US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 300 PM EST Mon Feb 10 2020 Valid Thursday February 13 2020 - Monday February 17 2020 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sat-Sun, Feb 15-Feb 16. - Heavy rain across portions of the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Mon, Feb 17. - Heavy rain across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sun, Feb 16. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Sun, Feb 15-Feb 16. - Flooding possible across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Southern Appalachians, the Southeast, and the Ohio Valley. - Flooding occurring or imminent across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Pacific Northwest, and the Ohio Valley. - Flooding likely across portions of the Southeast and the Mid-Atlantic. - Much below normal temperatures across portions of the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, the Northern Plains, and the Ohio Valley, Thu-Fri, Feb 13-Feb 14. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon, Feb 17. - Much below normal temperatures across portions of mainland Alaska, Thu-Sun, Feb 13-Feb 16. Detailed Summary: The medium range period (Feb 13-17) starts off with a moderately strong low and associated cold front moving quickly toward the eastern seaboard. While snow is expected over portions of northern New England for the first half of Thursday, amounts are not expected to be particularly heavy given the rapid pace of the system. Behind it, a shot of Arctic air will bring a period of much below normal temperatures to the northern Plains/upper Mississippi Valley and western Great Lakes region Thursday, with the core of the coldest air moving into the Ohio Valley and Northeast/mid-Atlantic states on Friday. The greatest temperature anomalies (around 20-25 degrees below normal) will mostly be confined to the upper Mississippi Valley and Upper Midwest, and given the transient nature of the air mass, did not opt to extend the hazard area into the eastern U.S. The next major system will be pushing into the Pacific Northwest during the latter part of the week and is expected to move into the Plains over the weekend. A southerly flow of Gulf of Mexico moisture will lift into the southeastern U.S. ahead of this system and bring the potential for another round of heavy rainfall to areas that have experienced wetter than normal conditions over the past 2-4 weeks. It looks like the greatest threat will be from central Mississippi into northern Georgia on Sunday, where locally 1-3 inches are possible. There are rather large difference among the various model solutions and little continuity from model run to model run handling this system, so confidence is lower than average. Farther west, a rather potent short wave trough and associated area of low pressure will move into the Pacific Northwest during Saturday. The latest guidance indicates that this feature will tap into subtropical Pacific moisture and thus is likely to bring a period of heavy precipitation to western Washington and Oregon (rain at the coast an in valleys...snow at the higher elevations). Local amounts of 2-3 inches are likely in favored upslope regions. The system is expected to amplify as it moves inland, so while the amount of moisture available will be less (due to the Cascades), there should be enough energy to produce moderate to heavy snowfall to sections of northeastern Oregon and the higher terrain in northern/central Idaho during the weekend. This activity will likely advance into the central Rockies and eastern sections of the Great Basin Sunday night - Monday, but it's a little too early to tell whether there will be enough moisture to produce heavy mountain snows. As the upper troughing moves across the West on Monday, low pressure developing in the High Plains will again draw Gulf moisture northward, with organized showers and thundershowers developing over the southern Plains/lower Mississippi Valley. Right now, it appears that this precipitation will be focused farther west than the activity expected in the southeast over the weekend, but there's a lot of uncertainty at this time range, so we'll need to monitor this feature closely through the week. Across Alaska, below to much below normal temperatures are expected through the period across much of the central and northern part of the mainland as an Arctic air mass remains well-entrenched. Farther south, a potentially very strong low will spread heavy rain and snow, along with locally high winds, into south central and southeastern sections of the mainland and northern/central Panhandle by early next week. The forecast evolution of this low involves phasing between the arctic and polar jet streams, something that is often quite difficult to forecast with confidence at this long a time range. So, we'll be watching future model runs to determine if there is consistency from run to run. Klein