Cold shot for the Northeast Thursday, then some recovery
Updated Apr 20, 2021 12:36 AM EST
Some showers crossed parts of the mid- and North Atlantic states on Monday, but most of the time at most locations it was a dry day. At my location in the middle of Pennsylvania, the day started almost perfectly clear. However, in response to surface heating and chilly air aloft, clouds soon formed. At times the clouds were threatening but not much rain fell
The radar satellite composite showed a band of precipitation from Ontario to Wyoming. The computer models have been predicting that the eastern portion of this shower zone would fall apart crossing the Appalachians and not reach the East Coast.
This view shows the showers more clearly than the composite:
On the GFS forecast map for Tuesday afternoon, it is dry throughout the Northeast except in northernmost New England. There is also a low pressure area north of Milwaukee, Wisconsin, on the map shows a band of snow across Missouri. The software that decides whether it's snow freezing rain or rain was developed for winter time. At this time of year when the lowest levels of the atmosphere are warmer than in the middle of winter, a meteorologist would have to do further investigating to see whether it would really be snowing where this map shows it or if instead there would be rain. The air mass in the northern Plains is truly cold. Mid-afternoon temperatures failed to get past the middle 30s and with the wind blowing it felt like it was in the teens and 20s in much of North Dakota. That's the air mass it'll be heading to theNortheast for the period from Wednesday night through Thursday night.
The forecast map for Wednesday afternoon shows the cold front advancing toward the East Coast. With warm air ahead of the front, and very cold air aloft farther west the stage could be set for thunderstorms with the cold front.
Indeed, the National Weather Service Storm Prediction Center has outlined the area of marginal risk for severe thunderstorms Wednesday afternoon and evening from eastern Virginia to extreme southeast New York.
Temperatures will tumble to the 20s Wednesday night in the mountains from Pennsylvania to New England and will not get out of the 30s on Thursday. Most residents of the Northeast realize it is not safe to plant annual plants in the garden until later in May. However, those who run orchards are at the mercy of even one-night freezes. Just as an inopportune hailstorm can wipe out a whole season's worth of work growing crops on a farm, a late-season freeze can ruin prospects for apple or peach orchards. The map below for Friday shows that while there will still be chilly winds in the Northeast it won't be quite as cold as Thursday.
So why are we getting these cold shots? Last week I showed how a blocking pattern forces the jet stream south of its usual location. The 500 millibar map dramatizes the wintry nature of the current setup. I drew an arrow showing where the air that is coming to the Northeast is originating. It is coming from the remote frozen hinterlands of the Arctic, a land where a woman or a man must go prepared or not go at all, a land where the first snow of September covers the tender tundra, which may not be seen again till the following June.
Let's compare the pattern with what was happening at this time last year. It actually looks similar!
OK, we've presented the cold facts. I'll leave you with a warming thought: the following map is for 11 months ago on May 19, 2020. I can tell you one thing that happened that day: any baby born that day will be a year old on May 19! And if you are one of the parents, you'll have a teenager in 12 years. As for the weather pattern, it looks quite warm in the Central and Eastern states. However, a low pressure area centered over the Tennessee Valley looks like the kind of system that causes a lot of rain. Looking back, I noticed that Knoxville, Tennessee, had more than 2 inches of rain from the storm.
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Weather Blogs / Northeast US weather
Cold shot for the Northeast Thursday, then some recovery
Updated Apr 20, 2021 12:36 AM EST
Some showers crossed parts of the mid- and North Atlantic states on Monday, but most of the time at most locations it was a dry day. At my location in the middle of Pennsylvania, the day started almost perfectly clear. However, in response to surface heating and chilly air aloft, clouds soon formed. At times the clouds were threatening but not much rain fell
The radar satellite composite showed a band of precipitation from Ontario to Wyoming. The computer models have been predicting that the eastern portion of this shower zone would fall apart crossing the Appalachians and not reach the East Coast.
This view shows the showers more clearly than the composite:
On the GFS forecast map for Tuesday afternoon, it is dry throughout the Northeast except in northernmost New England. There is also a low pressure area north of Milwaukee, Wisconsin, on the map shows a band of snow across Missouri. The software that decides whether it's snow freezing rain or rain was developed for winter time. At this time of year when the lowest levels of the atmosphere are warmer than in the middle of winter, a meteorologist would have to do further investigating to see whether it would really be snowing where this map shows it or if instead there would be rain. The air mass in the northern Plains is truly cold. Mid-afternoon temperatures failed to get past the middle 30s and with the wind blowing it felt like it was in the teens and 20s in much of North Dakota. That's the air mass it'll be heading to theNortheast for the period from Wednesday night through Thursday night.
The forecast map for Wednesday afternoon shows the cold front advancing toward the East Coast. With warm air ahead of the front, and very cold air aloft farther west the stage could be set for thunderstorms with the cold front.
Indeed, the National Weather Service Storm Prediction Center has outlined the area of marginal risk for severe thunderstorms Wednesday afternoon and evening from eastern Virginia to extreme southeast New York.
Temperatures will tumble to the 20s Wednesday night in the mountains from Pennsylvania to New England and will not get out of the 30s on Thursday. Most residents of the Northeast realize it is not safe to plant annual plants in the garden until later in May. However, those who run orchards are at the mercy of even one-night freezes. Just as an inopportune hailstorm can wipe out a whole season's worth of work growing crops on a farm, a late-season freeze can ruin prospects for apple or peach orchards. The map below for Friday shows that while there will still be chilly winds in the Northeast it won't be quite as cold as Thursday.
So why are we getting these cold shots? Last week I showed how a blocking pattern forces the jet stream south of its usual location. The 500 millibar map dramatizes the wintry nature of the current setup. I drew an arrow showing where the air that is coming to the Northeast is originating. It is coming from the remote frozen hinterlands of the Arctic, a land where a woman or a man must go prepared or not go at all, a land where the first snow of September covers the tender tundra, which may not be seen again till the following June.
Let's compare the pattern with what was happening at this time last year. It actually looks similar!
OK, we've presented the cold facts. I'll leave you with a warming thought: the following map is for 11 months ago on May 19, 2020. I can tell you one thing that happened that day: any baby born that day will be a year old on May 19! And if you are one of the parents, you'll have a teenager in 12 years. As for the weather pattern, it looks quite warm in the Central and Eastern states. However, a low pressure area centered over the Tennessee Valley looks like the kind of system that causes a lot of rain. Looking back, I noticed that Knoxville, Tennessee, had more than 2 inches of rain from the storm.