A deep upper vortex off the Southwestern Canadian/U.S. Pacific Northwest will be moving slowly east southeastward over the next few days.
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This will support a stormy weather pattern for the West coast, inland through the Cascades, Sierra, Great Basin and into the Northern Rockies.
A lead cold front that is moving inland Thursday across the Pacific Northwest will continue to push eastward into the Northern Rockies and southeastward through northern to central California.
This will be followed by a second cold front moving across the same regions later Friday into Saturday.
The combination of the two fronts will produce widespread heavy precipitation from the coastal Pacific Northwest, south into northern California, the Sierra and as far to the south as the central to southern California coast ranges.
The most persistent onshore southwesterly flow level flow in this stormy pattern will be directed into northern to central California.
Very heavy snows likely through the Sierra over the next two days, with snow totals of 4 to 6 feet forecast.
While not as great, heavy snowfall also likely through the Northern Rockies of Idaho, Montana, Wyoming, through the Cascades of Oregon and Washington, the Olympic Range and coast ranges of Washington and Oregon.
Lower elevation heavy rains also likely across the coastal Pacific Northwest, south into the coastal regions of California.
Much of California has seen above average precipitation over the past month, with additional heavy rains increasing the risk of isolated flash flooding.
At the moment, the greatest likelihood of flooding is across northwestern California and in the foothills of the Northern Sierra.
Wet weather also likely from the Central Gulf Coast, northeastward across the Southern Appalachians and much of the Mid-Atlantic.
Heavy rain is expected to develop tonight across the Central Gulf coast and spread east northeastward in association with fast moving areas of low pressure that are forecast to move from the northern Gulf of Mexico, northeastward and of the Carolina coast Friday into Saturday.
While widespread moderate to heavy rainfall totals are expected across these regions, the fast movement of the storm and the fact that much of this region has been dry over the past few weeks, allowing stream flows to fall and soil moisture values to decrease, will be a detriment to widespread flooding issues.
The stormy pattern affecting large portions of the West over the next two days will also keep temperatures below average across much of the West.
The cooler than average temperatures that had spread across much of the central to eastern U.S. behind the strong cold front moving from west to east across these regions over the past few days, will be warming over the next two days.
The core of the much above average temperatures are forecast across the Plains into the Upper Mississippi Valley, where high temperatures are forecast to be 20 to 30+ degrees above average for the end of the week going into the weekend.
A few record high maximum temperatures possible across the Upper Mississippi Valley Friday and Saturday, with more widespread record highs possible by the end of the weekend across the Upper to Middle Mississippi Valley and across portions of the Central and Southern Plains. ■
Modified arctic air combined with a moisture-laden area of low pressure along the Gulf Coast will continue to allow for a broad area of winter weather impacts from the Lower Mississippi Valley to the Southeast today into early Saturday morning.