Extended Forecast Discussion NWS Weather Prediction Center College Park MD 213 AM EST Thu Mar 11 2021 Valid 12Z Sun Mar 14 2021 - 12Z Thu Mar 18 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... ...Overview... A potent closed upper trough/low will track from the Southwest to the Southern Plains this weekend. This plus a well organized surface low over the Central Plains will spread significant snow to the Central Rockies and central High Plains, while severe weather and heavy rain are possible across the south-central U.S.. Another amplified trough may dig into am unsettled West early next week and serve as a kicker for the initial closed low, pushing it northeastward as it weakens. The second system may reach the south-central U.S. by next midweek. ...Model Guidance/Predictability Assessment... Model and ensemble guidance is in reasonable agreement with the overall pattern described above through the weekend and into early next week. The 18 UTC GFS and 12 UTC ECMWF/Canadian solutions seem best clustered, have good GEFS/ECMWF ensemble support and offer improving run to run continuity. A composite blend along with the 01 UTC National Blend of Models seems reasonable. The 18 UTC GFS and to a lesser extent the 18 UTC GEFS mean overall become more progressive with features than the rest of guidance days 5-7. Suggest a solution on the less progressive side of the full envelope of solutions given closed/amplified systems and stream separated nature of the flow. A composite blend of the 12 UTC ECMWF/Canadian and GEFS/ECMWF ensemble mean solutions seems to fit the bill and maintains good WPC continuity. The 00 UTC GFS trended slower, but the 00 UTC ECMWF has thrown a troublesome curve ball and no longer digs kicker upper trough energy strongly down over the West next week. ...Weather/Threats Highlights... Significant heavy snow along with gusty winds creating low visibility and possible blizzard conditions are forecast across the Central Rockies and central portions of the High Plains into the weekend. More moderate snows will spread across the central Plains into the Upper Midwest into early next week. In the warm sector, heavy rains/convection will also develop in earnest and spread from the south-central Plains to the mid-lower Mississippi Valley/Mid-South where increasingly deep moisture inflow from the Gulf of Mexico will wrap around the low into a slow-moving frontal zone. SPC shows a severe weather threat for the Southern Plains to the mid-lower Mississippi Valley unstable warm sector. Subsequent evolution is less clear but expect a weakening system will lift northeastward across the east-central U.S. early-mid next week. Amplified and reinforcing northern stream upper trough passage will in advance force cooled high pressure and lead cold frontal push down through the East. There is potential to spread some enhanced rainfall/convection across the South/Southwest and Mid-Atlantic. Wrap-back moisture may also support some Midwest snows and lead flow offers some chance for mainly light overrunning snows from the north-central Appalachians through the northern Mid-Atlantic. The upstream kicker system for the West/Southwest had trended stronger in guidance, except now for the much less diggy 00 UTC ECMWF. Other than this ECMWF run, the system showed potential for modest to moderate precipitation Sunday into Tuesday from the Pacific Northwest into California to the south-central Great Basin/Rockies. Forecast spread increases with time for overall system evolution, but possible system emergence could spread some renewed precipitation across the south-central Plains and the mid-lower Mississippi Valley/The South by Tuesday-next Thursday. 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