US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 232 PM EST Tue Dec 14 2021 Valid Friday December 17 2021 - Tuesday December 21 2021 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sat, Dec 18. - Heavy rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Southern Plains, and the Ohio Valley, Fri-Sat, Dec 17-Dec 18. - Heavy rain across portions of the Southern Plains, Sat-Sun, Dec 18-Dec 19. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Sun, Dec 18-Dec 19. - Heavy snow across portions of mainland Alaska, Fri-Sat, Dec 17-Dec 18. - Heavy snow across portions of mainland Alaska, Sun-Mon, Dec 19-Dec 20. - High winds across portions of mainland Alaska and the Aleutians, Fri-Sat, Dec 17-Dec 18. - High winds across portions of mainland Alaska, Fri-Mon, Dec 17-Dec 20. Detailed Summary: The medium range period (Friday, December 17 - Tuesday, December 21) will feature multiple weather systems and potential hazards across the Lower 48. Starting with the eastern half of the country, a stalled frontal boundary is forecast to extend from the Southern Plains to the Ohio Valley on Friday and Saturday. Periods of showers and thunderstorms will likely lead to instances of heavy rain and isolated flooding concerns here, roughly between northern Arkansas and southern Ohio. Widespread rainfall amounts over 1 inch appear probable in this area, with localized amounts up to 3 inches possible. A wave of low pressure is then expected to form along this boundary and race northeastward on Saturday, allowing a cold front and associated precipitation to push southward and into the Gulf Coast States by Sunday. A few repeating rounds of heavy rain may linger over eastern Texas and the western/central Gulf Coast into Sunday. Meanwhile, the aforementioned low pressure system is forecast to enter the Northeast by Saturday night and could produce a wintry mix/swath of snow throughout New England and the Interior Northeast into Sunday morning. Current snowfall projections don't appear high enough to reach winter storm warming criteria, but residents should continue to monitor forecasts over the next couple of days. The next potential weather system to impact the East will be associated with an upper-level trough approaching the region on Monday and interacting with a stalled frontal boundary along the Gulf Coast. Guidance currently hints at the potential for heavy rain across the Southeast on Monday, which would be welcome given the recent dryness over the last month. For the western U.S., a potent storm system entering the Pacific Northwest on Saturday will lead to potentially heavy snow across the Olympic and Cascade mountains, with heavy rain possible along the Washington and northern Oregon coastline. Precipitation is then expected to enter the Northern Rockies this weekend. A majority of the heavy snowfall is forecast to impact northern Idaho, northeast Oregon, and northwest Montana, where over a foot of snow is not out of the question by Sunday. By early next week, an upper-level low lingering off the West Coast may funnel an axis of moisture into portions of northern California. A heavy rain/precipitation area was not added to the hazards chart today due to rather large uncertainty regarding the timing of this moisture plume, but it is likely a highlighted area will be needed in future forecast cycles. The temperature outlook for this time period displays well above average temperatures over the south-central U.S. on Friday and Southeast/Mid-Atlantic into Saturday. Above average temperatures also appear to make a return to the southern/central High Plains by Sunday. Abnormally cold weather will be confined to the Intermountain West an far Northern Plains. Single digit lows are forecast over parts of Nevada, Utah, and western Colorado on Friday and Saturday as a strong high pressure system settles over a fresh snowpack. Meanwhile, subzero low temperatures are forecast across northern Montana, northern Minnesota, and North Dakota. These temperatures are around 10 degrees below average for this time of year, but not considered hazardous at this time. For Alaska, a busy weather pattern is set to impact western sections of the state. A low pressure system located over the Bering Sea is expected to produce high winds (gusts >50 mph) along the Aleutian Islands, including periods of heavy snow across Southwest Alaska through Saturday which may prompt blizzard conditions. A separate system is then forecast to bring a plume of moisture and warmer temperatures across the western half of Alaska on Sunday. In fact, temperatures may surge 20+ degrees above average for much of western, central, and northern Alaska. Heavy snow is also likely along the southern half of the Seward Peninsula and just south of the Brooks Range on Sunday and Monday. Heavy snow is possible across the Interior as well, but confidence is slightly lower and thus a heavy snow area was not included in today's hazards chart. Snell