Extended Forecast Discussion NWS Weather Prediction Center College Park MD 323 PM 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 Sat, with a deep coastal storm several hundred miles off Cape Cod. Only minor model differences with this system remain and a general model blend seems reasonable to initiate the WPC forecast. Meanwhile, lead upper shortwave/energy will cross the West Coast this weekend. This occurs as additional energy upstream drops southward to amplify troughing aloft and act to develop a closed low well off the West Coast by Sun. Agreement has improved overall, but the GFS remains flatter and more progressive with lead southern stream troughing into CA/Southwest then east-central states compared to a WPC preferred composite of well clustered 00 UTC ECMWF and latest GEFS/ECMWF ensemble guidance. ...Weather/Hazard Highlights... Modest lingering wrapback snows over eastern New England will diminish Sat as the associated deep coastal storm tracks well offshore past the Canadian Maritimes. Additional maritime threats (coastal wind and waves) will persist Saturday. 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. Inland progression of a northern and southern stream shortwave trough energies over the Northwest and down into CA/Southwest/Rockies will support swaths of rain/terrain enhanced snowfall this weekend. Downstream propagation of the southern stream shortwave, approach of a northern stream frontal surge, and potential dryline development also lends into a signal for Plains surface low development by early next week. Emerging/lead return flow from the Gulf of Mexico will fuel an expanding rain/strong convection pattern with the best focus across the eastern Plains/MS Valley. Activity will then out across the east-central U.S. as the main low/front low works downstream. Cold air to the north of the low may also support some risk of heavy snows from the Upper Midwest into the Great Lakes then northern Northeast early to middle of next week. This will be in stark contrast to the well above normal warm sector temperatures. The West should overall dry out into Mon as the lead energy moves inland, but heavier rain/mountain snows may target portions of south-central CA/Southwest into next midweek with anticipation of the slow approach toward the coast of a main east Pacific closed low and leading frontal system. Schichtel Hazards: - Heavy precipitation across portions of the Northern Great Basin, Sat, Mar 7. - Heavy precipitation across portions of the upper Great Lakes, Mon, Mar 9. - Heavy precipitation across portions of the Northeast, Tue, Mar 10. - Heavy precipitation across portions of northwestern Arizona, western Idaho, and southern Sierra Nevada, Wed, Mar 11. - Heavy rain across portions of the lower Mississippi Valley, coastal southern California, and parts of the eastern Gulf Coast, Mon-Tue, Mar 9-Mar 10. - Heavy rain across portions of the southern Appalachians into the Mid-Atlantic, Wed, Mar 11. - Heavy snow across portions of the northern Rockies near the Canadian border, Sat, Mar 7. - Flooding occurring or imminent across portions of the Southeast and the lower Mississippi Valley. - Flooding likely across portions of the northern Plains. 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