Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EDT Sun Mar 17 2019 Valid 12Z Wed Mar 20 2019 - 12Z Sun Mar 24 2019 ...Overview and Guidance Assessment/Preferences... Models/ensembles show broad agreement that an anomalous upper ridge axis initially extending from the Canadian Rockies and prairies south into the north central U.S. by the midweek should slowly shift eastward during the forecast period, while perhaps weakening of disbursing somewhat. Shortwave energy from the Pacific will undercut the ridge, slowly progressing east from California to the Mississippi Valley Thu-Sun. A mean trough will persist downstream of the ridge, reinforced across the lower Great Lakes and the Northeast late in the week by a vigorous shortwave traversing the northwesterly flow late in the week. Meanwhile, as the ridge slides east, height falls should reach the Pacific Northwest by the weekend, bringing a return to a more active weather pattern for the West Coast. A blend of the ECMWF/GFS/CMC was used a basis for the forecast through much of the period. Models have continued to trend deeper with shortwave energy crossing the Midwest and Mississippi Valley Wed-Thu, with some continued timing and structural differences. Consensus has improved over recent days with respect to the southern stream shortwave as well, with guidance in general agreement that an upper low should close off across the Southwest by Thu then slowly drifting east into the central U.S. Again, some timing differences are evident but solutions are generally well-clustered around the ensemble means, lending at least some degree of increased confidence to solutions within the center of the spread. Finally, while there is broad agreement on height falls and a cold front reaching the West Coast by next weekend, models continue to show variability on the structure of the trough and the embedded smaller-scale shortwaves. Given these considerations, weighting of the ECENS and NAEFS ensemble means in the forecast was increased significantly by days 6-7 (Sat-Sun). ...Weather Highlights and Hazards... The southern stream system will bring rain and mountain snows from California to much of the Four Corners region Wed-Thu. As moisture increases ahead of the system across the Southern Plains Fri-Sat, showers and thunderstorms are expected to become more widespread across that region, with the potential for some areas of heavy rain. Rain and mountain snow should spread into the Pacific Northwest and northern California by Fri-Sat as the upper trough and cold front approaches, with heavy precipitation possible in favored terrain areas. Gradually warming temperatures are expected across much of the northern tier. The warmest temperatures will initially be across the Pacific Northwest, with highs 5-15 deg F above average Wed-Thu. The warm conditions will spread east along with the upper-level ridge, with high temperatures anomalies of similar magnitude reaching the Midwest by Fri-Sat, and portions of the Mid-Atlantic and Northeast by next Sun. Ryan 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