US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 338 PM EDT Tue Apr 09 2019 Valid Friday April 12 2019 - Tuesday April 16 2019 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Tue, Apr 16. - Heavy precipitation across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, and the Northern Great Basin, Mon, Apr 15. - Heavy rain across portions of the Pacific Northwest, Tue, Apr 16. - Heavy rain across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Great Lakes, the Middle Mississippi Valley, the Northeast, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Sat-Sun, Apr 13-Apr 14. - Heavy snow across portions of the Central Plains and the Southern Plains, Sat, Apr 13. - Severe weather across portions of the Lower Mississippi Valley and the Southern Plains, Sat, Apr 13. - Severe weather across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sun, Apr 14. - Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Northern Plains, the Tennessee Valley, the Pacific Northwest, the Northern Rockies, the Middle Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, the Southern Plains, and the Ohio Valley. - Flooding likely across portions of the Upper Mississippi Valley, the Pacific Northwest, the Northern Plains, the Northern Great Basin, and the Tennessee Valley. - High winds across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Fri, Apr 12. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Northern Plains, the Southern Rockies, the Upper Mississippi Valley, and the Southern Plains, Fri-Sun, Apr 12-Apr 14. Detailed Summary: The powerful storm system expected to bring widespread heavy snow and blizzard conditions to parts of the Plains states during mid-week will be lifting up into the Upper Mississippi Valley by the beginning of this forecast period (Friday, April 12). The storm will be in its weakening phase, but there is still a strong enough pressure gradient on the northern and western side of the low to support a threat for high winds. Sustained winds up to 30 knots, with gusts to around 40 knots are expected, mainly early in the day Friday across the eastern Dakotas (where visibilities may be lowered by blowing snow), eastern Nebraska, southern Iowa. Also in this system's wake is a very cool Canadian air mass, with much below normal temperatures likely across the Plains and sections of the Upper Mississippi Valley from Friday through the weekend. The core of the most anomalously cold air will be across north-central Plains on Friday, then shift southward into the southern Plains Saturday. Temperatures will begin to moderate somewhat during Sunday. Farther upstream, the next upper level trough will be diving into the southern Rockies Friday and emerging into the Plains during Saturday. A surface frontal boundary associated with the abovementioned storm will serve as a focusing mechanism for deep Gulf of Mexico moisture and support heavy rainfall developing over the southern Plains and lower-mid Mississippi Valley during Saturday. Overall, there is pretty good agreement among the models for areal average rainfall totals in the 2-4 inch range across this region by Sunday morning. Farther north and west in the colder air entrenched over the Texas and Oklahoma panhandles, models are indicating temperatures will be marginally cold enough to support a period of moderate to heavy snowfall. There's some question as to whether there will be enough QPF to result in significant accumulations, but opted to add this hazard area given that it's getting late in the season for snow this far south. This system is expected to quickly lift northeastward through the Tennessee and Ohio Valleys during Sunday, with Gulf moisture and a pre-frontal unstable air mass resulting in organized convection across the mid-Atlantic and southeastern states. In general, rainfall amounts will mostly be lower than during Saturday as the system is moving along relatively quickly and the inflow of moisture will be a bit weaker. Nonetheless, total amounts of 1-2 inches are likely along the front, with higher amounts possible across the Southeast where a surface wave along the front may enhance lifting. In addition to the heavy rain threat, there's potential for severe weather across the lower Mississippi Valley and Southeast over the weekend ahead of the surface front. In the West, a series of systems will move across the Pacific Northwest and northern/central Intermountain region during this forecast period. It's hard to pinpoint which, if any, of them will be accompanied by especially heavy precipitation given the degree of model uncertainty with these features. Model consensus generally supports a marginal threat for heavy precipitation (mostly snow) across northern Utah and central Wyoming on Monday as an upper trough amplifies after crossing the West Coast. Across western Washington, there are indications that a system moving into the region Tuesday may tap into a little bit of deeper Pacific moisture and bring a chance for locally heavy valley rain/mountain snow. Confidence, however, is very low with the placement of this hazard. Over Alaska, the pattern looks rather quiet as the main polar jet steers storms south of the state. In Hawaii, there appears to be a threat of heavy rain during this Friday and Saturday over and near the Big Island as strong trade winds combine with increased instability under an upper-level low drifting westward across the island chain. Klein