Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Wed Mar 10 2021 Valid 12Z Sat Mar 13 2021 - 12Z Wed Mar 17 2021 ...A major weekend snowstorm for the central Rockies/High Plains and a heavy rainfall threat from the south-central Plains to the mid-Mississippi Valley... ...Weather/Threats Highlights and Guidance/Predictability Assessment... A powerful closed low/upper trough and ample height falls will track slowly over the Southwest to the Plains this weekend to spawn a deepening surface system. Favorable system track, deformation, and deep layered/moist upslope flow will support a significant heavy snow event with focus over the cooled central Rockies/High Plains. In this pattern, heavy rains/convection will also develop in earnest from the south-central Plains to the mid-Mississippi Valley where increasingly deep moisture inflow from the Gulf of Mexico will wrap around the low into a slow moving frontal zone. SPC also shows a threat for severe weather in the unstable warm sector from the southern Plains to the mid-lower Mississippi Valley. Subsequent evolution in guidance offers less than stellar model and ensemble forecast spread and run to run continuity, but overall suggest a weakening system will lift northeastward across the east-central U.S. early next week in response to the digging of an uncertain/amplified upper trough energies down through the West. Amplified and reinforcing norther stream upper trough passage will in advance force cooled high pressure and lead cold frontal push down through the Midwest and the East. There is potential to spread enhanced rainfall/convection out across the South, Ohio Valley, and Mid-Atlantic. Moisture still wrapping into the weakening main system may also provide fuel for some lingering Upper Midwest snows. There is also some chance for modest overrunning snow from the north-central Appalachians to the northern Mid-Atlantic. Meanwhile, the upstream kicker system for the West has potential to produce generally modest precipitation from the Northwest/Northern California and to a lesser extent southeastward across and Great Basin. Emergence into the south-central Rockies/Plains next midweek does offer some opportunity to eventually induce upslope flow and some return Gulf flow into/over a wavy lead frontal system. The WPC medium range product suite was primarily derived from best clustered guidance and continuity from the 12 UTC ECMWF and GEFS/ECMWF ensemble means days. 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