Extended Forecast Discussion NWS Weather Prediction Center College Park MD 141 AM EDT Mon Apr 08 2019 Valid 12Z Thu Apr 11 2019 - 12Z Mon Apr 15 2019 ...Major winter storm likely from the Northern High Plains to the Upper Midwest mid to late this week... ...Major spring cyclone to produce heavy snow and high winds in portions of the north central Plains to upper MS Valley and Upper Great Lakes... ...Overview and Guidance Assessment/Preferences... The models are in excellent agreement now on the developing cyclone in the central Plains that moves in to the upper midwest on day 3 Thu and across the upper Lakes Fri before exiting up into Canada Friday. Deterministic model solutions and ensemble members are now very well-clustered with respect to the surface low track Wed-Fri, with the ECMWF and UKMET the two solutions most well-centered within the broad consensus. The trailing cold front moves off the northeast/mid Atlantic coasts early Sat. In the western US, shortwave energy is expected to dive south across the Pacific Northwest Thu to the southwest US Fri, perhaps closing off as it crosses south through the Great Basin. The 12z ECMWF and 18z GEFS Means remain in better than average agreement, which serve to center in between the 12z ECMWF with its further west track of the 500 mb wave, the GFS/GFS parallel with its further east track. The WPC forecast blended the 2 ensembles with less weight to the operational ECMWF. Next weekend, the primary forecast concern becomes how quickly the energy across the Southwest Thu-Fri ejects eastward into the central U.S. The 18z GFS continues to move the upper trough and associated sfc low eastward faster than most other solutions, so was not used, given the GEFS Mean was slower like the 12z ECMWF and 12z ECMWF Ensemble Mean. The Canadian/Canadian ensemble mean was a few hours slower in moving the upper trough and sfc low northeast with a similar track to the GEFS/ECMWF. Most solutions spin up a low pressure system across the lower Mississippi Valley next Sun and move the low into the Ohio Valley and Great Lakes Mon, when the system occludes. The triple point crosses the mid Atlantic, with a new low developing and moving northeast towards coastal New York/New England or the adjacent coastal waters. The models also show the next upper trough over the northeast Pacific set to move onshore and inland late Sun into Mon 15 Apr. Timing and phasing differences persist with the ECMWF/GFS/Canadian all offering differing solutions, as more weighting was given to the ensemble means until better agreement develops. ...Weather Highlights/Hazards... The low pressure system crossing the central U.S. Thu-Fri is expected to bring major winter weather impacts from portions of the north central Plains to the Upper Midwest/upper Great Lakes. Models show strong signal for a band of heavy snow north of the surface low track. Peak probabilities for heavy snow cover SD, northern NE, southern to central MN, northern WI, and the UP of MI. Strong and gusty winds will likely result in blowing snow and perhaps blizzard conditions for some areas. On Thu-Thu night, increasing moisture return should lead to scattered to numerous showers and thunderstorms in the mid MS Valley to the OH Valley, some of which could be strong to severe. See the Storm Prediction Center outlooks for severe convective weather probabilities. The system across the western U.S. Thu-Fri should produce scattered areas of valley rain and mountain snow from the West Coast to the Great Basin and Rockies. As the system enters the central U.S. next weekend, a developing frontal wave along the Gulf Coast/lower Mississippi Valley should promote strong moisture return and widespread rain and thunderstorms from the lower Mississippi Valley to the Tennessee/Ohio Valleys and the Appalachians and mid Atlantic, with areas of heavy rainfall possible. High temperatures are forecast to be 10-15 deg above average across portions of the Mid MS Valley to Southeast and Tennessee/Ohio Valleys on Thu. The anomalous warmth spreads east into the Appalachians to the southeast on Fri, and then along the east coast Sat, then the southeast and FL Sun. In the wake of the low pressure system, much colder air is expected to spread into the Rockies and the central U.S., with high temperatures 15-25 deg below average possible late in the week. The anomalies taper on Sun, with the primary area of below normal temps next Mon 15 Apr under the upper trough in the Plains to the MS Valley. 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