Extended Forecast Discussion NWS Weather Prediction Center College Park MD 147 AM EDT Sun Apr 07 2019 Valid 12Z Wed Apr 10 2019 - 12Z Sun Apr 14 2019 ...Heavy rain and snow, and high winds are expected with a storm across the central to the Northern Plains and Upper MS Valley mid to late next week... ...Overview and Guidance Assessment/Preferences... An upper level trough amplifies as it crosses from the Rockies on to the Plains Wed, which results in a major cyclone across the central U.S. Wed-Fri. Models still have significant differences to resolve, with the 18z gfs northwest of the 12z ECMWF cyclone positions, in turn impacting the axis/orientation of the bands of precipitation, including snow. The 181z GEFS Mean track is southeast of the 18z GFS and overlaps the 12z ECMWF Ensemble Mean well, so this tandem is again given more weight that either operational model. The 12z Canadian global and 00z GFS Wed-Thu agree with the mean track as well, with the 12z UKMET within the dominant cluster of solutions as well. Spread increases during Fri-Sat, following interaction with the northern stream as it moves into Canada. Given significant continued run-to-run variability from Fri onward, opted to lean much more heavily on ECENS/GEFS ensemble means during that time frame. This preference holds along the West Coast as well, where models have struggled to deal with the specifics of a series of shortwaves dropping southward across the Pacific Northwest Thu southeast across the Great Basin Fri and southwest to southern high Plains Sat. The system moves east on Sun. On Sun 14 Apr, as the trough moves out of the southwest onto the southern Plains, low pressure develops in the lower MS Valley to southeast, and moves northeast towards the TN Valley or southern Appalachians. The models and ensembles have timing differences with greater weighting to the slower 18z GEFS/12z ECMWF Means applied as the high amplitude FL ridge has proven to be a persistent feature most of the winter and should act to shunt the system a bit further northwest. The 00z GFS and Canadian global now clusters well with this group. ...Weather Highlights/Hazards... The upper-level shortwave will initially bring potentially heavy mountain snows to much of the Rockies of Id/western MT/WY Tue into Wed. After the system emerges into the Plains, models show a large area of precipitation is likely to the north of the low track, from portions of eastern Wyoming and across most of Nebraska and the Dakotas east to the Upper Midwest. A variety of precipitation types are likely, but sufficient cold air should be in place to support a band of moderate to heavy snow. ECMWF and GEFS plume diagrams show potential for a foot of snow at multiple locations in SD and MN, in addition to those at higher elevations in WY. Additionally, the strong intensity of the low (central pressures likely in the mid 980-mb range), will likely result in the potential for strong and gusty winds across a large area of the central U.S. Farther south, limited moisture return and potential for a capping inversion will limit precipitation coverage ahead of the system from the Southern Plains to the lower Mississippi Valley, but scattered convection could be strong. As the low moves into Canada by Fri-Sat and the cold front sweeps into the eastern U.S., showers are likely from the Ohio Valley to the Mid-Atlantic and Northeast. Farther west, the series of shortwaves diving south along the West Coast Wed-Sat will support continued scattered and periodic rounds of valley rain and mountain snow showers along the path of falling heights. Once the trough moves east on to the high Plains, return low level southerly flow and moisture leads to rainfall amounts picking up in the southern Plains to lower MS valley next weekend, with locally heavy rain Sun 14 Apr. Warm temperatures are expected ahead of the deep low pressure system Wed from the south central to southern Plains to the lower/mid-Mississippi Valley, where high temperatures of 5 to 15 deg F above average are likely. In the wake of this low pressure system, a colder polar air mass will overspread areas from the Great Basin to the central Rockies and then to the Upper Midwest, with high temperatures as cold as 15 to 25 deg below average expected on Thu in the central high Plains. A broad area of cool temperatures is expected across the western and central U.S. next weekend, gradually modifying with time. 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