Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Fri Apr 05 2019 Valid 12Z Mon Apr 08 2019 - 12Z Fri Apr 12 2019 ...Overview and guidance assessment... The WPC medium range product suite was derived from a blend of the 12 UTC ECMWF and 12z ECMWF/GEFS ensemble means. These guidance options were well clustered with the forecast evolution of the larger scale systems. A composite blend provided good run to run continuity and addresses minor timing/intensity differences. ...Western and Central US... The models show two primary upper level troughs that move onshore across the west coast from the eastern Pacific and spread inland. The initial trough is offshore over the northeast Pacific 12z Mon, and moves onshore after 00z, an din most solutions onshore by 12z Tue 09 Apr. The models show steady forward progression across the Rockies and then high Plains by 12z Wed. The 12z ECMWF and 18z GFS runs continue to show once the upper trough reaches the high Plains, the low reforms in the high central Plains and intensifies into a strong cyclone Wed as the cyclone moves northeast, reaching the MS Valley by 12z Thu and then the Great Lakes by 12z Fri 12 Apr. The 12z ECMWF was on the northwest fringe of the suite of forecast models/members Upstream, an upper level trough energy reaching the northeastern Pacific is expected to reach the West Coast Thu 11 Apr, amplifying as it continues inland on Fri 12 Apr. There is better than average agreement among the 18z GEFS Mean/12z ECMWF Ensemble Mean, and 12z ECMWF to warrant a consensus of these solutions to be used in the forecast (for example, the 12z Fri surface low positions over southern NV near the AZ border are close among the 12z ECMWF/19-00z GFS models and the 12z ECMWF and 18z GEFS ensemble means). ...Eastern US... A leading upper trough over the Great Lakes Mon with a surface low and trailing wavy cold front progress slowly east with models models indicating triple point low development along the New England coast early Tue and then moving offshore thereafter. The trailing cold front moves off the southeast coast on Wed with building high pressure in the lakes producing cold air advection across the northeast and mid Atlantic. The next closed low coming out of the central US on day 6 is forecast to move towards the Great Lakes day 7. The respective ensemble means from the 18z GEFS and 12z ECMWF produced a low position in between the operational 12z ECMWF and 18z GFS, providing an intermediate solution that is where we would usually indicate a preferred cyclone position in between the 12z ECMWF and 18z GFS forecasts in most cases. The low would induce a warm front to move north across the mid Atlantic towards Long Island and southern New England Fri 12 Apr. The 00z GFS has come in with a forward progression that is much faster, and appears to be an outlier solution, so is considered low probability, particularly given . ...Weather Highlights/Hazards... Areas of terrain-enhanced rain and higher elevation snow are forecast from northern California and Oregon into Idaho, southern Montana, and Wyoming early next week. Current guidance suggests best potential for heaviest activity will be centered along the West Coast near the California/Oregon border and the Oregon Cascades. Continued progression of this system should spread precipitation across the north-central Rockies, Plains, Mid-Upper Mississippi Valley, and eventually Ohio Valley and Great Lakes. Some activity may be heavy and areas with ongoing flooding concerns will need to monitor this system. In addition there is potential for strong winds to be an issue north of the low pressure center as it tracks from the central Plains towards the lakes. There is also a threat of snow in the northern periphery of the precip shield from the n-central Plains to the Upper Midwest. The eastern half of the country will see a broad area of precipitation with the system progressing eastward from the Lower Mississippi Valley and central Gulf Coast region and southern Appalachians early next week. Convection may be strong to severe over southern areas. Check the SPC outlooks for the latest probabilities. Significant rainfall is also possible from the Ohio Valley into northern Mid-Atlantic/Northeast. Snow should be confined mostly to northern New England Mon-Wed in this pattern as moisture advects northward into a cooled/receding surface ridge. The warm sector of the central-eastern U.S. system Mon will provide much above normal temperatures. Morning lows will be particularly anomalous with many locations 15-25F above normal Mon in the Ohio Valley to central Appalachians and daily record warm low values may be challenged. On Tue the anomalies of 15-20F above normal for the min temperatures shift to the mid Atlantic states, and in southern NV to western AZ. As the western system moves east, those southwest warm temps shift into the southern Plains for Wed morning, and then lower MS Valley for Thu morning, followed by the Appalachians to east coast Fri morning 12 Apr. Petersen 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