Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Fri Apr 09 2021 Valid 12Z Mon Apr 12 2021 - 12Z Fri Apr 16 2021 ...Central Rockies/High Plains Heavy Snow Threat next week... ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a blend of best clustered guidance from the 18 UTC GFS/GEFS mean, the 12 UTC ECMWF/ECMWF ensemble mean and the 01 UTC National Blend of Models days 3-7 (Monday-next Friday). Applied most blend weighting to the GFS/ECMWF early next week and gradually shifted focus to the ensemble means into later next week consistent with slowly building forecast spread in a pattern with good guidance continuity and predictability. Latest 00 UTC guidance overall remains in line with this scenario. ...Weather/Hazards Highlights... An amplifying upper trough/closed low will dig and settle over a cooled West next week to the lee of an amplified and slow moving eastern Pacific to western Canadian upper ridge in a blocky pattern. Expect some deformation and terrain enhanced precipitation over the Great Basin, but there is a threat for protracted periods of heavy snows over the Central Rockies/High Plains as enhanced by upslope as ample Canadian surface high pressure digs and settles southward in an airmass inherent with 10-20F below normal temperature anomalies next week. Meanwhile, complex northern stream closed low energies over the Upper Midwest/Great Lakes Monday will struggle to consolidate and shift downstream to off the Mid-Atlantic coast late next week, blocked by a closed low slowly retrograding from the Canadian Maritimes. Moderate rains will accompany the path of this system early next week before losing frontal convergence, with some wrap-back snows possible for the Upper Midwest. A wavy trailing front will settle over The South/Gulf of Mexico and offers potential for some periods with moderate to heavier downpours next week with a changing multi-day focus over the Southern Plains, Lower Mississippi Valley and the Gulf Coast states/Florida as uncertain ejecting southern stream impulses locally focus lift and moisture. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php 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