Following a strong line of showers and thunderstorms that will move through eastern portions of the Northeast Tuesday afternoon and evening, several days of relief from both the heat and humidity will follow as a strengthening Canadian high pressure sweeps through the Northern Tier of the US mid to late-week.
High pressure contains sinking air. This sinking air generally allows for little cloud cover and dry weather. That will be the case with this Canadian high, brining seasonably cool conditions and making for a very-welcome break from the heat.
While storms affect parts of the Northeast on Tuesday, high pressure will be centered over the Upper Midwest, giving way to sunny skies and high temperatures in the 70s and 80s, about 5 degrees below average for most areas. Along parts of the lakefront, however, high temperatures will struggle to surpass the 70 degree mark during the day. This high pressure will not only keep the Upper Midwest dry but the entire Midwest, northern Plains, Great Lakes, and Ohio River Valley as well.
Then on Wednesday, the Northeast will get the chance to enjoy some beautiful mid-July weather. Instead of scorching temperatures in the 90s during typically the hottest time of the year, highs will only be in the 70s and 80s. That’s up to 10 degrees below average inland, while it’s about average at the coast. Temperatures will also remain below average but very comfortable back toward the Midwest. A few showers and thunderstorms may begin to enter the picture west of the Mississippi River as humidity and moisture streams back in on the backside of the high pressure.
On Thursday, the 1020 millibar high pressure will become centered over the Northeast, making it quite difficult for a cloud to be seen in the sky. Under this high pressure, the Northeast will see seasonable temperatures as highs top off into the 80s in most areas. Wirth the exception of the higher elevations of the Appalachian Mountains, highs will also hold into the 70s and 80s in the Midwest, but showers and storms will become more prevalent, mainly in northern portions of the region. This includes Minnesota, Iowa, Missouri, Wisconsin, and Illinois. A few of these storms may even be severe.
By Friday, temperatures will rise somewhat while humidity remains low in the northern Mid-Atlantic and all of New England. Meanwhile in the Midwest, dew points mainly into the 60s will be affecting the region, indicating a sticky and moist air mass. As a synoptic-scale storm system moves through, that will allow for another day of showers and thunderstorms across most of the region, including the Great Lakes and Ohio River Valley.
High pressure will stay in control for one last day for most of the Northeast on Saturday, allowing for sunny or partly cloudy skies with high temperatures in the 80s and low humidity. West of the Appalachian Mountains, heavy showers and strong thunderstorms will be affecting the Great Lakes and Ohio River Valley. The Midwest will begin to clear out while the Northeast prepares for the storms on Sunday, marking an end to the dry weather and air.
This all comes as a pattern change takes place, allowing for a more active and cooler weather pattern for much of the East, especially the interior, through at least the end of August.