National Weather Summary for Wednesday, December 20, 2017
by David Moran, on Dec 20, 2017 11:01:02 AM
An upper level system will bring snow from the Northern Rockies into the Upper Midwest on Wednesday. Snow is forecast for portions of the Central Rockies through Thursday as a cold front moves through the region. Heavy to excessive rainfall will continue for the Carolinas. Thunderstorms are expected to continue across portions of the Southeast.
- Snow through Friday from the Northern Rockies into the Northern Great Lakes
- Potential for Snow across the Central Rockies Wednesday into Thursday
- Thunderstorms for the Southeast on Wednesday
- Excessive Rainfall Wednesday for the Carolinas
- Snow Friday across the Northeast
- Excessive Rainfall across the Tennessee River Valley on Friday
Snow through Friday from the Northern Rockies into the Northern Great Lakes
A strong upper level trough will move eastward from the Pacific Northwest into the Rockies and Northern Plains through Thursday. At the surface, an area of low pressure will move southeastward across Montana into the Front Range, bringing moderate to heavy snowfall across portions of Montana and the higher elevations of the Rockies. Snow accumulations of 4-8 inches are forecast in the lower elevations of Montana and in excess of 12 inches in the higher elevations. Further east across the Northern Plains, 3-6 inches with locally heavier amounts in excess of 8 inches are expected,
Major Cities in Region: Great Falls, MT, Minot, ND, International Falls, MN, Minneapolis, MN
Potential for Snow across the Central Rockies Wednesday into Thursday
An area of low pressure moving through the region will bring light to moderate snow Wednesday into Thursday. Snow accumulations of 2-4 inches are forecast in the valleys and 5-10 inches in the higher elevations with locally higher amounts in excess of a foot. Across Wyoming, winds will range 20-30 mph with higher gusts in excess of 40 mph, allowing for blowing snow and near zero visibilities.
Major Cities in Region: Salt Lake City, UT, Aspen, CO, Casper, WY, Cheyenne, WY
Thunderstorms for the Southeast on Wednesday
Ongoing thunderstorm activity across Mississippi and Alabama will continue to track eastward throughout the day. Conditions ahead of this activity will support the risk for damaging winds and isolated tornadoes, especially across portions of southern Mississippi and into southern and central Alabama.
Major Cities in Region: Hattiesburg, MS, Birmingham, AL, Montgomery, AL, Columbus, GA, Atlanta, GA, Macon, GA
SPC Convective Outlook for Wednesday
Excessive Rainfall Wednesday for the Carolinas
Widespread moderate to heavy rainfall will continue across the Carolinas along a warm front associated with an area of low pressure across the Deep South. With ample moisture and lift, rainfall amounts of 0.50-1.50 inch with locally higher amounts in excess of 2 inches are expected, allowing for the potential for flooding and runoff.
Major Cities in Region: Knoxville, TN, Charlotte, NC, Columbia, SC, Raleigh, NC, Charleston, SC
Excessive Rainfall Risk Outline for Wednesday
Snow Friday across the Northeast
An area of low pressure in the Ohio River Valley and Great Lakes will track northeastward toward Quebec on Friday. As this occurs, ample moisture will interact with widespread cold air across portions of Maine, northern New York, Vermont, and New Hampshire resulting in some wintry precipitation. Snowfall accumulations of 3-6 inches with locally higher amounts in excess of 8 inches are forecast. In addition, ice accumulations up to a tenth of an inch will be possible for southern portions of the region.
Major Cities in Region: Buffalo, NY, Syracuse, NY, Albany, NY, Boston, MA, Augusta, ME, Bangor, ME, Caribou, ME
Significant Snowfall Risk Outline for Friday
Excessive Rainfall across the Tennessee River Valley on Friday
Moisture moving northward ahead of a cold front will allow for moderate to heavy rainfall across the Tennessee River Valley on Friday. With the cold front moving slowly eastward and ample moisture in place, rainfall amounts of 2-4 inches with locally higher amounts in excess of 5 inches are forecast. This will result in a potential for widespread flash flooding and excessive runoff.
Major Cities in Region: Little Rock, AR, Memphis, TN, Nashville, TN, Louisville, KY, Cincinnati, OH
Excessive Rainfall Risk Outline for Friday
A Look Ahead
An area of low pressure will continue to move northeastward on Saturday, bringing rain to much of the East Coast. Across the Southeast, moderate to heavy rainfall is expected ahead of the associated front. Going into Christmas Eve and Day, snow is forecast across the Northeast. By Christmas Day, snow will spread into the Mid Atlantic.
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