A deep upper-level low for this time of year is forecast to track across the Northwest over the next couple of days as a low pressure/frontal system tracks just ahead of it in the West.
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These features and ample moisture originating from the tropics will continue to lead to widespread heavy rainfall across portions of the West through tonight and into Thursday.
A large Moderate Risk of excessive rainfall is in effect through tonight for much of the Four Corners states, while a Slight Risk of flash flooding covers the Northern Rockies and a Marginal Risk for isolated flash flooding reaches the Great Basin.
Additionally, there is a threat for severe weather through this evening particularly across south-central Idaho and northern Utah, where Marginal to Slight Risks of severe weather (particularly wind and hail) are in place from the Storm Prediction Center.
The severe threat is expected to diminish by Thursday, but flash flooding will remain a likely hazard.
A Moderate Risk has been added for Thursday for southwestern Colorado, where very heavy rain is forecast, surrounded by a Slight Risk spreading into northern New Mexico.
Farther north, rain totals could cause some flash flooding as well, so another Marginal to Slight Risk is in place for the Northern Rockies to northern High Plains.
Particularly sensitive areas such as burn scars are at risk for flash flooding, along with the possibility for flooding of roads, urban areas, streams, and possibly rivers.
Meanwhile in the East, another frontal system is tracking through the Upper Ohio Valley and Northeast through tonight and into Thursday, leading to scattered thunderstorms there.
The Storm Prediction Center has delineated a Slight Risk of severe weather for parts of Ohio, Pennsylvania, and New York as storms occur in these areas this evening.
Tornadoes, high winds, and hail are all potential threats, and isolated flash flooding is also possible.
Lighter lake-enhanced showers are expected behind the main front on Thursday, but thunderstorms will be pushed southward by a front into parts of the Mid-Atlantic by then, with a lingering Marginal Risk of severe winds.
Elsewhere, scattered showers and thunderstorms are possible across southern Florida, and as the western low pressure system moves into the central U.S.
Friday, this could spread some rain to the Midwest.
The main concern regarding temperatures will be with much above average temperatures for fall over the Southern Plains and Lower Mississippi Valley with an upper high aloft.
Temperatures this afternoon are soaring well into the 90s with some places exceeding 100s for highs, which could set multiple daily records.
Warm temperatures are even spreading into the Ohio and Tennessee Valleys today, but these areas will drop into the 60s and 70s for highs Thursday behind a potent cold front, while the core of this cool air will be across the Central Plains with highs nearing 30 degrees below average.
Farther north, chilly lows have led to the issuance of a Frost Advisory for parts of the Dakotas and northern Minnesota for early Thursday morning.
Friday looks to spread cooler than normal temperatures across most of the Eastern Seaboard as well, with the exception of Florida.
Meanwhile Texas into Oklahoma look to be south of this front and remain well into the 90s through Friday. ■
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.