Extended Forecast Discussion NWS Weather Prediction Center College Park MD 450 PM EDT Mon Apr 08 2019 Valid 12Z Thu Apr 11 2019 - 12Z Mon Apr 15 2019 ...Major winter storm tracking from the central Plains into Upper Great Lakes Thu-Fri... ...Heavy rainfall threat from eastern Texas/Lower Mississippi Valley northeastward during the weekend... ...Overview and Guidance Assessment/Preferences... Guidance continues to show a moderately progressive pattern consisting of embedded strong/impactful systems. The forecast based on new 00Z-06Z guidance follows a similar approach to continuity, maintaining greater weight toward ECMWF/ECMWF mean solutions that show greater/slower digging of shortwave energy over the West versus GFS runs late this week followed by somewhat slower ejection into the central/eastern states. Confidence is only moderate at best though. Some 00Z GEFS members were actually quite slow for the system heading into the central/eastern states by late period but the 06Z GEFS has trended faster toward (but not quite to) the ECMWF mean. Also, there has been a notable trend in most guidance toward faster arrival of upstream Pacific energy into the Northwest by around day 6 Sun and the overall pattern suggests the potential for faster progression over the East by early next week. The trend for upstream flow is fairly recent so would like to wait at least another cycle before making any significant adjustments. There is reasonable agreement for the strong storm tracking from the Plains through the Great Lakes late this week. Based on forecast considerations the blend started with an operational model consensus on day 3 Thu, then replaced 06Z GFS input with the 06Z GEFS mean completely by day 5 Sat, followed by a focus primarily on the 00Z ECMWF-ECMWF mean/06Z GEFS mean on days 6-7 Sun-Mon. ...Weather Highlights/Hazards... Consensus still displays a high potential for significant snowfall and strong winds--leading to a period of blowing snow and possible blizzard conditions--from the north-central Plains into the Upper Great Lakes during the latter half of the week. Some strong to severe convection will be possible farther south/southeast in the warm sector. The late week/early weekend system digging into the West will spread rain and high elevation snow across the region. The greatest uncertainty will be the extent and intensity of precipitation over/near Arizona, due to sensitivity to exact amplitude and timing of the upper trough. Ejection of this system will lead to a heavy rainfall threat from eastern Texas and the Lower Mississippi Valley region into parts of the Mid-Atlantic and southern New England, and possibly including the Ohio Valley. The southwestern part of this broad area has the higher confidence due to a period of moist low level Gulf inflow intersecting a front stalled over the Gulf Coast (originally trailing from the late week Plains storm). The Pacific Northwest may see additional precipitation after the late week system in association with frontal systems pushed along by progressive flow aloft. The most extreme temperature anomalies will be of the cold variety over the Rockies/Plains Thu-Sat, behind the initial Plains-Great Lakes storm and then in easterly upslope flow ahead of the next system ejecting out of the West. Some highs may be 20-30F below normal for one or more days. Also during Thu-Sat expect above normal temperatures over the East, especially for morning lows which may be 10-20F above normal at some locations. Expect readings to moderate over much of the Lower 48 by next Mon. Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy precipitation across portions of the Pacific Northwest, Thu, Apr 11. - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sat-Mon, Apr 13-Apr 15. - Heavy precipitation across portions of the Central Rockies and the Central Great Basin, Fri-Sat, Apr 12-Apr 13. - Heavy precipitation across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Thu-Fri, Apr 11-Apr 12. - 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 rain across portions of the Great Lakes and the Ohio Valley, Fri, Apr 12. - Heavy snow across portions of the Northern Rockies, Sun-Mon, Apr 14-Apr 15. - Heavy snow across portions of the Central Plains, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Thu-Fri, Apr 11-Apr 12. - Severe weather across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Great Lakes, the Ohio Valley, and the Tennessee Valley, Thu, Apr 11. - Flooding possible across portions of the Lower 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 Northern Rockies, the Middle Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, the Pacific Northwest, and the Ohio Valley. - Flooding likely across portions of the Northern Plains, the Tennessee Valley, the Pacific Northwest, the Northern Great Basin, the Upper Mississippi Valley, and the Southern Plains. - High winds across portions of the Central Plains, the Central Rockies, the Lower Mississippi Valley, the Northern Plains, the Southern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southern Plains, and the Southwest, Thu, Apr 11. - 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, Thu-Sat, Apr 11-Apr 13. - Enhanced wildfire risk across portions of the the Southern Plains and the Southwest, Thu, Apr 11. - Heavy precipitation across portions of mainland Alaska and the Aleutians, Thu, Apr 11. - High winds across portions of mainland Alaska and the Aleutians, Thu, Apr 11. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml