US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 341 PM EST Tue Jan 26 2021 Valid Friday January 29 2021 - Tuesday February 02 2021 Hazards: - Heavy precipitation across portions of the Mid-Atlantic, Sun-Tue, Jan 31-Feb 2. - Heavy rain across portions of California and the Pacific Northwest, Sun-Tue, Jan 31-Feb 2. - Heavy rain across portions of California and the Pacific Northwest, Sat-Mon, Jan 30-Feb 1. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Southern Plains, the Middle Mississippi Valley, the Great Lakes, and the Ohio Valley, Fri-Sat, Jan 29-Jan 30. - Heavy rain across portions of the Mid-Atlantic, Sun-Mon, Jan 31-Feb 1. - Heavy snow across portions of California, the Pacific Northwest, and the Northern Great Basin, Sat-Mon, Jan 30-Feb 1. - Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sat-Tue, Jan 30-Feb 2. - Heavy snow across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Southwest, Fri, Jan 29. - Heavy snow across portions of the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley, Sat-Sun, Jan 30-Jan 31. - Heavy snow across portions of the Northeast, the Central Appalachians, the Mid-Atlantic, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Sun-Tue, Jan 31-Feb 2. - Flooding possible across portions of the Middle Mississippi Valley. - Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Fri-Sat, Jan 29-Jan 30. Detailed Summary: Hazards during the medium range period will be most prominently featured on the West Coast and extending from the Midwest to the Northeast. Starting out west, the storm system responsible for the copious amounts of rain and mountain snow across California heads east across the Southwest on Friday. Some lingering heavy rain may be possible in the low lying areas of Southern California early in the day, but areas of rain and mountain snow are a welcomed sight in the drought-stricken Southwest. In fact, heavy snowfall is also possible in parts of northern Arizona, southern Utah, and as far north as the Tetons of western Wyoming. Meanwhile, an elongated frontal system stemming from a potent area of low pressure in the Gulf of Alaska will introduce the next round of precipitation to the Northwest this weekend. As the frontal structure begins to lose its punch, a new shortwave trough diving south through the northeast Pacific looks to reinvigorate the lingering baroclinic boundary off the coast. This leads to another surge of warm air advection ahead of the deepening trough and taps into sub-tropical moisture in the East Pacific. The result is another round of heavy precipitation with additional coastal/valley rainfall and higher elevation snowfall from the Pacific Northwest at the end of the month to northern and central California for the start of February. Given recent heavy rainfall in these areas, there is the potential for addition flooding and landslides, along with plenty of mountain snow from the Cascades to the Sierra Nevada. Farther east, a highly anomalous upper trough (-2 to -2.5 STDs) deepens off the New England coast, forcing an fresh injection of frigid Canadian air to infiltrate Northeast. Temperatures are forecast to plummet below zero across northern New England Friday morning and may struggle to get out of the single digits for highs Friday afternoon. The cold temperatures persist into Saturday, as will bitterly cold wind chills that are currently forecast to range between -10 to -25 degrees. Daily temperature anomalies of 12 to 20 degrees below normal are anticipated both Friday and Saturday, which combined with the icy cold wind chills have led to the issuance of a much below normal temperature area. As high pressure settles in across southeast Canada and the Northeast this weekend, the Southwest storm system ejects into the southern Plains. The storm system taps into the Gulf moisture and directs it into the central Plains and mid-Mississippi Valley on Saturday where heavy rain is likely to occur. Meanwhile, the slug of warm/moist air overruns a column of sub-freezing air aloft, leading to a broad area of moderate-to-heavy snow across portions of the Midwest and lower Great Lakes. Model guidance remains at odds over where the axis of heavy snow lines up (GFS/GEFS farther north, Euro/EC mean farther south for example) but both models indicate sufficient moisture and cold air to produce a swath of heavy snow. By Sunday, general model consensus is for a deepening upper trough to move east into the Ohio/Tennessee Valleys while height rises begin to manifest over the Intermountain West. Downstream, a large upper low southeast of Nova Scotia and an upper level ridge over lower Hudson Bay and northern Quebec induce an area of confluent flow over the Northeast and southeast Canada. The GEFS mean is a more progressive storm track with the mid-level low aloft passing over the northern Mid-Atlantic on Monday. In contrast, the Euro ENS is slower and more amplified with a more southerly tracking mid-level low heading for the Chesapeake Bay late Monday. The Canadian ENS is slightly less amplified than the GEFS and also on the progressive side. The reasons for these differences vary wildly: from how they handle the speed/phasing of a trailing upper level disturbance coming out of south-central Canada, to the strength/position of the ridge near Hudson Bay, and the amplitude/placement of the ridge/(trough) in the Southwest/(northwest Atlantic). With that said, the signal from model guidance uniformly shows a potent upper level trough approaching the Northeast with a wedge of cold temperatures entrenched from New England southward into the southern Mid-Atlantic. The amplification of this trough as it reaches the East Coast suggests the growing potential for heavy snow and/or ice from the Mid-Atlantic to New England but the aforementioned unresolved atmospheric features 5-7 days out keeps both confidence in the storm track and resulting impacts low at this time. There is also a chance for heavy rain and thunderstorms over southeast Virginia and eastern North Carolina late in the period. Over Alaska, a strong low pressure system in the Gulf of Alaska makes for a damp and dreary forecast for parts of the Panhandle and along the immediate southern Gulf coast. As the low heads southeast this weekend, an axis of upper level ridging over the Aleutians heads east towards the upper peninsula. Meanwhile, an upper low over northern Alaska will funnel below normal temperatures into western regions this weekend and into the start of next week. While temperatures appear to be quite cold, expected anomalies are forecast to fall just shy of much below normal criteria. As a large cyclone very the northwest Pacific approaches early next week, an influx of Pacific moisture may be aimed at southern Alaska but plenty of spread in model guidance remains, making the potential hazards too low of confidence to include at this time. Mullinax