tuesday night in the Midwest, and at its worse from into Thursday in the East, high temperatures will be 10-15 degrees Fahrenheit below the historical average for early May.
For example, on Tuesday, temperatures struggled to top the mid 50s F in Chicago, peaking at 54 F, and the high temperature was 45 F in Detroit. Several cities recorded their coolest daily high temperatures Tuesday, such as Pittsburgh with a daily high of 44 F, breaking a record that has stood since 1897. In Morgantown, West Virginia, the daily high of 45 F was the coolest May 2 high to date, beating a record of 46 F set in 1877.
In New York City, highs will only be in the low to mid-50s each day through Thursday, including a high of 54 on Wednesday, with AccuWeather RealFeel® Temperatures in the 40s much of the time. In the central Appalachians, cities such as Bradford, Pennsylvania, will have high temperatures ranging from the upper 30s to the lower 40s through Wednesday with RealFeel temperatures in the 30s and even the 20s at times. Temperatures peaked at 43 F in Bradford on Tuesday.
Highly changeable weather conditions in store
With the air in the middle and upper portion of the atmosphere being much colder relative to near the ground, some thunderstorms could develop and produce gusty winds, small hail and lightning.
These conditions may persist in the Northeast through Thursday. In some cases in the Ohio Valley and east of the Appalachians, a term meteorologists use called "self-destruct sunshine" will come into play. This chaotic state of the atmosphere occurs when the sun pops out for a few hours in the morning, but due to the cold air higher up, clouds quickly form during midday and are followed by gusty showers and thunderstorms in some cases.
Weather conditions can change dramatically over short intervals of time during this type of pattern. It can be sunny and mild one minute ahead of a downpour with strong winds and noticeably lower temperatures a few minutes later.
Not enough rain will fall this week to aggravate existing high water levels on area rivers such as the Mississippi in the Midwest and the Susquehanna in the Northeast.
Monitoring conditions for frost
Along with the daytime chill comes the risk of nighttime temperatures that may dip to frosty or freezing levels in some cases this week.
"The combination of wind and cloud cover may work to prevent widespread frost in parts of the Midwest and the Northeast most nights this week," AccuWeather Meteorologist Nicole LoBiondo said. "However, where winds drop off and the sky is clear most of the night there could be some damaging frost."
Clouds tend to act as a blanket, while winds tend to prevent the coldest air from collecting near the ground.
The risk of a frost or freeze will shift to the interior Northeast starting as early as Thursday night and perhaps as late as Saturday night with the greatest chance likely to be Friday night.
AccuWeather meteorologists are projecting Bradford to dip to near the freezing mark Thursday night and Friday night. Official temperature readings are taken about 6 feet above the ground. This means temperatures could dip into the 20s at ground level in the coldest spots around the Bradford area.
Normally, a frost in early May would not pose a significant problem. However, because of temperatures well above the historical average this winter and most of the spring, buds have broken through and the leafing out process has begun much earlier than usual. The cold weather this week could lead to damage where blossoming plants and trees are at a critical stage.
A warmup awaits this coming weekend
"Beginning around midweek in portions of the northern Plains and on Friday in parts of the Northeast, a warming trend will begin during the daytime hours," Rayno said. This will occur as the Omega Block begins to weaken a bit and allow weather systems to gradually resume their normal west-to-east movement.
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