Extended Forecast Discussion NWS Weather Prediction Center College Park MD 319 PM 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 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 into Monday. 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 central U.S. from the short range period into early next week as the medium range period begins. Another amplified trough may dig into an 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 central U.S. by next midweek and spread additional precipitation to the central/eastern CONUS. ...Model Guidance/Predictability Assessment... Model guidance agreement is good for the initial portion of the medium range with the closed upper low as well as upper troughing over the eastern Pacific and the Northeast. Then, model diagnostics become trickier as differences arise with the troughing/energy moving into the West from the Pacific beginning Monday. After several days of fairly consistent model runs (for the most part, with the main exception of the weaker UKMET that has not been favored) with strong energy/troughing coming in, now the 00Z ECMWF is also weaker with the kicker as most of its energy remains across Canada. Ensemble members show a good bit of spread with the troughing, especially the EC and CMC ensembles. So confidence lowers from around Monday onward with this feature and its interaction with the initial upper low. The differences become even more notable around Tuesday night/Wednesday, as the 00Z EC wraps energy from its central Canadian upper low southward, producing a trough axis across the Great Lakes region and south. This is unlike consensus and unlike the 00Z EC mean. Meanwhile, the 00Z CMC has a solution with stronger energy producing a slower-moving low staying across the Four Corners to central U.S. on Wednesday/Thursday. Overall, going with the well-clustered GEFS and EC ensemble means by the latter part of the period seemed like the safest bet for now, along with some component of the 06Z GFS that had better alignment with the means than other deterministic models. ...Weather/Threats Highlights... Significant heavy snow along with gusty winds creating low visibility and possible blizzard conditions are forecast to continue from the short range period into Sunday across the Central Rockies and central portions of the High Plains. More moderate snows could 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 Lower/Middle Mississippi Valley unstable warm sector through Sunday. Subsequent evolution is less clear, but expect a weakening system will lift northeastward across the east-central U.S. early next week and into the Atlantic by Wednesday. This could spread some enhanced rainfall/convection to the Southeast and Southern Appalachians. With a cold high pressure wedge in place, wrap-back moisture in cooler than normal temperatures may support a chance for mainly light overrunning snows from the north-central Appalachians through the northern Mid-Atlantic and Northeast Monday and Tuesday, but uncertainty in precipitation type and amounts are high. While uncertainty also remains with the strength of the trough coming into the West, at least some precipitation is likely for the early week from the West Coast into the Intermountain West. Another round of snow is possible for the Central Rockies/central High Plains around Tuesday and Wednesday. As a low pressure system may track across the south-central U.S. towards the Ohio Valley through the middle part of the week, renewed precipitation is possible for portions of the central and eastern U.S., but with low confidence as to the details. Tate 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 Hazards: - Heavy precipitation across portions of the Central Plains and the Middle/Upper Mississippi Valley, Sun, Mar 14. - Heavy rain across portions of the Central/Southern Plains, the Tennessee/Ohio Valley, the Great Lakes and the Middle Mississippi Valley, Sun, Mar 14. - Heavy rain across portions of the Southeast, Wed-Thu, Mar 17-Mar 18. - Heavy rain across portions of the Southern Appalachians and the Tennessee Valley, Sun-Mon, Mar 14-Mar 15. - Heavy snow across portions of the Central Rockies, the Northern/Central Plains, and the Middle/Upper Mississippi Valley, Sun, Mar 14. - Severe weather across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, Sun, Mar 14. - Flooding possible across portions of the Central/Southern Plains, the Mississippi Valley, the Tennessee/Ohio Valley and the Great Lakes. - Flooding occurring or imminent across portions of the Middle/Lower Mississippi Valley and the Tennessee/Ohio Valley. - Flooding likely across portions of the Middle Mississippi Valley. - Enhanced wildfire risk across portions of the Southern Plains, Sun, Mar 14. 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