A front extending from the Upper Great Lakes to the Northern High Plains will move to the Northeast and stall out over the Great Lakes to the Southern Plains through Monday.
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Moisture pooling along the front will aid in producing showers and thunderstorms over parts of the Great Lakes to the Northern Rockies that will move with the front through Monday.
Some of the storms will produce heavy rain.
Therefore, the WPC has issued a Slight Risk of excessive rainfall over parts of the Upper Great Lakes to the Northern Plains through Sunday morning.
The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable.
In addition, some thunderstorms will be severe.
Therefore, the SPC has issued a Slight Risk of severe thunderstorms over parts of the Upper Mississippi Valley through Sunday morning.
The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and minimal risk of tornadoes.
On Sunday, the excessive rainfall threat increases over the Upper Midwest.
Therefore, the WPC has issued a Moderate Risk of excessive rainfall with these thunderstorms over parts of the Upper Great Lakes and Upper Mississippi Valley on Sunday into Monday morning.
The associated heavy rain will create numerous areas of flash flooding.
Furthermore, many streams may flood, potentially affecting larger rivers.
The severe thunderstorm threat decreases to general thunderstorms on Sunday into Monday morning.
However, that may change on Sunday.
On Monday, the excessive rainfall threat moves to Northern New England.
Furthermore, on Saturday into Sunday, showers and thunderstorms over parts of the Northeast to the Central Gulf Coast; some of these storms may produce heavy rain.
Therefore, the WPC has issued a Slight Risk of excessive rainfall over parts of the Mid-Atlantic, Central/Southern Appalachians, and Ohio Valley into Sunday morning.
The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable.
The threat of excessive rainfall decreases slightly on Sunday to a Marginal Risk over this area.
Furthermore, monsoonal moisture will trigger diurnal showers and thunderstorms over parts of the Southwest/Great Basin and the Rockies on Saturday.
As a result, the threat of excessive rainfall increases on Sunday over parts of Arizona, New Mexico, and Colorado.
Parts of this area will experience heavy rain.
Therefore, the WPC has issued a Slight Risk of excessive rainfall over parts of the Southwest and parts of the Central/Southern Rockies from Sunday into Monday morning.
On Monday, the Slight Risk of excessive rainfall continues over parts of the Central/Southern Rockies.
The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable.
Meanwhile, an upper-level high over the Central Plains and Middle Mississippi Valley will aid in allowing temperatures to reach into the hundreds over the region and along with high humidity, have prompted Excessive Heat Warning and Heat Advisories over parts of the Middle Mississippi Valley and Central Plains through Saturday evening.
Furthermore, weak ridging will allow temperatures to rise into the mid to upper nineties over parts of the Pacific Northwest, also prompting Heat Advisories.
In addition, temperatures in the low to mid-nineties and dew points in the upper sixties to low seventies have prompted Heat Advisories over parts of the Northeast Coast to parts of Lake Ontario through Saturday evening, too. ■
An upper level high pressure system is expected to continue aiding well above average and potentially dangerous temperatures throughout the West into the first full weekend of September.