Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Wed Mar 04 2020 Valid 12Z Sat Mar 07 2020 - 12Z Wed Mar 11 2020 ...Guidance/Predictability Assessment... Amplified troughing will be exiting the Northeast to begin the medium range period (Saturday), with a deep surface low likely to be a few hundred miles off the coast of Cape Cod. Only minor model differences with this system remain, mainly with low placement, but a general model blend seemed reasonable for the WPC forecast with this system, which is not a concern anymore after day 3. Meanwhile, out west, an initial upper shortwave/energy will cross the West Coast Saturday into Sunday, while additional energy upstream drops southward to amplify troughing aloft and act to develop a closed low well off the West Coast by Sunday. The agreement is better than recent nights with the initial batch of energy across the West and eventually into the Plains states early next week, with normal forecast spread after day 5. The eventual closed low off the West Coast though does show rather significant spread by day 4-5 and beyond, with the ECMWF farther north/east than the GFS and CMC. After day 6, the GFS seems too quick to open the low and bring it eastward into the Southwest U.S. The ensemble means generally follow suite with their deterministic counterparts, but the GEFS mean is still farther west than the GFS, lending a bit more confidence in the ECMWF/CMC solution. WPCs blend uses a general model blend for the initial shortwave into the West, and then mainly leans on the ensemble means later in the period, with about 30 percent of the ECMWF for additional definition. ...Weather/Hazard Highlights... Any coastal rain and snow across the Northeast with the deepening surface low should be exiting by the start of the period. Additional maritime threats (coastal wind and offshore waves) may linger through Saturday though. Up and down the East Coast max temperatures on Saturday will be modestly below normal, but should quickly bounce back above normal by Sunday and especially early next week. The initial shortwave into the West would support rain/terrain enhanced snowfall as it progresses across the West this weekend. There remains a reasonable signal for Plains surface low development early next week whose emerging/lead return flow from the Gulf of Mexico could fuel an expanding rain/strong convection pattern with the best focus across the eastern Plains/MS Valley. Cold air to the north of the low may also support some risk of heavy snows from the Upper Midwest into the Great Lakes and eventually the interior Northeast early to middle of next week. Ahead of this system though, well above normal temperatures will progress from the northern Plains into the Upper Midwest where daytime highs 20+ degrees above normal are likely Saturday and Sunday. The West Coast may briefly dry out on Sunday as the lead energy moves inland, but heavy rain/mountain snows may again target portions of Central and Southern California early next week as the closed low lingers off the coast. Of course, this is highly dependent on how close the low is to the coast, with the ECMWF the most robust in showing a heavy rainfall signal for Southern California since it has the low closest to the coast. Given the spread, confidence is low to average for this system. Santorelli 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