Weather across America

(NATIONAL) Heavy rainfall and flash flooding shift from the Southern Plains to the Central Plains and Gulf Coast, a significant winter storm to likely impact parts of the Central Plains and upper Midwest to see White Christmas and treacherous travel.

Unusually mild temperatures along and east of the Mississippi River with some record-breaking warmth are possible in the Midwest and Great Lakes both Sunday and Christmas Day. Meanwhile, a low pressure system currently developing over the central Plains in conjunction with an amplifying upper-level trough dipping into the northern Plains are setting the stage for more active weather to come across much of the central to eastern U.S. just in time for Christmas holiday activities through the next couple of days.  

Warm and moist air from the Gulf of Mexico is streaming northward across the western Gulf Coast region into the southern and central Plains ahead of the developing low pressure system, producing widespread moderate to heavy rainfall from the upper Texas coast to the Louisiana coast while bands of heavy rain with embedded thunderstorms are marching eastward across Kansas, Oklahoma and Texas ahead of a cold front.  

A cold air mass from Canada is dipping into the northern portion of the U.S. Areas of snow over the central Rockies are beginning to extend northeast into the central Plains toward the northern Plains behind the low pressure system. The complex interaction among the low pressure system, the upper-level trough, and the cold air mass is forecast to kick the entire system farther east toward the Mississippi Valley by tonight, before a more rapid intensification of the low pressure system expected to take place over the western portion of the Midwest by Christmas Day.  

A swath of showers and thunderstorms ahead of the cold front will steadily shift eastward through the Deep South, reaching into the Southeast by Christmas Day. The highest threat of heavy rain and flash flooding is expected to likewise shift eastward while remaining near the Gulf Coast. Less rainfall is expected farther inland. By Monday night into Tuesday morning, the rain and embedded thunderstorms should slow their progression over the Southeast while spreading farther north into the Appalachians, Ohio Valley, and the upper Midwest. 

As the low pressure system begins to intensify more rapidly Monday night into Tuesday morning, strong and gusty winds are expected to increase and expand across the north-central U.S. With cold air being wrapped around this intensifying storm, the chance of a blizzard has continued to increase across the northern Plains, with Monday night to Tuesday morning being the estimated time frame for the most impactful conditions to occur. Over a foot of snow can be expected along with gale force winds in the affected areas.  

In addition, icing will likely be an issue farther east and northeast from the northern Plains to Minnesota during this period. Over the Pacific Northwest, moisture from the next Pacific cyclone is forecast to reach the coast on Christmas Day before reaching well inland by Tuesday morning.  Heavier precipitation totals are forecast for the Olympics and the Cascades. Temperatures will be rather warm for Christmas from much of the Midwest to the East Coast through this extended holiday weekend. 

Record warm minimum temperatures will be common in the Midwest where many low temperatures will be considerably higher than the average high temps for late December. Even parts of the Southern Plains and Middle Mississippi Valley may witness record breaking warm highs and lows on Christmas Eve. By Christmas Day, the most unusually mild temperatures are expected in the Upper Midwest and Great Lakes where highs could range between 15-25 degrees above normal. 

The East Coast will not witness quite the anomalous warmth that the Midwest and Great Lakes will, but daily average temps will still be rather mild and could still range between 10-15 degrees above normal in parts of the Northeast by Christmas Day. In contrast, the central/southern Plains and central/southern Rockies will be the coolest versus normal thanks to a recent cold frontal passage injecting the region with an air-mass that feels a lot more like Christmas compared to their neighbors on the East and West Coasts.