Extended Forecast Discussion NWS Weather Prediction Center College Park MD 243 AM EDT Sat Apr 10 2021 Valid 12Z Tue Apr 13 2021 - 12Z Sat Apr 17 2021 ...Central Rockies/High Plains Heavy Snow Threat and additional rains for a soggy central Gulf Coast... ...Pattern Overview and Guidance/Predictability Assessment... The WPC medium range product suite for days 3-5 (Tuesday-Thursday) was primarily derived from a composite blend of best clustered guidance from the 12 UTC GFS/ECMWF/Canadian in a pattern with above normal predictability. Opted to use a composite blend of the still compatible 12 UTC GEFS/NAEFS/ECMWF ensemble means days 6-7 (Friday-next Saturday) amid growing forecast spread. This strategy maintains good WPC continuity and remains generally in line with latest 00 UTC guidance, but forecast spread remains less than stellar at longer time frames. ...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 upper ridge in a blocky pattern. There is some uncertainty with trough evolution/undercutting of the shifting ridge later next week as a closed high builds over western Canada. Expect some deformation and terrain enhanced precipitation over the Great Basin, but there is a protracted threat for 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 generally 10-20F below normal temperature anomalies next week. Slow system progression/influence may shift a moderate rain focus over the central Plains late period, but there is uncertainty at these longer time frames. Meanwhile, complex/main northern stream closed low energies over the Upper Midwest/Great Lakes early next week will struggle to consolidate and shift downstream to off the Mid-Atlantic coast late next week, blocked by a closed upper trough/lows slowly retrograding uncertainly from offshore the Canadian Maritimes toward New England. Moderate rains will accompany the path of the main 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/Florida as uncertain ejecting southern stream impulses 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