Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Mon Mar 08 2021 Valid 12Z Thu Mar 11 2021 - 12Z Mon Mar 15 2021 ...Late week heavy rain threat from the south-central Plains to the Mid-South... ...Heavy snow threat for the south-central Great Basin/Rockies/High Plains... ...Weather/Threats Highlights and Guidance/Predictability Assessment... An amplified and southern stream upper trough/closed low will settle over the West/Southwest later this week into the weekend in a pattern with above normal forecast predictability. System track, deformation and upslope will favor some enhanced rain and higher elevation snow over the south-central CA/Great Basin/Rockies/High Plains along with advent of below normal temperatures. Lead energies forecast to eject from the trough will support a quite wavy and slow-moving south-central to Mid-South front whose Gulf moisture and instability pooling will fuel a focus for locally enhanced rainfall and training convection. Ahead of this evolution, upper ridging will support much above normal temperatures for the East into later this week. A cold front will dig through the East later week into the weekend in response to amplified northern stream upper trough passage. A composite blend of reasonably well clustered guidance from the 18/00 UTC GFS/GEFS mean, 12/00 UTC ECMWF/ECMWF ensemble mean and the 01 UTC National Blend of Models seems to offer a good forecast starting point and continuity days 3-5. Forecast uncertainty increases by later weekend when the Southwest feature seems slated to eject to the south-central U.S.. Height falls and instability may re-invigorate moisture inflow and heavy precipitation potential over and onward from the south-central U.S.. This would include a wintry threat focus for the south-central Rockies/High Plains that has potential to spread across the central Plains and Mid-MS Valley/Midwest by early next week on the cooled northern edge of the expanding precipitation shield with system progression and wrapping flow. For this day 6/7 period, the 12/18 UTC GFS/GEFS are progressive compared to the 12 UTC ECMWF/ECMWF ensemble mean and to a lesser extent the 12 UTC Canadian. Prefer a solution on the less progressive side of the full envelope of guidance closest to the ECMWF ensemble mean considering flow separation and closed trough/low nature. The 00 UTC ECMWF trended closer to the ECMWF ensemble mean. The 00 UTC GFS/Canadian/GEFS mean have trended significantly slower and more in line, bolstering forecast confidence, but forecast spread and continuity remain less than ideal. 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