Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri Mar 20 2020 Valid 12Z Mon Mar 23 2020 - 12Z Fri Mar 27 2020 ...Guidance/Predictability Assessment... Guidance depicts a reasonably similar theme regarding the synoptic pattern evolution through the medium-range period. However, forecast spread persists for a protracted series of lower-predictability shortwaves and especially surface system developments, both within the southern Canada/northern tier U.S. stream and the flow emerging from the West into a southern stream flow. This effects continuity and keeps confidence lower than desired for individual surface systems and associated weather impacts. The WPC medium-range product suite was mainly derived from a blend of best clustered guidance from the ECMWF, NBM and ECMWF/NAEFS ensembles days 3-5 (Mon-Wed). The still compatable ensemble means were used for days 6-7 along with the NBM. The 00 UTC GFS/GEFS are overall trending favorably in this direction. ...Weather/Hazard Highlights... Expect an active wintry pattern for much of the West next week as broad areas of moderate rains and terrain enhanced snows periodically overspread the region with approach and passage of several lead systems and eventual upper trough amplification. Highest totals for the period should be over the Sierra Nevada while favored terrain along much of the West Coast. The Great Basin/Southwest and Rockies will likely see episodes of organized precipitation as well. The potential still exists for some locally heavy rains across portions of the Mid-South and vicinity early next week. Specifics will take more time to resolve though. Precipitation coverage and intensity farther north Mon-Tue will depend on uncertain details of expected surface low development near the East Coast on Mon-Tue. Current solutions for track are far enough apart to make a difference between only light precipitation over New England or a meaningful snowfall between the central Appalachians and New England. Latest WPC winter weather probabilities show at least 30 percent potential for a quarter inch or more liquid equivalent in the form of snow over parts of New England, with higher values upwards to 70% over the Catskills. Then a system emerging over the Plains Tue should spread another area of precipitation across the eastern half of the country. The majority of precipitation with this system should be in the form of rain, except for possibly some snow at northernmost latitudes. Modestly below normal temperatures over the eastern U.S. Sun-Mon will be followed by increasing coverage of above normal readings to the east of the Rockies, while the amplifying West Coast trough and the eventual start of its eastward progress will bring a cooling trend to much of the West. By next Wed-Thu expect a fairly broad area of plus 10-20F anomalies over the eastern half of the country and generally minus 5-15F anomalies for highs (with more moderate temperatures for morning lows) over the West. Schichtel 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