Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 AM EDT Thu Apr 18 2019 Valid 12Z Sun Apr 21 2019 - 12Z Thu Apr 25 2019 ...Overview and Guidance Preferences... Increasingly zonal flow over the CONUS by early next week will lead to lower predictability of generally weaker frontal systems next week. Continued a blended/consensus approach to minimize future shifts in system timing/track. Ensembles generally agree that troughing will slowly exit the Southwest/Four Corners region early next week and push into the southern Plains as the northern stream along the US/Canadian border wobbles downstream of an upper low in the Gulf of Alaska. 12Z ECMWF was closest to the ensemble consensus, which differed on the speed of the western trough (ECMWF ensembles generally quicker than the GEFS/Canadian members). A deterministic blend early in the period gave way to a blend of the ECMWF ensemble mean (which has trended slower by next Wed/Thu toward the GEFS mean) with the slower 00Z ECMWF and 18Z GEFS mean. Questions in specifics (e.g., will low pressure lift toward the Great Lakes next Wed or stay flatter?) will remain unanswered for now. ...Weather Highlights/Threats... The overall shortwave trough aloft affecting the western/central U.S. and associated surface features will spread rain and high elevation snow over central latitudes of the West and then rainfall of varying intensity over central/southern parts of the Plains and possibly the Mississippi Valley. Confidence in specifics of this precipitation area is lower than desired due to the guidance spread for details aloft. There is a signal for low-level upslope flow to provide some precipitation enhancement along the eastern slopes of the central Rockies around Sun (snow at relatively high elevations). Thereafter ensemble guidance shows relatively higher probabilities for locally heavy rainfall over the southern Plains which should see a multi-day feed of moisture from the Gulf, though placement differences (especially north-south) exist between the farther south ECMWF ensembles and farther north GEFS ensembles. The Pacific Northwest should see periods of generally light precipitation from Mon onward as multiple fronts approach/cross the region. Behind the exiting eastern system a brief period of chilly temperatures are expected for the Mississippi Valley/East on Sunday. Thereafter, temperatures should otherwise be near to above normal given the flatter trend of flow aloft. Exception may be over Texas later next week given extensive cloud cover and rainfall. Expect the highest warm anomalies over the West and into the northern High Plains with one or more days of max and/or min readings 10-20F above normal. Fracasso/Rausch 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