US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 422 PM EDT Thu Oct 22 2020 Valid Sunday October 25 2020 - Thursday October 29 2020 Hazards: - Heavy precipitation across portions of the Southern Rockies, the Central Plains, and the Southern Plains, Mon-Wed, Oct 26-Oct 28. - Heavy rain across portions of the Central Plains, the Mid-Atlantic, the Lower Mississippi Valley, the Central Appalachians, the Great Lakes, the Middle Mississippi Valley, the Northeast, the Southern Plains, and the Ohio Valley, Sun-Mon, Oct 25-Oct 26. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Tue-Wed, Oct 27-Oct 28. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Thu, Oct 29. - Heavy snow across portions of the Central Rockies, the Central Plains, the Central Great Basin, and the Southwest, Sun-Mon, Oct 25-Oct 26. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Mon-Wed, Oct 26-Oct 28. - Flooding occurring or imminent across portions of the Southeast. - Flooding likely across portions of the Southwest. - High winds across portions of the Central Great Basin and California, Sun-Mon, Oct 25-Oct 26. - Much below normal temperatures across portions of the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, California, the Northern Great Basin, the Upper Mississippi Valley, and the Pacific Northwest, Sun-Wed, Oct 25-Oct 28. - Much below normal temperatures across portions of the Central Rockies, the Central Great Basin, the Southern Rockies, California, the Southern Plains, and the Southwest, Mon-Wed, Oct 26-Oct 28. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Lower Mississippi Valley, the Great Lakes, the Southern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Mon-Thu, Oct 26-Oct 29. - Much below normal temperatures across portions of the Central Plains, the Northern Plains, the Great Lakes, the Central Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Sun-Thu, Oct 25-Oct 29. - Enhanced wildfire risk across portions of California, Sun, Oct 25. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Mon, Oct 25-Oct 26 and lower Alaskan Panhandle, Sun-Thu, Oct 25-Oct 29. Detailed Summary: An Arctic outbreak is set to plunge much of the west-central U.S. into a wintry like pattern this weekend and into the first half of the upcoming week. An impressive upper trough will dig south across the Intermountain West eventually reaching the Southwest next Monday and Tuesday. An injection of frigid temperatures will overtake the Northwest, the Rockies, and the Great Plains this weekend and the first half of next week. Much below normal temperatures will also spread into the Midwest Latest NDFD forecast suggests numerous daily record cold max/min temperatures may be broken. Sub-zero temperatures are a good bet across the northern Rockies and High Plains where bitterly cold wind chills of -10 to -20 degrees are possible. The coldest temperatures are likely to occur where fresh and deep snow pack is present. Speaking of which, a late October snow storm looks to blanket much of the Intermountain West, including low lying valleys, in snow with the higher elevations most at risk for significant snow accumulations. Expect numerous travel delays in these areas which combined with gusty winds may lead to near whiteout conditions Sunday and into Monday. How long the snow threat last in the Four Corners region next week is dependent upon what happens when the jet stream pattern lifts north and an intense ridge builds over the Northwest. This should force a cut-off upper low to take shape and keep mountain snow and inclement weather in the forecast through mid-week. A heavy precipitation area has been introduced to parts of the southern High Plains as there could be a series of potential scenarios. The first is the free-falling temperatures and over-running of southwest flow aloft may support heavy wintry precipitation across eastern New Mexico, western Oklahoma, and the Texas Panhandle. Should the low remain slower though, the threat for heavy rain and thunderstorms, or a heavy wintry mix in some cases, could transpire instead. Either way, the opportunity is there for disruptive precipitation amounts. Farther west in California, as the base of the trough swings through the Great Basin on Sunday, intense low-mid level winds will be embedded within the base and the backside of the upper trough. Combined with a very strong surface high pressure diving south over the Northwest, this may generate high winds in the northern Sierra Nevada and potential for downsloping winds in the Sacramento Valley. As a result, High Winds and Fire Weather hazards are in place. It is possible for favorable fire weather conditions in parts of central and southern California late Sunday and into Monday as well. In the East, upper level ridging over the Southeast is likely to keep most of the region (as well as the Mid-Atlantic) under the influence of a persistent above normal temperature regime. Sunday looks to be a brief break in the abnormally warm temperatures in the norther Mid-Atlantic, but a warm-up arrives quickly on Monday as a low pressure system tracks into the eastern Great Lakes and a warm front tracks through northern New England. Some rain and mountain snow is possible in across northern New England on Monday, but the primary precipitation type ahead of an approaching cold front from the mid-Mississippi Valley to the Ohio Valley and northern Mid-Atlantic. As the upper low in the Southwest gradually advances east into the South Central U.S. around mid-week, rich moisture from the Gulf of Mexico should stream north from Texas to the Lower Mississippi Valley. This could lead to a threat for excessive rainfall and some severe storms in parts of these regions. Timing and totals are still subject to change in the days 6-7 time frame due to the lower confidence in when the upper trough exits the Four Corners region and how slowly it progresses through the southern Plains. Across Alaska, an area of low pressure in the Gulf of Mexico will head towards the southeast mainland and be preceded by a southwesterly flow of very moist Pacific air. Expect heavy precipitation from southeastern portions of the mainland (Prince William Sound eastward) through Yakutat starting late in the weekend and continuing through Monday. The heaviest precipitation will then spread southward across nearly the entire Panhandle during Monday into Tuesday. Heaviest rainfall will generally be along the coast, with snow over higher elevations. A second round of heavy precipitation is possible across the Panhandle towards mid-late week as there may be another storm system that takes aim at the region. Mullinax