Extended Forecast Discussion NWS Weather Prediction Center College Park MD 612 PM EDT Tue Apr 07 2020 Valid 12Z Fri Apr 10 2020 - 12Z Tue Apr 14 2020 ...Rapidly deepening coastal storm with heavy snows/high winds moves off New England Fri... ...Heavy rainfall/runoff/winds threat for the South then Appalachians/East Coast Sat-Mon... ...Heavy snow threat/cold winds to spread southward over the Rockies/High Plains Sat-Tue... ...Overview and Guidance/Predictability Assessment... The Weather Prediction Center (WPC) medium range product suite was primarily derived from a blend of the 00 UTC ECMWF ensemble mean and to a lesser extent the 06 UTC GEFS mean, WPC biased corrected QPF, and the National Blend of Models (NBM). Deterministic models have been showing less than stellar run to run continuity much beyond day 3 recently, so an ensemble mean forecast strategy was preferred through the Easter holiday weekend into next week in an active and stormy weather pattern in a nation with a lot going on. Despite model continuity issues and greater than normal uncertainty with system details, there is still a good model and ensemble guidance signal for an emerging heavy rainfall/runoff and strong to severe weather threat for the South and then up the East Coast Sat-Mon. There is a developing heavy snow/cold surge threat for the northern and central Rockies/High Plains, with cold air set to spread over the lower 48 next week and lingering into Climate Prediction Center (CPC) time scales. These threats and messaging have been collaborated with affected NWS regions/offices. ...Weather/Hazard Highlights... Wrap-around heavy snows/high winds will linger over New England Fri as a rapidly deepening low pressure system/storm pulls away from the region as a maritime risk as per the Ocean Prediction Center (OPC). Much farther south, expect a heavy rainfall/runoff threat along with the potential for strong to severe weather as suggested by the Storm Prediction Center (SPC) will become increasingly widespread across the South this weekend as deepened Gulf of Mexico moisture and instability returns inland ahead of a ejecting/amplified southern stream upper trough/low and well organized surface based low/frontal system tracks across the region. As the main low pressure system continues to deepen and move north along/near the Eastern Seaboard late Sun into Mon, rain and an enhanced wind risk should also overspread the Appalachians, Mid-Atlantic and Northeast as enhanced by Atlantic moisture. Depending on the exact track and intensity of the surface low, there is some possibility for gusty winds along the New England coast and enhanced snowfall across interior/high elevation areas of northern New England. However, forecast confidence is not sufficiently high at this time to place too much confidence in the specific system aspects. Upstream, a northern stream shortwave expected to dive into the northwestern/north central U.S. late in the week will be accompanied by a cold front and digging cold air mass. This system will increase a threat for heavy snow across the northern and central Rockies/High Plains by the weekend as enhanced by upper support and low level upslope flow. Schichtel 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 rain across portions of the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Sat-Tue, Apr 11-Apr 14. - Heavy rain across portions of the Northeast, Mon-Tue, Apr 13-Apr 14. - Heavy snow across portions of the High Plains, the Rockies, and the Central Great Basin Sat-Mon, Apr 11-Apr 13. - Flooding possible across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding occurring or imminent across portions of the Mississippi Valley, the Northern Plains, the Tennessee Valley, the Southern Plains, and the Ohio Valley. - Much below normal temperatures across portions of the High Plains, the Rockies, the Mississippi Valley, the Central Great Basin, and the Plains, Sat-Tue, Apr 11-Apr 14. 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