A front extending from the Lower Great Lakes roughly southwestward to the Southern High Plains will move slowly eastward off the East Coast by Saturday evening.
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Showers and thunderstorms will develop along and ahead of the boundary from the East and the Midwest through Friday; some of these thunderstorms will be severe.
Therefore, the SPC has issued an Enhanced Risk of severe thunderstorms over parts of Lower Great Lakes/Central Appalachians through Friday morning.
The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and a few tornadoes.
In addition, there is an increased threat of hail two inches or greater over parts of western Pennsylvania and adjacent parts of Ohio/New York State.
In addition, the thunderstorms will have heavy rain associated with them.
Therefore, the WPC has issued a Marginal Risk of excessive rainfall over parts of the Northeast to the Mid-Atlantic/Southern Appalachians through Friday morning.
The associated heavy rain will create localized areas of flash flooding, affecting areas that experience rapid runoff with heavy rain.
Furthermore, there is a Slight Risk of severe thunderstorms along parts of the cold front over parts of the Middle Mississippi Valley/Central Plains through Friday morning.
The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and a few tornadoes.
In addition, there is a Slight Risk of excessive rainfall over parts of the Middle Mississippi Valley/Central Plains through Friday morning.
The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable.
On Friday into Saturday morning, the severe thunderstorm threat decreases slightly as the front settles southward over the southern Mid-Atlantic/Southeast.
Therefore, the SPC has issued a Slight Risk of severe thunderstorms over parts of the southern Mid-Atlantic/Southeast.
The hazards associated with these thunderstorms are frequent lightning, severe thunderstorm wind gusts, hail, and a minimal threat of tornadoes.
Meanwhile, a second front over the Northern Intermountain Region/Great Basin will slowly move eastward to the Northern Rockies/Great Basin/Southern California and stall by Saturday.
The system will produce rain over parts of the Northwest on Thursday and expand into the Northern Intermountain Region on Friday with embedded thunderstorms.
Moreover, early-season monsoonal moisture will stream into parts of the Central/Southern Rockies and Southwest Thursday evening into Saturday.
As a result, diurnally driven showers and thunderstorms will also develop over the area through Saturday.
In addition, dangerous heat will continue over the Southeast, with Excessive Heat Watches, Excessive Heat Warnings, and Heat Advisories currently extending from the Middle Mississippi Valley to the Southeast.
Upper-level ridging will contribute to record-breaking temperatures across the region for Thursday into Friday.
This heat, combined with high humidity, will likely produce heat indices well into the triple digits over the Southeast Thursday and Friday.
Upper-level troughing will force the upper-level ridging to move southward on Friday, allowing temperatures to moderate on Saturday.
Additionally, on Thursday and Friday, dry conditions and gusty winds will produce a Critical Risk of fire weather over parts of the Great Basin and Southwest. ■
A strong storm that originated over the Pacific has tracked through the Great Basin and is currently transitioning across the Rockies to redevelop across the central High Plains later today into early Saturday morning.