Extended Forecast Discussion NWS Weather Prediction Center College Park MD 216 PM EDT Fri Mar 27 2020 Valid 12Z Mon Mar 30 2020 - 12Z Fri Apr 03 2020 ...Heavy rain possible for the South Mon-Tue... ...Overview... Atmospheric shuffling over North America next week has resulted in model uncertainty and poor run-to-run continuity. The larger anomaly centers will be across far northern Canada (70-80N) where a closed high will move out of the North Slope eastward to the Canadian archipelago near Resolute. The other center will be the subtropical ridge/upper high over Florida on Monday that will slide westward into Mexico and weaken. This generally favors weaker troughing astride the US/Canadian border with a couple lead impulses through the South/East. ...Guidance/Predictability Assessment... Model guidance continues to struggle with the synoptic setup next week across the CONUS. For the southern stream system, there is slightly better agreement in the timing and track of an expected area of low pressure from the south-central Plains toward the Deep South Mon-Tue. The ECMWF low track is slightly ahead of the GFS now, but the differences has lessened from earlier model cycle and allowed for a near equal blend of the available deterministic guidance for day 3-4. The system is expected to track toward the Southeast U.S. and then off the Mid-Atlantic coast where spread begins to increase. To maintain WPC continuity, the ECMWF and its ensemble mean was favored for later forecast periods (day 5-7) as the synoptic setup favors more quasi-zonal flow (an inherently low-predictability pattern). ...Weather/Hazard Highlights... System moving out of the southern Rockies Mon will spread rain and embedded convection across the ArkLaTex and Mid-South/TN Valley to the southern Appalachians by Tue. Rainfall could be heavy in local areas. Light to modest rainfall and maybe some snowfall over the higher elevations of the Northeast will spread ENE on Wed as the system moves out to sea. In the West, precipitation will be heaviest early in the week with the leading stronger systems, tapering to lighter rain/snow showers as the upper low settles over British Columbia. Temperatures will trend cooler in the East behind the exiting system midweek. Some record highs may still be possible across Florida Mon/Tue. Milder temperatures are expected over the Southwest after Mon when the upper trough exits. Temperatures are much more uncertain (50-60 deg spread in the guidance) over eastern Montana to the Dakotas Tue-Thu depending on where the frontal boundary lies. Strong high pressure (>1050mb) north of Hudson Bay will try to funnel cold air across the border but it will battle milder air over the central Plains. Fracasso/Taylor 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