Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Fri May 17 2019 Valid 12Z Mon May 20 2019 - 12Z Fri May 24 2019 ...Overall Weather Pattern... A stormy and unsettled weather pattern is expected across much of the central U.S. during the medium range period with a large scale upper trough becoming established over the Intermountain West and a building upper level ridge over the southeastern states. Three well defined storm systems are expected next week, with the first affecting the northeastern U.S. on Monday. The second storm gathers strength across the Plains on Tuesday and tracks towards the Great Lakes, and the third one develops over the Intermountain West midweek and reaches the Plains by the end of the week. ...Guidance/Predictability Assessment... Models and ensemble means indicate decent overall agreement on the synoptic scale on Monday. By Tuesday, the 00Z UKMET begins to differ with the surface low well to the south of the model consensus across the southern Plains, and farther north with the next low over the eastern Pacific. By the middle of the week, noteworthy differences are apparent with the next upper level trough crossing the West Coast region, with the ECMWF/EC mean slower with the progression of the closed low, and the 00Z GFS more amplified and faster across the Desert Southwest. The feature with the greatest predictability will be the upper level ridge over the Southeast, where a general model blend suffices. Elsewhere, the forecast was derived from a blend of the ECMWF/GFS/parallel GFS and increasing percentages of the GEFS and EC mean for the second half of the forecast period. ...Weather Highlights and Hazards... Numerous showers and thunderstorms continue to be in the forecast going into next week across the central/southern Plains and extending to the Upper Midwest. Multiple rounds of MCS activity are likely with both of the low pressure systems that are progged to track across the Plains. This will have the potential to produce very heavy rainfall capable of flash flooding, and severe weather is also likely from northern Texas to the Midwest based on recent SPC forecasts. The greatest chance of flooding would be from the Texas Panhandle region to Iowa with the strong low pressure system for the early to middle part of the week. Additional heavy rain is also possible from the next storm system tracking eastward from the Intermountain West later in the week, although details on timing and placement are less certain. There will also be a dichotomy of temperature anomalies given the amplified flow pattern in place. Temperatures are expected to be well above normal across much of the southeastern U.S. owing to the strength of the upper ridge, and this will also serve to keep rainfall chances minimal. The opposite will be the case across much of the western U.S. and also the northern Plains that will be under the influence of the upper level trough and to the north of the low tracks. Late season snow is likely for the Sierra Nevada and the northern Rockies. D. Hamrick 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