Extended Forecast Discussion NWS Weather Prediction Center College Park MD 149 AM EST Tue Mar 03 2020 Valid 12Z Fri Mar 06 2020 - 12Z Tue Mar 10 2020 ...Overview and Guidance/Predictability Assessment... An amplifying shortwave crossing the Ohio Valley/Great Lakes to start the medium range period (Friday) will eventually close off into a low off the Northeast coast by Saturday. This will induce rapid cyclogenesis off the East Coast with many models showing a mid-970s low a couple hundred miles east of Cape Cod. There remains plenty of spread especially concerning exact placement of the low pressure system, which would have implications for weather along the Northeast Coast. The GFS remains the fast outlier, and thus is not preferred for the blend. An upper low off British Columbia will send an initial shortwave of energy into the West early this weekend, while additional energy drops southward further amplifying the trough and resulting in a deep closed low well off the West Coast by late Sunday. The biggest forecast consideration for this system continues to be the GFS is the quickest to bring the initial energy inland, and also noticeably flatter with the wave as it progresses across the Rockies early next week. The slower solution presented by the ECMWF/CMC is better supported by the ensemble means. The resulting WPC blend used a majority deterministic model blend (ECMWF/UKMET) for days 3-5, increasing usage of the ensemble means thereafter. Continued to include about 30 percent of the ECMWF beyond day 5 just for some additional definition/detail. This maintains good continuity with the previous shift. ...Weather/Hazard Highlights... The low pressure system supported by the amplifying northern stream trough reaching the East late this week should promote a period of lake-effect and terrain-enhanced snow between the central Appalachians and New England. Uncertainty is too great at this time to specify effects from deepening Atlantic low pressure Fri-Sat. There is greater confidence in a period of brisk to strong winds in the gradient between the low and surface high to the west, versus coverage/intensity of any snow, given the current spread for low track. Light to moderate rainfall may also be likely for locations close to the coast. Over the western states precipitation will initially focus over the Northwest, associated with low pressure that develops off British Columbia. A broader moisture shield will likely spread across the West by next weekend as some eastern Pacific upper trough energy ejects inland. Highest totals should align with favored terrain from the Sierra Nevada into the northern-central Rockies. As the energy enters the central U.S. on day 6, precipitation chances should increase across the Central/Southern Plains and into the Mississippi Valley. Snow accumulations are possible within the northern side of the precipitation shield across the Upper Midwest and Upper Great Lakes. Expect the greatest warm temperature anomalies to be over the north-central Plains Friday into the weekend as upper level ridging builds aloft. The pattern appears favorable for some areas to reach at least 15-25F above normal. Moderately cool temperatures will traverse the Eastern states this weekend underneath the upper level trough, though should moderate back to above normal (some areas +10F) by early next week. 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