Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM 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... The models continue to really struggle with the evolution details right from Monday onward. The slower 12Z/26 ECMWF/ECMWF ensembles have sped up quite noticeably over the Four Corners Mon and out of the southern Plains Tue closer to the quicker GFS/Canadian 24 hrs ago. Upstream, this resulted in weaker troughing/zonal flow into the Pac NW by Tue as an upper low elongates eastward from British Columbia. The ECMWF seemed to cluster with its mean and the 18Z GEFS mean in this idea but with a question as to how much height falls would move into the Great Lakes around next Thu or simply lift back through Canada. Along the East Coast, low pressure may lift northeastward off the VA coast just outside the 40/70 benchmark but with continued ensemble disagreement/spread in all directions. 12Z/18Z GFS runs were too different from the ensemble consensus to use but was still hesitant to weight the 12Z ECMWF given its inconsistency. Ultimately utilized the ECMWF as the best fit at this time with low confidence. Increased ensemble weighting by the end of the period which points to quasi-zonal flow across the CONUS (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 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