Extended Forecast Discussion NWS Weather Prediction Center College Park MD 141 AM EST Sat Mar 09 2019 Valid 12Z Tue Mar 12 2019 - 12Z Sat Mar 16 2019 ...North-Central U.S. Heavy Snow Threat Wed-Thu... ...South-Central to Mid-South/Southeast U.S. Heavy Rain Threat Tue-Fri... ...Overview... Another potent storm system will trek out of the Southwest/Four Corners region Tuesday and lift northeastward toward the Great Lakes by Thursday. This will spread a large area of potentially heavy rain from the southern Plains eastward into the Southeast while marginally cold air to the north will support a heavy snowfall threat over the High Plains and Upper Midwest. By the start of next weekend, the pattern appears to be much quieter with high pressure forecast to dominate the western/central parts of the lower 48. ...Guidance and Uncertainty Assessment... The ECMWF has led the way with the timing of the system out of the Southwest, but the GFS (especially the 18Z FV3-GFS) clustered well with the 18Z GEFS mean and the 12Z ECMWF/ECMWF ensemble mean so that a blend/consensus position offered a reasonable starting point. By next Fri/Sat, the upstream Pacific will become more uncertain as the shape of the upper ridge into British Columbia will dictate the amount/strength/orientation of troughing in the west/Rockies. ...Weather Highlights and Hazards... Main system of interest in the medium range will lift out of the Southwest and deepen quite smartly into southeastern Colorado by Wednesday morning. Precipitation will expand in coverage out of Arizona and New Mexico eastward, focused on the central/southern Plains (northern Texas northward) Tue/Wed. To the east, a front across the Gulf will lift northward as a warm front and bring widespread rainfall and embedded convection into the Mississippi/Tennessee Valley Wednesday then into Alabama/Georgia/southern Appalachians Thursday. The potential for several inches of rain exists over a large area that will be further refined over the next several days, but atmospheric and ensemble signals continue to be strong. To the north, cold enough air will support snow on the northwest/north side of the surface low that will occur with strong winds (i.e., possible blizzard conditions). A cold rain (perhaps over an inch to an inch and a half) will fall to the southeast of the surface low over some areas that will receive significant snow in the short term (e.g., southern Minnesota). The surface low will depart through southern Canada Friday as colder air is dragged in behind it across the Great Lakes, enhancing lake-effect snows. Temperatures will remain below average in the west but perhaps moderate just a bit by next weekend. In the east, post-front airmass Tuesday will be chilly (below average by a few degrees) but then warm up ahead of the central states' system by Thursday into Friday. Fracasso Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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