An amplifying upper-level trough digging into the western U.S. is gradually pushing the unsettled weather out of the Pacific Northwest into the Intermountain region.
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The interaction of the upper trough with colder air filtering southward is setting the stage for a long-duration snow event from the central Rockies and down into the Four Corners over the course of the next few days.
The precipitation will first be focused over the central Rockies from this evening into Thursday when wet snow is forecast to be the heaviest across the Front Range of Colorado where a few feet of new snow could fall.
Lesser amounts are expected in adjacent areas but one to two feet of wet snow is possible down into the High Plains at locations such as Boulder and Denver, Colorado.
Hazardous to very difficult travel is expected as heavy snow and intense snow rates at times (1-2 inches plus per hour) will lead to deteriorating travel conditions beginning Wednesday and Wednesday night across the central/southern Rockies and beginning across the Four Corners region Thursday night.
A second phase of the winter storm will then impact the Four Corners Region beginning Thursday night, as the upper trough closes off into a slow-moving upper low.
Waves of heavy snow will impact the terrain areas north of the Mogollon Rim and northeast toward the San Juans and southern Colorado Rockies.
Snow probabilities for 8 inches are moderate to high (greater than 50%).
Localized totals above a foot are possible for the higher terrain.
On the warm side of the system, low relative humidity and gusty winds will continue to raise the danger of wildfires to locally extreme levels from the Texas Panhandle to western Texas today.
The dry environment in the Plains states will initially limit the formation of showers and some thunderstorms across the mid-Mississippi Valley into the Midwest.
However, as a low pressure system develops and tracks across the central Plains towards the Midwest, influx of moisture from the Gulf of Mexico is forecast to organize an area of enhanced rainfall across Arkansas and neighboring areas Thursday evening into early Friday when severe weather is possible.
The heavy rain and severe weather threat will then shift northeast toward Tennessee by Friday morning as the trailing cold front associated with the low pressure system approaches from the west.
The low pressure system itself will bring widespread moderate to locally heavy rain with a slight threat of severe weather across the Midwest tonight, followed by the southern half of the Great Lakes on Thursday, and into New England Friday morning.
The rain may mix with wet snow over the upper Midwest tonight and over interior New England Friday morning.
As the winter storm develops over the western U.S., much of the eastern U.S. will enter an extended period of very warm and pleasant weather.
High temperatures in the 60s and 70s from the Ohio Valley to the Mid-Atlantic states will be 20-25 degrees above normal for this time of year. ■