Cooler, drier air coming to the Northeast as July ends
Updated Jul 29, 2021 8:09 PM EST
On Wednesday night, thunderstorms developed in the upper right Great Lakes region and moved southeastward. The picture above shows the mesoscale convective complex, which looks in some ways like a hurricane over land. This is what the radar looked like before midnight when 50 to 60 mph wind gusts came through parts of central Wisconsin.
By Thursday morning, the system had weakened. The following two maps showed the pressure analysis at noon and 7 p.m. on Thursday. There had been some thinking that the storms could re-intensify along a warm frontal boundary that was just ahead of the approaching cold front. I sketched in the warm front on the first map but did not do so on the second map. You may be able to see where the front was on the second map by where the isobars turned around. In any case, the front had not moved much and that is typical east of the Appalachians, where there is some cool air damming because of the effect of the mountains and the ocean which is cooler than the adjacent land.
At mid-morning Thursday, the sun was largely hidden by a deck of high cloudiness over a central Pennsylvania. The effect was not that much different than that of smoke dimming the sun the previous week.
At around the same time Thursday at midday, you can see the precipitation mostly extending from northern New York state to northwest Pennsylvania. In their discussion the day before, the NWS storm prediction center noted that there was considerable uncertainty about how much intensification the thunderstorms would undergo the next day. As it turned out, the cloudiness out ahead of the remaining precipitation held down the temperature just enough to prevent a widespread and deadly severe thunderstorm outbreak. I don't want to imply that nothing bad happened. It's just that less happened, in this case, than if there had been a lot of hot sunshine before the precipitation arrived. The following maps show the progression of the pre-frontal showers and thunderstorms from midday through mid-afternoon.
Note on the map above there's a little spike of extra intensity in the middle of Pennsylvania. I didn't think about that very much as sporadic showers moved through the middle of the state with alternating heavy downpours and lighter showers. I heard no thunder and there was hardly any wind. The visible picture below shows the impressive amount of cloudiness across central and eastern Pennsylvania and New York plus New Jersey and New England.
Suddenly, however, there was a brief squall with wind gusts to 20 to 30 mph at my location. I happened to be running a time-lapse camera and it caught the event pretty well. View the turmoil here:
Late in the afternoon, showers and thunderstorms extended from central New England to northeast Virginia. The following set of maps show the Nam model predictions from Thursday night into the weekend.
Friday and Saturday should turn out to be pretty nice days across most of the Northeast. The days will be warm but with lower humidity, and the nights will be cooler.
On Sunday, it looks like another cool front will come into the Northeast with some showers and maybe a thunderstorm.
If this was wintertime, you would be feeling Arctic winds, snow flurries and squalls with an upper air pattern looking like this. However, we know that it is the end of July, and it's not going to be blustery and cold and it's definitely not going to snow for quite some time!
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Weather Blogs / Northeast US weather
Cooler, drier air coming to the Northeast as July ends
Updated Jul 29, 2021 8:09 PM EST
On Wednesday night, thunderstorms developed in the upper right Great Lakes region and moved southeastward. The picture above shows the mesoscale convective complex, which looks in some ways like a hurricane over land. This is what the radar looked like before midnight when 50 to 60 mph wind gusts came through parts of central Wisconsin.
By Thursday morning, the system had weakened. The following two maps showed the pressure analysis at noon and 7 p.m. on Thursday. There had been some thinking that the storms could re-intensify along a warm frontal boundary that was just ahead of the approaching cold front. I sketched in the warm front on the first map but did not do so on the second map. You may be able to see where the front was on the second map by where the isobars turned around. In any case, the front had not moved much and that is typical east of the Appalachians, where there is some cool air damming because of the effect of the mountains and the ocean which is cooler than the adjacent land.
At mid-morning Thursday, the sun was largely hidden by a deck of high cloudiness over a central Pennsylvania. The effect was not that much different than that of smoke dimming the sun the previous week.
At around the same time Thursday at midday, you can see the precipitation mostly extending from northern New York state to northwest Pennsylvania. In their discussion the day before, the NWS storm prediction center noted that there was considerable uncertainty about how much intensification the thunderstorms would undergo the next day. As it turned out, the cloudiness out ahead of the remaining precipitation held down the temperature just enough to prevent a widespread and deadly severe thunderstorm outbreak. I don't want to imply that nothing bad happened. It's just that less happened, in this case, than if there had been a lot of hot sunshine before the precipitation arrived. The following maps show the progression of the pre-frontal showers and thunderstorms from midday through mid-afternoon.
Note on the map above there's a little spike of extra intensity in the middle of Pennsylvania. I didn't think about that very much as sporadic showers moved through the middle of the state with alternating heavy downpours and lighter showers. I heard no thunder and there was hardly any wind. The visible picture below shows the impressive amount of cloudiness across central and eastern Pennsylvania and New York plus New Jersey and New England.
Suddenly, however, there was a brief squall with wind gusts to 20 to 30 mph at my location. I happened to be running a time-lapse camera and it caught the event pretty well. View the turmoil here:
Late in the afternoon, showers and thunderstorms extended from central New England to northeast Virginia. The following set of maps show the Nam model predictions from Thursday night into the weekend.
Friday and Saturday should turn out to be pretty nice days across most of the Northeast. The days will be warm but with lower humidity, and the nights will be cooler.
On Sunday, it looks like another cool front will come into the Northeast with some showers and maybe a thunderstorm.
If this was wintertime, you would be feeling Arctic winds, snow flurries and squalls with an upper air pattern looking like this. However, we know that it is the end of July, and it's not going to be blustery and cold and it's definitely not going to snow for quite some time!