Thunderstorms arriving Thursday precede cooler air in Northeast
Updated Jul 28, 2021 5:39 PM EDT
Weather comments from neighbors in the middle of Pennsylvania have switched from "it sure has been wet" to "we need some showers" during the past week. There have been a few spotty showers and thunderstorms around Pennsylvania on Tuesday night and Wednesday, but most places have had nothing judging from the radar. A weak cold front moved through the Northeast Tuesday night brought in more comfortable air for the region on Wednesday. More humid air will move into the Middle Atlantic region late Wednesday night and Thursday ahead of a stronger cold front and thunderstorms.
In the Upper Midwest/central Great Lakes region, violent thunderstorms with damaging winds will affect some areas Wednesday night as the storms race southeastward. That activity is likely to affect parts of the Northeast later Thursday and Thursday night, but saying who will get what and when remains elusive.
The premier National Weather Service agency tasked with predicting severe storms is the National Storm Prediction Center. They are top-notch, IMHO. Their experts issue outlooks for severe weather every day as well as commentaries to accompany their maps. Today, they are challenged about the specifics of tomorrow. The map below shows predicted severe thunderstorm threats for Thursday, suggesting the greatest threat - which is still a slight risk - is from southern Illinois to New Jersey. Below the map is an excerpt of their commentary discussing the uncertainty.
However, the most immediate concern is what happens from late Wednesday into early Thursday. The radar picture below shows the extensive activity that already existed early Wednesday afternoon.
SPC's map and commentary for day one (Wednesday through early Thursday) convey a sense of urgency that people in that area must be on alert about tonight:
In alerting about severe thunderstorms, it is important to know the relative severity of each classification. To me, they are not entirely intuitive. On the map above, the risk levels are marginal, slight, enhanced and moderate. Moderate is a higher category than enhanced. It is easy enough to realize that when you see them all on the same map, but when you consider the terms independently, there could be some confusion. Perhaps the most important thing to remember is that when a watch is issued for your area, it means that a risk has been identified for your region. When a warning is issued, life and property are at risk, and so it is vital to move to the safest place you can find right away.
The enhanced infrared satellite picture from mid-afternoon shows the system over the Upper Midwest and the relatively meager array of smaller showers farther east.
The forecast map below for Thursday morning at 2 a.m. shows basically dry conditions over the Northeast while strong thunderstorms and perhaps a derecho cross the Great Lakes.
The map below suggests that Thursday morning will be stormy from Ohio into western Pennsylvania.
Showers and thunderstorms will cross the rest of the Middle Atlantic region and New England later Thursday and Thursday night.
Cooler and drier will take over from the Great Lakes to the Middle Atlantic region to pave the way to nice weather in most of the area on Friday. The cluster of thunderstorms on the Friday evening map over South Dakota and Iowa may be part of a system that will bring a second cold front through this weekend. Some models have been suggesting that one of the nights will be about as cool as we ever see in the middle of summer.
In the sample forecasts below, I did not include the second week because it looks like there is greater-than-usual uncertainty. Some models have suggested that a strong trough will develop over the Ohio Valley and that a big rainstorm could affect the Middle Atlantic region and perhaps New England during next week. Other models suggest that threat is overblown. All I will conclude at the moment is that forecasting can be hazardous when it relates to the future!
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Weather Blogs / Northeast US weather
Thunderstorms arriving Thursday precede cooler air in Northeast
Updated Jul 28, 2021 5:39 PM EDT
Weather comments from neighbors in the middle of Pennsylvania have switched from "it sure has been wet" to "we need some showers" during the past week. There have been a few spotty showers and thunderstorms around Pennsylvania on Tuesday night and Wednesday, but most places have had nothing judging from the radar. A weak cold front moved through the Northeast Tuesday night brought in more comfortable air for the region on Wednesday. More humid air will move into the Middle Atlantic region late Wednesday night and Thursday ahead of a stronger cold front and thunderstorms.
In the Upper Midwest/central Great Lakes region, violent thunderstorms with damaging winds will affect some areas Wednesday night as the storms race southeastward. That activity is likely to affect parts of the Northeast later Thursday and Thursday night, but saying who will get what and when remains elusive.
The premier National Weather Service agency tasked with predicting severe storms is the National Storm Prediction Center. They are top-notch, IMHO. Their experts issue outlooks for severe weather every day as well as commentaries to accompany their maps. Today, they are challenged about the specifics of tomorrow. The map below shows predicted severe thunderstorm threats for Thursday, suggesting the greatest threat - which is still a slight risk - is from southern Illinois to New Jersey. Below the map is an excerpt of their commentary discussing the uncertainty.
However, the most immediate concern is what happens from late Wednesday into early Thursday. The radar picture below shows the extensive activity that already existed early Wednesday afternoon.
SPC's map and commentary for day one (Wednesday through early Thursday) convey a sense of urgency that people in that area must be on alert about tonight:
In alerting about severe thunderstorms, it is important to know the relative severity of each classification. To me, they are not entirely intuitive. On the map above, the risk levels are marginal, slight, enhanced and moderate. Moderate is a higher category than enhanced. It is easy enough to realize that when you see them all on the same map, but when you consider the terms independently, there could be some confusion. Perhaps the most important thing to remember is that when a watch is issued for your area, it means that a risk has been identified for your region. When a warning is issued, life and property are at risk, and so it is vital to move to the safest place you can find right away.
The enhanced infrared satellite picture from mid-afternoon shows the system over the Upper Midwest and the relatively meager array of smaller showers farther east.
The forecast map below for Thursday morning at 2 a.m. shows basically dry conditions over the Northeast while strong thunderstorms and perhaps a derecho cross the Great Lakes.
The map below suggests that Thursday morning will be stormy from Ohio into western Pennsylvania.
Showers and thunderstorms will cross the rest of the Middle Atlantic region and New England later Thursday and Thursday night.
Cooler and drier will take over from the Great Lakes to the Middle Atlantic region to pave the way to nice weather in most of the area on Friday. The cluster of thunderstorms on the Friday evening map over South Dakota and Iowa may be part of a system that will bring a second cold front through this weekend. Some models have been suggesting that one of the nights will be about as cool as we ever see in the middle of summer.
In the sample forecasts below, I did not include the second week because it looks like there is greater-than-usual uncertainty. Some models have suggested that a strong trough will develop over the Ohio Valley and that a big rainstorm could affect the Middle Atlantic region and perhaps New England during next week. Other models suggest that threat is overblown. All I will conclude at the moment is that forecasting can be hazardous when it relates to the future!